JP7080428B2 - Substrate for thermal head - Google Patents

Description

The present invention relates to a substrate for a thermal head. More specifically, the present invention relates to a substrate for a thermal head used in a facsimile, a color printer, a bar code printer and the like.

A thermal head in which a heating element and a drive circuit are integrally formed is known.

Patent Document 1 discloses a thermal head using a thin film transistor as a drive circuit. In Patent Document 1, the heat dissipation amount is controlled by changing the thickness of the substrate on which the heat generation resistor and the drive circuit are formed to 10 to 800 μm and adhering to the heat sink, and changing the thermal resistance of the substrate. It is described that the print quality is improved by heat storage.

Patent Document 2 discloses a thermal printer head such as a facsimile or a word processor. In Patent Document 2, in order to improve the temperature rise of the drive circuit and the heat storage in the heat generation resistor forming region by using the thin film thin film as the drive circuit, in the vicinity of the heat generation resistor and between the drive circuit and the heat generation resistor formation region. It is described that heat propagation from the heat generation resistor is prevented by interposing a metal pattern.

Japanese Patent Application Laid-Open No. 62-242552 Japanese Unexamined Patent Publication No. 4-140152

A conventional thermal head in which a heating element and a drive circuit are integrally formed is provided on a brittle, thick substrate having relatively poor heat conduction such as glass or quartz. Therefore, the problems are improvement of malfunction and failure due to temperature rise of the drive circuit due to heat propagation from the heating element that hinders the miniaturization of the thermal head, improvement of print quality by heat storage of the substrate, and improvement of substrate strength. ..

In Patent Document 1, since both the heating element and the drive circuit are formed on the heat storage layer having a uniform thickness, the heat storage amount cannot be controlled individually for the heating element and the drive circuit. Until now, the heat storage layer was used only for controlling the heat storage amount of the heating element. That is, in the case of low-speed printing applications, the on / off cycle of the heating element becomes long. Therefore, in order to increase the thermal time constant, the heat capacity is increased. That is, the thickness of the heat storage layer is increased. On the other hand, in the case of high-speed printing, the thermal time constant is reduced. Therefore, the heat storage layer is thinned.

However, when the thickness of the heat storage layer is increased, heat propagation in the drive circuit formation region direction increases, which causes the temperature of the drive circuit to rise, and malfunctions and failures due to malfunctions cannot be ignored. It is necessary to keep a certain distance larger than the thickness of the heat storage layer, which makes it difficult to reduce the size of the substrate. Further, if the heat storage layer is made uniformly thin, the strength of the substrate becomes weak and it becomes difficult to handle it at the time of assembly. The challenge is to provide a thermal head that uses a thin film transistor that can be miniaturized, has strong substrate strength, and is easy to assemble, regardless of the application for low-speed and high-speed printing.

Further, Patent Document 2 proposes to arrange a metal pattern for heat dissipation between a heating element and a drive circuit to improve heat storage and malfunction due to a temperature rise of the drive circuit. However, the interposition of the metal pattern for heat dissipation increases the distance between the heating element and the drive circuit, making it difficult to reduce the size.

The substrate for a thermal head according to the present invention includes a substrate having a first region, a second region, and a third region arranged in order in the first direction, and a heating element provided on the main surface of the substrate. A drive circuit provided on the main surface of the substrate for driving the heating element, wiring provided on the main surface of the substrate and electrically connected to the heating element and the driving circuit, and the above. A heat radiating plate bonded and fixed via an adhesive is provided on the back surface of the substrate. The heating element, the wiring, and the drive circuit are provided in the first region, the second region, and the third region, respectively, and the first recess is formed on the back surface of the second region of the substrate. It is characterized by having.

Since the thermal head substrate according to the present invention has the first recess on the back surface of the substrate in the second region, the heating element provided on the main surface of the substrate in the first region can be used as the main substrate in the third region. It is possible to prevent heat propagation to a drive circuit for driving a heating element provided on the surface.

Further, the substrate for a thermal head according to the present invention may be characterized in that it is a back surface of the substrate and has a second recess on the side opposite to the first recess with the first region interposed therebetween. Since the second recess is provided on the side opposite to the first recess with the first region interposed therebetween, the heat generation temperature distribution can be improved and the print quality can be improved.

Further, the substrate for a thermal head according to the present invention may be characterized in that the first recess extends from the second region to the third region. Since the first recess extends from the second region to the third region, it is possible to improve the heat dissipation of the drive circuit region provided in the third region.

Further, the substrate for a thermal head according to the present invention may be characterized in that it has a convex region in the first region and the heating element is formed in the convex region. Since the first region has a convex region and a heating element is formed on the convex region, the adhesion to the heat-sensitive medium can be improved and the print quality can be improved.

Further, the substrate for a thermal head according to the present invention is characterized in that the length of the first recess in the first direction is equal to or greater than the thickness of the substrate on which the first recess is formed. May be. A heating element provided on the main surface of the substrate in the first region by having a length of the first recess in the first direction equal to or greater than the thickness of the substrate on which the first recess is formed. Therefore, it is possible to prevent heat propagation to the drive circuit for driving the heating element provided on the main surface of the substrate in the third region.

Further, the substrate for a thermal head according to the present invention may be characterized in that the first recess is filled with the adhesive. Since the first recess is filled with an adhesive, the heat dissipation to the heat sink can be improved.

Further, the substrate for a thermal head according to the present invention may be characterized in that the heat radiating plate has a convex portion region that fits into the first concave portion. Since the heat radiating plate has a convex region that fits into the first concave portion, the adhesive layer can be made thin, so that the heat radiating property to the heat radiating plate can be improved.

It is possible to provide a substrate for an all-thin film type thermal head, which has a heat storage layer having a uniform thickness and is smaller than an all-thin film type thermal head. In addition, the sagging of the base of the heat generation temperature distribution is improved, and clear pixels can be obtained.
Further, since the substrate has recesses (holes or grooves) having different thicknesses locally, the substrate strength can be increased as compared with the all-thin film type thermal head having a heat storage layer having a uniform thickness.

1 (a) and 1 (b) are a plan view and a cross-sectional view schematically showing a substrate for an all-thin film type thermal head according to the present embodiment. 2 (a) and 2 (b) are a plan view and a cross-sectional view schematically showing a substrate for an all-thin film type thermal head according to the present embodiment. FIG. 3 is a diagram schematically showing the configuration of a substrate for an all-thin film type thermal head according to the present embodiment. FIG. 3A is a diagram showing the arrangement of a wear-resistant layer, a heat generating resistor, a drive circuit, a common electrode, a branch electrode, and a terminal electrode on the main surface of the substrate for an all-thin film type thermal head. 3 (b) is an enlarged view of a portion A of FIG. 3 (a), and FIG. 3 (c) is a diagram showing an enlarged cross-sectional view of the X3-X3 line portion. FIG. 4 shows a circuit diagram of a substrate for an all-thin film type thermal head according to the present embodiment. Further, it is a figure explaining the symbol which represents the arrangement area of a circuit element on the main surface of a substrate. FIG. 5 is a diagram illustrating an object and an effect of a substrate for an all-thin film type thermal head according to the present invention. FIG. 6 is a diagram illustrating the configuration of another embodiment of the all-thin film type thermal head substrate according to the present embodiment. FIG. 7 is a diagram illustrating the configuration of another embodiment of the all-thin film type thermal head substrate according to the present embodiment. FIG. 8 is a diagram illustrating the configuration of another embodiment of the all-thin film type thermal head substrate according to the present embodiment. FIG. 9 is a diagram showing a schematic diagram comparing the heat generation temperature distribution on the heating element forming region with each example. FIG. 10 is a diagram for explaining a manufacturing process of a substrate for an all-thin film type thermal head according to the present embodiment. FIG. 11 is a diagram illustrating the configuration of another embodiment of the all-thin film type thermal head substrate according to the present embodiment.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description is omitted.

The thermal head substrate according to this embodiment is configured by a substrate in which a heating element and a drive circuit are integrally formed, and a heat sink is fixed to the substrate with an adhesive. A substrate in which such a heating element and a drive circuit are integrally formed, and a thermal head substrate in which a heat sink is fixed with an adhesive are hereinafter referred to as an all-thin film type thermal head substrate.

1 and 2 show a plan view and a cross-sectional view of a substrate for an all-thin film type thermal head according to the present embodiment. FIG. 3 schematically shows the configuration of the all-thin film type thermal head substrate according to the present embodiment. FIG. 3A is a diagram showing the arrangement of a wear-resistant layer, a heat generating resistor, a drive circuit, a common electrode, a branch electrode, and a terminal electrode on the main surface of the substrate for an all-thin film type thermal head. 3 (b) is an enlarged view of a portion A of FIG. 3 (a), and FIG. 3 (c) is a diagram showing an enlarged cross-sectional view of the X3-X3 line portion. FIG. 4 shows a circuit diagram of a substrate for an all-thin film type thermal head according to the present embodiment.

Hereinafter, the wear-resistant layer, electrodes, and the like are omitted depending on the drawings. Only the heating element forming region and the drive circuit forming region according to the present invention are displayed. Further, in the following embodiments, it is assumed that the configurations of the heating element, the drive circuit, and the like formed on the main surface of the substrate are the same as those in FIGS. 3 (a), (b), and (c). I have to. FIG. 1A is a plan view for explaining the configuration of the substrate 1 for an all-thin film type thermal head according to the present embodiment. 1 (b) is a cross-sectional view of the X1-X1 line portion of FIG. 1 (a). This is an all-thin film type thermal head substrate 1 having a recess 8 formed on the back surface of the substrate 3. FIG. 1A shows the positional relationship of each region as seen from the main surface of the substrate, so that each region such as the recess on the back surface of the substrate and the position of the laminated film is seen through.

First, the configuration will be described. The substrate 3 is fixed to the heat sink 4 with the adhesive 5. The outer shape of the board is smaller than the outer shape of the heat sink. The pattern shown in FIG. 3A is formed on the main surface of the substrate. In FIG. 1 (a), an electrode for a heating element and a joint is formed in the first region 3a on the main surface. The formation region is shown by 3A. A branch electrode is formed in the same second region 3c. The wiring formation area is shown in 3C. In the same third region 3b, a drive circuit including a drive element and a logic circuit is formed. The drive circuit formation region is shown by 3B. Further, each pattern example and each region are shown in FIG. 3 (b).

Further, in FIGS. 1A and 1B, the first region 3a, the second region 3c, and the third region 3b are adjacent to each other and are continuous in the first direction. The first recess 8 is formed on the back surface of the second region of the substrate. In FIG. 1 (a), the position of the first recess 8 is shown by a broken line. In both figures, each region is shown by each broken line. In FIGS. 1A and 1B, the broken lines are shown separately for convenience, but can be formed continuously in the first direction. The same applies to the following drawings. The length "L2" of the first recess is equal to or longer than the print width "L1", and can be formed within "L" of the total width of the substrate.

In FIG. 1 (b), the first recess is filled with the adhesive 5 and its width “Wb” is shown. The substrate thickness of the recess is indicated by "t1". The width "Wb" can be set to a value equal to or larger than "t1". Further, the first recess 8 is formed in the second region of the boundary between the second region and the third region when viewed from the main surface of the substrate. Further, in the cross-sectional configuration of FIG. 1B, the first region is composed of a heating element forming region 3A, a substrate 3, an adhesive 5, and a heat radiating plate 4. The second region is composed of a substrate including a wiring forming region 3C and a first recess 8, an adhesive, and a heat sink. The third region is composed of a drive circuit forming region 3B, a substrate 3, an adhesive, and a heat sink.

First, each region on the main surface of the substrate will be described. In FIG. 1A, the broken line 3a indicates the region of the first region 3a. It contains a region 3A in which multiple heating elements are formed on the main surface. The first region is a region including a heating element portion and an electrode joint portion on the main surface. The heating element is formed in a row at a constant pitch and is composed of a heat generating portion and an electrode portion. The pattern of the heat generating portion includes a square type, a meander type, and the like, and print pixels are formed on the heat-sensitive medium. The material of the heating element is polysilicon, TaSiO2, TaN, or the like. It also has a joint of electrodes that joins with a heating element with low resistance. The electrode material is, for example, gold, aluminum, copper, or the like. The cross section of the first region is the region of the broken line 3a in FIG. 1 (b). It is composed of a substrate 3, an adhesive layer 5, and a heat sink 4. As the substrate material, glass, quartz, silicon or the like can be used. As the adhesive, an organic or inorganic adhesive can be used.

Further, an adhesive in which metal particles and inorganic particles are mixed can be used. As the heat sink, a metal such as iron, aluminum, 42 alloy, or amber can be used. In particular, in a substrate for an all-thin film type thermal head having a large printing length, it is necessary to make the coefficient of thermal expansion substantially the same as that of the substrate material. This is to reduce the warpage of the all-thin film type thermal head substrate due to heat generation during printing of the all thin film type thermal head substrate. When warpage occurs, the contact with the heat-sensitive medium deteriorates, uneven color density occurs, and the print quality deteriorates. Further, the 42 alloy is a metal developed so that the coefficient of thermal expansion is equivalent to that of glass. Further, it is a matter of course that the outer shape of the heat sink can be made slightly larger than the outer shape of the board to prevent the board from being cracked or chipped by an external force due to contact with other substances at the end of the board. Further, the cross-sectional structure has the same material structure from the first region to the third region.

Next, the second region 3c includes the wiring region 3C formed on the main surface of the substrate in FIG. 1 (a). Further, it can be said that there are two types of wiring patterns on the main surface of the second region. One is wiring that connects one end of the heating element to the driving element. The other is the wiring of a common electrode that connects a plurality of heating elements together to the power supply. The drive element is formed in 3B, in the drive circuit forming region. For example, as the driving element, a FET or the like can be used as a switching element. One of the above is a wiring that connects the drain of the FET and one end of the heating element. The other one is a common electrode in which the other ends of the heating element are collectively connected to the power supply.

The second region is a wiring portion in terms of configuration, and an electrode (common electrode) connected to the other end of the heating element can also be said to be a wiring portion. Therefore, it can be said that the second region 3c, the first region 3a, the second region 3c, and the third region 3b are continuous in the first direction.

Next, the third region 3b is a region in which the drive circuit 3B is formed on the main surface of the substrate. The drive circuit 3B includes a logic circuit such as a drive element and a shift register, a power supply wiring, and the like. A current is passed or stopped in the heating element for a short time. The transistors (FETs) that make up the circuit are elements that are particularly sensitive to temperature. In particular, the FET of the element that drives the heating element generates heat by itself because a relatively large current flows. Furthermore, heat propagation from the heating element is added, and heat dissipation measures are required. Further, it is desirable that the FETs constituting the logic circuit also have an operation guaranteed temperature range, maintain the range, and maintain the temperature closer to room temperature. As described above, the malfunction due to the temperature rise of the drive circuit unit causes deterioration of print quality, failure, and the like.

By the way, in order to reduce the size of the substrate, the arrangement distance between the heating element pattern and the driving element pattern in the driving circuit is prevented while preventing malfunction due to self-heating of the driving circuit and heat generation due to heat propagation from the heating element. Must be made smaller. That is, one of the purposes is to reduce the width "W1" (length in the first direction) of the second region sandwiched between the first region and the third region. In the conventional board for thermal heads with a hybrid configuration, the thickness of the heat storage layer is set according to applications such as low-speed printing and high-speed printing, considering only the thermal time constant (the product of thermal resistance and heat capacity) in the heating element formation region. Was.

This is because the driving IC mounting area having the heating element and the convex portion formed on the main surface of the substrate is arranged in consideration of the contact with the platen roller, so that heat is generated because it is separated from a sufficient distance of, for example, several millimeters. It was not necessary to consider the malfunction due to the temperature rise of the drive circuit due to the heat propagation from the body. In the thermal head substrate according to the present invention, the first recess 8 is provided on the back surface of the second region sandwiched between the first and third regions, which are wiring regions, and the thickness of the recess is "t1". The width "Wb" of the recess reduces the thermal resistance and heat capacity, dissipates heat to the heat sink 4, prevents heat propagation from the heating element to the drive element of the drive circuit, and reduces the width "W1" of the second region. It realizes miniaturization.

In the all-thin film type thermal head, the substrate thickness "t" in the first to third regions corresponding to the heat storage layer is the same. The temperature of the drive circuit formation region rises due to heat propagation from the heating element. In order to lower the temperature of the drive circuit forming region to the heat sink temperature, the distance must be equal to or greater than the distance between the heating element and the heat sink, which is the same as the thickness "t" of the substrate. The reason is that heat propagation propagates isotropically. in short. The width (length in the first direction) of the second region sandwiched between the first and third regions must be separated by a distance equal to or more than the same value "t" as the thickness of the substrate. For example, there is a proposal to change the thickness of the all-thin film type thermal head of Patent Document 1 to 10 to 800 μm. This changes the distance between the heating element and the drive circuit forming end to 10 to 800 μm. However, in this all-thin film type thermal head substrate, by providing the first recess 8 on the back surface of the substrate in the second region, the thickness “t” of the substrate excluding the recess in the second region is obtained. Regardless of, the width of the second region is reduced to enable the miniaturization of the all-thin film type thermal head substrate.

More specifically, for example, the interval of 10 to 800 μm corresponds to the dimension “W1” of the second region. In low-speed printing applications, the heat capacity of the heat storage layer is increased in order to increase the thermal time constant. Therefore, the thickness of the substrate is increased. Unless the length of the second region in the first direction is separated by the thickness of the substrate or more, the temperature of the third region in which the drive circuit is formed cannot be maintained at the heat sink temperature. Therefore, the width of the second region becomes large, and the size of the entire substrate cannot be measured.

Further, by providing a recess on the back surface of the substrate in the second region and radiating heat from the recess to the heat radiating plate, heat propagation to the third region where the drive circuit is formed is prevented. For example, if the thickness of the recess in the second region is 10 μm, the width of the recess should be 10 μm or more. Since the temperature drops to the heat sink temperature in this recess, the pattern of the drive element can be arranged at a position separated by 10 μm or more on the main surface of the substrate. This is because the recess is formed in the second region and the end of the recess is in contact with the adjacent third region.
Further, in FIG. 2, an example in which the second regions 3c and 3ca are configured with the heating element forming region 3A interposed therebetween can be shown. This is an example in which two recesses are formed on the back surface of the substrate 3 at the position of the dimension "W1a" from both ends of the heating element pattern formed on the main surface of the substrate. The dimension "W1a" can be equal to the dimension obtained by subtracting the width Wb1 of the first recess from the width W1 of the second region. For the second region 3ca and (wiring portion region 3Ca), a common electrode 106 can be formed on the main surface of the substrate.

Now, with reference to FIGS. 3 and 4, what kind of circuit and its pattern are arranged in the first to third regions on the main surface of the substrate and the first to third regions viewed from the cross-sectional structure, and how. Explain whether it is composed of various materials.

As shown in FIG. 4, a circuit of the 3A portion surrounded by a broken line is formed on the main surface of the substrate in the first region. The region surrounding the plurality of heating elements 29 arranged in a row at a constant pitch is the heating element forming region 3A. The heating element is composed of a heat generating portion and an electrode (joint portion). Further, on the main surface of the substrate in the second region, one is a circuit of the 3C portion surrounded by a broken line. This is a wiring portion 3C (branch electrode 109a) that connects the heating element and the drive element (switching element) 28. The other is a wiring portion of a common electrode 106 in which the other end of the heating element is commonly connected. It is 3Ca surrounded by a broken line. Further, a circuit of the 3B portion surrounded by a broken line is formed on the main surface of the third region. It is a drive circuit forming region 3B including the drive element 28.

More specifically, the other end of each heating element can pass through the branch electrode 109a and be connected to the individual switching element 28. The other end can be collectively connected to the common electrode 106. Then, the switching element 28 can be connected to a logic circuit that controls the on / off of the current and its time. The logic circuit can be composed of serial-in and parallel-out shift registers, 22 and a gate circuit for split printing, 27 and a data holding latch circuit, and 25 and a circuit power supply (not shown). The switching element 28 can be arranged in the end region near the heating element in the drive circuit forming region.

As the signal type, each signal terminal of the strobe 26 used for split printing, the latch 24 for holding data, the data 21, and the clock 23 can be derived. 108 and 108a are terminal electrode groups and indicate various signals and power supply terminal groups. Further, there are various application circuits, and it goes without saying that the above circuit is not limited.

By the way, FIG. 3 is a diagram illustrating an example of an arrangement position and a pattern in which the elements and wiring of the circuit diagram of FIG. 4 are formed on the main surface of the substrate 3 of the all-thin film type thermal head substrate. Further, the relationship between each circuit pattern forming region on the main surface and the first to third regions will be described.
FIG. 3A is a diagram showing an example of a pattern arrangement diagram of circuit elements of the entire substrate arranged on the main surface of the substrate 3 of the all-thin film type thermal head substrate. For example, the plurality of heating element 29 groups are arranged in the 3A region of the main surface of the substrate. Further, the symbol 106 represents a common electrode in the circuit diagram of FIG. 4, and the arrangement region thereof is indicated by 3Ca. Further, the branch electrode 109 indicates the arrangement region 3C. Further, the area where the wear-resistant layer is formed is indicated by the symbol 9. FIG. 3 (b) shows an enlarged plan view of part A of FIG. 3 (a). The pattern for two heating elements, the branch electrode, 109a and FET, 28 are shown. The width of the second region on the main surface of the substrate is "W1". Further, for example, the symbol 3A (3a) indicates that the heating element forming region 3A on the main surface of the substrate is included in the first region 3a. In this way, the positional relationship between the patterns of the first to third regions and the regions is explained.

FIG. 3 (c) is a cross-sectional view of the X3-X3 line portion of FIG. 3 (a). The laminated structure of the TFT and the wear-resistant layer 9 is shown. In each cross section of the substrate, the first region is represented as 3a, the second region is represented as 3c, and the third region is represented as 3b. Further, the description of the symbols such as the TFT portion in FIGS. 3 (b) and 3 (c) will be described in the manufacturing process described later.

More specifically, on the main surface of the substrate, the first region 3a including the heating element forming region 3A can be a region having the same width. The second region 3c including the wiring region (branch electrode 109a) 3C can be a region having the same width. The third region 3b, including the drive circuit forming region 3B, can be a region of the same width. In FIG. 3A, a heating element forming region 3A (first region 3a on the main surface) including a heating element and one end thereof are connected to a common electrode 106 (Vh in FIG. 4), and the other end is connected. , Is connected to the drive circuit forming region 3B (third region 3b on the main surface, 3B in FIG. 4) via the branch electrode 109a (second region 3c on the main surface, 3C in FIG. 4). The branch electrode is connected via the drive element 28 by the electrode 109 (Gh in FIG. 4).

Further, various signals and power supply terminals are collectively arranged at the symbol 108. The uppermost layer can form the wear resistant layer 9. Further, the length of the substrate is indicated by "L", the depth width of the substrate is indicated by "W", and the printing length is indicated by "L1".

FIG. 3B is an enlarged plan view, and the width of the heating element is represented by RW and the length is represented by RL. The first direction is the direction in which the heat-sensitive medium travels during printing. The switching element (driving element) of the current flowing through the heating element is composed of FETs, a source electrode 203, a gate 205, and a drain electrode 207. FIG. 3B is an enlarged cross-sectional view of part A in FIG. 3A. A plurality of heating elements are arranged in a row in the region 3A (here, two), and a branch electrode 109a is formed in the region 3C. "W1" is the width dimension of the 3C region. The drive element 28 is arranged at the end of the drive circuit forming region in order to connect to the heating element. The first region on the main surface of the drive circuit forming region has the same width as the 3A region. The heating element is a region including a joint portion (X portion in the figure) between the heat generating portion and the electrode. The second region on the main surface is the wiring portion regions 3C and 3Ca in FIG. 3 (b).

In this example, the width “W1” of the wiring portion region 3C is equal to the length of the branch electrode 109a. One of the purposes is to reduce the width "W1" of the 3C region to reduce the size of the substrate "W". Next is the definition of the dimension "W1". As shown in FIG. 3B, it is the distance from the joint portion of the heating element to the joint portion of the driving element. The switching element (driving element) does not include the FET junction portion (X portion in the figure) in the 3C region. Further, in FIG. 3C showing the cross-sectional structure, the uppermost layer is the wear-resistant layer 9, the next is the protective film 206, the electrode, the insulating film 204, the active layer 10a (same as the heating element layer 29), and the substrate. It is a figure which shows that it is composed of three. Further, although the drive circuit and the heating element configured by the TFT on the glass substrate 3 have been described above, it goes without saying that the drive circuit, the heating element, etc. may be formed on the so-called silicon substrate by semiconductor technology or the like. be.

Further, in the all-thin film type thermal head, the convex portion of the drive IC chip mounting region existing in the hybrid type thermal head is not formed, and it is possible to have a substantially flat surface. Since contact with the platen roller or the like does not occur, the size can be reduced by reducing the distance between the heating element and the drive circuit. However, in the all-thin film type thermal head, if the distance between the heating element and the drive circuit is reduced and brought closer, heat propagation from the heating element and the temperature rise of the driving element itself may occur, exceeding the guaranteed operating temperature range in a short time. It has become clear that there is a problem of causing malfunction.

FIG. 5 is a diagram for explaining the purpose and effect according to the present invention. It will be explained that the configuration of the substrate for the all-thin film type thermal head can shorten the distance between the end of the heating element and the end of the drive circuit forming region as compared with the all-thin film type thermal head, and can be miniaturized. In addition, the concept of the thermal time constant that determines the temperature rise and fall time of the heating element will be described. Then, the control method will be described with reference to a structural example applied to the substrate for an all-thin film type thermal head according to the present invention.

FIG. 5A is a cross-sectional view showing the configuration of an all-thin film type thermal head having a uniform 150 μm thick “t” substrate 3 (which functions as a heat storage layer). The substrate 3 is adhesively fixed to the heat sink 4. (The adhesive layer is not shown) is a cross-sectional view in which a heating element (length RL), a drive circuit forming region 3B, and a wear-resistant layer 9 are formed on the main surface of the substrate. The distance “W1” from the end of the heating element to the end of the drive circuit forming region is 150 μm. T0 to T3 show isothermal curves representing heat propagation in the heat storage layer when heat is generated by this structure.

The curve T0 is an isotemperature curve after the time T0 o'clock from the start of heat generation. It shows the temperature propagation between T0 and T3 hours. The time increases from T0 to T3, and the temperature decreases from T0 to T3. The isotropic heat propagation means that the temperature is the same on the line of the semicircular portion (heat storage layer region portion) of the circle T3 having a radius of 150 μm with a radius of “r”. That is, it is shown that the distance "W1" from the heating element on the main surface of the substrate, which drops to the heat sink temperature (room temperature), is 150 μm.

Next, the case of the structure of FIG. 5B will be considered. The difference from FIG. 5A is that a recess 8 is provided on the back surface of the substrate 3, the width “Wb” thereof is 10 μm, and the thickness “t1” of the recess is also 10 μm. The protrusion 4a of the heat radiating plate 4 is inserted and fixed. The dimension "W1" is 60 μm. Here, the point is the temperature distribution on the main surface at the position corresponding to the recess 8 on the back surface of the substrate. The curve T3 is an isotemperature curve after T3 hours have elapsed after heat generation. The temperature on the T3 line, which is in contact with the heat sink, is the heat sink temperature. That is, at the position on the main surface corresponding to the width (10 μm) of the recess 8, the temperature is lowered to the heat sink temperature. This can be considered in the same way as the structure in which "t" in FIG. 5A is 10 μm and “W1” is 10 μm. In this way, an ultra-thin recess is provided on the back surface between the heating element of the substrate and the drive circuit forming region to lower the temperature of the corresponding main surface and prevent heat propagation. The heat sink temperature can be approximately equal to room temperature.

As described above, the recess 8 can prevent heat propagation to the drive circuit forming region, but the problem is the deformation of the distribution of the curves of the isothermal curves T0 to T3 in FIG. 5 (b). The rough and dense shape of the isotemperature curve in the substrate is distorted. Therefore, a structural example devised as a solution is shown in FIG. 5 (c). That is, the structure is such that the recesses 8a are provided at equal distances with the heating element interposed therebetween. The heat transfer is confined to the region 3aa. The deformation of the heat generation temperature distribution can be solved by these two recesses 8 and 8a.

Now, the function of the heat storage layer will be described. In the all-thin film type thermal head having the configuration of FIG. 5 (a), the transient thermal response is considered by an equivalent electric circuit. When the thermal resistance R near the heating element, the heat capacity C, and the heat dissipation plate (earth end) are used, the temperature change of the heating element is when the voltage E is turned on and off in the series circuit of R (resistance) and C (capacitor). It is considered to be close to the transient response waveform of the charge / discharge current flowing through. The symbol τ is a time constant and can be represented by τ = C * R. τ indicates the speed of temperature rise and fall in the thermal circuit. If τ is small, it can be used for high-speed printing in which temperature rise and fall are repeated in a short time. If τ is large, it can be used for low-speed printing in which temperature rise and fall are repeated for a long time.

Further, R (resistance) correlates with thermal conductivity and surface area, and C (condenser) correlates with mass and specific heat. Therefore, the heat storage layer of the thermal head for high-speed printing can be formed thin (small mass), and the thermal head for low-speed printing can be formed with a thick heat storage layer (large mass). By the way, glass is used as the material. Empirically, although it depends on the structure, the thickness of the heat storage layer of the thermal head for high-speed printing applications (barcodes, label printers, etc.) is about 40 to 60 μm, and for low-speed printing applications (tone printing (photo) printers, etc.). The thickness of the heat storage layer of the thermal head is about 100 to 500 μm.

By the way, FIG. 5C is also a diagram showing a configuration in which the thermal time constant τ of the heating element can be adjusted. That is, the area of the semicircle of the area of the circle having the radius "r" in FIG. 5 (a), the area of the broken line rectangular portion "3aa" in FIG. 5 (c), and the heat capacity are correlated. Considering that the area of the circle with the radius "r" of 5 (a) is equal to the area of the half circle, the thickness of the substrate 3 is calculated to be about 176 μm when calculated based on the marked numerical values. can. As a result, it can be considered that the thermal time constants of the heating elements of FIGS. 5 (a) and 5 (c) are the same and have the same temperature rise and fall characteristics. The heating temperature distribution on the heating element will be described with reference to FIG. 9 described later. In reality, as will be described later in the examples, since the adhesive layer is interposed, the thermal resistance and heat capacity of the adhesive layer also have an effect. The optimum value of the actual configuration can be determined through trial production.

Similarly, the area of 3 cc, which is determined by the thickness (10 μm) and the width (10 μm) of the recess 8 on the back surface of the substrate, determines the thermal time constant for preventing heat propagation from the heating element. Similarly, the cross-sectional area of 3bb in the drive circuit formation region determines the thermal time constant in the drive circuit formation region. For example, if the recess 8 is extended to the bottom of the drive circuit forming region, the thermal time constant of the driving circuit forming region becomes small and the heat dissipation can be improved. If the heat generated by the driving element itself cannot be ignored, it becomes effective.

Further, when the thickness of the substrate is increased to about 176 μm in the above example, the temperature in the direction of the adjacent heating element does not decrease, and the separation of the color-developing pixels tends to be insufficient. In that case, it can be improved by forming a groove between the adjacent heating elements parallel to the 3aa surface and corresponding to the heating element pitch, the adhesive surface between the substrate and the heat sink, that is, the back surface of the substrate with a laser or the like. Practically, the thickness of the substrate can be designed in consideration of the thermal time constant and the separated state of the color-developing pixels, and can be set without forming a groove on the back surface of the substrate on the opposite surface between the adjacent heating elements. Further, it goes without saying that the dimensions in FIGS. 5 (b) and 5 (c) are shown as examples for explanation and are not limited.

In other words, the all-thin film type thermal head substrate according to the present embodiment includes a plurality of heat storage regions in which the thickness of the substrate is changed, and a configuration in which the heat storage regions are bonded to a heat radiating plate. It is possible to provide an all-thin film type thermal head that does not deteriorate the printing quality even in high-speed printing applications and low-speed printing applications by reducing the distance "W1" between the heating element and the drive circuit and changing the substrate thickness "t". can. Furthermore, since the distance between the heating element and the drive circuit forming region can be made constant regardless of the application, the pattern distance "W1" of the all-thin film type thermal head substrate can also be made constant, and the all-thin film type thermal head substrate can be made constant. It is possible to prevent an increase in the number of pattern varieties. In this way, in the substrate for the all-thin film type thermal head, the distance between the heating element and the drive circuit formation region is shortened compared to the all-thin film type thermal head with a uniform thickness of the heat storage layer, and the depth dimension of the substrate is "W". , Can be achieved in miniaturization.

Next, the improvement of the heat generation temperature distribution will be described. By forming the structure in which the two recesses are formed as shown in FIG. 2, the temperature distribution on the surface of the heating element and its vicinity is improved, blurring and tailing of the color-developing pixels are reduced, and clear printed pixels can be obtained. In addition, pixels close to the length RL of the heating element can be obtained, and fine pixels can be obtained. FIG. 9 is a schematic diagram showing a comparison of heat generation temperature distributions centered on the heating element along the line X3a-X3a of FIG. 3 (b) on one heating element. The vertical axis represents the heat generation temperature, and the coaxial broken line indicates the color development temperature of the heat-sensitive medium. For example, black is developed at a temperature higher than the color developing temperature. The horizontal axis indicates the position in the first direction, and the length of the heating element is represented by RL ,. The curve C represents the width of the second region by "W1". It shows that there is a temperature peak in the center of the heating element length "RL".

Now, when the heating element is formed on a heat storage layer having a uniform thickness on the lower surface of the heating element (cross-sectional configuration of FIG. 5A), the heat generation temperature distribution curve A and the local recess 8 on the lower surface of the heating element (Cross-sectional configuration of FIG. 5 (b)) and heat-generating temperature distribution curve B, and recesses 8 and 8a formed on the back surfaces of the substrates on both sides of the heat-generating body row (cross-sectional configuration of FIG. 5 (c)). It is a figure which compared with the heat generation temperature distribution curve C.

Further, Wx1 indicates the length of the color-developing pixel having the structure of FIG. 5 (a) on the curve A. Further, Wx2 indicates the length and position of the color-developing pixel of the structure of FIG. 5 (b) on the curve B. Further, Wx3 indicates the length of the color-developing pixel having the structure of FIG. 5 (c) on the curve C. From these, it can be seen that the center of the coloring part of Wx2 is deviated from the center of the length RL of the heating element. Further, it can be seen that the temperature of the curve C drops sharply at a distance of "W1" around the heating element. Furthermore, it can be seen that the length Wx3 of the color-developing pixel is also close to the heating element length RL.

Considering these facts, the curve C indicates that a clear pixel with less bleeding of the color-developing pixel can be obtained. On the other hand, the curve B is an asymmetric curve centered on the heating element because only the first recess is formed on the back surface of the substrate. It shows that the pixel position is slightly deviated from the heating element position. Depending on the application, it can be used without problems, but it is necessary to use it properly.

Next, the manufacturing process of the substrate for the all-thin film type thermal head will be described with reference to FIG. All figures are cross-sectional views. Although an example of the manufacturing process of the structure shown in FIG. 1 is shown, the manufacturing process of the other embodiment is omitted because the manufacturing process of the other embodiment can be achieved by the combination of the following steps.
[Thin film forming process]

First, the thin film forming step will be described with reference to FIG. 10 (a). A heating element 29 is formed in the heating element forming region 3A on the main surface of the substrate 3. Further, a drive circuit for controlling the current flowing through the heating element is formed in the drive circuit formation region 3B. The element configuration and arrangement formed on the glass substrate 3 in the thin film process are as shown in FIGS. 3 (b) and 3 (c). A non-alkali glass substrate for a liquid crystal display having a thickness of about 0.3 to 0.6 mm can be used. A large format substrate (hereinafter referred to as a mother glass substrate) is possible, and a substrate of about 1 m square can be obtained. First, the polysilicon layer 29 was deposited on the glass substrate 3 by using the LPCVD method (low-pressure chemical-vapor deposition method). The thickness of the polysilicon layer 29 is about 1000 Å.

Next, a photoresist is applied on the polysilicon layer 29, and an active region 10a of the heating element and the thin film transistor (TFT) is formed in a region to be a heating element forming region 3A and a drive circuit forming region 3B by using a photolithography technique. Formed a pattern for the including drive circuit. Next, after forming the gate insulating film 206 (thickness of about 750 Å), the polysilicon layer (thickness of about 3000 Å) was deposited again. Next, the portion 205 to be the gate electrode of the thin film transistor was etched by using a photolithography technique to form a gate electrode pattern.

Then, by sequentially ion-implanting phosphorus (P) and boron (B) into the polysilicon layer using an ion implantation method, the source region 203a and the drain region 207a of the thin film transistor (TFT) constituting the drive circuit are sequentially ion-implanted. Was formed. At the same time, a heating element region 29 was formed. In the ion implantation step, the impurities (phosphorus (P) or phosphorus (P) or , The dose amount of boron (B) and the depth of ion implantation (ion acceleration energy, etc.) were controlled and adjusted.

Next, the interlayer insulating film 204 is formed by using the LPCVD method. The interlayer insulating film 204 is made of, for example, silicon dioxide (SiO ₂ ) and has a thickness of about 500 nm. Next, the interlayer insulating film 204 in the electrode forming region is etched by using a photolithography technique, a contact hole is opened, a multilayer electrode metal (Ti / Al / Ti) is formed by a sputter method, and then a lift-off method is used. Wiring 106, 104, and 109 were formed. The thickness of each metal layer of the multilayer electrode metal (Ti / Al / Ti) can be, for example, (Ti film 100 nm / Al film 800 nm / Ti film 100 nm).

Finally, the protective layer 209 was formed on the uppermost layer of the glass substrate 3. For the protective layer 209, for example, a silicon-based inorganic insulating film such as silicon nitride (SiN _x ) can be used, and the thickness can be about 1000 Å. Through the above steps, a heating element (resistor) and a drive circuit were formed on the glass substrate 3. In the present embodiment, the heating element (resistor) and the drive circuit are composed of the polysilicon layer 10a and are formed at the same time. Further, since the manufacturing process of the array substrate of the liquid crystal display element can be applied, the mass production effect is large.

Further, as the resistor material constituting the heating element, a Ti metal layer can be used in addition to the polysilicon layer. Of course, it is also possible to form a film of another material such as TaSiO2, NiCr, and TaN as a heating element, form a pattern, and then create a TFT drive circuit in the thin film forming step. The substrate can be made of, for example, quartz (SiO2), silicon (Si), or glass such as non-alkali glass or crystallized glass.
[Abrasion resistant layer forming process]

Next, a process for forming the wear-resistant layer will be described with reference to FIG. 10 (b). The wear-resistant layer is formed on a surface on which at least the heat-sensitive medium slides while being pressurized by the platen roller. As shown in FIG. 10B, the wear-resistant layer 9 is formed so as to cover at least the heating element forming region 3A and the drive circuit forming region 3B on the main surface of the glass substrate 3. Further, the wear-resistant layer 9 can be formed on the entire surface as a protective film in a region other than the terminal electrode terminal 108 shown in FIG. 3A.

As the material of the wear-resistant layer, a substance such as SiC, Ta2O5, Si3N4, which is hard and has heat resistance and is hard to wear is used. The forming method can be a vapor deposition method, but it is mainly formed by a mask sputter method. The thickness is relatively thick for bar code applications and relatively thin for applications such as photo printing. Generally, the thickness is about 2 to 10 μm. In many cases, the substrate is heated to several hundred degrees Celsius or reverse sputter is added to improve the adhesion.
[Recess forming process]

Next, the first recess forming step will be described with reference to FIG. 10 (c). The first recess has a groove or hole shape. It has a function to prevent heat propagation from a heating element. The width “Wb” of the concave portion shown in FIG. 1 (b) is about 10 to 50 μm, and the thickness “t1” is also about 10 to 50 μm. The thickness "t0" of the mother substrate is about 0.3 to 0.6 mm. As a processing method, a rubber-based photosensitive resist may be used to create a pattern in which a portion to be processed is exposed in advance, and the pattern can be processed by a sandblasting method.

It can also be formed by using a device called a dicer (a silicon wafer chip dividing device) and using an outer peripheral blade that rotates at high speed. The processing position can be aligned because the pattern on the main surface can be confirmed from the back surface of the glass substrate. What is important is the removal of machining strain. After processing, it is lightly etched with an etching solution such as hydrofluoric acid to remove processing strain.

However, if hydrofluoric acid or the like is etched in the next substrate thinning step, this process becomes unnecessary in this step. Further, when the thickness "t1" of the recess is as thin as about 10 μm, it is possible to prevent cracking during processing of the substrate by temporarily adhering a temporary protective plate to the main surface of the substrate for processing. Further, this temporary protective plate can be peeled off after the heat sink bonding step in the subsequent step to prevent cracks in the recesses of the ultrathin portion. Further, a photoetching technique with high mass productivity can be used for forming the recesses when the width of the recesses is large and the etch factor (ratio of the side etching dimension and the depth dimension) is small.
The above method can be applied to all of the formation of other recesses such as the second recess.
[Substrate thinning process]

Next, the substrate thinning step will be described with reference to FIG. 10 (d). First, the main surface is covered with a protective resist on the entire surface, and the back surface is etched with an etching solution such as hydrofluoric acid. This step is a step of determining the thickness "t" of the substrate in the regions other than the recesses in the first region and the second region. It is a value that determines the temperature rise and fall time (heat time constant) of the heating element, which differs depending on the application. The thickness "t1" is in the range of about 40 to 200 μm. The etching time can be several tens of hours. Further, as the protective resist to be applied to the main surface of the glass substrate 3, a film resist or the like can be used in addition to the photosensitive resist. As a resist coating method, dip coating, spray coating, screen printing and the like can be used. In addition, since the thickness of the recess is further etched in this step, it can be set to be thicker in advance in the previous step.
[Individual piece division process]

Next, a step of dividing the substrate for an all-thin film type thermal head into individual pieces (not shown) will be described. The substrate pattern for an all-thin film type thermal head shown in FIG. 3A is manufactured by multi-imposing it on a mother glass substrate. The individual piece division is a process of dividing a multi-faceted all-thin film type thermal head substrate into individual pieces. As the individual dividing device for the mother glass substrate, the wafer dividing device described above can be used.

In addition, the following two methods can be adopted as the method.
First, the mother glass substrate is divided into individual pieces, and then bonded to the heat sink. The heat sinks are individually mounted on the mother glass substrate for all thin film type thermal heads. This is a method of dividing the heat sink, which is integrally bonded to the mother glass substrate after being bonded to the glass. In the latter case, the outer shape of the heat sink forms a collar around the heat sink, a relief for the cutting blade is created around the heat sink, and the outer shape is larger than the outer shape of the all-thin film type thermal head board, and the scribe line is on the mother glass board. Along, scribe in the XY direction to individualize. The latter method is advantageous in terms of cost.
[Heat sink bonding process]

Next, the heat sink bonding process will be described with reference to FIG. 10 (e). Here, the method is to divide the mother glass substrate into individual pieces and then bond them to the heat sink. The individualized glass substrate and the preformed heat sink are adhered with an adhesive. First, the adhesive 5 is applied to the adhesive surface of the heat radiating plate in advance using a dispenser or the like. In this embodiment, the adhesive is applied by screen printing or a dispenser.

Next, as the adhesive, for example, an epoxy adhesive mixed with alumina particles can be used. An individualized glass substrate was pressed against the adhesive surface coated with the adhesive, and in that state, it was heated at a temperature of 150 ° C. for 10 minutes to cure and bond the adhesive. The heat sink is made of, for example, aluminum, and the thickness can be, for example, about 1.0 mm. The thickness of the adhesive material after the heat sink is bonded is about 10 μm, and the thinner the adhesive material, the more preferable. Further, as the adhesive, for example, an epoxy adhesive having a high thermal conductivity and used as a liquid underfill material can also be used. Further, in the present embodiment, as the adhesive, an adhesive having a relatively low heat resistant temperature of about 150 ° C. can be used. The thermal conductivity of the epoxy adhesive used in this example is 2.0 w / m2k. The glass is 1.1w / m2k. Of course, an inorganic adhesive can be used.
[Terminal cable connection process]

Next, the terminal cable connection process will be described with reference to FIG. 10 (f). This is a step of connecting the terminal electrode forming regions 108 and 108a shown in FIG. 3A to the terminal cable. As a terminal cable, FPC is thermocompression bonded with ACF (anisotropic conductive film) (not shown). As the FPC, for example, a polyimide sheet (thickness 50 μm) formed with a flash gold-plated copper thickness of 18 μm as wiring can be used. ACF can be pressure-bonded and heat-cured at 180 ° C. for 5 seconds at a pressure of 3 MPs. Through the above steps, a thermal head using an all-thin film type thermal head substrate is completed.

Next, an embodiment will be described. In the description of the following examples, the wear resistant layer is not shown. Further, the pattern arrangement and configuration of the heating element forming region, the drive circuit forming region, and the like on the main surface of the substrate are all the same as those in FIGS. 3A, 3B, and 3C.

[Example 1]
1 (a) and 1 (b) are a plan view and a cross-sectional view for explaining the configuration of the all-thin film type thermal head substrate 1 according to the present embodiment. FIG. 1A is a perspective view of each region in order to show the positional relationship of each region. FIG. 1 (b) is a cross-sectional view of the X1-X1 line portion of FIG. 1 (a).

The configuration will be described. The substrate 3 is fixed to the heat sink 4 with the adhesive 5. The outer shape of the substrate is smaller than the outer shape of the heat sink 4. In FIG. 1 (a), an electrode for a heating element and a joint is formed in the first region 3a on the main surface. The formation region is shown by 3A. A branch electrode is formed in the same second region 3c. The formation region is shown in 3C. In the same third region 3b, a drive circuit 3B including a drive element and a logic circuit is formed. The formation region is shown by 3b. (In each figure, the dashed lines indicating each area appear to be separated, but they are actually continuous.)

The first to third regions are adjacent to each other and are continuous in the first direction. The first recess 8 is formed on the back surface of the second region of the substrate. In FIG. 1 (a) of the plan view, the position of the first recess 8 is shown by a transparent broken line. The first recess is formed to have a length equal to or longer than the print width "L1" and a length of "L2". The length "L2" of the first recess is a length within the substrate length "L". In FIG. 1 (b), the adhesive 5 is also filled in the first recess, and “Wb” indicates the width of the recess. The substrate thickness of the recess is indicated by "t1". The width “Wb” of the first recess is set to a value equal to or higher than the substrate thickness “t1”. Further, the first recess is located on the boundary side between the second region and the third region when viewed from the main surface, and is formed in the second region. “W1” indicates the width of the second region 3c, and indicates the width of the wiring region 3C on the main surface of the substrate 3.

[Example 2]
2 (a) and 2 (b) show a plan view and a cross-sectional view of the all-thin film type thermal head substrate 301 in which the second recess 302 is formed on the back surface of the substrate. In FIG. 2B, the cross-sectional structure is a structure in which the first region 3a is sandwiched between the two second regions 3c and 3ca. However, the wiring portion of the branch electrode 109a exists on the main surface of the second region 3c sandwiched between the first region 3a and the third region 3b, but the wiring portion is on the substrate main surface of the second region 3ca. Has a wiring portion of the common electrode 106.

By providing a recess 8 on the back surface of the substrate in the second region to prevent heat propagation from the heating element 29 to the drive circuit side, the heating temperature distribution on the surface of the heating element in the first region is measured in the first direction. It turned out that the distribution was not normal, and it was found that the shape of the printed pixels changed. Therefore, by providing the second recess 302 on the side opposite to the first recess 8 with the first region interposed therebetween, a bilaterally symmetric heat generation distribution centered on the peak temperature at which the temperature distribution is normally distributed was obtained. .. In terms of the cross-sectional structure, the first region can be formed between the first recessed end and the second recessed end, the first region can be sandwiched between the first region, and the second region can be formed at a symmetrical position. That is, the dimension "W1a" is equal to "W1"-"Wb". Recesses 302 and 8 are formed at positions of dimension "W1a" from both ends of the heating element. Further, in this configuration, the heat generation temperature distribution has the effect of shortening the tail portion of the normal distribution, that is, the temperature change becomes steep at the tail portion, and the blurred portion of the printed pixel is reduced. can.

Further, the substrate portion of the region sandwiched between the first recess 8 and the second recess 302 is a region that determines the thermal time constant of the heating element. The time for raising and lowering the temperature is determined by the thermal resistance and heat capacity in this region. That is, by changing the thickness "t1" of the substrate in this region, it is possible to obtain a substrate for an all-thin film type thermal head for low-speed and high-speed printing. Thick for low-speed applications and thin for high-speed applications. In addition, as another effect, the color-developing pixels become clear and the print quality is improved. Further, the widths "Wb" and "Wb1" of each recess do not have to be the same. There are no restrictions on the "Wb1" dimension, and it can be formed outside the region.

[Example 3]
FIG. 6 (a) is a plan view and a cross-sectional view of the all-thin film type thermal head substrate 401 in which the first recess formed on the back surface of the second region 3c of the substrate is extended to the third region and the recess 402 is formed. ) And (b). In FIG. 6A, which shows a plan view of the main surface of the substrate, the broken line region 402 is a broken line indicating the position of the recess 402 region. It is shown that the back surface of the drive circuit formation region is formed in a region including the entire surface corresponding to the drive circuit formation region 3B.

In this example, the shape of the recess 402 region is one hole shape. However, when the drive circuit is arranged at regular intervals, which is aggregated by blocks for driving several tens of units of heating elements, it can be formed into a plurality of hole shapes corresponding to the blocks. Further, since the width "Wb1" of the second recess 302 and the width "Wb" of the first recess 402 can be made larger than those in the above embodiment, a photo-etching technique having a high mass productivity with an etch factor of about 1.0 is used. Can be processed. For example, "Wb1" can be as large as several tens of μm or more, and "Wb" can be as large as several hundreds of μm or more. Further, it is of course possible to form a convex portion on the heat radiating plate and bond it to the concave portion on the back surface of the substrate in order to improve the heat radiating property.

Further, the width (length in the first direction) of the second region including the wiring portion on the main surface is better as it is smaller. For example, when the width "W1" is about 100 μm, the first recess must be formed within the range, so that the width “Wb” can be an extremely narrow recess of about 10 μm. High-precision processing is required in manufacturing. Therefore, the stretching widens the width of the recesses, facilitating manufacturing. Further, when the convex portion 4a that is in contact with the first concave portion or the second concave portion is formed on the heat radiating plate, the width of the convex portion is widened and the manufacturing becomes easy. Further, since the thermal resistance in the drive circuit forming region can be further reduced, it is possible to prevent the temperature from rising due to the heat generation of the drive element itself.

[Example 4]
A recess 502 having a second recess and a recess having a shape surrounding the heating element forming region 3A on the back surface of the substrate, and the first recess being integrated with the recess extending to the third region. 7 (a) and 7 (b) show a plan view and a cross-sectional view of the all-thin film type thermal head substrate 501 formed by the above. The recess 502 can be machined using a highly mass-producible photo-etching technique.

[Example 5]
An all-thin film type formed on the top of a substrate having a second recess and a first recess on the back surface of the substrate and having a heating element forming region 3A on the main surface of the substrate processed into a convex shape 602 in advance. The plan view and the cross-sectional view of the thermal head substrate 601 are shown in FIGS. 8 (a) and 8 (b).

The shape of the convex portion 602 is preferably a shape having a cross section close to a semicircle so that the medium slides smoothly. Further, the length can be formed up to the width "L" of the substrate with the print width "L1" or more. As a method for manufacturing the convex portion 602, a so-called photoetching technique can be used. By controlling the adhesion of the photosensitive resist with the heating temperature and increasing the underetch, it is possible to smooth the shoulders of the convex portions and prevent defects such as breakage of the formed thin film from occurring. Further, the step "t3" of the convex portion requires some ingenuity in applying the photosensitive resist. A roll coater or spray coating method can be used. The step of the convex portion is generally limited by the step limit in the exposure process. For example, by using the projection exposure method, it is possible to develop a fine pattern up to a height of about several tens of μm, “t3”. The height "t1" can be about several μm to 100 μm.

As described above, the substrate on which the convex portion is formed in advance is processed by the manufacturing process described above to complete the thermal head using the all-thin film type thermal head substrate.
Further, the higher the height "t3", the higher the contact with the heat-sensitive medium and the better the print quality.
Of course, the substrate having the convex portion 602 can be applied to all of the above-described embodiments.

By the way, there is a partial glaze type thermal head in which a heating element is formed on a convex portion. The substrate is alumina, a thin glass layer is formed on the surface thereof, a thick glass layer formed in a chevron shape is formed in the heating element forming region, and a heating element is formed on the top thereof, and the mounting area of the drive circuit IC is formed. Is formed on a thin flat glass layer. However, the purpose of this type is only to improve the contact with the heat sensitive medium. One of the purposes of the all-thin film type thermal head substrate 601 is to reduce the size of the substrate. One of the purposes is to narrow the width "W1" (the length of the first recess in the first direction) of the second region sandwiched between the first and third regions when viewed from the main surface of the substrate. It was done. Further, the substrate material and composition are different from those of the partial glaze type thermal head.

Further, the effect of the protrusion is that the heat stored in the chevron protrusion comes into contact with the heat-sensitive medium, so that the contact area is increased, heat is dissipated, and heat propagation toward the drive circuit forming region is reduced. Further, since the creepage distance from the heating element to the driving element becomes long, the temperature propagating to the driving element also decreases. Therefore, the width of the second region seen from the main surface of the substrate can be narrowed, so that miniaturization can be achieved. The chevron-shaped protrusions on the substrate can be formed by a grinding method, an etching method, sandblasting, or the like. The height of the protrusion can be about several microns to about 100 μm.

[Example 6]
The thickness of the substrate sandwiched between the first recess 8 and the second recess 302 is reduced, leaving the thickness of the mother glass substrate 702 (t0), and the thermal time constant of the heating element is set to the thickness "t". 11 (a) and 11 (b) show a plan view and a cross-sectional view showing an embodiment of the all-thin film type thermal head substrate 701 that has been adjusted and the first recess is extended to the third region. A second recess (groove) 8 and a first recess (groove) 8a are formed across the substrate and sandwich the heating element forming region 3A on the main surface. The first recess (groove) extends to the back surface including the drive circuit forming region 3B. The thermal time constant can be adjusted when the thickness of the substrate in the region sandwiched between the first and second recesses is "t". The thickness of the recess is "t1". Further, since the thickness of the adhesive layer 5 becomes thicker, the thermal resistance increases, and the heat dissipation property deteriorates, the heat dissipation plate 4 forms a convex portion 4a that fits into the substrate recesses 8, 8a, and is fixed with the adhesive 5. Has been done.

For example, the thickness 702 (t) of the mother glass substrate is 0.5 mm, the thickness “t” of the substrate in the region sandwiched between the first and second recesses is 0.1 mm, and the first and second recesses are The thickness "t" of the substrate in the region sandwiched between the two can be 30 μm. The recesses are machined by grinding or photoetching. In the case of grinding, it is possible to grind in one pass by using a copying grindstone in which the grinding surface of the outer peripheral blade is machined into the shape of a recess. In addition, the thickness of the substrate can be increased, and the strength can be increased.

As described above, the substrate for the all-thin film type thermal head is a wiring formed at the end of the heating element and the end of the drive circuit forming region from the all-thin film type thermal head having a heat storage layer formed with a uniform thickness. The distance can be reduced and miniaturization can be achieved. Further, since the wiring distance is shortened, the wiring resistance is lowered and the power efficiency can be improved. In addition, since heat propagation can be confined in the region between the first recess and the second recess of the substrate, the tail of the heat generation temperature distribution becomes smaller, and the pixel with less bleeding and tailing of the color-developing pixel (color-developing dot). Is obtained, and the print quality is improved. Further, since the region between the first recess and the second recess of the substrate determines the thermal time constant of the heating element, the thickness of the region can be varied to control the thermal time constant. Therefore, it is possible to provide a substrate for an all-thin film type thermal head for low-speed to high-speed printing.

Further, in the all-thin film type thermal head substrate according to the present invention, the first or second recesses have grooves and holes locally formed on the back surface of the substrate, and thus have a uniform thickness. Compared to the substrate, the strength of the substrate is increased, and the durability against external stress during manufacturing and assembly, processing, and printing is improved.

1,301,401,501,601,701 Substrate for all thin film type thermal head 3 Board 3a 1st area 3c 2nd area 3b 3rd area 3A Heating element forming area 3B Drive circuit forming area 3C Wiring forming area 4 Heat sink 5 Adhesive layer 8th Concave part of 1
L Overall width of the substrate for all thin film type thermal head L1 Effective printed length L2 Length of the first recess t1 Thickness of the first recess Wb Width of the first recess

Claims (7)

A substrate having a first region, a second region, and a third region arranged in order in the first direction,
A heating element provided on the main surface of the substrate and
A drive circuit provided on the main surface of the substrate and for driving the heating element, and
Wiring provided on the main surface of the substrate and electrically connecting the heating element and the drive circuit,
A heat radiating plate bonded and fixed via an adhesive is provided on the back surface of the substrate.
The substrate is made of glass, quartz, or silicon.
The heating element, the wiring, and the drive circuit are provided in the first region, the second region, and the third region, respectively.
It has a first recess on the back surface of the second region of the substrate, and has a first recess.
The adhesive is filled in the first recess, and the back surface of the substrate and the heat sink are adhesively fixed.
The thermal head substrate is characterized in that the first recess extends from the second region to the third region .
The substrate for a thermal head according to claim 1, wherein the back surface of the substrate has a second recess on the side opposite to the first recess with the first region interposed therebetween.
The substrate for a thermal head according to claim 1 or 2, wherein the drive circuit includes a thin film transistor. The substrate has a convex region in the first region.
The substrate for a thermal head according to any one of claims 1 to 3, wherein the heating element is formed in the convex region.
The length of the first recess in the first direction has a value equal to or greater than the thickness of the substrate on which the first recess is formed, and the length of the second region in the first direction. The substrate for a thermal head according to any one of claims 1 to 4, wherein the substrate is as follows .
The substrate for a thermal head according to any one of claims 1 to 5, wherein the first recess is filled with the adhesive.
The substrate for a thermal head according to any one of claims 1 to 6, wherein the heat radiating plate has a convex region that fits in the first concave portion .

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