JPH06115135A - Production of thermal head - Google Patents

Abstract

PURPOSE:To uniformize calorific value of the respective heating elements at a time of printing and to decrease density unevenness of the picture quality of printing by trimming the resistance of the heating element so as to lower the resistance thereof from the initial resistance to the specified resistance after trimming. CONSTITUTION:A plurality of individual electrodes 4a and a common electrode 4b corresponding to the tip parts thereof are provided on the surface of an insulating substrate 4. Moreover the intervals of the individual electrodes 4a and the common electrode 4b are connected by heating elements 4c1. A thermal head H is produced by trimming the resistance of the heating elements 4c1 so as to lower the resistance of the heating elements 4C1 from the initial resistance Ri to the specified resistance Rt after trimming. The thermal head H performs thermal recording (printing) on a thermal recording paper B conveyed along the external circumference of a platen roller A. In such case, calorific value of the heating elements 4c1 is made uniform. Therefore density unevenness of picture quality of printing is more decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thermal head used in a thermal printer, a facsimile or the like as an output device of a word processor, a personal computer or the like, and more particularly, to a uniform heating element of each heating element. The present invention relates to a method of manufacturing a thermal head.

[0002]

2. Description of the Related Art Conventionally, thermal heads are widely used because they have advantages such as low noise during printing and easy handling because they do not require developing and fixing steps. In such a thermal head, a heating element 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 tips thereof. Then, electric power is supplied between the selected individual electrode and the common electrode to cause the heating element in that portion to generate heat, thereby performing thermal recording (printing). by the way,
Each heating element arranged between each individual electrode and the common electrode (that is, unless the resistance value of the heating element corresponding to each print dot is uniform, a difference occurs in the temperature of the heating element when heat is generated). When printing on thermal transfer paper, etc., density unevenness occurs in the printed “characters” or “figure.” In order to prevent the density unevenness, the resistance of the heating element corresponding to each dot has been conventionally used. The value is made uniform by utilizing the property that when a predetermined electric field is applied to the heating element within a range that does not cause resistance breakdown, the resistance value of the heating element decreases according to the electric field strength. As a conventional technique for equalizing the resistance value of such a heating element, for example, Japanese Patent Application Laid-Open No. 61-83053 is known. Is constant and the voltage value is different A trimming pulse having a constant width and voltage value and a different number of trimming pulses are applied to the heating element. What has been done is described.

In the device described in the embodiment, the initial resistance value of the heating element corresponding to each dot on the insulating substrate is measured, and when the initial resistance value is larger than the target resistance value, the heating element is A trimming pulse having a predetermined voltage Vo is applied to the heating element to reduce the resistance value of the heating element. If the reduced resistance value is still greater than the target resistance value Ro,
Voltage Vo + Δ obtained by adding ΔV to the predetermined voltage Vo
A V trimming pulse is applied to further reduce the resistance value of the heating element. When the further reduced resistance value is still larger than the target resistance value Ro, the predetermined voltage Vo is obtained.
A trimming pulse of voltage Vo + 2ΔV, which is obtained by adding 2ΔV to, is applied to further reduce the resistance value of the heating element. In this way, the resistance value of the heating element is set to the target resistance value Ro.
Voltage plus + V each time until it falls below Vo + nΔ
A V trimming pulse is applied.

However, even if the resistance values are made uniform by applying the trimming pulse to the heating elements as described above, the resistance values of the heating elements vary during long-term use of the thermal head. Will end up. This is because the heating element immediately after being formed on the surface of the insulating substrate is unstable and its resistance value changes with time. However, the heating element whose resistance value is adjusted by the trimming pulse still has the same resistance value. It is considered to be unstable.
Therefore, even in a thermal head using a heating element whose resistance value is made uniform by trimming, the resistance value decreases with time and variation occurs. The print density is darker than the area printed with a small heating element. Then, the printed matter had uneven density. Therefore, a method of performing thermal annealing in order to suppress the resistance value fluctuation after trimming (Japanese Patent Laid-Open No. 3-266650) and a method of trimming every half dot (Japanese Patent Laid-Open No. 63-5955).
5) etc. are proposed.

[0005]

However, even if the trimming is performed based on the above proposal and the trimming accuracy thereof is reduced to ± 1% or less, it is still effective for improving the image quality, but it is still not effective. There was uneven density for each bit (print dot). Therefore, the present inventor discovered the facts shown in FIGS. 9 and 10 while conducting research to investigate the cause. In FIG. 9, the horizontal axis represents the sample number of the resistor trimmed to a predetermined target resistance value Ro,
The vertical axis represents the resistance temperature coefficient TCR (unit is ppm). As shown in FIG. 9, even if the resistance value of each heating element is adjusted to the target resistance value Ro by trimming,
The temperature coefficient of resistance differs between samples. Therefore, even if the resistance values are uniform at room temperature, the resistance value varies from sample to sample at the temperature (220 ° C) at the temperature reached by the heating element during actual printing (hereinafter referred to as "actual use temperature"), and the amount of heat generated varies. Has occurred. As described above, even if the resistance values of all the heating elements are aligned with high accuracy at room temperature, there is a difference in the resistance values of the heating elements at the actual use temperature (220 ° C). In this case, the amount of heat generated in each heating element varies, and the temperature also varies.

FIG. 10 shows the drop width (Ri-Rt) / Ri and the temperature coefficient of resistance (hereinafter referred to as "TCR" when the resistance value of the heating element is lowered from the initial resistance value Ri to the post-trimming resistance value Rt by applying a trimming pulse. ] Is also described). In FIG. 10, the horizontal axis represents the drop width (Ri
-Rt) / Ri (unit: "%"), and the vertical axis represents resistance temperature coefficient (unit: "ppm"). That is, this FIG.
Is the temperature coefficient of resistance TCR of the untrimmed resistor
Is about -90ppm in average and about -100ppm in minimum
However, the TCR increases linearly as the trimming drop width increases, and the TCR of the resistor dropped by 50% by trimming is about 0 ppm.

As described above, even if the resistance values of all the heating elements are aligned with high accuracy at room temperature, there is a difference in resistance value at high temperature during actual use. The cause of the difference is that the temperature coefficient of resistance TCR changes in accordance with the drop width (Ri-Rt) / Ri when the resistance value is reduced by trimming from the initial resistance value Ri to the resistance value Rt after trimming. To do. Therefore, even if the resistance values of all the heating elements are aligned with high accuracy at room temperature, since the temperature coefficient of resistance TCR is different, the actual use temperature state (the temperature state during actual printing, about 2
There is a variation in the resistance value at 20 ° C).
The amount of heat generated by each heating element will change significantly.

Due to the variation in the temperature coefficient of resistance, even if the resistance values of the heating elements are set to the same resistance value at room temperature (room temperature), a difference in resistance value occurs in the actual operating temperature state. The maximum value of this resistance difference is usually about 2 to 3%. Resistance value difference is 1
When it is more than%, the resistance of the room begins to be affected, so that the resistance value cannot be ignored. The approximate value of the resistance difference can be predicted by the following calculation. Let Ri be the initial resistance value of the heating element, Rt be the resistance value at room temperature (20 ° C) after trimming, Rt be the resistance value at the actual operating temperature state (220 ° C) after trimming, and TCR be the resistance temperature coefficient. If so, the following formula is established. R = Rt (1 + TCR × 200) In this equation, Rt is constant and the maximum value of TCR is 0,
When the minimum value is -100 ppm, the R value when TCR is 0 is R = Rt, and when the TCR is -100 ppm, the R value is R = Rt (1-0.02) = 0.98Rt. Becomes Therefore, when the TCR value is 0,
The difference in R at 0 ppm is 0.02 Rt. This 0.
The ratio of 02Rt to 0.98Rt is (0.02Rt
t / 0.98Rt) = about 0.02 = about 2%. That is, the maximum value of the resistance difference is about 2%. When the resistance values of the heating elements are set to the same resistance value at room temperature (room temperature) and the TCR is the same as above and the actual operating temperature of the heating resistor is 300 ° C. higher than room temperature, the resistance value is The maximum value difference is about 3%. Therefore, the Rt of the resistance value after trimming at room temperature is not made uniform, and the drop width (Ri-R
In consideration of t) / Ri, it is necessary to trim so that the resistance value becomes uniform in the actual use temperature state.

The present invention has been made in view of the above circumstances and consideration results.
In the method of manufacturing a thermal head, the contents described in (A11) below are subjects. (A11) To reduce the density unevenness of the print image quality by evenly aligning the resistance values of the heating elements 4c1 of the thermal head in the temperature state during actual use.

[0010]

The constitution of each invention of the present application devised to solve the above problems will be described below.
In order to clarify the correspondence with the constituent elements of the embodiments described later, the constituent elements of the present invention are appended with the reference numerals of the constituent elements of the embodiment enclosed in parentheses. The reason why the present invention is described in association with the reference numerals of the embodiments described later is to facilitate the understanding of the present invention and not to limit the scope of the present invention to the embodiments. In order to solve the above-mentioned problems, a method of manufacturing a thermal head according to a first invention of the present application is arranged on a surface of an insulating substrate (4) so as to correspond to a plurality of individual electrodes (4a) and tips of the individual electrodes. Common electrode (4b),
A heating element (4c1) for connecting between the individual electrode (4a) and the common electrode (4b) is formed, and then a heating element for connecting between the individual electrode (4a) and the common electrode (4b).
A method for manufacturing a thermal head having a step of applying a trimming pulse to (4c1) so as to reduce the resistance value of the heating element (4c1), and having the following requirements (A1) to (A3): Characteristic, (A
1) Step of individually measuring the initial resistance value Ri of each heating element (4c1), (A2) Each heating element (4) measured in the above step
trimming the resistance value of the heating element (4c1) so as to reduce the resistance value of c1) from the initial resistance value Ri to a predetermined post-trimming resistance value Rt at room temperature,
(A3) The resistance value Rt after trimming of each of the heating elements (4c1) at room temperature is a function of the resistance value drop width (Ri-Rt) / Ri in the trimming step, and the resistance temperature coefficient TCR.
And a resistance value calculated from the target resistance value Ro in the actual use temperature state, and a value determined to be uniform in the actual use temperature state.

[0011]

Next, the operation of the present invention having the above features will be described. According to the method of manufacturing a thermal head of the present invention having the above-mentioned characteristics, a plurality of individual electrodes (4
a), a common electrode (4b) arranged corresponding to the tip of each individual electrode, and a heating element (4c1) connecting the individual electrode (4a) and the common electrode (4b). Next, a trimming pulse is applied to the heating element (4c1) connecting between the individual electrodes (4a) and the common electrode (4b) to reduce the resistance value of the heating element (4c1) from the initial resistance value Ri. A trimming process for adjusting the target resistance value Rt to a value within a predetermined range is executed. In the trimming step, the initial resistance value of each heating element (4c1) is individually measured at room temperature. Next, the resistance value of the heating element (4c1) is trimmed so as to decrease from the initial resistance value Ri measured in the above step to a predetermined resistance value Rt after trimming. The predetermined resistance value Rt after trimming
Is the width of the drop in the resistance value (Ri-R
t) / Ri, which is a value calculated from a temperature coefficient of resistance TCR and a target resistance value Ro in a temperature state when actually used (hereinafter referred to as an actual use temperature state), and each heat generation at room temperature. Resistance value R after trimming of element (4c1)
Even if there is variation in t, it will be uniform under actual operating temperature conditions.

When the thermal head is used for actual printing, the heat generation amount Q in the actual use temperature state is expressed by the following equation. Q = (V ² / Ro) × t (1) Here, V: voltage, Ro: target resistance value in actual use temperature state, t: pulse application time. Since the target resistance value in the actual use temperature state is substituted for Ro in the equation (1) and the target resistance values Ro are evenly arranged, the heat generation amount of each heating element 4c1 becomes uniform. Therefore, it is possible to further reduce the density unevenness of the print image quality.

[0013]

【Example】

(Embodiment 1) Next, Embodiment 1 of the present invention will be described with reference to the drawings. In FIG. 1, a thermal head H for performing thermal recording (printing) on a thermosensitive recording paper B conveyed along the outer periphery of a platen roller A is a support plate made of a metal material having a high thermal conductivity such as aluminum or cast iron. 1, an upper surface of the support plate 1 is provided with a ceramic insulating substrate 4 and a plastic printed wiring board 5 on the left side portion and the right side portion in FIG. 1 via adhesives 2 and 3, respectively. It is stuck. In FIG. 1, an IC is arranged 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 arranged on the printed wiring board 5 is connected to the wiring 5a of the printed wiring board 5 and the individual electrode 4a of the insulating substrate 4 by wires 8 and 9.

As shown in detail in FIGS. 2 and 3, the insulating substrate 4 has a plurality of individual electrodes 4a on its surface (that is, upper surface), in the length direction of the insulating substrate 4 (that is, main scanning direction). It is lined up along 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 along the main scanning direction X and a sub-scan in a comb-teeth shape from the main body portion 4b1. It has a plurality of connecting portions 4b2 extending in the direction Y. The individual electrodes 4a and the connection portions 4b2 of the common electrodes 4b are arranged alternately along the main scanning direction X. Each of the individual electrodes 4a and the common electrode connecting portion 4b2 that are alternately arranged are heating elements 4c1 that constitute a heating resistor (heating unit) for one print dot of the strip heating resistor 4c extending in the main scanning direction. 4c
1, ... (See FIG. 3). Figure 1 again
Referring to, the IC and wires 8 and 9 are sealed with resin 10 and protected by cover member 11. The thermal head H has the symbols 1 to
Each of the heating elements 4c1 is pressed against the thermosensitive recording paper B on the platen roller A for thermal recording.

Next, a method of manufacturing the thermal head of Example 1 will be described. As shown in FIG. 3, the electrode 4a on the surface,
The insulating substrate 4 on which the 4b and the heating element 4c1 are formed is manufactured by a conventionally known manufacturing technique such as a screen printing technique. The resistance value of each heating element 4c1 of the insulating substrate 4 is trimmed by the trimming device shown in the block diagram of FIG.

In FIG. 4, the prober 21 contacts the electrode pad (not shown) of the individual electrode 4a (connection terminal portion used for connection with the wire 9 when the thermal head is assembled later) 21a. , 21a, ... A multiplexer relay 22 is connected to the prober 21, and the prober 21 and the multiplexer relay 22 are controlled by a computer 23, and the heating elements 4c1, 4c1, 4c1, 4c1, It is configured to select one bit (heat generating element for one print dot) in the ... The multiplexer relay 22 is configured to be selectively connected to the output terminal of the pulse generator 25 or the input terminal of the resistance measuring instrument 26 via the changeover switch 24 controlled by the computer 23.

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. When the process (trimming flow) for trimming each of the heating elements 4c1 formed on the surface of the insulating substrate 4 is started, the probes 21a, 21a, ... Of the prober 21 are connected to the individual electrodes 4a, 4 in step S1.
are contacted with a, ... And the initial resistance value Ri of the number of heating elements 4c1 (for example, 128) corresponding to the number of the probe 21a is measured.
Next, in step S2, n = 1 is set. Next, in step S3, the bit corresponding to n = 1 is selected. Next, in step S4, the post-trimming resistance value Rt after the trimming is calculated.

The resistance value Rt after trimming is calculated using the following equation (2).

[Equation 1]

Here, a and b are constants determined by the method described below. Next, the method of obtaining the constants a and b and the reason for using the above equation (2) will be described in the following (a) to (d). (B) A plurality of samples are taken out from the insulating substrate 4 manufactured in the same lot as the insulating substrate 4 on which the heating element 4c1 to be trimmed is formed. And
Using the samples of the insulating substrate 4 and the trimming device shown in FIG. 4, the initial resistance value R of each heating element 4c1 is set.
Measure is. The subscript s of Ris is the sample (samp
le) means. (B) Resistance value Rts at room temperature (25 ° C) after trimming
(This subscript s means the sample) is the initial resistance value R
Trimming is performed by setting it to be 50% to 100% of is. After trimming, for those samples,
The resistance value Rts at 25 ° C. (room temperature) and the resistance value Ros at 300 ° C. (actual use temperature state) (the suffix s means the sample) are measured. In this case, the temperature difference ΔT between the actual use temperature of 300 ° C and the room temperature of 25 ° C is 275 ° C. This ΔT = 275 and the measured values Rts and Ros are given by the following equation (4).
Then, the actual temperature coefficient of resistance TCRs (the subscript s means the sample) for each heating element 4c1 of the sample is calculated. Ros = (1 + TCRs × ΔT) × Rts (3)

(C) The value of trimming drop width (Ris-Rts) / Ris of each heating element 4c1 of the sample and the actual temperature coefficient of resistance TCRs of the heating resistor 4c1 of the sample calculated by the equation (3) are shown. The black dots in FIG. 6 are shown in the graph. The trimming drop width (R
From the relationship between is-Rts) / Ris and the actual temperature coefficient of resistance TCRs obtained from the sample, the temperature coefficient of resistance TCRs of each heating element 4c1 of the sample can be approximately obtained by the following equation (4). I understand. TCRs = a * {(Ris-Rts) / Ris} + b (4) The above equation (4) is a multiple regression equation having a and b as regression coefficients,
TCRs and Ri obtained by the heating resistor 4c1 of the sample
It can be determined by multiple regression analysis using the least squares method using the actual values of s and Rts.

When the values of the coefficients a and b are determined, the resistance temperature coefficient TCR of each heating element 4c1 other than the sample is determined.
Is calculated by the following equation (5). TCR = a * {(Ri-Rt) / Ri} + b (5) (d) The difference between the temperature of the heating resistor 4c1 during actual use (actual use temperature) and the temperature during the trimming process (room temperature) is T. Then,
The target resistance value Ro of the heating resistor 4c1 in the actual use temperature state is expressed by the following equation (6).

Ro = (1 + TCR × T) × Rt (6) Substituting the TCR of the equation (5) into the equation (6) and rearranging it yields the following equation (7) regarding the variable Rt.

ATRt ² − (1 + aT + bT) RiRt + RoRi = 0 (7) When this equation (7) is solved, the resistance value Rt after trimming is given by the following equation (8).

[0024]

[Equation 2] In the equation (8), the second term in the route is smaller than the first term, so the route in the equation (8) is approximately 2Ri. Since 2aT of the denominator is about 10 −2, if the plus sign is selected from the solutions of ± in front of the route of the equation (8), the resistance value Rt after trimming is equal to the initial resistance value Ri. Since the value is about 100 times larger and does not match the reality, the solution with the sign before the route being − is a solution. Therefore, the correct value of the target resistance value Rt at room temperature after trimming can be obtained by the above equation (2).

Returning to the explanation of the flowchart of FIG.
After performing the processing of step S4, the next step S5
At, it is determined whether the resistance value is within a predetermined range of the post-trimming resistance value Rt after the trimming is completed. If no (N), the process proceeds to step S6. In step S6, the voltage value of the trimming pulse applied to the heating element 4c1 is calculated. As a method of calculating this voltage value, for example,
JP-A-61-83053 or 1-2.
The method described in Japanese Patent No. 71262 is adopted. Next, in step S7, a trimming pulse is applied to the heating element 4c1. Next, in step S8, the heating element 4c
After measuring the resistance value of 1, the process returns to step S5. If yes (Y) in step S5, the process proceeds to step S9.

In step S9, n = n + 1 is set.
Next, in step S10, it is determined whether n = no. However, no is the number of the probe 21a of the probe 21 which contacts the individual electrode 4a plus 1, for example, if the number of the probe 21a is 128, no = 129.
Is. If NO in step S10, the process returns to step S3. If YES, each heating element 4c connected to all the probes (for example, 128 probes) 21a.
Assuming that the trimming of 1 is completed, the next step S1
Go to 1. In step S11, it is determined whether or not the trimming of all the heating elements 4c1 on the surface of the insulating substrate 4 is completed. If NO in step S11, the process returns to step S1, and the probe 21a of the prober 21 is brought into contact with the pad of the individual electrode connected to the heating element 4c1 which has not been trimmed, and the heating element 4c1.
The initial resistance value Ri of is measured. If YES in step S11, the heating element 4c1 on the surface of the insulating substrate 4
The trimming flow of is finished. In the trimming flow described above, each heating element 4c1 has its initial resistance value Ri.
The resistance value Rt after trimming after trimming is set to a different value (value determined by the equation (2)) according to the value of

Next, the operation of the thermal head manufactured by the manufacturing method of Embodiment 1 will be described. When the thermal head H of the above-mentioned embodiment is actually used, each heating element 4c1 generates heat, and the substantially constant actual operating temperature, for example, 2
Reach 20 ° C. The resistance value before use is the after-trimming resistance value Rt determined by the above equation 2, but when the actual operating temperature is reached, the actual resistance value becomes the after-trimming resistance value Rt represented by the equation (2) in the equation (6). Target resistance value Ro obtained by substitution
The heating element 4c1 of the thermal head has a substantially constant value (a value within a predetermined range, in other words, a value within the design range). Therefore, the amount of heat generated by each heating element 4c1 is also constant. This is well shown in FIG. In FIG. 7, the numerical value on the horizontal axis indicates the sample number of the heating element 4c1, and the vertical axis indicates the measured value of the surface peak temperature (° C) of the heating element 4c1. In the plot, white circles indicate the embodiment of the present invention, and black circles indicate the conventional product in which the target resistance value is at room temperature. As can be seen from FIG. 7, the variation of the surface temperature was improved to about half or less, and the density unevenness was remarkably reduced when actually printed.

(Modifications) The embodiments of the thermal head according to the present invention have been described in detail above, but the present invention is not limited to the above-mentioned embodiments, and the present invention described in the claims is not limited thereto. Various design changes can be made without departing. For example, instead of the thermal head using the strip-shaped heating element 4c1, as shown in FIGS. 8A and 8B, a plurality of individual heating elements 4c1 and 4c1 along the main scanning direction X are provided.
c1, ... are arranged in a row, and their individual heating elements 4c1, 4c1,
... and a plurality of individual electrodes 4a, 4a, ... And a common electrode 4b
It is also possible to apply the present invention to a thermal head in which and are individually connected.

[0029]

The method of manufacturing a thermal head of the present invention having the above-described structure has the following effects (A21). (A21) Since the resistance value of each heating element 4c1 of the thermal head becomes uniform in the temperature state during actual use, the heating value of each heating element during printing becomes uniform, and uneven density of print image quality is reduced. be able to.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a thermal head H manufactured according to a first embodiment of a method for manufacturing a thermal head of the present invention.

FIG. 2 is a perspective view of a main part of the thermal head.

FIG. 3 is a partially enlarged view of the main part.

FIG. 4 is an explanatory diagram of a trimming device used for manufacturing the thermal head.

FIG. 5 is a flow chart for explaining the operation of the trimming device of FIG.

FIG. 6 is an explanatory diagram of a method for obtaining the relationship between the trimming drop width of the heating element and the temperature coefficient of resistance TCR.

FIG. 7 is a diagram showing variations in surface temperature of a heating element applied to a conventional thermal head and variations in surface temperature of a heating element applied to the thermal head of the present invention.

FIG. 8 is a diagram showing another example of a thermal head to which the present invention can be applied, and FIG. 8A shows a general individual opposing type thermal head (a common electrode connecting portion and an individual electrode facing this are individually heated. Showing a thermal head connected with a resistor,
FIG. 8B shows a thermal head in which the common electrode connection part is omitted.

FIG. 9 is a diagram generally showing a resistance temperature coefficient TCR of a heating element for each sample.

FIG. 10 is a graph showing a trimming resistance drop width and T
It is a figure which shows the relationship with CR (resistance temperature coefficient).

[Explanation of symbols]

4 ... Insulating substrate, 4a ... Individual electrode, 4b ... Common electrode, 4c1 ...
Heating element, Ri ... initial resistance value, Rt ... resistance value after trimming, Ro ... target resistance value, TCR ... resistance temperature coefficient.

Claims (1)

[Claims] 1. A plurality of individual electrodes and a common electrode arranged on the surface of an insulating substrate so as to correspond to the tips of the individual electrodes,
A heating element (4c) connecting between the individual electrode and the common electrode.
1) and a thermal head including a step of applying a trimming pulse to the heating element (4c1) connecting the individual electrodes and the common electrode to reduce the resistance value of the heating element. The method for manufacturing a thermal head, characterized by comprising the following requirements (A1) to (A3), (A1) a step of individually measuring the initial resistance value of each heating element, (A2) the step Trimming the resistance value of each heating element (4c1) so as to reduce the resistance value of each heating element measured in step (a) from the initial resistance value Ri to a certain predetermined resistance value Rt after trimming at room temperature, (A3) The resistance value Rt of each heat generating element after trimming at room temperature is a function of the temperature drop coefficient TC of the resistance value drop width (Ri-Rt) / Ri in the trimming step.
The resistance value is calculated from R and the target resistance value Ro in the actual use temperature state, and is a value determined to be uniform in the actual use temperature state,