JP2919239B2 - Optical printhead mounting structure and method of forming the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting structure of an optical print head using an LED (light emitting diode) element as a light emitting source and a method of forming the same.

[0002]

2. Description of the Related Art In a conventional optical print head mounting structure, an LED (light emitting diode) array element is provided on a substrate.
A method has been adopted in which the drive elements are aligned in rows, and the drive elements are aligned in parallel with the rows, and the respective electrodes are directly connected using wire bonds.

[0003] The method using the wire bond enables very compact mounting, so that the size and cost of the printer can be reduced. However, since a wire bond is used for connection, a large amount of capital investment for wire bonding is required when mass production is attempted.

For this reason, in recent years, instead of the wire bonding method, the structure of an optical print head connected without using a wire bond has been attracting attention in order to improve productivity per unit time. Examples of such a connection include JP-A-2-3354 (hereinafter referred to as Document 1) and JP-A-62-167645 (hereinafter referred to as Document 2).
Is disclosed.

FIG. 5A is a cross-sectional view of a main part showing a structure of an optical print head disclosed in Document 1. As shown in FIG.

According to this, reference numeral 40 denotes a metal substrate,
2 is a polyimide insulating film, 44 is an external input electrode pattern,
46 is a connection bump, 48 is a drive element, 50 is a p-type electrode,
52 is an LED array element and 54 is a die bond resin.

A method for mounting the optical print head is as follows.
The LED array elements 52 are aligned and mounted on the metal substrate 40. A polyimide insulating film 42 having the same height as the upper surface of the p-type electrode
0. Next, the LED driving element 48 is connected to the driving element 48 and the electrode 50 on the LED array element and the polyimide insulating film 42 through solder bumps 46 having a height of 20 μm to 200 μm by using solder reflow or thermocompression bonding. The external input electrode pattern 44 is directly connected by applying pressure.

FIG. 5B is a cross-sectional view of a main part showing the structure of the optical print head disclosed in Document 2. As shown in FIG.

According to this, 60 is the first and second 2
A support substrate having a step of two planes, 62 an electrode pattern formed on the first surface, 64 a common electrode pattern formed on a second plane of the support substrate, 66 an LED array element, 68 an LED array element An electrode pattern formed thereon, 70 is a driving element, 72 is an electrode pattern for the driving element, 74 is a conductive adhesive for fixing the LED array element 66 on the common electrode pattern 64 on the second surface, 76 Is a solder bump for connecting each electrode pattern.

Next, the mounting method shown in FIG. 5B will be briefly described.

First, first and second planes having steps are formed on the support substrate 60. Further, the LED array element 66 is fixed on the common electrode pattern 64 on the second plane via the conductive adhesive 74. The height of the electrode pattern 68 on the LED array element is substantially the same as the height of the electrode pattern 62 on the first plane of the support substrate.

The drive element electrode pattern 72 and the LE
The electrode pattern 68 for the D array element and the electrode pattern 62 on the first surface are directly connected by using solder bumps 76. Note that the support substrate 60 may be an integrated substrate or two types of support substrates having different thicknesses. Further, the structure may be such that the support substrate 60 can be separated at the step portion.

[0013]

However, when the optical print heads disclosed in the prior art documents 1 and 2 were to be manufactured, there were the following problems.

First, in the mounting structure disclosed in Document 1,
It is necessary to use an expensive polyimide insulating film in a thickened state, and after forming a polyimide insulating film on a metal substrate, a copper foil is attached and etched to a desired electrode pattern. With this method, it is difficult to achieve mass productivity. For this reason, a method of forming a wiring substrate using a polyimide insulating film on a metal substrate requires many steps of coating, curing, forming a metal thin film for wiring and forming a circuit pattern, and one by one. This is because the batch processing described above is added during the process, which makes it difficult to automate by the inline method.

The height of the LED array element provided on the substrate surface is usually 0.3 mm to 0.5 mm, and the height of the LED array element is almost the same as that of the LED array element. Requires a thick insulating film. The manufacturing cost for forming such a thick film increases.

In Document 2, since the common electrode pattern is formed on the second surface of the step portion of the supporting substrate, the electrode pattern is formed on the first surface in the case of an integrated substrate, and A common electrode pattern is formed on the second surface.
In such a manufacturing method, the steps are complicated, and mass production is difficult. In addition, even when a step is formed by bonding two substrates, the number of laminating steps and the number of substrates increase, and there is a problem that the cost of the substrate increases in any of the methods.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and a first object of the present invention is to provide a low-cost and mass-producible structure for mounting an optical print head. And a method for forming the same.

A second object of the present invention is to provide a mounting structure of an optical print head having a stable connection between a common electrode pattern-LED driving element and an LED array element-driving element, and a method of forming the same.

[0019]

According to the present invention, there is provided an optical print head comprising:
An individual LED array element comprising an ED array, each having an upper electrode and a lower electrode, an insulating layer, provided on the lower surface of the insulating layer, and protruding from the lower surface end in a cantilever shape. And a first conductive layer having a lower electrode of each LED array element which is fixed in a state of being electrically connected thereto and having flexibility, and a driving element for driving the LED array element on the upper surface of the insulating layer. A wiring substrate having a second conductor layer provided on the substrate, and the upper electrode and the upper electrode of each LED array element being aligned substantially on the same plane. A driving element electrically connected to the second conductor layer.

In practicing the present invention, it is preferable that the lower electrode and the first conductor layer are connected to each other by using an adhesive resin having conductivity.

According to the forming method of the present invention,
(A) an insulating layer, and a first conductive layer common to each of the LED array elements on the lower surface of the insulating layer, and a separate second conductive layer provided on the upper surface of the insulating layer corresponding to the input terminal of the driving element.
A step of preparing a double-sided wiring board having a conductive layer and a drive element provided with bumps on input and output terminals; and (b) a part of the second conductive layer and the insulating layer from the second conductive layer side of the double-sided wiring board. Removing (c) until the surface of the first conductor layer is exposed; (c) fixing the upper electrode of the LED array element and the output terminal of the driving element so as to be electrically coupled; (E) applying a conductive adhesive to the exposed surface of the conductive layer; (e) fixing the input terminal of the drive element to the second conductive layer so as to be electrically coupled; (f) LED array Fixing the lower electrode of the element to the exposed surface of the first conductive layer with the conductive adhesive.

[0022]

According to the configuration of the optical print head of the present invention described above, the LED array element having the upper and lower electrodes, the insulating layer, the lower surface of the insulating layer, and the cantilever from the lower surface end. Each LED is provided so as to protrude like a beam and
The lower electrode of the array element is fixed on the upper surface of the flexible first conductor layer and the insulating layer, which are fixed in a state of being electrically connected.
A wiring board provided with a second conductor layer provided for driving the ED array element, and an upper electrode of each LED array element and an upper surface of each of the second conductor layers are aligned on substantially the same plane; And a driving element electrically connected to the upper electrode and the second conductor layer. For this reason, according to this mounting structure, at the time of fabrication, a wiring board (here, a wiring board was a part of the second conductor layer and the insulating layer of the double-sided wiring board was removed until the surface of the first conductor layer was exposed. Since the existing double-sided wiring board having excellent productivity can be used for the processing board, the processing step of the wiring board or the multi-face removal is facilitated, and mass production can be achieved. Therefore, it is not necessary to provide an expensive polyimide resin on a substrate as in the conventional case, and it is not necessary to separately provide a conductor layer on a substrate having a new step. Can be planned.

Further, since the first conductor layer can be used as a common electrode pattern, there is no need to use a metal substrate as in the prior art, and it is not necessary to newly provide a common electrode pattern on the substrate. Therefore, the number of manufacturing steps can be reduced, and the structure is simple.

Further, since the lower electrode of the LED array element and the flexible first cantilever-shaped conductor layer are fixed with a conductive adhesive, the resistance value of the connection portion can be reduced. There is an advantage.

Further, according to the forming method of the present invention, a double-sided wiring board, a driving element and an LED array element are prepared, and an existing copper-clad glass epoxy substrate is used for the double-sided wiring board, and then the second conductor is formed. The second conductor layer and the insulating layer are removed until a part of the surface of the first conductor layer is exposed from the layer side. At this time, since the wiring board can be formed by easily removing the second conductor layer and the insulating layer by using an etching or a machining method, the insulating layer and the external electrode input pattern can be formed, and the supporting substrate can be formed in a lower level than before. It is no longer necessary to form a step-like step and provide an electrode pattern on the substrate. For this reason, the mass productivity of the wiring board can be improved.

Thereafter, the upper electrode of the LED array element and the output terminal of the drive element are fixed so as to be electrically coupled. At this time, it is preferable to perform positioning so that the height of the upper electrode and the height of the second conductor layer are substantially equal. Subsequently, a conductive adhesive is applied to the exposed surface of the first conductor layer. Subsequently, the input terminal of the drive element and the second conductor layer are fixed so as to be electrically coupled. Thereafter, the lower electrode of the LED array element is fixed to the first conductor layer via the conductive adhesive. The resistance value of the joint between the lower electrode and the first conductor layer fixed in this manner becomes lower because the conductive adhesive is used.

In the case where the lower electrode of the LED array element and the first conductor layer are finally bonded with a conductive adhesive, LE
Even if there is a slight difference in height between the D array element and the wiring board, as shown in the second embodiment (described later), the thickness of the cantilever-shaped protrusion of the first conductor layer is several tens μm. Since it is thin, it can bend easily. That is, it has flexibility. Therefore, the upper surfaces of the upper electrode and the second conductor layer can be positioned substantially on the same plane, and as a result, the alignment adjustment between the drive element and the upper electrode and between the drive element and the second conductor layer can be performed at a high height. This is easier than the conventional structure which requires alignment of two wirings at different positions.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. In each of the drawings, the structure obtained during this manufacturing process is merely a cross-sectional view schematically showing the shape, size, and arrangement of each component so that the present invention can be understood.

Further, actually, a plurality of LED array elements and driving elements are mounted on a substrate to constitute an optical print head, but each figure shows a main structure of each LED array element and driving element portion. Only is shown.

FIG. 1 is a sectional view of an essential part of an optical print head for explaining a first embodiment of the present invention.

Next, the mounting structure of the optical print head of the first embodiment will be described with reference to FIG.

The mounting structure of the first embodiment of the present invention can be roughly divided into three parts, namely, an LED array element 3
0, a wiring board 32, and a driving element 26. The LED array element 30 includes a light emitting section 18 provided on the upper surface of the main body section 16 and an upper electrode 20.
A lower electrode 22 is provided on the lower surface of the main body 16. The wiring board 32 includes an insulating layer 10a, a flexible first cantilever-shaped conductor layer 12a protruding from the lower end of the insulating layer, and an LED on the upper surface of the insulating layer 10a. Second conductor layer 1 individually provided for each array element
4a. Further, the drive element 26 is provided with a bump 28 on its lower surface.

The lower electrode 22 of the LED array element 30 is fixed to the surface of the protruding first conductor layer 12a in a state where it is electrically connected by the conductive adhesive layer 24a.

The upper electrode 2 of the LED array element 30
0 and the second conductor layer 14a are connected in a state of being electrically bridged by the drive element 26, and this connection is performed by connecting the upper electrode 20 and the drive element 26 and the second conductor layer 14a and the drive element 26 to each other. Are fixed via the bumps 28. In this case, it is preferable that the upper surface of the upper electrode 20 of the LED array element main body 16 and the upper surface of the second conductor layer 14a of the wiring board 32 be located at the same position. The reason is that the light amount of the light emitting unit 18 provided on the upper surface of the LED array main unit 16 is designed to show the maximum value when it is vertical. For this reason, if the angle deviates extremely from the vertical direction, the luminous efficiency decreases, which is not preferable. In addition, about each material, a component, and a mounting method used for this 1st Example,
The method of forming the optical print head will be described in detail as necessary.

Next, the structure of a second embodiment of the present invention will be described with reference to FIGS.

FIG. 2A shows that the wiring board 32 has a thickness L.
The case where the thickness is larger than the thickness of the ED array element 30 is shown. FIG. 2B shows a case where the LED array element 30 is larger than the thickness of the wiring board 32.

The mounting structure shown in FIGS. 2A and 2B is the same as that of the first embodiment except that the thickness of the insulating layer 10a in the wiring board 32 is different. Description is omitted. In these cases, as in the case of the first embodiment, the upper surface of the upper electrode 20 and the upper surface of the second conductor layer 14a are arranged at substantially the same plane position. Therefore, L
When the thickness of the ED array element 30 is different from that of the wiring board 32, the upper electrode 20 and the upper surface of the second conductor layer 14a are aligned substantially horizontally, so that the thickness of the protrusion of the first conductor layer 12a is thin (about 36 μm). Therefore, the upper electrode and the second conductor layer can be easily vented upward or downward to maintain the parallelism between the upper electrode and the second conductor layer.

Next, the formation method of the first embodiment will be described with reference to FIGS. 3A, 3B and 4C and FIGS. 4A and 4B.

First, the first conductor layer 12 is formed on the lower surface of the insulating layer 10.
And a second conductor layer 1 on the upper surface corresponding to the driving element.
4 is prepared. The first conductor layer 12 is a common conductor layer for each LED element of the LED array element, and the second conductor layers 14 are provided corresponding to the input terminals of the drive element. This double-sided wiring board 15
As the substrate (hereinafter, referred to as a substrate), for example, preferably, an existing copper-clad glass epoxy substrate is used. Preferably, the material of the first and second conductor layers of the substrate 15 is a copper foil, and the thickness of each of the copper foils is about 36 μm.

Separately from this, the driving element 2 having the bumps 28 provided on the input terminal and the output terminal (not shown) is provided.
6 is prepared (FIG. 3A). The thickness of the double-sided wiring board 15 prepared at this time depends on the LED array element body 16.
(See FIG. 3C).

Next, a part of the second conductor layer 14 and a part of the insulating layer 10 is removed from the side of the second conductor layer 14 of the double-sided wiring board 15 by, for example, milling until the surface of the first conductor layer 12 is exposed. (FIG. 3B). Here, the remaining insulating layer 10a and first conductor layer 12a
The structure including the second conductor layer 14a is referred to as a wiring board 32.

As a method of removing the second conductive layer 14 and the insulating layer 10, the second conductive layer 14 may be first etched under any suitable conditions, and then the glass epoxy base 10 may be removed by milling. . In FIG. 3B, although a part of the second conductive layer 14a is illustrated as being removed from the insulating layer 10a, the insulating layer 10a has
It may be extended to 1.

Next, the output terminal (not shown) of the drive element 26 of the upper electrode 20 of the LED array element 30 is fixed to the output terminal (not shown) of the LED array element 30 using a bump 28 by using, for example, a thermocompression bonding method. Are electrically coupled (FIG. 3C). At this time, for example, a gold (Au) bump is preferably used as the bump 28. In this case, after the upper electrode 20 and the second conductor layer 14a are previously aligned so as to be substantially parallel, the upper electrode 20 and the driving element 26
Is preferably fixed to the bump 28 on the output terminal side.

Next, a conductive adhesive, preferably, for example, a silver paste (Able Bond manufactured by Ablestech Co.) is applied to the exposed surface of the first conductive layer 12a (FIG. 4A).

Thereafter, a rubber sheet or the like is spread on the lower surface of the first conductor layer 12a, and the second conductor layer 14a is fixed to the input terminal of the drive element 26 with the bump 28 interposed therebetween, for example, by a thermocompression bonding method. .

Thereafter, the structure in which the LED array element 30, the wiring board 32 and the driving element 26 are fixed to each other is put into a heating furnace or a thermostat, and preferably, for example, 150
The adhesive is cured by performing a heat treatment at about 1 ° C. for about 1 hour.
The portion to which the conductive adhesive is applied by performing such a process becomes the conductive adhesive layer 24a, and is shown in FIG.
Is obtained. The structure thus obtained is the mounting structure of the optical print head of the present invention.

Through the above-described steps, the main structure of the first embodiment of the present invention is formed.

Next, a method of forming the second embodiment will be described with reference to FIGS.

Even when parts having different thicknesses of the LED array element 30 and the wiring board 32 are used, the first
The mounting structure of the second embodiment can be formed in the same steps as the forming method of the embodiment. Therefore, a detailed description of the forming method of the second embodiment is omitted here.

The order of the formation method of the first embodiment is as follows.
This is only an example, and the order is not necessarily limited to this order as long as the upper electrode 20 and the first conductive layer 14 can be accurately matched.

Further, as can be understood from the above description, the first and second embodiments of the present invention are constructed using the existing copper-clad glass epoxy substrate, and thus are excellent in mass productivity due to the multi-cavity. The double-sided wiring board can be processed at extremely low cost.

As can be understood from FIGS. 2A and 2B, even if the height of the LED array element and the wiring board are different, the copper foil of the first conductor layer can be freely moved upward or downward. It is possible to bend, that is, since the copper foil of the first conductor layer is flexible, the upper surface of each of the upper electrode and the second conductor layer of the LED array element can be located substantially on the same plane. As a result, the driving element and the upper electrode,
There is also an advantage that alignment with the second conductor layer becomes extremely easy.

Further, the lower electrode of the LED array element and the first
Since the conductive layer and the conductive layer are fixed using a conductive adhesive, the resistance value of the connection portion is reduced.

[0054]

As can be understood from the above description,
According to the mounting structure of the optical print head of the present invention, an individual LED array element including an upper electrode and a lower electrode,
An insulating layer, which is attached to the lower surface of the insulating layer, and is provided so as to protrude from the lower surface end in a cantilever manner, and that the lower electrodes of the LED array elements are electrically coupled to each other. A wiring substrate including a second conductive layer provided on the upper surface of the fixed first conductive layer and the insulating layer fixed to the LED so as to correspond to the driving element for driving the LED array element; A drive element electrically connected to the upper electrode and the second conductor layer, with the upper surfaces of the electrode and the second conductor layer being aligned on substantially the same plane.

For this reason, an existing double-sided wiring board having excellent productivity (for example, a copper-clad glass epoxy board) can be used as the wiring board, so that multiple wiring boards can be easily formed and mass production is possible. Therefore, it is not necessary to provide an expensive polyimide resin on a substrate as in the related art, and it is not necessary to separately provide a conductor layer on a substrate having a new step, so that the number of manufacturing steps and the working time can be reduced. Can be planned. Therefore, manufacturing costs can be reduced.

Further, since the first conductor layer can be used as a common electrode pattern, there is no need to use a metal substrate as in the prior art, and it is not necessary to provide a new common electrode pattern on the substrate. The number of steps can be reduced.

The lower electrode of the LED array element and the first electrode
Since the conductive layer and the conductive layer are fixed to each other with a conductive adhesive, there is an advantage that the resistance value of the connection portion is reduced. In addition, since the copper foil of the first conductor layer has flexibility, the upper surfaces of the upper electrode and the second conductor layer of the LED array element can be positioned substantially on the same plane, and as a result, the drive element and the drive element can be located on the same plane. There is also an advantage that alignment with the upper electrode and the second conductor layer becomes extremely easy.

Further, according to the forming method of the present invention, an existing double-sided printed wiring board is used as a double-sided wiring board, and is first removed from the second conductor layer side until the surface of the first conductor layer is exposed.
At this time, since the second conductor layer and the insulating layer can be easily removed by using a mechanical processing method or the like, the insulating layer and the external electrode input pattern can be formed, or the support substrate can be processed into an L-shaped step compared to the conventional case. Thus, it is not necessary to provide an electrode pattern on the substrate, and mass production of the wiring substrate can be achieved, which contributes to reduction in the number of manufacturing steps. Furthermore, since an existing double-sided wiring board can be used, the cost can be reduced.

Thereafter, the upper electrode of the LED array element and the output terminal of the drive element are fixed so as to be electrically coupled. At this time, it is preferable to perform positioning so that the height of the upper electrode and the height of the second conductor layer are substantially equal. Subsequently, a conductive adhesive is applied to the exposed surface of the first conductor layer. Subsequently, after the input terminal of the drive element and the second conductor layer are fixed so as to be electrically coupled, the lower electrode is fixed to the first conductor layer via the conductive adhesive. The resistance value of the joint between the lower electrode and the first conductor layer fixed in this manner becomes lower because the conductive adhesive is used.

In the case where the lower electrode and the first conductor layer are finally bonded with a conductive adhesive, the first conductor layer is projected even if there is a slight difference in height between the LED array element and the wiring board. Since the thickness of the portion is as thin as several tens of μm, the first conductor layer is easily bent. Therefore, the adjustment of the alignment between the upper electrode and the second conductor layer is easier than in the related art.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a mounting structure of an optical print head for explaining a first embodiment of the present invention.

FIGS. 2A and 2B are cross-sectional views showing a mounting structure of an optical print head for explaining a second embodiment of the present invention. (A) shows the case where the thickness of the wiring board is larger than the LED array element, and (B) shows the case where the thickness of the LED array element is larger than the wiring board.

FIGS. 3A to 3C are process diagrams for explaining a forming method according to the first embodiment of the present invention.

FIGS. 4A and 4B are process diagrams subsequent to FIG. 3 for explaining the formation method of the first embodiment of the present invention.

FIGS. 5A and 5B are cross-sectional views for explaining the structure of a conventional optical print head.

[Explanation of symbols]

 10, 10a: insulating layer 11: cut 12, 12a: first conductive layer 14, 14a: second conductive layer 15: double-sided wiring board 16: LED array element body 18: light emitting section 20: upper electrode 22: lower electrode 24 : Conductive adhesive 24a: conductive adhesive layer 26: drive element 28: bump 30: LED array element 32: wiring board

Continuation of the front page (72) Inventor Ryo Fujiwara 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (56) References JP-A-2-278889 (JP, A) JP-A-2- 3354 (JP, A) Japanese Utility Model Sho 62-167645 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41J 2/44 B41J 2/45 B41J 2/455 H01L 33/00

Claims (3)

(57) [Claims] 1. An individual LED array element comprising an LED array and comprising an upper electrode and a lower electrode, respectively; an insulating layer, a cantilever attached to a lower surface of the insulating layer, and a cantilever from an end of the lower surface. The LED array element is provided on the upper surface of the flexible first conductor layer and the insulating layer, which are provided so as to protrude, and are fixed in a state where the lower electrodes of the LED array elements are electrically connected to each other. A wiring board including a second conductor layer provided corresponding to the driving element to be driven; and an upper surface of each of the upper electrode and the second conductor layer of each LED array element positioned on substantially the same plane. A mounting structure for an optical print head, comprising a driving element electrically connected to the upper electrode and the second conductor layer in a combined state. 2. The optical print head mounting structure according to claim 1, wherein the lower electrode and the first conductor layer are connected to each other using a conductive adhesive resin. Printhead mounting structure. 3. (a) An insulating layer and LE on the lower surface of the insulating layer.
A double-sided wiring board including a first conductor layer common to each of the D array elements and an individual second conductor layer provided on an upper surface of the insulating layer corresponding to an input terminal of the driving element; Preparing an LED array element provided with a lower electrode and a drive element provided with bumps on input terminals and output terminals; and (b) preparing the second conductor layer from the second conductor layer side of the double-sided wiring board. Removing a portion of the insulating layer until the surface of the first conductor layer is exposed; and (c) fixing the upper electrode of the LED array element and the output terminal of the driving element so as to be electrically coupled. (D) applying a conductive adhesive to the exposed surface of the first conductor layer, and (e) electrically coupling the input terminal of the drive element to the second conductor layer. To fix it,
(F) fixing the lower electrode of the LED array element to the exposed surface of the first conductive layer with the conductive adhesive. .