JP2830325B2 - Manufacturing method of thermal head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention 1) Field of the Invention The present invention relates to a method for manufacturing a thermal head used for a thermal printer or facsimile as an output device of a word processor, a personal computer or the like.

2) Prior Art Conventionally, the thermal head has been widely used because it has advantages such as low noise during printing and easy handling because a developing / fixing step is not required.

In such a thermal head, a heating resistor for connecting them is formed between a plurality of individual electrodes arranged in a row on an insulating substrate and a common electrode arranged corresponding to the tip of the individual electrodes. Then, electric power is supplied between the selected individual electrode and the common electrode to cause the heat generating resistor in that portion to generate heat, thereby performing thermal recording (printing).

By the way, if the resistance value of each heating resistor (that is, the heating resistor corresponding to each dot) disposed between each of the individual electrodes and the common electrode is not uniform, the temperature of the heating resistor at the time of generating heat is different. Occurs. Then, when printing is performed on thermal transfer paper or the like, density unevenness occurs in the printed “character” or “figure”.

Conventionally, in order to prevent the occurrence of the density unevenness, the resistance value of the heating resistor corresponding to each dot has been made uniform. This utilizes the property that when a predetermined electric field is applied within a range that does not cause resistance breakdown to the heating resistor, the resistance value of the heating resistor decreases according to the electric field strength.

As a conventional technique for equalizing the resistance value of such a heating resistor, for example, Japanese Patent Laid-Open No. 61-83053 is known.

In this publication, a trimming pulse having a constant width and different voltage values or a different number of trimming pulses having a constant width and voltage value is applied to the heating resistor. The publication describes, as an embodiment, an example in which a trimming pulse having a constant width and a different voltage value is applied to a heating resistor.

The one described in the embodiment measures the initial resistance value of the heating resistor corresponding to each dot on the insulating substrate, and when those initial resistance values are larger than the target resistance value R0, the heating resistor is measured. , A trimming pulse of a predetermined voltage V0 is applied to reduce the resistance value of the heating resistor. If the reduced resistance value is still larger than the target resistance value R0, a trimming pulse of a voltage V0 + ΔV obtained by adding ΔV to the predetermined voltage V0 is applied to further reduce the resistance value of the heating resistor. If the further reduced resistance value is still larger than the target resistance value R0, a trimming pulse of a voltage V0 + 2ΔV obtained by adding 2ΔV to the predetermined voltage V0 is applied to further reduce the resistance value of the heating resistor. Thus, the trimming pulse of the voltage V0 + nΔV added by ΔV is applied until the resistance value of the heating resistor falls below the target resistance value R0.

3) Problems to be Solved by the Invention However, as described above, even if the resistance values are made uniform by applying a trimming pulse to the heating resistors, each heating resistor can be used while the thermal head is used for a long period of time. The resistance value of the body varies. this is,
The heating resistor immediately after being formed on the insulating substrate surface is unstable and its resistance value changes with time. However, the heating resistor whose resistance value is uniformed by the trimming pulse still has an unsatisfactory resistance value. Probably because of stability.

Therefore, even with a thermal head that uses a heating resistor whose resistance value has been aligned by trimming, the resistance value decreases over time, causing variations, and the portion printed with a heating resistor with a large decrease in resistance value decreases. The printing density is higher than that of the portion printed with the small amount of the heating resistor. Then, there is a problem that density unevenness occurs in a printed matter.

Therefore, the present inventor studied a method of reducing the change over time of the resistance value of the heating resistor during a long use period of the thermal head, and as a result, when the heating resistor was thermally annealed, the heating resistor after the thermal annealing was heated. It has been found that the change over time in the resistance value is small.

FIG. 10 shows the change with time of the resistance value A when a continuous pulse for heating is applied to the heat-annealed heating resistor and the resistance value when a continuous pulse for heating is applied to the heating resistor that is not thermally annealed. Is shown over time. As can be seen from FIG. 10, since the heat-annealed heating element indicated by A has little change with time, the thermal head manufactured using the insulating substrate on which the heating resistor is formed can be used for a long time. Print density does not change.

Further, the present inventor, when thermally annealing the heating resistor,
The resistance value of the heating resistor changes (decreases) before and after the thermal annealing, and the amount of decrease may depend on the magnitude of the trimming voltage when the resistance value of the heating resistor is trimmed before the thermal annealing. discovered.

These will now be described in more detail with reference to FIGS.

FIG. 6 shows that when a trimming pulse is applied to a heating resistor having an initial resistance value Ri indicated by a circle and a target resistance value R0 = 1000Ω is trimmed to a value indicated by a square within a predetermined range, the heat generated by the trimming pulse is generated. This shows that when the resistor is thermally annealed, its resistance value changes to the value indicated by the symbol Δ.

FIG. 7 shows the trimming voltage V when the heating resistor is trimmed and the rate of change of the resistance value before and after thermal annealing with respect to the initial resistance value Ri (that is, drift: (Rt-Ra)
/ Ri, where Ra is the resistance value after thermal annealing). FIG. 7 shows that the higher the trimming voltage V, the greater the rate of change in resistance value due to thermal annealing. By the way, the fact that the trimming voltage V is high means that
As can be seen from JP-A-61-83053 or JP-A-1-271262, the amount of decrease Ri in the resistance during trimming is Ri.
-Rt is large. This means that, as the trimming voltage V is higher, the initial resistance Ri is higher as the trimming voltage V is higher, considering that the resistances Rt of the respective heating resistors after the trimming are completed are substantially uniform. In other words, a heating resistor having a high initial resistance Ri has a trimming end resistance value.
It can be seen that when Rt is substantially uniform, the trimming voltage V is high, and when the trimming voltage V is high, the rate of change in resistance Rt-Ra before and after thermal annealing is large. This is also apparent in FIG. 6, where the trimming end resistance value is shown.
When Rt is made substantially uniform, the heating resistor having a higher initial resistance Ri has a larger resistance change due to thermal annealing, and has a lower resistance Ra after thermal annealing.

Therefore, the resistance value after thermal annealing should be made uniform by increasing the value of the heating resistor having a higher initial resistance value Ri without making the trimming end resistance value Rt uniform.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to make uniform the resistance values of the heating resistors of a thermal head and reduce the amount of decrease in the resistance values over time.

B. Configuration of the Invention 1) Means for Solving the Problems In order to solve the above problems, a method of manufacturing a thermal head according to the present invention provides a method for manufacturing a thermal head that supports a plurality of individual electrodes and a tip of the individual electrodes on an insulating substrate surface. A common electrode arranged as
After forming the heating resistor connecting between the individual electrode and the common electrode, the initial resistance value of the heating resistor connecting between the individual electrode and the common electrode is larger than a predetermined trimming end target resistance value. A trimming pulse is applied to trim the resistance value of the heating resistor to a value within a predetermined range of the trimming end target resistance value, and then, the insulating substrate having the trimmed heating resistor formed on the surface is removed. A method for manufacturing a thermal head, comprising: a step of thermally annealing the heating resistor by maintaining the heating resistor at a predetermined temperature for a predetermined time, wherein the heating resistor has a larger initial resistance value than a heating resistor having a smaller initial resistance value. And setting a large trimming end target resistance value.

2) Operation In the method of manufacturing a thermal head according to the present invention described above, a large trimming termination target resistance value is set for a heating resistor having a larger initial resistance value than a heating resistor having a small initial resistance value. The resistance value becomes uniform. And
Since the resistance value of the heat-treated annealed heating element is stable, the amount of decrease in the resistance value of the heat-generated resistor of the manufactured thermal head with time is reduced.

3) Example Next, an example of the present invention will be described with reference to the drawings.

In FIG. 1, a thermal head C for performing thermal recording (printing) on a thermal recording paper B conveyed along the outer periphery of a platen roller A has a support made of a metal material having a high thermal conductivity such as aluminum or cast iron. 1 is provided on the upper surface of the support plate 1 on the left and right portions in FIG.
A ceramic insulating substrate 4 and a plastic printed wiring board 5 are adhered via adhesives 2 and 3, respectively.

In FIG. 1, an IC is provided on the upper surface of the printed wiring board 5 near the insulating substrate 4, and a wiring 5a is provided by printing on the right side of the IC in FIG. The input end side (the right side in FIG. 2) of the wiring 5a is connected to a socket 7 as a drive signal input terminal via a lead wire 6 penetrating the printed wiring board 5. The IC provided on the printed wiring board 5 is connected to wires 5 a of the printed wiring board 5 and individual electrodes 4 a of the insulating substrate 4 by wires 8 and 9.

As shown in detail in FIGS. 2 and 3, the insulating substrate 4 includes:
A plurality of individual electrodes 4a on the surface (ie, the upper surface)
The insulating substrates 4 are arranged in a row along the length direction (that is, the main scanning direction) X. A common electrode 4b is provided along the main scanning direction X, and the common electrode 4b is
A main body portion 4b1 extending in the main scanning direction X and a plurality of connecting portions 4 extending in the sub-scanning direction Y from the main body portion 4b1 in a comb shape;
b2. Then, the individual electrode 4a and the common electrode
The connection portion 4b and the connection portion 4b2 are alternately arranged along the main scanning direction X. Each of the alternately arranged individual electrodes 4a and the common electrode connecting portions 4b2 constitutes one of the heating resistors 4c1, 4c1,... (See FIG. 3).

The strip-shaped heating resistor 4c is thermally annealed.

Referring again to FIG. 1, the IC and wires 8, 9
Is sealed by a resin 10 and protected by a cover 11.

The thermal head H is composed of the members indicated by the reference numerals 1 to 11, and the respective heating resistors 4c1 are pressed against the thermosensitive recording paper B on the roller platen A to perform thermal recording.

Next, an embodiment of the method of manufacturing the thermal head will be described.

The insulating substrate 4 having the electrodes 4a, 4b and the heating resistor 4c formed on the surface as shown in FIG. 3 is manufactured by a conventionally known manufacturing technique such as a screen printing technique.

The resistance value of each heating resistor 4c1 of the insulating substrate 4 is trimmed by a trimming device shown in a block diagram of FIG.

In FIG. 4, a prober 21 is an electrode pad (not shown) of the individual electrode 4a (connection terminal portion used for connection with the wire 9 when assembling a thermal head later).
Are provided with deep needles 21a, 21a,. A multiplexer relay 22 is connected to the prober 21, and these prober 21 and multiplexer relay 22 are connected.
Is controlled by a computer 23 to select one bit among the heating resistors 4c1, 4c1,... Via the deep needle 21a and the individual electrode 4a.

The multiplexer relay 22 is connected to the computer 23
It is configured to be selectively connected to an output terminal of a pulse generator 25 or an input terminal of a resistance measuring instrument 26 via a changeover switch 24 controlled by the switch.

Next, the operation of the trimming device shown in the block diagram of FIG. 4 will be described with reference to the flowchart of FIG.

Each of the heating resistors 4c formed on the surface of the insulating substrate 4
When the process (trimming flow) for performing trimming 1 is started, the deep needle 21 of the prober 21 is
a, 21a,... contact the individual electrodes 4a, 4a,.
The initial resistance value Ri of the number (for example, 128) of the heating resistors 4c1 corresponding to the number (1) is measured.

 Next, in step S2, n = 1 is set.

Next, in step S3, a bit corresponding to n = 1 is selected.

Next, in step S4, a target resistance value Rt0 after completion of the trimming is calculated.

The target resistance value Rt0 is calculated using the following equation (1).

 Rt0 = a × Ra0 + b × Ri (1) where a and b are constants, Ra0 is a target resistance value after thermal annealing, and Ri is an initial resistance value.

The constants a and b are numbers that have been obtained in advance, and how to obtain those constants a and b will be described in the following (a) to (h).

(B) A plurality of samples are taken out of the insulating substrate manufactured by using the same rod as the insulating substrate on which the heating resistor to be trimmed is formed. Then, using the samples of these insulating substrates, for example, for a 128-bit heating resistor (see FIG. 6), using the trimming device shown in FIG. 4, the initial resistance value R1 of each heating resistor 4c1 is determined.
Measure i.

(B) Initial resistance value of each 128-bit heating resistor 4c1
The average value of Ri (see FIG. 6) is calculated.

(C) Each of the heating resistors 4c1, 4c1,... Is trimmed by setting, for example, a value of 70% of the average value Rh of the initial resistance Ri as the target resistance R0 (R0 = 0.7Rh) after the trimming is completed.

(D) Each of the heating resistors 4c1, 4c1,.
Resistance for 30 minutes after thermal annealing
Measure Ra.

(E) The value of the rate of change (Ri−R0) / Ri of the 128-bit heating resistor 4c1 after trimming and the rate of change after annealing (R
i−Ra) / Ri were calculated, and those values were plotted on the horizontal axis as shown by the solid line in FIG. 8, where the rate of change after trimming (Ri−R0) / Ri
Is plotted on coordinates where the vertical axis represents the rate of change after annealing (Ri−Ra) / Ri.

(F) Instead of 70% in (c) above, 80% and 60%
And the above (a) to (e) are repeated.

(G) The 128 × 4 data obtained by the above (a) to (f) are plotted on the coordinates in FIG. 8 and a straight line (see the solid line in FIG. 8) that can approximate the distribution of the data is plotted. Then, the straight line is approximated by the following equation (2). Then, values of α and β that can approximate the straight line are obtained.

(Ri−Ra) / Ri = α (Ri−R0) / Ri + β (2) The above α and β can be obtained by actually plotting the data on the coordinates shown in FIG. It can also be determined by computer processing.

(H) The following equation (3) is obtained by modifying the equation (2).

R0 = (1 / α) Ra + (α + β-1) Ri / α (3) In this equation (3), a = 1 / α (4) b = (α + β-1) / α ( 5), the above equation (3) becomes the following equation (6).

R0 = aRa + bRi (6) In the equation (6), the values of the coefficients a and b are constants determined by the above α and β. Therefore, from this equation (6),
If the resistance value Ra of the heating resistor 4c1 after thermal annealing is set to a certain target value (target resistance value after thermal annealing) Ra0, the resistance value after the end of the trimming according to the value of the initial resistance value Ri of the heating resistor 4c1 The target value of R0 (target resistance value after trimming) Rt0 is determined. That is, the values of a and b in the expression (1) are determined by the expressions (4) and (5).

 Returning to the description of the flowchart of FIG.

After performing the processing of step S4, step S5
It is determined whether or not the resistance value is within a predetermined range of the target resistance value Rt0 after the end of the trimming. If no (N), the process moves to step S6.

In step S6, the voltage value of the trimming pulse applied to the heating resistor 4c1 is calculated. As a method of calculating the voltage value, for example, the method described in the above-mentioned Japanese Patent Application Laid-Open No. 61-83053 or Japanese Patent Application Laid-Open No. 1-2271262 is adopted.

Next, in step S7, a trimming pulse is applied to the heating resistor 4c1.

Next, in step S8, the resistance value of the heating resistor 4c1 is measured, and the process returns to step S5. If yes (Y) in step S5, the process moves to step S9.

 In step S9, n = n + 1 is set.

Next, in step S10, it is determined whether n = n0. Where n0 is the probe that contacts the individual electrode 4a
This is a number obtained by adding 1 to the number of the 21 deep needles 21a. For example, if the number of the deep needles 21a is 128, n0 = 129. If no in step S10, the process returns to step S3. If yes, it is determined that the trimming of each heating resistor 4c1 connected to all the deep needles (for example, 128 deep needles) 21a is completed, and the next Move to step S11.

In step S11, it is determined whether or not all the heating resistors 4c1 on the surface of the insulating substrate 4 have been trimmed. If no in step S11, the process returns to step S1, and the prober 2 is attached to the pad of the individual electrode connected to the heating resistor 4c1 that has not been trimmed.
The first deep needle 21a is brought into contact with the heating resistor 4c1 to measure an initial resistance value Ri of the heating resistor 4c1. In the case of YES in step S11, the trimming flow of the heating resistor 4c1 on the surface of the insulating substrate 4 ends.

In the trimming flow described above, the target resistance value Rt0 after the end of the trimming of each heating resistor is determined to be different according to the value of the initial resistance value Ri. The target resistance value Rt0 is determined to be larger as the value of the initial resistance value Ri is larger.

Therefore, the heating resistor 4c1 after this trimming is completed.
Have variations in resistance values. Each of those heating resistors 4c
1 is then thermally annealed at, for example, 200 ° C. for 30 minutes, all the resistance values of the respective heating resistors 4c1 substantially fall within a predetermined range of the target resistance value Ra0 after the thermal annealing. .

As in the previous embodiment, a sample is taken out of an insulating substrate manufactured in the same lot and having a heating resistor formed on the surface, and the relationship between the rate of change after trimming and the rate of change after thermal annealing obtained from the sample (No. When the resistance value of the heating resistor after thermal annealing is made substantially uniform using the relationship, the resistance value of the heating resistor of the thermal head can be maintained substantially uniform over a long period of time. . that's all,
Although the embodiment of the thermal head according to the present invention has been described in detail, the present invention is not limited to the above-described embodiment, and various design changes can be made without departing from the present invention described in the appended claims. It is possible to do.

For example, when trimming the resistance value of each heating resistor 4c1, according to the magnitude of the initial resistance value Ri of each heating resistor 4c1, the target resistance value after the end of the trimming is larger for a heating resistor having a larger initial resistance value Ri. Although it is necessary to set Rt0 large,
Instead of determining the equation of the straight line shown in FIG. 8 and using the equation of the straight line to determine the target resistance value after the end of the trimming of each heating resistor, each heating resistor is changed according to the magnitude of its initial resistance value. It is also possible to set the target resistance value after trimming according to each of the classified steps.

9A and 9B, a plurality of individual heating resistors 4c1, 4c1,... Are arranged in the main scanning direction X in place of the thermal head using the strip-shaped heating resistors 4c. The present invention can also be applied to a thermal head in which the plurality of individual electrodes 4a, 4a,... And the common electrode 4b are individually connected by the individual heating resistors 4c1, 4c1,. .

C. Effects of the Invention According to the method for manufacturing a thermal head of the present invention described above, each heating resistor is trimmed such that a heating resistor having a larger initial resistance value has a larger trimming end resistance value than a heating resistor having a smaller initial resistance value. Therefore, the resistance value of each heating resistor after the thermal annealing can be made substantially uniform. In the method of manufacturing a thermal head according to the present invention, since the heating resistor of the thermal head is thermally annealed, the amount of decrease in the resistance value of the heating resistor over time can be reduced. Therefore, even when the thermal head is used for a long period of time, printed matter does not have density unevenness due to variation in resistance value.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a thermal head manufactured by one embodiment of the thermal head manufacturing method of the present invention, FIG. 2 is a perspective view of a main part of the thermal head, and FIG. 3 is a partial view of the main part. FIG. 4 is an enlarged view of a portion III in FIG. 2 as viewed in the direction of arrow, FIG. 4 is an explanatory diagram of a trimming device used for manufacturing the thermal head, and FIG. 5 is a diagram for explaining the operation of the trimming device of FIG. FIG. 6 is an explanatory diagram of a change in resistance value of a heating resistor due to trimming and thermal annealing;
FIG. 7 is a diagram showing the relationship between the magnitude of the trimming voltage and the rate of change of the resistance value of the heating resistor due to thermal annealing. FIG. 8 is a graph showing the rate of change of the heating resistor after trimming, the rate of change after annealing, and the initial resistance value. FIGS. 9A and 9B are explanatory diagrams of a thermal head to which the present invention can be applied, and FIGS.
FIG. 10 is a diagram showing a change with time of a heat-generating resistor subjected to thermal annealing and a heat-generating resistor not subject to thermal annealing. 4 ... insulating substrate, 4a ... individual electrode, 4b ... common electrode, 4c
1 ... Heating resistor,

Claims (1)

(57) [Claims] 1. A plurality of individual electrodes (4a) on a surface of an insulating substrate (4), a common electrode (4b) arranged corresponding to the tip of the individual electrodes, and the individual electrodes (4a) and the common electrode. (4b) After forming the heating resistor (4c1) connecting between them, the initial resistance value (Ri) of the heating resistor (4c1) connecting between the individual electrodes (4a) and the common electrode (4b). Is larger than a predetermined trimming end target resistance value (Rt0), a trimming pulse is applied to change the resistance value of the heating resistor (4c1) to a value within a predetermined range of the trimming end target resistance value (Rt0). After the trimming, the insulating substrate (4) having the trimmed heating resistor (4c1) formed on the surface thereof is maintained at a predetermined temperature for a predetermined time,
A method for manufacturing a thermal head, comprising a step of thermally annealing the heating resistor (4c1), wherein the heating resistor (4c1) has a small initial resistance value (Ri).
A method for manufacturing a thermal head, comprising setting a large trimming end target resistance value (Rt0) to a heating resistor (4c1) larger than the heating resistor.