JP2590916B2 - Method of manufacturing thick film type thermal head - Google Patents

Description

The present invention relates to a method for manufacturing a thick-film type thermal head,
In particular, the present invention relates to a pulse trimming method for eliminating a variation in resistance value of a heating resistor.

[Prior art and its problems]

2. Description of the Related Art In a thermal recording head (thermal head) used in a recording unit such as a printer or a facsimile apparatus, a demand for higher image quality has recently been increasing. Therefore, it has become a serious problem to stabilize the resistance value for a long time as well as to make the resistance value of each heating resistor uniform.

In particular, thick-film type thermal heads, in which peripheral circuits including heat-generating resistors are formed by the thick-film printing method, are easy to manufacture, have low cost, and have high mechanical strength. On the other hand, on the other hand, there is a problem that the pattern accuracy is lower than that of the thin film type, the resistance value tends to vary, and the resistance value tends to deteriorate early.

By the way, this thick film type thermal head is generally
It is manufactured according to the flowchart shown below.

That is, first, an insulating substrate such as a glazed ceramic substrate is used as a starting material, a conductor is printed by a screen printing method, and then baked, and the conductor is patterned by a photolithographic etching method to form an electrode.

Thereafter, a resistor layer pattern for forming the heating resistor is formed by screen printing and firing.

 Finally, the wear-resistant layer is printed and fired to complete.

The resistance value of each heating resistor element of the completed thermal head is determined by the sheet resistance value of the resistor paste to be used, the pattern size of the resistor pattern, and the firing temperature.

However, there are many variation factors, such as component differences of the resistance paste due to lot variation or viscosity change, printing conditions such as screen tension of a screen to be used or a degree of abrasion of a squeegee, and firing conditions such as reproducibility of a firing profile. It has been said that it is extremely difficult to equalize the resistance values of each heating resistance element with an accuracy within ± 10%.

The thick-film type thermal head is configured to selectively apply an electric pulse of a certain magnitude (power value) to a heating resistor element composed of a thick-film resistor according to image information so as to generate heat to a desired temperature. What is used. This thick film resistor is
Generally, it has a property that the resistance value changes according to the applied power. Therefore, the resistance value changes during use, and a change in the amount of heat generated causes a problem such as a change in print density. For this reason, there has been a drawback that conventionally, only a relatively small power can be used so that a change in the resistance value is small, and that a large change in the resistance value results in a large change in the resistance value and an extremely short life.

In addition, when driven at a constant voltage, the voltage is fixed in accordance with the initial resistance value, so that the resistance value decreases as the power application is continued. As a result, the actual applied power increases,
The change in resistance value was accelerated, and in some cases, it was destroyed.Therefore, in order to reduce the variation in the resistance value of each heating resistance element and stabilize the printing characteristics, the thick film method was used. A method is proposed in which after forming a thick film resistor, a high voltage pulse of a desired magnitude is applied to each thick film resistor to adjust (trim) the resistance value and to apply an electrical load for a short time. Have been. As described above, the so-called pulse trimming method of applying a pulse having a value corresponding to the width to be corrected in order to eliminate the variation in the resistance value of each thick-film low antibody is extremely difficult. Although it is an excellent method, conventionally, a method has been adopted in which pulse application is continued while increasing a voltage by a constant width until a desired resistance value is obtained.

However, in this method, it is necessary to apply a large number of pulses per bit to adjust the resistance value with high accuracy, and there is a problem that workability is poor.

That is, in a thick-film type thermal head formed by a normal method, there is a variation of about ± 25% in the resistance value, which can be suppressed to ± 3% or less in a pulse trimming step. Then, there was a problem in mass productivity, and there was a contradictory relationship that accuracy was deteriorated when trying to increase mass productivity.

The present invention has been made in view of the above circumstances, and has as its object to provide a thick-film type thermal head with good mass productivity and small resistance value variation.

[Means for solving the problem]

Therefore, in the present invention, when performing pulse trimming of a thick film type thermal head, a calibration curve indicating a relationship between an applied pulse and a change in resistance value is created in advance for at least one heating resistor for each process or for each head. In advance, the applied voltage value is determined based on the calibration curve and the initial resistance value of the bit. That is, according to the present invention, in a method of manufacturing a thick-film type thermal head in which a large number of thermal resistors formed by a thick-film method are arranged on the same substrate, after forming the heating resistors, the resistance value of each heating resistor is determined. A pulse trimming step of applying a voltage pulse to each heating resistor in order to make the heating resistor uniform, selects at least one heating resistor, and measures a change in resistance value of the selected heating resistor with respect to a change in the voltage pulse. Then, based on the measurement result, a reference voltage setting step of setting a voltage value that is smaller than the target value by a predetermined amount as a trimming reference voltage, and when trimming each heat-generating low antibody, starting from the reference voltage. The voltage is applied while measuring the resistance value after application, and the voltage value of the applied voltage pulse is gradually increased by a predetermined width until the target resistance value is reached. Characterized in that to include an adjustment process.

[Action]

According to the present invention, the behavior of the resistance value of a thick film resistor due to the application of a pulse can be either a resistance value change with respect to a voltage value or a resistance value change with respect to the number of pulses. Although it changes sensitively depending on the paste, firing conditions, firing conditions of the upper layer, that is, the overglaze layer, etc., attention is paid to the fact that there is some regularity and reproducibility within the same lot or within the same substrate. By performing a calibration curve in advance and determining an application pulse in accordance with the calibration curve, it is possible to perform high-precision trimming with a small number of application times.

In other words, conventionally, as shown in FIG. 2 (a), a method is employed in which the applied pulse is increased from the initial resistance value Rn at every constant voltage Δv, and this is repeated until the target resistance value _R0 is reached. On the other hand, in the method of the present invention, as shown in FIG. 2 (b), a value Vn >> Δv calculated from the beginning based on the previously calculated calibration curve is applied,
After approaching the target value, the applied voltage is gradually increased.

The outline of the pulse trimming method of the present invention will be described with reference to the flowchart shown in FIG.

First, a calibration curve to be applied to the thermal head is created (Step 101).

This calibration curve may be selected from a few bits in the same substrate, trimmed at a constant voltage step, and created from the value and the variation width of the resistance value, or a dummy bit may be formed beforehand. It may be created by performing a pulse test.

If a slight deviation is recognized, it may be obtained in advance by another test.

Next, trimming after each bit is performed according to this configuration curve.

First, an initial resistance value Rn is measured for each bit (Step 10).
2).

Then, an applied voltage is calculated based on the initial resistance value and the calibration curve (step 103).

Thereafter, a smaller application pulse is applied depending on the target accuracy (step 104), and measurement is performed (step 105).

Then, the determination (106) is performed. If the target value has not been reached, the process returns to the applied voltage calculation step (step 104).

When the target value is reached in this manner, the trimming is completed, and the trimming can be performed with much higher operability and higher precision than in the related art. In the conventional trimming of a constant voltage step, a large number of pulse applications were required to obtain the same level of accuracy, whereas in the method of the present invention, the voltage value was set so as to take a smaller value, Since the voltage value is gradually increased by a predetermined width until the target resistance value is reached while measuring the resistance value after applying the voltage pulse, 1 /
By requiring only about three pulse applications, mass productivity is greatly improved, and high-speed and more accurate trimming can be achieved.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIGS. 3, 4 (a) and 4 (b) are a flow chart showing a manufacturing process of an 8 dot / mm thick film type thermal head according to the embodiment of the present invention and a sectional view of the same thick film type thermal head. . (Note that FIG. 4 (b) corresponds to A- in FIG. 4 (a).
(A sectional view).

This thick-film type thermal head is composed of lead electrodes (A ₁ ) composed of all thick-film patterns arranged at predetermined intervals on a glazed ceramic substrate 10... Am, Am + 1, Am + 2, Am +
3, Am + 4,... (An) and a linear thick film resistor R mainly composed of ruthenium oxide disposed on the upper layer, and a current is applied to each lead electrode according to image information. The predetermined element region of the thick-film resistor R is supplied with heat and is selectively heated.

Next, a method of manufacturing the thick film type thermal head will be described.

First, as shown in the block diagram of FIG. 5, the pulse trimming device used here is a probing device 2 for bringing a probe into contact with a heating resistor of a thermal head 1 to be measured, and the probing device via a switching means 3. 2, a resistance measuring device 4 that is switchably connected to 2 and measures a resistance value of each bit; and a pulse application circuit 5. A pulse applied to the heating resistor is controlled while measuring the resistance value of each bit. It is configured to control up to the area.

The pulse applying circuit 5 includes a pulse generator 50 and a constituent curve creating unit 51 for creating a calibration curve from a change in resistance value with respect to the peak value of the applied pulse, and an applied pulse based on the calibration curve and the measured resistance value of the bit. A pulse control circuit 52 for controlling the peak value and the number of pulses is provided so that trimming can be performed efficiently according to a calibration curve.

First, a glazed ceramic substrate 10 is prepared (N ₁ ), and a full-thickness film layer is formed on this surface by screen printing and firing (900 ° C.) (N ₂ ).
The lead electrodes A ₁ ... An are patterned by photolithography. (N ₃ ) Thereafter, screen printing and baking (870 ° C.) are performed using a resistive paste containing ternium oxide as a main component to form a linear thick-film resistor R. (N ₄ ) Next, the overglaze paste is opened, screen-printed, and fired to form the wear-resistant layer Q.

Subsequently, each resistance value of the thick film resistor of the thick film thermal head is measured. (N ₅ ) The variation of the resistance value at this time was as large as about ± 25% as shown in FIG. 6 (a).

Next, the first 32 bits are trimmed in constant voltage steps to create a calibration curve. (N ₆ ) This result can be approximated by a temporary curve as shown in FIG. 7 (a), and has a relational expression shown by the following equation (1).

Then, for each-bit, each initial resistance value R and target resistance R ₀
A difference ΔR = R−R ₀ from the _value is calculated, and V is obtained by applying this to the equation (1). First, half of the voltage V calculated in this way, that is, V ₁ = 1 / 2v is applied, and the resistance value is measured.
When the target resistance region has not yet reached the target resistance region (R ₀ ± ΔR ₀ , where ΔR ₀ is determined according to the required accuracy), V ₂ = 1 / 2V + 1 / 4V is applied. And also, to measure the resistance value - continuing the pulse trimming to reach the target region while reducing the sequentially width so that (N _7). When reaching the target area, the peak value of the pulse actually applied and ΔR /
The relationship with R is shown in FIG. FIG. 4 (a) and (b)
It can be seen from the comparison that the calibration curve was correct.

After trimming for each bit in this way, annealing is performed at about 200 ° C. for 30 minutes to stabilize the resistance value (N ₈ ).

As shown in FIG. 6 (b), the resistance value of the heating resistor of the thermal head thus formed has a variation of ± 3.
% And extremely high accuracy.

In conventional trimming in constant voltage steps, more than 20,000 pulses must be applied to achieve this accuracy, whereas the above method requires only about one-third the number of pulses to be applied. Is greatly improved.

Note that in the embodiment, the first 32
Using the result of pulse trimming for bits,
The number and position of the measurement bits can be changed without being limited to the embodiment, and a dummy bit may be formed in advance, and a calibration curve may be created from the measured value of the dummy bit. .

Further, the calibration curve may be created for each same lot or may be created for each substrate.

〔The invention's effect〕

As described above, according to the present invention, when performing pulse trimming of a thick film type thermal head,
A calibration curve is created for each process or head, and the applied power value is determined based on the calibration curve and the initial resistance value of the bit. It can be formed.

[Brief description of the drawings]

FIG. 1 is a flow chart showing the outline of the pulse trimming method of the present invention, FIG. 2 is an explanatory view showing a comparison between the method of the present invention and the conventional method, and FIG. 4 (a) and 4 (b) are cross-sectional views of the same thick film type thermal head, and FIG. 5 is a method according to the embodiment of the present invention. FIG. 6 (a) and FIG. 6 (b) are block diagrams showing a pulse trimming device used in FIG. 7, and FIG. 7 (a) is a diagram showing variations in resistance values of respective bits before and after pulse trimming, respectively. FIG. 7B is a diagram showing the calibration curve used in the method of the embodiment of the present invention and the peak value of the last pulse actually applied. 10: Glazed ceramic substrate, 1: Thermal head, 2: Probing device, 3: Switching means, 4, Resistor, 5, Pulse application circuit, 50: Pulse generator, 51: Calibration curve Creation unit, 52 ... Pulse control circuit.

Claims (1)

(57) [Claims] 1. A method of manufacturing a thick-film type thermal head, comprising arranging a large number of thermal resistors formed by a thick-film method on the same substrate, wherein after forming the heating resistors, the resistance value of each heating resistor is determined. A pulse trimming step of applying a voltage pulse to each heating resistor to make it uniform is to select at least one heating resistor and measure a change in resistance value of the selected heating resistor with respect to a change in the voltage pulse. A reference voltage setting step of setting, as a trimming reference voltage, a voltage value that is smaller than a target value by a predetermined amount based on the measurement result; Apply voltage while measuring the resistance value afterwards,
An adjusting step of gradually increasing the voltage value of the applied voltage pulse by a predetermined width until the resistance value reaches a target resistance value.