JP2810243B2 - Thermal head resistor trimming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistor trimming method for adjusting a resistance value of a heating resistor of a thermal head.

[0002]

2. Description of the Related Art In a thermal head used in various printing output devices, a plurality of heating resistors are formed on a head substrate, and the heating resistors are selectively energized to perform thermal printing.

At this time, in order to realize the designed printing density, the resistance values of the respective heating resistors need to be uniform.
For this reason, a trimming technique has been employed in which a voltage pulse is applied to the heating resistor after the heating resistor is formed to reduce the resistance value and minimize the variation.

As a conventional example of performing such trimming, when manufacturing a thermal head, in the same lot or on the same substrate, a change in resistance value when the same trimming pulse is applied to each heating resistor is regulated. The correlation between the voltage value of the trimming pulse to be applied and the rate of change ΔR / R of the resistance value R, that is, the calibration curve is determined in advance, and the initial voltage is calculated according to the calibration curve. V0 is determined, and the resistance value is made as close as possible to the target resistance value by applying the initial voltage V0.
Thereafter, a pulse whose voltage is increased by the increment ΔV is applied to gradually reduce the resistance value.

[0005]

SUMMARY OF THE INVENTION Such a conventional example is as follows.
Although it is intended to suppress the variation in the resistance value of each heating resistor, there is no known method for trimming each heating resistor and determining an appropriate target resistance value as a target for changing the resistance value. If such a target resistance value is not properly determined, the following problem occurs.

(1) In the conventional example, the trimming process cannot be performed if the initial resistance value before the trimming process is smaller than the target resistance value because the resistance value of the heating resistor is reduced.

(2) Even if the trimming process for each heating resistor is completed over all the heating resistors and the resistance value distribution in the thermal head is improved, the average resistance value of the thermal head is reduced. It is unknown whether the average resistance value required for the thermal head is within the range of the maximum allowable value and the minimum allowable value.

(3) When the resistance value is reduced by the trimming process, if the change amount is excessive, the heating resistor is destroyed.

In the thermal head, there are the following three types of variations in resistance value that cause density unevenness during application.

(1) Variations between heads, that is, even for thermal heads of the same standard, variations occur in the average resistance value of each head.

(2) Variations in the head, that is, variations in the resistance value of the heating resistor in a single thermal head.

(3) Variation between adjacent dots, that is, variation between adjacent heating resistors in a single thermal head.

Here, in the thick-film thermal head, since the heating resistor is formed by printing a paste-like resistor material on the electrically insulating substrate by printing, the variation in the resistance value is most affected by the printing accuracy. It is known that the variation within the head and between adjacent dots is large, and the variation between heads is relatively small because the variation is an average resistance value of each head. On the other hand, in the case of a thin-film thermal head, after forming a resistor material layer by sputtering or vapor deposition, it is etched as a predetermined pattern to form a heating resistor. Thereby, the variation in the resistance value is, for example, ±
It is known that the variation is as small as about 0.5% and the variation in the head is relatively small. On the other hand, since it is difficult to form the same film thickness every time for each head, variation between heads is relatively large.

Of the three types of resistance value variations, variations between heads greatly affect the specifications of a power supply for driving a thermal head. That is, since the average resistance value for each thermal head varies, if such a thermal head is driven with the same configuration of power supply, the capacity of the power supply increases, and a circuit for adjusting the drive voltage for each thermal head is required. The configuration becomes complicated.

On the other hand, variations in the head and variations between adjacent heads may cause unevenness in density when performing high-precision thermal printing such as half-tone thermal printing, but do not perform halftone display. During the printing operation of various characters, such variations in the head and between adjacent dots have a small effect on quality. When trimming the resistor of the thermal head when performing such low-precision thermal recording, a high-speed and easy method is desired.

A first object of the present invention is to solve the above-mentioned technical problems, to determine an appropriate target resistance value, and to significantly improve the quality of a manufactured thermal head. An object of the present invention is to provide a resistor trimming method.

A second object of the present invention is to focus on only the variation of the average resistance value between the heads and determine an appropriate target average resistance value. It is to provide.

[0018]

SUMMARY OF THE INVENTION The present invention relates to a method of trimming a plurality of heating resistors linearly arranged on an electrically insulating substrate of a thermal head. Then, the lower resistance value of trimming based on the maximum resistance value and the upper resistance value of trimming based on the minimum resistance value in the resistance value change curve of the heating resistor are obtained, and thereafter, the fever is trimmed against the antibody. And setting the average resistance value of each heating resistor within a range between a predetermined maximum allowable value and a predetermined minimum allowable value.

[0019]

According to the present invention, the maximum resistance value and the minimum resistance value of a plurality of heating resistors arranged linearly on an electrically insulating substrate are measured. A lower limit value of the resistance value in the maximum trimming process based on the maximum resistance value in the resistance value change curve of the heating resistor and an upper limit value of the resistance value in the minimum trimming process based on the minimum resistance value are calculated. With respect to the average value of each heating resistor, the target resistance value is determined by comparing a predetermined maximum allowable value and a minimum allowable value with the upper limit value and the lower limit value.

Here, the target resistance value must be larger than the minimum allowable value and smaller than the maximum allowable value. In addition, it is necessary to be smaller than the upper limit and larger than the lower limit. When the resistance value before the trimming process satisfies the above condition, for example, the smaller of the upper limit value and the maximum allowable value is selected as the target resistance value and the trimming process is performed. Except when the two conditions are compatible, it is impossible to perform trimming. In this way, an appropriate target value can be automatically determined, the usability is excellent, and the quality of the manufactured thermal head can be remarkably improved.

According to the present invention, the average resistance value is calculated by measuring the resistance values of a plurality of heating resistors arranged linearly on the electrically insulating substrate. Based on this average resistance,
A lower limit value of the resistance value during the minimum trimming process and an upper limit value during the minimum trimming process are calculated. Regarding the average resistance value of each heating resistor, a target maximum resistance value is determined by comparing a predetermined maximum allowable value and a minimum allowable value with the upper limit value and the lower limit value.

Here, the target average resistance value must be larger than the minimum allowable value and smaller than the maximum allowable value. In addition, it must be smaller than the upper limit and larger than the lower limit. When the resistance value before the trimming process satisfies the above condition, for example, a smaller one of the upper limit value and the maximum allowable value is selected as a target average resistance value, and a condition for realizing the target average resistance value as a trimming process. Pulse for each heating resistor
Apply only once. Except when the two conditions are compatible, it is impossible to perform trimming. In this manner, an appropriate target value can be automatically determined, and high-speed, easy-to-manufacture thermal heads can suppress variations in average resistance value between heads.

[0023]

FIG. 1 is a sectional view for explaining the structure of a thin film thermal head (hereinafter abbreviated as thermal head) 21 manufactured by using the trimming method of the present invention. The thermal head 21 includes a heat radiating plate 22 made of a metal material such as aluminum, for example, and a head substrate 23 is fixed thereon with an adhesive layer 32. On the head substrate 23, a large number of heating resistors 24 are formed linearly in a direction perpendicular to the paper surface of FIG. 1, and are arranged in parallel with the arrangement direction of the heating resistors 24, and are not shown as the heating resistors 24. A plurality of drive circuit elements 25 connected by electrodes are arranged. These drive circuit elements 25 are covered with a protective layer 26 made of a synthetic resin material.

On the head substrate 23, a heat storage layer 35 is formed by a thick film technique such as screen printing, and a thick film common electrode layer 27 is formed along the outer periphery of the head substrate 23. On the heat storage layer 35, a heating resistor layer 34, a common electrode layer 36, and a plurality of individual electrodes 37 are formed, and a plurality of heating resistors 24 on a straight line are formed. Heating resistor 24
Performs thermal printing on the thermal paper 32 with the platen roller 31 via a wear-resistant layer 39 formed by a thin film technique such as sputtering. The heating resistor 24 is a driving circuit element 25 realized as an integrated circuit element.
Is controlled by The drive circuit element 25 is connected to the individual electrode 37 covered with the insulating layer 28, and receives a signal for driving the heating resistor 24 and the like to the drive circuit element 25, and receives an external connection covered with the insulating layer 28. The terminal 29 is connected, and a protective layer 26 made of a synthetic resin material or the like is formed to cover the drive circuit element 25 and its periphery.

According to the present invention, when the heating resistor layer 34, the common electrode 36, and the plurality of individual electrodes 37 are formed on the head substrate 23, the resistance value of each of the plurality of heating resistors 24 defined by these is determined. This is to trim and equalize. As a result of conducting an experiment on the thermal head 21, the following facts were found.

(1) Before forming the wear-resistant layer 39, a trimming pulse is applied in the air atmosphere. At this time, by appropriately selecting the pulse width, the resistance value of the heating resistor 24 can be increased as well as reduced. A summary of the experimental results is shown in the graph of FIG. That is, the abscissa indicates the applied power, and the ordinate indicates the resistance value change rate ΔR / R of the heating resistor 24.
It was confirmed that, when the value was taken, the obtained characteristic curve was significantly changed by changing the pulse width of the applied trimming pulse. The lines L1, L2, L shown in FIG.
3 shows a case where the pulse widths are different from each other, and when the corresponding pulse widths are represented by WL1, WL2, WL3 (collectively referred to as WL if necessary), these relations become:

[0027]

## EQU1 ## WL1> WL2> WL3.

That is, when the pulse width WL is relatively long, the resistance value increases when the applied power is increased as shown by the line L1. On the other hand, when the pulse width WL is relatively short, the resistance value does not change in the range A less than the threshold power Pth as indicated by the line L3, but the threshold power Pth
When the applied power is increased to the above range B, the resistance value decreases. In addition, an intermediate pulse width W of the pulse widths WL1 and WL3
In L2, both the rising phenomenon and the falling phenomenon of the resistance value appear depending on the degree of the applied power P as shown in the line L2. That is, in the range A of the applied power that is less than the threshold power Pth with respect to the applied power, the resistance value gradually decreases as the applied power increases, but the resistance decreases gradually to 0.
Becomes In the range of the applied power P equal to or higher than the threshold power Pth,
The resistance value gradually increases as the applied power P increases.

As described above, the pulse width W of the trimming pulse
The phenomenon that the resistance value of the heating resistor 24 can change either upward or downward depending on L is described as follows with reference to FIG. That is, the resistance value of the heating resistor 24 changes due to the application of the trimming pulse because the heating effect of the heating resistor layer 34 itself results in an annealing effect,
That is, this is due to crystallization of the heating resistor layer 34 and oxidation of the heating resistor layer 34 itself due to heat generation. Among them, the annealing effect appears as a decrease in resistance at the point where crystallization of the heating resistor layer 34 progresses, and the oxidation appears as an increase in resistance.

As shown in FIG. 3A, when the pulse width WL1 of the applied trimming pulse is set relatively long and the applied voltage is set low, the heating resistor layer 34 has a low temperature because the applied voltage V1 is relatively low. Does not show a rapid and significant rise, while a relatively long pulse width WL1 results in a relatively low temperature for a long time. The progress of the annealing effect in the heating resistor layer 34 is determined by the temperature. In this case, the temperature T1 does not reach the temperature Ta at which the annealing effect is generated, and the resistance value decreases due to the annealing effect. Does not occur. However, since the temperature is equal to or higher than the temperature Tox at which the oxidation phenomenon occurs, and this state is continued for a relatively long time, the oxidation of the heating resistor layer 34 progresses and the resistance value increases.

On the other hand, the applied trimming pulse is shown in FIG.
As shown in (1), when the pulse width WL3 is relatively short and the applied voltage V2 is relatively high, the heating resistor layer 34
The temperature change shown in FIG. 4B is in the state shown in FIG. That is, the temperature of the heating resistor layer 34 rapidly rises and reaches a temperature T2 exceeding the temperature Ta at which the annealing effect occurs. on the other hand,
Since the pulse width WL3 is relatively short, the temperature T2 hardly lasts, and quickly returns to room temperature. In this case, the annealing effect proceeds in accordance with the temperature T2, and the resistance value of the heating resistor layer 34 decreases. On the other hand, since the period during which the temperature exceeds the temperature Tox at which the oxidation occurs is relatively short, the oxidation hardly occurs and the resistance value does not increase.

That is, the pulse width WL of the trimming pulse
By appropriately selecting the power and the applied power, it is possible to control which of the above-described annealing effect and oxidation becomes the dominant phenomenon. That is, control for increasing or decreasing the resistance value of the heating resistor layer 34 can be performed.

(2) As shown in FIG. 3A, when a trimming pulse having a pulse width WL1 that causes only a rise in the resistance value in the heating resistor layer 34 is applied, the pulse width WL1 of the trimming pulse is fixed. If the resistance value before the application of the trimming pulse is different for each heating resistor 24, each heating resistor 24 shows a substantially constant resistance value change rate by applying the same applied power, even if the resistance value differs for each heating resistor 24. On the other hand, the same applies to the case where a trimming pulse having a pulse width WL3 that causes only a decrease in the resistance value as shown in FIG. 4A is applied. If the applied power is the same, the resistance value before the application of the trimming pulse is changed to the heating resistance. Even if it differs for each body 24, it shows a substantially constant resistance value change rate.

The present inventor has found that the heating resistor 24 shown in FIG.
1, the length in the left-right direction is 151 μm, the width in the direction perpendicular to the plane of FIG. Measured. The relationship between the applied voltage and the change in the resistance value is shown in lines L6 and L7 in FIG.
As described above, it is understood that the state of the resistance value change is significantly different from the relationship with the applied voltage.

On the other hand, the relationship between the applied power and the change in the resistance value is shown in lines L8 and L9 in FIG. As shown in the figure, if the applied power is the same, it is understood that the same resistance value change is exhibited regardless of the difference in the initial resistance value before trimming. When these are combined, the line L shown in FIG.
It can be concluded that the characteristic curves of 1 and L3 do not depend on the resistance value of each heating resistor 24.

The above phenomenon is explained as follows. As described above, the progress of the annealing effect and oxidation, which are factors that change the resistance value of the heating resistor layer 34, are as shown in FIG. 3 (2) of the heating resistor layer 34 itself corresponding to the state of the applied trimming pulse. ) And the characteristics of the temperature change as shown in FIG. 4 (2). Therefore, if the pulse width WL and the applied power P are the same, even if the resistance values of the heating resistors 24 are different from each other,
The characteristics of the temperature change of each heating resistor 24 with time become the same between the heating resistors 24, and a substantially constant resistance value change rate is obtained as described above.

(3) After the trimming pulse of the predetermined applied power P0 is applied to the heating resistor 24,
By applying a trimming pulse in which the applied power is increased by increments of the applied power ΔP, the resistance value can be gradually reduced. The present inventor has shown in FIG.
Length 151 μm in the left-right direction, width 1 in the direction perpendicular to the plane of FIG. 1
With respect to the heating resistor 24 having a thickness of 05 μm, the first pulse is applied at the pulse width WLd where the resistance value decreases, the resistance value is reduced, and then the applied power is increased by the increment ΔP after the second time. Was measured. The result is shown in lines L10 and L11 in FIG. The manner in which the resistance value decreases as described above depends on the applied power of the first pulse, but in any case, the resistance value gradually decreases.

(4) In the description of the third item, the resistance value is gradually increased by setting the second and subsequent trimming pulses to be trimming pulses having a relatively long pulse width as shown in FIG. Can be. The inventor of the present invention has described that the plurality of heating resistors 24 having mutually different resistance values in the description of the above-mentioned item 3 are, for example, 5
A change in resistance value when a trimming pulse having a pulse width of 0 ms was applied was measured. This state is shown in FIG.
2, L13. It is understood that the resistance value can be gradually increased as shown in FIG. At this time, the line L
12 shows a case where the applied power is higher than that of the line L13. In addition, as shown by the line L13 in the case where the applied power is set lower, the change in the resistance value in one application of the trimming pulse can be set very small. Thereby, the heating resistor 2 by trimming is formed.
4 can be controlled with extremely high precision.

(5) The annealing effect that causes the resistance value of the heating resistor layer 34 to decrease as described above promotes rearrangement and crystallization of constituent molecules in the heating resistor layer 34.
Therefore, the durability of the heating resistor 24 to applied pulses (such as a trimming pulse and a driving pulse accompanying use) is improved. On the other hand, the oxidation phenomenon that causes an increase in the resistance value narrows the region of the heating resistor 24 having a predetermined resistance value, and thus substantially reduces the film thickness. Therefore, the durability against the applied pulse is deteriorated. That is, the process of significantly increasing the resistance value of the heating resistor 24 is as follows.
The heating resistor 24 is deteriorated, and the life is shortened.

(6) When the heating resistor 24 is made of tantalum Ta, the present inventor has confirmed that the resistance value can be reduced to about -70% with a pulse width of 1 ms or less. However, when the resistance value is excessively reduced, the heat generating resistor 24 aggregates, and the heat storage layer 35 immediately below the heat generating resistor 24 is broken by heat. In consideration of these points, the inventor of the present invention has determined that the maximum trimming amount -DR1 at which the reliability of the thermal head 21 can be maintained is:
As shown in FIG. 8, for example, it was confirmed to be about -40%.

(7) On the other hand, the pulse width of the trimming is fixed to a pulse width WLd (for example, 1 ms or less) in which the resistance value decreases, and a pulse of the same applied power is applied only once to each heating resistor, and thermal trimming is performed. In the case of the trimming method in which the average resistance value of the head 21 is changed within the allowable range between the maximum allowable value and the minimum allowable value with respect to the average resistance value, the resistance value decreases as described above. However, the resistance change rate actually varies due to irregularities in the heat storage layer 35 and variations in the dimensions of the heating resistor 24.

Therefore, the applied power P and the resistance value change rate Δ
The graph showing the relationship with R / R is as shown in FIG.
Line L4a, line L4a,
It has a width in a range surrounded by L4b. However, when the applied power is low and the resistance value does not change much,
This width is small and the variation is small, so it does not matter much.

For this reason, there is a limit to the change in the resistance value depending on whether or not this variation can be tolerated. For example, if the resistance value is changed to a limit value DR3 of about -15% or more, the variation in the resistance value in the head of the thermal head and the variation in the resistance value in the vicinity of It was confirmed that the resistance value variation was worsened.

(8) As described above, the relationship between the applied power P and the resistance value change rate ΔR / R varies, and it is not possible to accurately approach the target resistance value by one pulse application. However, after the second time, the applied power was further increased,
Since the resistance value can be further lowered or the resistance value can be increased by applying a pulse with a relatively long pulse width,
This variation is not a problem in accuracy. However, due to this variation, when the resistance value becomes considerably lower than the target resistance value, it becomes necessary to greatly increase the resistance by oxidation. By this large oxidation,
As described above, the reliability of the heating resistor 24 decreases.

If the resistance value is excessively reduced by the first pulse application, the resistance value does not decrease and rises conversely even if a trimming pulse for further decreasing the resistance value is applied after the second time. , The control of the resistance value becomes impossible, or conversely, the resistance value greatly exceeds the predetermined reduction amount, and the heating resistor 2
4 causes agglomeration, the heat storage layer 35 immediately below is destroyed by heat, or in the worst case, the heating resistor 24 itself is destroyed. Therefore, even when the above-described resistance value increase or decrease control is performed, the resistance value change is, for example, −3.
It was confirmed that it could not be more than the limit value -DR2 of about 0%.

(9) With respect to the heating resistor 24, it was confirmed that when the trimming was not performed, the resistance value decreased by, for example, about 2 to 3% with the use of the thermal head 21. This is because in the heating resistor 24 that has been subjected to the trimming process, the reliability with respect to the applied pulse is improved by the above-described annealing effect, and therefore, the resistance does not decrease during use. On the other hand, the resistance value of the heating resistor 24 that has not been subjected to the trimming process is reduced because it does not have the annealing effect. For this reason, in a single thermal head 21, the amount of heat generation varies with use, resulting in uneven density. Therefore, all the heating resistors 24 of the thermal head 21 need to be trimmed by a minimum trimming amount DR4 of, for example, about -3%.

Based on the above conditions, a description will be given of a method of applying the above-described phenomenon of increasing and decreasing the resistance value to the adjustment of the resistance value of the heating resistor 24. FIG.
As shown in (1), when a trimming pulse having a relatively short pulse width WL3 is applied and the pulse width WL3 is kept constant, the relationship between the applied power and the rate of change in resistance value is changed as described above. Although the resistance value does not depend on the resistance value, the resistance value change rate actually varies due to unevenness of the heat storage layer 35 and dimensional variation of the heating resistor 24.

As described above, the resistance change rate actually varies due to the unevenness of the heat storage layer 35 and the size variation of the heating resistor 24, and the applied power P and the resistance change rate ΔR / R As shown in FIG. 9, the graph indicating the relationship has a width in a range surrounded by lines L4a and L4b with respect to the line L4 indicating the ideal correspondence. The variation between the lines L4a and L4b increases as the applied power increases and the change in the resistance value increases. As described in the related art, the head substrate in the same lot when manufacturing the thermal head is used. 23 and a heating resistor 24 in the same head substrate 23, a trimming pulse is applied to obtain a calibration curve of line L4 in FIG. 9, and the pulse width and applied power of the trimming pulse are determined based on the calibration curve. Such a trimming pulse is applied to the heating resistor 2.
Even if the voltage is applied every four, high-precision control is impossible.

For example, in order to change the resistance value by -n%, data of the corresponding applied power P0 (-n%) is obtained from the calibration curve of line L4 in FIG. 9, and a trimming pulse having this applied power is applied. In this case, the resistance value change rate actually varies in the range of the width δ shown in FIG. Therefore, the obtained rate of change in resistance is −nd−2% at the lower limit and −n + at the upper limit.
It will vary between d1% (d1 + d2 = δ).
This variation increases as the applied power increases as described above, and increases as the resistance value change increases. As shown in FIG. 9, the variation + d3 when the applied power P0 (-m%) corresponding to -m% is applied. , -D4 become considerably large.

Therefore, in trimming the heating resistor 24, it is necessary to increase or decrease the resistance value by applying a trimming pulse once and then further applying a trimming pulse. It has been confirmed that such processing can be realized by the following method.

When the resistance value is further decreased after the first trimming pulse is applied, only the annealing effect described above needs to be advanced. Therefore, a trimming pulse having the same pulse width as the first trimming pulse and having the applied power increased by the predetermined power ΔP is applied. As a result, the heating resistor 24 reaches a higher temperature than when the first trimming pulse is applied, so that the annealing effect further proceeds and the resistance value further decreases.

In order to further reduce the resistance value, the power may be further increased by the applied power ΔP to apply the trimming pulse. At this time, since the pulse width is set to be relatively short, the above-described oxidation phenomenon hardly occurs. However, when the applied power ΔP is too small, the oxidation phenomenon cannot be ignored, and conversely, the resistance value may increase. Therefore, the predetermined applied power ΔP is determined in consideration of such conditions comprehensively.

When the resistance value is increased after the first trimming pulse is applied, only the oxidation phenomenon described above needs to proceed, and FIG. 3 (1) showing a characteristic like line L1 in FIG.
As shown, a trimming pulse having a relatively long pulse width WL1 is applied. As a result, the heating resistor 24 basically cools down from the temperature after the first trimming pulse application, and the annealing effect hardly progresses, and only the oxidation phenomenon progresses. Thereby, the resistance value of the heating resistor 24 can be reliably increased. Further, by selecting the applied power P1 at this time to be relatively small, the rate of increase of the resistance value every time the trimming pulse is applied can be changed little by little, for example, about +0.1 to 0.2%. 24
Can be controlled with high precision.

The following method can be considered as long as the above-mentioned variation in the resistance value of the thermal head is improved only in the variation in the average resistance value between the heads. In other words, considering that the variation in the relationship between the applied power and the rate of change in resistance at a constant pulse width shown in FIG. 9 is small when the applied power is reduced and the rate of change in resistance is reduced, this variation is considered. This is a method in which applied power is determined so that variation does not cause a problem, and a pulse in the thermal head is applied.

By applying a pulse under the same condition to each of the heating resistors 24, each of the heating resistors exhibits the same rate of change in resistance value, and the variation is small. Only the variation of the average resistance value of.

FIG. 10 shows a trimming device 41 according to the present invention.
It is a block diagram of. The trimming device 41 is mounted on the head substrate 23 of the thermal head 21 and
A probing device 42 for individually contacting the probe with the upper common electrode 36 and the individual electrode 37 for each heating resistor 24 is provided. The probing device 42 is connected to a resistance value meter 44 and a trimming device via a switching unit 43. Pulse generator 4
5 is connected. The resistance value measured by the resistance value meter 44 is input to a change amount calculation unit 46 in the control device 51 and a calibration curve creation storage unit 47 that creates and stores a calibration curve.

The trimming pulse generator 45 includes a reference pulse generator 48. The generated reference pulse is output as a trimming pulse as described later by passing through a pulse width adjuster 49 and a voltage adjuster 50.
The voltage is applied to the selected heating resistor 24 via the switching circuit 43 and the probing device 42.

FIG. 11 is a process chart for explaining the overall process of manufacturing the thermal head 21. In step a1 of FIG.
A thick film common electrode layer 27 and a heat storage layer 35 are formed on the thermal head 21. In step a2, the thermal head 21
The heating resistor layer 34 is formed thereon, and in step a3, the common electrode 36 and the individual electrode 37 are formed on the heating resistor layer 34. In step a4, a trimming process, which will be described in detail later, is performed, and the resistance value of each heating resistor 24 is adjusted to be uniform. Then, in step a5, the wear-resistant layer 39 is formed. Thereafter, through other processes, the thermal head 21
Is completed.

FIG. 12 is a process diagram for explaining a trimming method according to the first embodiment of the present invention, and FIG. 13 is a process diagram for explaining a method for creating a calibration curve in the process of FIG. In step b1 in FIG. 12, a sample head on which the heating resistors 24 are arranged as shown in FIG. 1 is prepared, and the pulse conditions as described above are obtained.

The details of this process will be described with reference to a process chart for creating a calibration curve shown in FIG. That is, a sample head substrate is set, and a trimming pulse application test is performed on the sample head substrate using the trimming device 41 shown in FIG. 10 to determine the following pulse conditions 1 to 5.

(Condition 1) When one pulse is applied, a pulse width WLd at which the resistance value decreases is obtained in step c1, and a test pulse is applied by changing the applied power variously in the pulse width WLd. The resistance change rate due to the application of the test pulse is measured to obtain a calibration curve shown by a line L4 in FIG. From the calibration curve, the resistance value change rate ΔR / R is −1%, −2%,.
% Applied power P0 (-1%), P0 (-2%),
, P0 (-n%) are obtained in step c2.

(Condition 2) Under the pulse width WLd, the maximum trimming amount -DR2 [%] previously determined by an experiment and stored in the control device 46 as control data is calculated in step c3.
Is read and determined. As described above, the maximum trimming amount -DR2 [%] is a limit value of, for example, about -30% at which the control of the resistance value can be reliably controlled.

(Condition 3) The pulse width W obtained under the above condition 1
In Ld, after one pulse is applied to lower the resistance value, an increase power ΔP required to further reduce the resistance value by d1% (for example, 2 to 3%) is obtained in step c4.

(Condition 4) The pulse width WLu at which the resistance value rises when one pulse is applied is determined in step c5, and a test pulse in which the applied power is variously changed in the pulse width WLu is applied, and the rate of change of the resistance value due to this is applied. Is measured, and the resistance value is d2% (for example, 0.
The applied power P1 required to increase the power is increased by 2% to 0.3% in step c6.
Ask for.

(Condition 5) The minimum trimming amount-DR4 [%] previously determined by an experiment and stored in the control device 46 as control data is read and determined in step c7.

In step b2 in FIG. 12, the probing device 4
2 is mounted on the head substrate 23 to be trimmed, and the initial resistance value R0 of the heating resistor 24 is measured.

That is, the head substrate 2 to be trimmed
The initial resistance values R0 of the plurality of heating resistors 24 are sequentially measured with respect to No. 3 using the trimming device 41. In step b3, it is determined whether or not the measurement of the initial resistance value R0 has been completed for all the dots, and if not, the measurement operation is continued. If the determination in step b3 is affirmative, the process proceeds to step b4. In step b4, a maximum resistance value Rma and a minimum resistance value Rmi are calculated. Further, when it is expected that the overall resistance value of the thermal head 21 fluctuates due to the maximum allowable value and the minimum allowable value of the average resistance value as the product specification of the thermal head 21 or the manufacturing process after the trimming process. Calculates the maximum permissible value Rau and the minimum permissible value RaL of the average resistance value corrected for the variation, and
6 is stored as control data. Next, from the maximum resistance value Rma and the maximum trimming amount -DR2, a lower limit value R4 at the time of the maximum trimming process is obtained.

[0068]

[Mathematical formula-see original document] R4 = Rma (100-DR2) / 100 is calculated.

Further, based on the minimum resistance value Rmi and the minimum trimming amount -DR4, the upper limit value R3 at the time of the minimum trimming process is obtained.

[0070]

[Mathematical formula-see original document] R3 = Rmi (100-DR4) / 100 is calculated.

In step b5, it is determined for each of the target heating resistors 24 whether trimming is possible or not, as described later. If it is determined in step b6 that the trimming is impossible, the thermal head 21 including the heating resistor 24 becomes a defective product, and the above-described processing is started for another thermal head 21. If the determination in step b6 is affirmative, the target resistance value Rf is determined as described later in step b7. Thereafter, the process proceeds to step b8.

In step b8, the required change amount -DR is calculated. That is, regarding the target resistance value Rf determined in the step b7,

[0073]

Calculate -DR = (Rf-R0) / R0 × 100 [%].

In step b9, in order to reduce the resistance value by the required change amount -DR, the pulse width WLd of condition 1 and the applied power P0 (-DR%) obtained in step b1 are obtained. In step b10, the initial resistance value R0 and the applied power P0 (-DR
%) And the applied voltage V0

[0075]

(Equation 5)

After the reference pulse generated by the reference pulse generator 48 based on these data is adjusted by the pulse width adjuster 49 and the voltage adjuster 50, the reference pulse is transmitted through the switch 43 and the probing device 42. Heating resistor 2
4 is applied.

In step b11, the switching means 43 is switched to the resistance value measuring device 44 side, and the resistance value R after the first pulse application is measured by the resistance value measuring device 44. In step b12, it is determined whether or not the resistance value R is within a range considered to be equal to the target resistance value Rf.

[0078]

It is determined whether or not | R−Rf | / Rf ≦ ε holds. If the determination in step b12 is affirmative, the trimming process ends. If not, the process proceeds to step b13 where the measured resistance value R is equal to the target resistance value Rf.
Determine if it is greater than. If this determination is negative, the process proceeds to step b14 where the pulse width WLu obtained under the condition 4 in which the pulse width for increasing the resistance value is relatively long and the applied power is low, and the applied power P1 is applied. Is applied, and the process returns to step b11.

If the determination in step b13 is affirmative, the process proceeds to step b15, where the pulse width WLd is maintained and the applied power is increased by ΔP obtained in condition 3 as described above for reducing the resistance value. The trimming pulse for lowering the resistance value is applied, and the process returns to step b11.

FIG. 15 is a process diagram showing in detail the processes of steps b5 to b7 in FIG. 12, and FIG. 16 is a diagram for explaining the operation of this embodiment. In step d1 in FIG. 15, the upper limit R3 and the lower limit R4

[0081]

## EQU7 ## It is determined whether or not R4.ltoreq.R3 holds. If it does not hold,
6 (1), in which the magnitude relationship between the lower limit R3 and the upper limit R4 is reversed. In such a case, trimming cannot be performed, and the thermal head 21 is determined to be defective.

If the judgment in the step d1 is affirmative, the processing shifts to the step d2, where the value between the upper limit value R3 and the maximum allowable value Rau is set.

[0083]

## EQU8 ## It is determined whether or not Rau ≦ R3 holds. If this determination is affirmative, the process proceeds between the maximum allowable value Rau and the lower limit value R4 in step d3.

[0084]

It is determined whether or not R4 ≦ Rau is satisfied. If this determination is negative, this is the case of FIG. 16B, and both the upper limit value R3 and the lower limit value R4 exceed the standard as a product of the thermal head 21, and trimming is impossible.

When the determination in step d3 is affirmative, FIG.
This is the case of (4), in which case trimming is possible, and the target resistance value Rf is

[0086]

## EQU9 ## Rf = Rau is set, and the process proceeds to step b8 in FIG.

If the above step d2 is negative, the process proceeds to step d
5 and between the upper limit value R3 and the minimum allowable value RaL,

[0088]

It is determined whether or not RaL ≦ R3 holds. In the case of a negative, FIG.
6 (3), wherein the upper limit R3 and the lower limit R
In any of the four cases, the thermal head 21 is out of the standard as a product, and it is determined that the thermal head 21 cannot be trimmed. Step d
When the judgment of 5 is affirmative, it is the case of FIG.
The process proceeds to step d6, where the target resistance value Rf is

[0089]

[Mathematical formula-see original document] Rf = R3 is set, and the process proceeds to step b8 in FIG.

As described above, in the present embodiment, the target resistance value Rf can be automatically calculated and the trimming process can be performed.
With regard to, the processing is stopped without performing the trimming processing.

Thus, during the trimming, the heating resistor 2
It is possible to prevent the occurrence of problems such as application of a trimming pulse exceeding the limit of 4 and breakage. In addition, this effect can eliminate waste of time in which the thermal head 21 is destroyed and discarded despite performing the trimming process. Also, the thermal head 21 determined to be impossible to trim is a good product except that there is a variation in the resistance value of each heating resistor 24, and the production yield of the thermal head 21 is greatly improved, for example, for a different use.

The target resistance value Rf is selected so that a change in the resistance value is small even in the case of performing the trimming process, and the disadvantage that the characteristics of the heat generating resistor 24 are undesirably changed during the trimming process is possible. To prevent it.

As described above, the rate of change of the resistance value by the pulse width WLu and the applied power P1 for increasing the resistance value is selected to be about 0.2 to 0.3%, which is extremely small. Therefore, even if the controllability requirement for the target resistance value of the thermal head 21 is, for example, about ± 0.3%, the trimming of the resistance value can be executed with high accuracy. If such a process is performed on all the heating resistors 24 of the head substrate 23, the resistance value variation between the head substrates 23 ± 0.3%, and the resistance value variation within the head substrate 23 ± 0.3% In addition, it is possible to realize the thermal head 21 in which the resistance value is adjusted with high accuracy such that the variation in the resistance value between the adjacent heating resistors 24 becomes ± 0.6%.

FIG. 17 is a process diagram for explaining the trimming process of the second embodiment of the present invention in which only the variation in the average resistance value between the thermal heads is suppressed, and the process is fast and easy. Details of the step e1 are shown in FIG.
Details will be described later. Steps e2 and e3 correspond to step b in FIG.
2 and b3. In step e4 in FIG. 17, the average resistance value Rav of each heating resistor is calculated. Steps e5 to e7 subsequent to this processing will be described later in detail with reference to FIG. In step e8, in order to reduce the required change amount -DR% of the resistance value common to all the heating resistors obtained in step e7, the pulse width WLd of the condition 1 obtained in step f1 described later is used.
And the applied power P0 (−DR%). In step e9, the initial resistance value R0 of each heating resistor and the applied power P
0 (−DR%), the applied voltage V0 shown in the fifth equation

[0095]

(Equation 5)

Is calculated and applied. In step e10, it is determined whether or not the pulse application process has been completed for all dots, and the pulse application process in step e9 is repeated until the process is completed. When the pulse application process is completed, the process proceeds to another thermal head trimming process.

FIG. 18 shows the details of the step e1.
Steps f1, f2 and f4 of FIG. 13 correspond to steps c1, c2 and c of FIG.
Same as 7. In step f3, the data is determined in advance by an experiment and stored in the control device 46 as control data. The maximum trimming amount is determined by reading out the maximum trimming amount. Here, the maximum trimming amount is, for example, about -15%, which is a limit that does not cause a problem because the variation in the resistance value change rate is small.
DR3 [%].

FIG. 19 is a process chart for explaining the processes of steps e5 to e7 in detail. In step e4, the lower limit value R4 of the average resistance value at the time of the maximum trimming process is calculated from the calculated average resistance value Rav of each heating resistor and the maximum trimming amount -DR3%.

[0099]

R4 = Rav · (100−DR3) / 100 is calculated.

Further, from the minimum trimming amount -DR4 to the upper limit value R3 of the average resistance value during the minimum trimming process.

[0101]

R3 = Rav · (100−DR4) / 100 is calculated.

Based on the upper limit and the lower limit, it is determined whether trimming is possible or not in the first embodiment.

Steps g1, g2 and g4 are the same as steps d2, d3 and d5 in FIG. 15, respectively. If the determination in step g2 is negative, this is the case shown in FIG. 16B, in which both the upper limit value R3 and the lower limit value R4 exceed the standard as a product of the thermal head 21, and trimming is impossible. .

If the determination in step g2 is affirmative, FIG.
This is the case (4), in which case trimming is possible, and the necessary resistance change amount -DR may be determined so that the average resistance after trimming becomes Rau. That is, step g
3,

[0105]

(Equation 15)

Then, the process proceeds to step e8 in FIG.

If the determination in step g4 is negative, FIG.
In the case of (3), both the upper limit R3 and the lower limit R4 exceed the standard of the thermal head 21 as a product, and trimming is impossible.

If the determination in step g4 is negative, FIG.
This is the case (5), in which case trimming is possible, and the resistance change amount -DR may be determined so that the average resistance value after trimming becomes R3. That is, in step g5,

[0109]

(Equation 16)

Then, the process proceeds to step e8 in FIG.

In the second embodiment, the average resistance value Rav of all the heating resistors 24 of the thermal head 21 to be trimmed and the lower limit value R3 or the maximum allowable value R
au and the required resistance value change amount -D
R has been obtained. That is, in this embodiment, by applying a pulse under the condition giving the same resistance value change amount -DR to all the heating resistors 24 only once, as shown in FIG. Change only the value. At this time, the resistance change amount -DR is selected such that the average resistance value after trimming matches the optimum target resistance value Rf, and the same effect as that described in the above-described embodiment is achieved. Can be.

In the above-described embodiment, the trimming process is performed for each heating resistor 24. However, a plurality of sets of the resistance value meter 44 and the trimming pulse generator 45 are provided so that the plurality of heating resistors 24 are provided. May be performed in parallel. Heating resistor 2
The means for changing the resistance value of 4 is not limited to the application of the trimming pulse. For example, the calibration curve shown in FIG. 2 may be obtained by irradiating a laser beam with the laser beam intensity and the irradiation time.

[0113]

As described above, according to the present invention, the target resistance value needs to be larger than the minimum allowable value and smaller than the maximum allowable value. In addition, it is necessary to be larger than the lower limit and smaller than the upper limit. When the resistance value before the trimming process satisfies the above condition, for example, the smaller of the upper limit value and the maximum allowable value is selected as the target resistance value and the trimming process is performed.
Except when the two conditions are compatible, it is impossible to perform trimming. In this way, an appropriate target value can be automatically determined, the usability is excellent, and the quality of the manufactured thermal head can be remarkably improved.

Further, since no pulse application process is performed on the thermal head determined to be impossible to trim,
A substantial processing speed is improved without wasting processing time.

Also, a thermal head judged to be impossible to trim is a good product except for the variation in resistance value, and a good product except for the maximum allowable value variation as another standard. If the minimum allowable value is set again, trimming may be possible, so that the yield is greatly improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a thermal head 21 to which the present invention is applied.

FIG. 2 is a graph showing a relationship between applied power and a resistance value change rate when the pulse width of a trimming pulse is variously changed.

FIG. 3 is a graph showing a waveform of a trimming pulse having a relatively long pulse width and a temporal change in the temperature of a heating resistor 24;

FIG. 4 is a graph showing a waveform of a trimming pulse having a relatively short pulse width and a temporal change of a temperature of a heating resistor 24;

FIG. 5 is a graph illustrating the operation of the present invention.

FIG. 6 is a graph illustrating the operation of the present invention.

FIG. 7 is a graph illustrating the operation of the present invention.

FIG. 8 is a graph illustrating the operation of the present invention.

FIG. 9 is a graph showing a calibration curve illustrating the operation of the present embodiment.

FIG. 10 is a block diagram of a trimming device 41.

FIG. 11 is a process diagram for explaining the entire manufacturing process of the thermal head 21.

FIG. 12 is a process diagram illustrating a trimming process according to the first embodiment of this invention.

FIG. 13 is a process diagram illustrating a process of determining various conditions in the first embodiment.

FIG. 14 is a graph showing the relationship between the applied power and the rate of change in resistance value at a pulse width that is relatively long and has an increasing resistance value.

FIG. 15 is a process diagram illustrating the determination of whether or not trimming is possible according to the first embodiment.

FIG. 16 is a diagram illustrating an operation of determining a target resistance value Rf according to the present embodiment.

FIG. 17 is a process diagram illustrating a trimming process according to the second embodiment of the present invention.

FIG. 18 is a process chart illustrating a process of determining various conditions in the second embodiment.

FIG. 19 is a process diagram illustrating a process of determining whether or not trimming is possible according to the second embodiment.

FIG. 20 is a diagram illustrating a change in resistance value distribution before and after the trimming process according to the second embodiment.

[Explanation of symbols]

 21 Thermal Head 23 Head Substrate 24 Heating Resistor 41 Trimming Device 44 Resistance Measurement Meter 45 Trimming Pulse Generator 47 Calibration Curve Storage 49 Pulse Width Adjuster 50 Voltage Adjuster

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-83050 (JP, A) JP-A-62-92411 (JP, A) JP-A-63-59550 (JP, A) JP-A-63-59550 116403 (JP, A) JP-A-63-159066 (JP, A) JP-A-63-252760 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41J 2/335 H01C 17 /twenty two

Claims (1)

(57) [Claims] In a method of trimming a plurality of heating resistors arranged linearly on an electrically insulating substrate of a thermal head, a maximum resistance value and a minimum resistance value of each heating resistor are measured, and The lower limit of the trimming resistance based on the maximum resistance value and the upper limit of the trimming resistance based on the minimum resistance value in the resistance change curve of the heating resistor are obtained, and then, the heating is performed to trim the antibody, and each heating resistor is trimmed. Wherein the average resistance value is set within a range between a predetermined maximum allowable value and a minimum allowable value.