JP2831854B2 - Resistor trimming method for thin film thermal head - 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 formed on a thermal head by a thin film technique.

[0002]

2. Description of the Related Art In a thermal head used in various printing output devices, a plurality of heating resistance elements are formed on a head substrate, and the heating resistance elements are selectively energized to perform thermal printing. Variations in the resistance value that causes density unevenness during printing with the thermal head are as follows.
There are types.

(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) Variation in the head, that is, variation in the resistance value of the heating resistor element in a single thermal head.

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

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

At this time, in order to realize the designed printing density, it is necessary that the resistance values of the respective heating resistance elements are uniform. For this reason, a trimming technique has been employed in which a voltage pulse is applied to the heating resistor element after the heating resistor element is formed to reduce the resistance value and minimize variations.

As a conventional example of performing such trimming, in manufacturing a thermal head, in the same lot or on the same substrate, a change in the resistance value when the same trimming pulse is applied to each heating resistor element 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.

In determining the calibration curve in the above conventional example, a test pulse is applied in advance to the heating resistor element of the thermal head. The following three methods are used depending on the type of the thermal head to which the test pulse is applied. Is mentioned.

(1) Dozens of dots are selected from a thermal head which is actually used by performing a trimming process, and test trimming is performed on the selected dot.

(2) A dummy dot for performing a trimming test without performing printing in actual use is prepared in a thermal head which is actually used after actually performing a trimming process, and test trimming is performed on the dummy dot. .

(3) The sample head is set for each lot only for the purpose of performing the trimming test, and several tens of dots are selected from the sample head and the test trimming is performed.

[0013]

Of the three types of resistance value variations described above, variations between heads greatly affect the specifications of a power supply for driving a thermal head. That is,
Since the average resistance value varies from one thermal head to another, driving such a thermal head with a power supply of the same configuration increases the capacity of the power supply and requires a circuit to adjust the drive voltage for each thermal head. Is complicated.

On the other hand, the variation in the head and the variation between adjacent dots can be caused by the fact that when performing high-precision thermal printing such as half-tone thermal printing, characters or non-halftone display that may cause density unevenness but do not perform halftone display. At the time of character printing operation, the influence of such variations in the head and between adjacent dots on the quality is reduced. When trimming the resistor of the thermal head when performing such low-accuracy thermal printing, a high-speed and easy method is desired.

Further, the following problems arise in the method of applying the above three types of test pulses.

In the first method, since the trimming test is performed using the heating resistor element in the thermal head which is actually trimmed and put to practical use, the accuracy of the obtained calibration curve is increased. However, since the heating resistor element to which the test pulse is applied also prints during actual use, if the test pulse is destroyed by a high voltage or the like after the application of the test pulse, the thermal head becomes a defective product. However, in the test trimming, in order to confirm a limit such as a voltage that can be trimmed, a test is performed by setting various pulse conditions such as a voltage value and a pulse duration until the heating resistor element is destroyed. Therefore, as described above, there is a problem that the possibility of destruction increases.

Even if a good calibration curve is created in a state that does not lead to destruction, the heating resistance element subjected to test trimming needs to approach a target resistance value set in advance. Further, a trimming pulse may be applied, which may result in destruction or reduced reliability.

Moreover, since the calibration curve needs to be created for each thermal head, it is difficult to efficiently determine the pulse conditions of the test pulse and create the calibration curve over a large number of thermal heads. .

In the second method, since the heating resistance element to which the test pulse is applied is not used during actual use, the problem in the first conventional example is solved. Requires a dummy dot, which requires a new design of the thermal head, which requires a great deal of labor.
Also, it is difficult to prepare a large number of dummy dots set in the thermal head, and it is difficult to obtain a highly accurate calibration curve.

Although the third method is relatively practical, it takes a lot of time to prepare a calibration curve by performing test trimming with a sample head for each lot, which reduces the productivity of the thermal head. Would. Therefore, once a calibration curve is created, there is a demand for a versatile trimming method that can use this calibration curve with any thermal head regardless of the lot or the like.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned technical problems and to provide a high-speed and easy-to-use thermal head for performing relatively low-precision thermal recording without performing halftone display. It is an object of the present invention to provide a method of trimming a resistor of a thin film thermal head having the same.

[0022]

SUMMARY OF THE INVENTION The present invention provides a trimming method for adjusting the electric resistance of a heating resistor element by applying a trimming voltage pulse to a plurality of heating resistor elements of a thin film thermal head. The average resistance value is calculated by measuring the electric resistance value of the resistance element, and based on a calibration curve representing the relationship between the magnitude of the voltage pulse for trimming and the amount of change in resistance value when the pulse is applied to the heating resistance element. A predetermined trimming voltage pulse is determined to cause a resistance change corresponding to the difference between the average resistance value and the target resistance value, and the determined trimming voltage pulse is applied to all the heating resistor elements. In this method, the electrical resistance value of each heating resistance element is changed by a substantially constant ratio.

Further, according to the present invention, when the average resistance value is larger than the target resistance value, a large amount of electric power is applied to all the heating resistance elements, and a voltage pulse for trimming having a small pulse width is applied to the heating resistance elements. To reduce the electric resistance.If the average resistance is smaller than the target resistance, all the heating resistance elements have a small amount of electric power, and a voltage pulse for trimming having a large pulse width is applied to the atmosphere. It is characterized in that the electric resistance value is increased by oxidizing at least a part of the heat-generating resistance element by applying it inside.

[0024]

According to the present invention, a voltage pulse is applied to a heating resistor element formed on an electrically insulating substrate of a thin-film thermal head, and the voltage pulse corresponds to the pulse width of the applied voltage pulse and the applied power. A change in the resistance value of the heating resistance element is measured, and a so-called calibration curve that gives a pulse condition for generating a required resistance value change is created. From this calibration curve, a predetermined trimming voltage pulse that causes a resistance change corresponding to the difference between the average resistance value of the heating resistance element and the target resistance value is determined and applied to all the heating resistance elements in common. Thus, the resistance values of all the heating resistance elements can be changed by a substantially constant ratio, and the average resistance value can be changed at a desired ratio. In this trimming method, the number of times of pulse application to each heating resistor element is one and complicated control is not required, and a high-speed and easy thin-film thermal head resistor trimming method is achieved.

Further, according to the present invention, whether the average resistance value of the heating resistance element is larger or smaller than the target resistance value can be adjusted to the target resistance value.

[0026]

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 resistance elements 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 resistance elements 24. A plurality of drive circuit elements 25 connected by electrodes are arranged. These drive circuit elements 25 are formed of a protective layer 2 made of a synthetic resin material.
6 coated.

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 linear heating resistors 24 are formed. Heating resistance element 2
4 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 resistance element 24 is controlled by a driving circuit element 25 realized as an integrated circuit element. The drive circuit element 25 has an insulating layer 2
8 are connected to the individual electrodes 37,
A signal or the like for driving the heating resistor element 24 is input to the drive circuit element 25, and an external connection terminal 29 covered with an insulating layer 28 is input.
Are 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 values of the plurality of heating resistor elements 24 defined by these are reduced to one. In order to suppress variations in the average resistance value of the thermal head 21. 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 resistance element 24 can be increased as well as reduced. A summary of the experimental results is shown in the graph of FIG. That is, the horizontal axis represents the applied power, and the vertical axis represents the resistance value change rate Δ of the heating resistance element 24.
It has been confirmed that when R / R is taken, the obtained characteristic curve greatly changes by changing the pulse width of the applied trimming pulse. Lines L1 and L shown in FIG.
2, L3 indicate cases 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 relationships are

[0030]

## 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 decreases with an increase in the applied power, and the rate of decrease gradually increases in a small range of the applied power. To a negative value (that is, increase), the threshold value Pth is applied, and the resistance value becomes an initial resistance value. In a range B higher than the threshold value Pth, the resistance value gradually increases as the applied power increases.

As described above, the pulse width W of the trimming pulse
The phenomenon that the resistance value of the heating resistance element 24 can change either upward or downward due to L is described as follows with reference to FIG. That is, the change in the resistance value of the heating resistor element 24 due to the application of the trimming pulse is due to the annealing effect due to the heating of the heating resistor layer 34 itself, that is, the crystallization of the heating resistor layer 34 and the heating of the heating resistor layer 34 itself. Oxidation. Among them, the annealing effect is a progress of crystallization of the heating resistor layer 34 and appears as a phenomenon of a decrease in resistance value, and the oxidation appears as a phenomenon of an increase in resistance value.

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 relatively low applied voltage V1. 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. 4A, when a trimming pulse having a pulse width WL1 that causes only a decrease in the resistance value is applied to the heating resistor layer 34, the pulse width WL3 of the trimming pulse is fixed. Even if the resistance value before the application of the trimming pulse is different for each heating resistor element 24, each heating resistor 24 shows a substantially constant resistance value change rate by applying the same applied power.

The present inventor has proposed a heating resistor element 2 shown in FIG.
4, the width in the left-right direction in FIG. 1 is 151 μm, the width in the direction perpendicular to the plane of FIG. 1 is 105 μm, and the change in the resistance value of the heating resistance element 24 is two types. 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 resistance 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, it can be concluded that the characteristic curves of the lines L1 and L3 shown in FIG.

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 resistance elements 24 are different from each other, the characteristics of the time change of the temperature of each heating resistance element 24 are different from each heating resistance element. It becomes the same between the elements 24, and a substantially constant resistance value change rate is obtained as described above.

(3) 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 resistance element 24 to applied pulses (such as a trimming pulse and a driving pulse accompanying actual use) is improved. On the other hand, an oxidation phenomenon that causes an increase in the resistance value narrows the region of the heating resistance element 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 greatly increasing the resistance value of the heating resistance element 24 deteriorates the heating resistance element 24 and shortens the life.

(4) When the heating resistor element 24 is of a tantalum Ta type, 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 elements 24 aggregate, and the heat storage layer 35 immediately below the heat-generating resistive elements 24 is destroyed by heat. In view of these points, the present inventor has determined that the maximum trimming amount −D which can maintain the reliability of the thermal head 21 is the limit.
It was confirmed that R1 was, for example, about -40% as shown in FIG. However, in the trimming method in which only one trimming pulse is applied to uniformly trim each heating resistance element 24 and suppress the variation of the average resistance value, the resistance value controllability of one pulse is all. Therefore, the rate of change of the resistance value due to this pulse application varies,
Even if the variation of the average resistance value can be suppressed, the variation in the thermal head 21 and the variation between adjacent dots are greatly deteriorated as compared to before the trimming.

As shown in FIG. 6, the variation in the rate of change in resistance depends on the slope of a curve showing the relationship between the applied power and the rate of change in resistance. That is, if the slope of this curve is steep, slight applied power and other variations appear as a large resistance value change rate. It can be understood that the slope of the curve is gentle in a range where the applied power is small and the resistance value change rate is small, and that the curve slope is steep in a place where the applied power is large and the resistance value change rate is large. Therefore, for example, the limit value -DR2 of about -15%
It has been confirmed that it is difficult to change the above.

(5) Heating resistance element 2 whose enlarged view is shown in FIG.
For example, two types of thermal heads having different areas (W × LL) due to the product of the width W along the array direction D1 and the length LL in the direction orthogonal to the array direction D1 are assumed. In this case, the ratio of the areas S1 and S2 of each thermal head is

[0045]

## EQU2 ## If S1: S2 = 1: α, the characteristics showing the correlation between the applied power and the rate of change of the resistance value of the two types of thermal heads when the pulse width is constant, that is, a calibration curve as shown in FIG. Has a correlation with respect to the numerical value α, and the characteristic of one of the thermal heads is

[0046]

When P = f (ΔR / R), the characteristics of the other thermal head are as follows:

[0047]

## EQU4 ## P = α × f (ΔR / R) This state is represented as lines LA and LB in FIG.

Such a phenomenon is explained as follows. When considering the heating resistance elements having different areas as described above, as shown in FIG. 9, a reference area S0 having a width W0 and a length LL0,

[0049]

## EQU5 ## Assume a heating resistance element 24 of S0 = W0 × LL0. This heating resistor element 2
4 has a resistance value R, a voltage V, and an applied power P (=
V × I).

Here, as shown in FIG. 10A, assuming a heating resistor element 24a having a width W1 twice the width W0 and a length equal to the length LL0, this heating resistor element 24a Is equivalent to a configuration in which two heating resistance elements 24 shown in FIG. 9 are connected in parallel as shown in FIG. 10 (2). When a pulse of voltage V is applied to such a heating resistor element 24a, the applied power P is

[0051]

(Equation 6)

Thus, it is understood that the applied power is required to be twice as large as the applied power required for the heating resistor element 24 shown in FIG.

As shown in FIG. 11A, the length LL
Assuming that 1 is twice the length LL0 of the heating resistor element 24 shown in FIG. 9 and the width is the same as the width W0 of the heating resistor element 24b, this is shown in FIG. Thus, the configuration is equivalent to the configuration in which two heating resistance elements 24 shown in FIG. 9 are connected in series. When a pulse of the current I is applied thereto, the applied power P becomes

[0054]

## EQU7 ## It can be understood that P = I ² × (R + R) = 2 × (I ² R), which also requires twice as much power.

By assuming a heating resistor element having a certain reference area as described above and calculating the area ratio α of the heating resistor element to be actually trimmed, Equation 4 can be obtained.

Based on the above facts, a method for adjusting the average resistance value with only one pulse will be described. As shown in FIG. 4A, when a trimming pulse having a relatively short pulse width WL3 is applied, the pulse width W
When L3 is kept constant, the relationship between the applied power and the rate of change of the resistance value does not depend on the resistance value of the heating resistor element 24 as described above.
Actually, the rate of change of the resistance value varies due to the variation of the dimension 4 and the variation of the pulse width or applied voltage of the applied pulse.

Therefore, the applied power P and the resistance change rate ΔR
As shown in FIG. 6, the graph showing the relationship with / R is different from the line L4 showing the ideal correspondence with the line L4.
a, L4b. However, the variation of the resistance value change rate ΔR / R due to this width largely depends on the value of the applied power P. That is, as described above, the variation is small when the applied power is small and the resistance change is small, and the variation is large when the applied power is large and the resistance change is large.

For example, in order to change the resistance value by -n% in FIG. 6, data of the corresponding applied power P0 (-n%) is obtained from the calibration curve of line L4 in FIG. 6, and a trimming pulse having this applied power is obtained. Is actually applied, FIG.
In the range of the width δ shown in FIG. Therefore, the obtained rate of change in resistance varies between −n−d2% at the lower limit and −n + d1% (d1 + d2 = δ) at the upper limit. However, it has been confirmed that this variation is small and practically causes little problem.

However, for example, in order to change the resistance value by -m% in FIG. 6, data of the corresponding applied power P0 (-m%) is obtained from the calibration curve of line L4 in FIG. When the trimming pulse is applied, the rate of change in resistance actually obtained as shown in FIG.
m-d4%, and the upper limit is -m + d3%, and this variation is large and impractical.

Therefore, in trimming the heating resistance element 24 by only one pulse application and adjusting the average resistance value, it is necessary to pay attention so that this variation does not occur. For example, it is performed in a range smaller than the limit value -DR2 of about -15%.

First, the resistance values of all the heating resistance elements 24 of the thermal head 21 are measured, and the average resistance value is determined. Next, the required resistance change rate is obtained from the average resistance value, and the calibration curve is referred to from the resistance change rate on the assumption that the required resistance change rate is in a range smaller than the aforementioned limit value -DR2. By applying a pulse of the applied power P0 (−n%) obtained by the above to all the heating resistance elements 24, the resistance value can be reduced uniformly and the average resistance value can be adjusted.

Also, by making the pulse width WL1 relatively long, the resistance value can be similarly increased to adjust the average resistance value. However, it is obvious that increasing the temperature significantly impairs the quality of the heating resistor element 24 as described above, and shortens the service life.

FIG. 12 shows a trimming device 41 according to the present invention.
It is a block diagram of. The head substrate 23 of the thermal head 21 is mounted on the trimming device 41 and the resistor layer 5
The heating resistor element 2 is connected to the common electrode 36 and the individual electrode 37 on
A probing device 42 is provided for bringing the probe into contact with each of the probes 4 individually. The probing device 42 is connected to a resistance value meter 44 and a trimming pulse generator 45 via a switching unit 43. 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 unit 47 that creates and stores a calibration curve.
The head substrate 23 is mounted on an XY stage 52,
The stage 52 positions the head substrate 23 by a positioning mechanism 53 controlled by the control device 46.

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

FIG. 13 is a process chart for explaining the entire process of manufacturing the thermal head 21. In step a1 in FIG. 13, a thick film common electrode layer 27 and a heat storage layer 35 are formed on the thermal head 21. In step a2, the heating resistor layer 34 is formed on the thermal head 21. In step a3, the common electrode 36 and the individual electrode 37 are formed on the heating resistor layer 34.
To form In step a4, a trimming process, which will be described in detail later, is performed to adjust the resistance value of each heating resistance element 24 to be uniform. Then, in step a5, the wear-resistant layer 39 is formed. Thereafter, through other processing, the thermal head 21 is completed.

FIG. 14 is a process chart for explaining a method of creating a calibration curve required for performing the trimming processing according to the first embodiment of the present invention. In this embodiment, the fact that regularity and reproducibility appear in a change in resistance value when the head substrate 23 has the same standard is applied. That is, a sample head substrate of the same standard as the head substrate 23 to be trimmed is set, and the trimming device 41 shown in FIG.
A test for applying a trimming pulse is performed.

First, in step b1, a pulse width WLd at which the resistance value decreases is determined, and a test pulse is applied in the pulse width WLd by changing the applied power in various ways. The resistance value 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 this calibration curve, the resistance value change rate ΔR / R is −
1%, -2%,..., -N%
%), P0 (-2%),..., P0 (-n%) in step b2.
Ask at.

FIG. 15 is a flowchart for explaining details of the trimming processing according to the first embodiment of the present invention. In step c1, a calibration curve is created and stored in the calibration curve storage unit 47 as described with reference to FIG. In step c2, the probing device 42 is mounted on the head substrate 23 to be trimmed, and the initial resistance value R0 of the heating resistance element 24 is measured.

In step c3, it is determined whether or not the measurement of the initial resistance value R0 in step c2 has been performed for all the heating resistance elements 24. If this determination is negative, the heating resistance element 24 for which the initial resistance value has not yet been measured remains, and the process returns to step c2 to repeat the measurement of the initial resistance value R0.

If the determination in step c3 is affirmative, the process proceeds to step c4, where the average resistance value R
av is calculated. Next, in step c5, the required resistance value change amount -DR is calculated. That is, in the specification of the thermal head 21, the target resistance value Rf is set in advance,

[0071]

-DR = (Rf-Rav) / Rav * 100
Calculate [%].

In step c6, the required change amount -DR
In order to lower the resistance value only, the pulse width WLd and the applied power P0 (−DR) are obtained from the calibration curve obtained in step c1. In step c7, the applied voltage V0 is calculated based on the initial resistance value R0 and the applied power P0.

[0073]

(Equation 9)

After the reference pulse generated by the reference pulse generator 48 based on the calculation result and the data of the pulse width WLd is adjusted by the pulse width adjuster 49 and the voltage adjuster 50, the switching unit 43 And probing device 42
Is applied to the heating resistor 24.

In step c8, it is determined whether or not the pulse application in step c7 has been performed on all the heating resistance elements 24. If this determination is negative, there is a heating resistor element 24 to which no pulse has been applied yet, so the process returns to step c7, and the initial resistance value R0 of this heating resistor element 24 is determined.
And the applied power P0, the initial voltage V0 is calculated again as described above, and the pulse application is repeated. If the determination in step c8 is affirmative, the trimming of all the heating resistance elements 24 is completed, and thus the trimming of the head substrate 23 is completed.

FIG. 16 is a flowchart for explaining details of the trimming processing according to the second embodiment of the present invention. In step d1, step c in FIG. 15 described in the first embodiment is used.
As in the case of 1, calibration curves are created in steps b1 and b2 in FIG. However, the sample head used here does not need to have the same standard as the thermal head to be trimmed, and may be of a type having only a different heater size.

That is, a sample head having the same specifications other than the heater size is selected, and the area of the heating resistor element 24 is set as a reference area.
, A calibration curve is created, and the pulse width WLd and the applied power at which the rate of change in resistance ΔR / R is −1%, −2%,. P0 (-1%), P0 (-2%), ..., P0 (-n
%) Is obtained and stored in the calibration curve storage unit 47 together with the reference area S0.

Steps d2, d3, d4, d5 and d6 correspond to steps c2 and c of FIG. 15 in the first embodiment.
3, c4, c5, and c6. Step d
In step 7, the obtained applied power P0 is corrected by the ratio between the heater size of the trimming target head substrate 23 and the reference size S0. That is, the heater size S1 of the head to be trimmed is apparent in advance as a standard, and the ratio α between the heater size S1 and the reference size S0 is defined as:

[0079]

[Formula 10] α = S1 / S0, and the corrected applied power P0 ′ is

[0080]

Calculated as P0 '= α · P0.

Steps d8 and d9 are the same as steps c7 and c8 in FIG. 15 in the first embodiment, and the applied voltage V0 'calculated from the initial resistance value R0 and the corrected applied power P0'.

[0082]

(Equation 12)

Is calculated, and a trimming pulse is applied based on the calculation result and the data of the pulse width WLd, and step d8 is repeated until the trimming pulse is applied to all the heating resistance elements 24.

When the processing has been completed for all the heating resistance elements 24, the trimming is completed, and the trimming processing for the head substrate 23 is completed.

In the above embodiment, by applying a trimming pulse of the same applied power with the same pulse width determined based on the calibration curve created in advance, the resistance value of all the heating resistance elements 24 can be reduced uniformly. . Therefore, a trimming method can be realized in which the average resistance value can be made close to the target resistance value while the resistance value distribution of the head substrate 23 remains almost unchanged, and the average resistance value can be adjusted.

Further, only one pulse application is required for the trimming process, and there is no need for complicated control, so that a high-speed and easy trimming method is realized.

According to the second embodiment, the calibration curve can be used even in a thermal head having a heater size different from that of the sample head for which the calibration curve is created, and a versatile trimming method is realized. Will be.

In each of the above-described embodiments, the trimming process is performed for each heating resistor element 24. However, the plurality of heating resistor elements 24 and the trimming pulse generators 45 are provided in plural sets so that a plurality of heating resistor elements are provided. 24 may be performed in parallel. The calibration curve shown in FIG. 6 is not limited to the application of the trimming pulse. For example, the calibration curve shown in FIG.

[0089]

As described above, according to the present invention, it is possible to uniformly change the electric resistance of all the heat generating resistance elements by the amount of change obtained as the difference between the average resistance and the target resistance. As a result, the trimming of all the heating resistance elements can be performed easily and with high precision, and the reliability of the thermal head is 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 element.

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

FIG. 5 is a graph illustrating a phenomenon in which the relationship between the applied power and the resistance value change rate is not affected by the resistance value of the heating resistance element 24.

FIG. 6 is a graph showing the relationship between the applied power and the rate of change in resistance when the pulse width is constant.

FIG. 7 is a plan view of the heating resistance element 24.

FIG. 8 is a graph showing a calibration curve for explaining the operation of the present embodiment.

FIG. 9 is a plan view of a heating resistor element 24 having a reference area.

FIG. 10 is a plan view showing an example in which the width and the length are increased.

FIG. 11 is a plan view showing an example in which the width and the length are increased.

FIG. 12 is a block diagram of a trimming device 41.

FIG. 13 is a process diagram illustrating the entire manufacturing process of the thermal head 21.

FIG. 14 is a process diagram illustrating a calibration curve creation process.

FIG. 15 is a process diagram illustrating a trimming process according to the first embodiment of the present invention.

FIG. 16 is a process diagram illustrating a trimming process according to a second embodiment of the present invention.

[Explanation of symbols]

 21 Thermal Head 23 Head Substrate 24 Heating Element 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 front page (56) References JP-A-63-252759 (JP, A) JP-A-63-252760 (JP, A) JP-A-4-226767 (JP, A) JP-A 63-252767 178059 (JP, A) JP-A-63-59550 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41J 2/335 B41J 2/35

Claims (2)

(57) [Claims] In a trimming method for adjusting a resistance value of a heating resistor by applying a voltage pulse for trimming to a plurality of heating resistors of a thin-film thermal head, measuring a resistance value of all heating resistors. The average resistance value is calculated based on a calibration curve representing the relationship between the magnitude of the voltage pulse for trimming and the amount of change in resistance value when the pulse is applied to the heating resistance element. A predetermined trimming voltage pulse is determined so as to cause a resistance change corresponding to a difference from the value, and the determined trimming voltage pulse is applied to all the heating resistor elements to thereby determine the electric resistance of each heating resistor element. A method of trimming a resistor of a thin-film thermal head, wherein a resistance value is changed by a substantially constant ratio. 2. When the average resistance value is larger than a target resistance value, all the heating resistance elements have a large amount of power,
The electric resistance value is reduced by applying a voltage pulse for trimming with a small pulse width to anneal the heating resistance element, and when the average resistance value is smaller than the target resistance value, a small power is supplied to all the heating resistance elements. 2. The electric resistance value according to claim 1, wherein the electric resistance value is increased by applying a trimming voltage pulse having a large pulse width in an air atmosphere to oxidize at least a part of the heating resistance element. Resistor trimming method for thin film thermal head.