JP2938222B2 - Thermal head resistor trimming device - 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 device for adjusting the resistance of a plurality of heating resistors formed linearly on an electrically insulating substrate 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 value of each heating resistor needs to be uniform.
However, the resistance value of the heating resistor by thick film technology is ± 25%
Because of the above-mentioned variation, a trimming technique has been adopted in which a voltage pulse is applied to the heating resistor after the formation of the heating resistor to reduce and adjust the resistance value and to minimize the variation. .

As a first conventional example of performing such trimming, when the initial resistance value of a heating resistor is larger than a target resistance value, a trimming pulse of an initial voltage V0 is applied to reduce the resistance value, and thereafter, the resistance value is reduced. There is known a method of applying a trimming pulse whose voltage is increased by an increment ΔV until the value becomes equal to or less than a target resistance value. However, in this method, in order to equalize the resistance value of each heating resistor with high precision,
It is necessary to set the initial voltage V0 and the increment ΔV to relatively small values, the number of trimming pulses to be applied to each heating resistor increases, and the trimming process takes time, and the production efficiency decreases. There is a problem that it will.

[0004] As a second prior art, the following trimming method is known. In other words, when manufacturing a thermal head, within the same lot or on the same substrate, attention was paid to the phenomenon in which the change in the resistance value when the same trimming pulse was applied to each heating resistor showed regularity and reproducibility. , The rate of change Δ between the voltage value of the applied trimming pulse and the resistance value R
A correlation between R / R, that is, a calibration curve is obtained in advance, an initial voltage V0 is determined according to the calibration curve, and the resistance value is made as close as possible to a 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]

According to the second conventional example, the resistance value of a thick-film thermal head conventionally manufactured by a thick-film technique such as printing is adjusted relatively sufficiently. The degree of approach to the target resistance value when the resistance value is adjusted using the second conventional example, that is, the controllability, is about -3% to + 0%. Moreover, since this value does not depend on the original resistance value of each heating resistor, the variation of the resistance value of the thick film thermal head after the trimming process is ± 1.5% between the thermal heads and ± 1.% within the thermal head. 5%,
± 3% between adjacent heating resistors. This can be said to be a sufficient technique for improving the variation because the variation in the initial resistance value of the thick-film thermal head is usually ± 25% or more.

On the other hand, in recent years, a thin film thermal head manufactured by a thin film technique such as vapor deposition or sputtering has been used. In the case of this thin-film thermal head, the variation of the initial resistance value between adjacent heating resistors is about ± 1%, and the thin-film thermal head for an image capable of halftone display without density unevenness has an adjacent heating thin-film resistor. The variation of the resistance value between the bodies is required to be about ± 0.5%. For this reason,
The second conventional example is extremely insufficient as a trimming technique for a thin film thermal head.

Further, when the second prior art is applied to trimming of a thin film thermal head, the following problems occur, and controllability to a target resistance value is extremely poor.

(1) Even if a trimming pulse of a constant voltage level V0 is applied, the resistance value varies depending on the resistance value of each head or each heating resistor within a target range of about ± 0.5%. Because the rates are so different, it is not possible to create a calibration curve.

(2) The increase ΔV in trimming
Even if the initial voltage V0 is repeatedly applied with = 0, the rate of change of the resistance value is large, and the application of this trimming pulse often results in a resistance value that is too low below the target resistance value.

(3) In the case where the trimming process is actually performed on the heating resistor, accuracy in measuring the resistance value becomes a problem.
High-precision trimming as theoretically impossible. Here, the resistance value measurement accuracy refers to a state in which, even when the measurement is performed on the same heating resistor, the measured value varies with the true resistance value line L16 as shown in line L17 in FIG. It is. For this reason, when performing a trimming process of increasing the resistance value while measuring the resistance value, the measured value varies with respect to the true resistance value change line L18 in FIG. 24 as shown by the line L19, and the resistance value is adjusted. However, there is a problem that it is difficult to make the accuracy higher than the variation in the measured value.

An object of the present invention is to provide a thermal head resistor trimming apparatus which solves the above-mentioned technical problems, has good workability, and can adjust the resistance value with high accuracy to a target resistance value. It is to be.

[0012]

According to the present invention, there is provided an apparatus for trimming a plurality of heating resistors arranged on an electrically insulating substrate of a thermal head, wherein power from a plurality of input lines is supplied to the same number of heating resistors. Power supply means for individually supplying power; low-voltage pulse generating means for generating a first pulse having a relatively low voltage and a long duration for oxidizing at least a part of the heating resistor to increase the electric resistance value; A high-voltage pulse generating means for generating a second pulse having a relatively high voltage and a short duration for lowering the electric resistance value by annealing the heating resistor; and a power supply means for supplying an output of the low-voltage pulse generating means. Switching means for simultaneously connecting to the plurality of input lines or switching the output of the high-voltage pulse generating means to be sequentially connected to each of the input lines. A trimming device.

The present invention is characterized in that a plurality of the low-voltage pulse generating means are used.

[0014]

According to the present invention, a plurality of heating resistors arranged on an electrically insulating substrate of a thermal head are individually supplied with power from a plurality of input lines to the same number of heating resistors by a feeding means. Is done. At this time, a first pulse from the low-voltage pulse generating means for oxidizing at least a part of the heating resistor to increase the electric resistance value and a high pulse for annealing the heating resistor to lower the electric resistance value. One of the second pulse from the voltage pulse generating means is selected by the switching means, and the first pulse from the low voltage pulse generating means is simultaneously connected to a plurality of input lines of the power supply means,
The second pulse from the high voltage pulse generating means is switched so as to be sequentially connected to each input line of the power supply means.

Therefore, the resistance value of each heating resistor can be adjusted by increasing or decreasing the resistance value of the heating resistor by applying the first pulse and the second pulse. That is, since trimming is performed by measuring a change in the resistance value of the heating resistor from a drop or a rise based on the pulse width of the voltage pulse applied in advance and the applied power, a so-called calibration curve can be measured, greatly improving workability. To improve.
By appropriately selecting the state of the voltage pulse to be applied, the resistance value can be reduced or increased, and the workability and controllability with respect to the target resistance value are significantly improved. Further, the operation of applying the first pulse, which requires a relatively long time for one pulse application, is performed simultaneously and in parallel with a plurality of heating resistors, so that the time required for the trimming process can be significantly reduced. In this respect, workability is significantly improved. Further, according to the present invention, since a plurality of low-voltage pulse generating means are used, when the increasing range of the electric resistance value of the heating resistor differs, each low-voltage pulse generating means can be used.

[0016]

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 a trimming apparatus according to the present invention. The thermal head 21 includes a heat radiating plate 22 made of a metal material such as aluminum, on which an insulating substrate 23 is fixed with an adhesive layer 30. The heat storage layer 35 is formed on the insulating substrate 23 by a thick film technique such as screen printing, and the thick film common electrode layer 27 is formed along the outer periphery of the insulating substrate 23. On the heat storage layer 35, a heating resistor layer 34,
The common electrode 36 and the plurality of individual electrodes 37 are formed, and the plurality of heating resistors 24 are arranged in a straight line.
The heating resistor 24 performs thermal printing on the thermal paper 32 between the heating resistor 24 and the platen roller 31 via a wear-resistant layer 39 formed by a thin film technique such as sputtering.

A plurality of drive circuit elements 25 are arranged in parallel with the arrangement direction of the heating resistors 24 and connected to the heating resistors 24 by electrodes (not shown). These drive circuit elements 25 are covered with a protective layer 26 made of a synthetic resin material. The heating resistor 24 is controlled by a drive circuit element 25 realized as an integrated circuit element. The drive circuit element 25 includes the individual electrodes 3 covered with an insulating layer 28.
7 is connected, a signal for driving the heating resistor 24 and the like are input to the drive circuit element 25, and the external connection terminal 29 covered with the insulating layer 28 is connected to cover the drive circuit element 25 and its periphery. Thus, a protective layer 26 made of a synthetic resin material or the like is formed.

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 insulating 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 horizontal axis represents the applied power, and the vertical axis represents the rate of change of the resistance value of the heating resistor 24, ΔR /
When R was taken, it was confirmed that the obtained characteristic curve greatly changed by changing the pulse width of the applied trimming pulse. The lines L1, L2, shown in FIG.
L3 indicates a case where the pulse widths are different from each other. When the corresponding pulse widths are represented by WL1, WL2, and WL3 (when necessary, they are collectively referred to as WL), these relations are expressed as follows.

[0020]

## EQU1 ## WL1>WL2> WL3, and the pulse widths WL1, WL2, WL3 are, for example,
Several msec or more, several 100 μsec, several 10 to several μsec
c.

That is, when the pulse width WL is relatively long, as indicated by the line L1, the resistance value increases as the applied power increases. On the other hand, when the pulse width WL is relatively short, the first threshold power P
Although the resistance value does not change in the range A less than th1, the resistance value decreases when the applied power is increased to about the range B equal to or more than the first threshold power Pth1. Further, in the intermediate pulse width WL2 between the pulse widths WL1 and WL3, 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, the second
In the range of the applied power less than the threshold power Pth2, the resistance value initially decreases gradually as the applied power increases, but at a certain point, the rate of change of the decreasing rate gradually decreases to zero. In the range of the applied power P equal to or more than the second threshold power Pth2, 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 will be described with reference to FIGS. 3 and 4 as follows. That is, the resistance value of the heating resistor 24 changes due to the application of the trimming pulse because of 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 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 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 applied power P and the applied power P, 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 is applied to the heating resistor layer 34, 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 the resistance value drop 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 increased by the heating resistor 24. It shows a substantially constant rate of change in resistance value, even if it differs from one to another.

The present inventor has found that the heating resistor 24 shown in FIG.
As for the two types of heating resistors 24 having a length of 151 μm in the left-right direction in FIG. 1 and a width of 105 μm in the direction perpendicular to the plane of FIG.
The change in the resistance value of the heating resistor was measured. The relationship between the applied voltage and the rate of change of the resistance value is shown in lines L6 and L7 in FIG. Thus, it is understood that the state of the resistance value change rate is significantly different from the relation with the applied voltage.

On the other hand, the relationship between the applied power and the rate of change of the resistance value is shown by 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 rate 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 to L3 shown in FIG. 2 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 time conversion of the temperature of each heating resistor 24 become the same between each heating resistor 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 heat generating resistor 24, the pulse width is relatively short as shown in FIG. By applying the trimming pulse in which the applied power is gradually increased, the resistance value can be gradually reduced. The inventor of the present invention measured the resistance value change of the heating resistors 24 having different resistance values in the description with reference to FIG. 5 and FIG. 6 when the applied power was increased by increment ΔP after the second time. The result is shown in FIG.
Shown in lines L10 and L11. As described above, the degree of decrease in the resistance value is different from each other depending on the initial applied power, but in any case, the resistance value is gradually reduced.

(4) In the description of the third section, the resistance value can be gradually increased by setting the second and subsequent trimming pulses to have a relatively long pulse width as shown in FIG. it can. The inventor of the present invention first applies a trimming pulse for greatly reducing the resistance value to the plurality of heating resistors 24 having mutually different resistance values in the description of the third item, and a second or later pulse of, for example, 50 msec. The change in resistance value when a width trimming pulse was applied was measured. The resistance change rate is shown in lines L12 and L13 in FIG.

In FIG. 8, line L12 corresponds to line L13.
In this case, the applied power is higher than in the case of FIG. If the pulse width is fixed in advance such as the above 50 msec, the resistance value change rate can be changed by changing the applied power. That is, by appropriately selecting the applied power, the degree of increase in the resistance value can be made steep or relatively slow. This makes it possible to control the resistance value of the heating resistor 24 by trimming with extremely high precision.

On the other hand, the pulse width W described with reference to FIG.
Regarding L1 to WL3, the following is understood. That is, in the line L1, as the applied power increases, the resistance value gradually increases and increases to just before destruction. In the line L2, as the applied power increases, the resistance value decreases. When the resistance value reaches a constant resistance value, if the power is further increased and applied, the rate of decrease in the resistance value decreases. In the line L3, when the applied power is increased, the rate of decrease in the resistance value is gradually increased, and is reduced to just before destruction. The inventor of the present invention has confirmed the state of deterioration of the heating resistor 24 in the states P1 and P2 that caused the same rate of change in resistance in the lines L2 and L3 in FIG. According to this, at the position P2, no change in the appearance of the heating resistor 24 is observed, whereas at the position P1, the aggregation of the heating resistor 24
Discoloration or swelling was detected.

Therefore, when applying a pulse for lowering the resistance value, it is preferable that the pulse width be as short as possible. However, when the pulse width is shortened, the applied power increases to obtain the same degree of resistance change, and in some cases, a high voltage of 200 V or more is required. Therefore, a circuit that generates such a trimming pulse requires a high-voltage and high-speed switching operation (for example, a voltage of 150 V).
V, and a pulse width of about 10 μsec), which causes a problem that the configuration is complicated and the cost is increased.

On the other hand, in applying a pulse for increasing the resistance value, it is advantageous that the pulse width is as long as possible. As described with reference to FIG. 2, when the pulse width is reduced, the resistance value may be lowered without increasing, or when the resistance value is significantly increased, deterioration of characteristics such as aggregation and discoloration of the heating resistor 24 may occur. Because there is. However, if the pulse width is increased, the time required for one pulse application becomes longer, the processing time of the entire trimming process becomes longer, and there arises a problem that the working efficiency is reduced and the productivity is reduced.

(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 is the generation of an electrically insulating region, and the region of the heating resistor 24 having a predetermined resistance value is narrowed, and the substantial film thickness is reduced. . Therefore, the durability against the applied pulse is deteriorated. That is, the heating resistor 24
The process of greatly increasing the resistance value of the above results in deterioration of the heating resistor 24 and shortens the service life.

(6) In the case where the heating resistor 24 is a tantalum Ta-based material, 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 view of these points, the present inventor has determined that the maximum trimming amount -DR1 that can maintain the reliability of the thermal head 21 is limited.
Was, for example, about -40% as shown in FIG.

(7) With respect to the heating resistor 24, it was confirmed that the resistance value was reduced by, for example, about 2 to 3% with the use of the thermal head 21 when the trimming was not performed. 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 -DR3 of, for example, about -3%.

Based on the above-described conditions, a description will be given of a method of applying the above-described rise and fall of 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.

Therefore, the applied power P and the rate of change in resistance ΔR
As shown in FIG. 11, a graph showing the relationship with / R
The line L4 showing the ideal correspondence is compared with the line L4
a, L4b. Therefore, as described as the second related art, a trimming pulse is applied to the insulating substrate 23 in the same lot or the heating resistor 24 in the same insulating substrate 23 when the thermal head is manufactured, and the line L4 in FIG. Even if a calibration curve is obtained and the pulse width and applied power of the trimming pulse are determined based on the calibration curve, and such a trimming pulse is applied only once to each heating resistor 24, the line shown in FIG. Due to the variation between L4a and L4b, it is impossible to control the rate of change of the resistance value with high accuracy only by setting such conditions.

For example, in order to change the resistance value by -n%, data of the corresponding applied power P0 (-n%) was obtained from the calibration curve of line L4 in FIG. 11, and a trimming pulse having this applied power was applied. In this case, the resistance value change rate actually varies within 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 −−d2% at the upper limit.
It will vary between n + d1% (d1 + d2 = δ).

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 decrease 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. In addition, 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.

FIG. 12 is a block diagram of a trimming device 41 according to one embodiment of the present invention, and FIG.
FIG. 2 is a cross-sectional view of a configuration related to 1. Thermal head 21
Are mounted on an XYZ stage 51 and a positioning mechanism 52
Thus, a predetermined three-dimensional coordinate position with respect to the probing device 42 is determined. The probing device 42 is provided with a predetermined number n of input lines 59, and a pair of probes 58 shown in FIG. 13 is connected to each of the input lines 59. The pair of probes 58 is connected to a common electrode shown in FIG. 36 and individual electrodes 37
Contact The plurality of input lines 59 of the probing device 42 are connected to a resistance meter 44 via a switching circuit 43 having a configuration described later, and furthermore, n sets of low-voltage pulse generators 45 and one high-voltage pulse generator Connected to the unit 54. Each heating resistor 24 measured by the resistance meter 44
Is input to the control device 53 for controlling the operation of the trimming device 41, and the above-described calibration curve is created and stored in the calibration curve storage unit 47.

The low-voltage pulse generator 45 includes a reference pulse generator 48 and outputs the generated reference pulse as a trimming pulse as described later by passing through a pulse width adjuster 49 and a pulse voltage adjuster 50. Is done. The trimming device 41 includes a pulse generator 5 for high voltage.
The high-voltage pulse generator 54 includes a reference pulse generator 55, a pulse width adjuster 56, and a pulse voltage adjuster 57. The high voltage pulse generator 54
For example, a circuit shown in FIG. 14 is employed as the pulse voltage adjusting unit 57, for example. In other words, the high-voltage pulse generator 54 generates several μm at a high voltage of, for example, 200V.
A high-speed switching operation in seconds is required, and a field-effect transistor (FET) for high-voltage high-speed switching is used for this purpose.

The pulse voltage adjusting unit 57 shown in FIG.
Three field-effect transistors 60, 61, and 62 are used, and the gate of the transistor 60 has a transistor-level voltage (for example, 5 V) from the pulse width adjustment unit 56.
Are input via the resistor 63. The multi-drain of the transistor 60 is grounded, the source is connected to a power supply potential of, for example, +12 V via a resistor 64, and the gate is connected to the gate of the transistor 61 via a resistor 65. The multi-drain of the transistor 61 is grounded, the source is connected to the power supply potential via a resistor 66, and connected to the gate of the transistor 62 via a resistor 67. The gate of transistor 62 is connected to a negative potential of, for example, -5 V via resistor 68, and the multi-drain is grounded. The source of the transistor 62 is the load 6
9 to a power supply potential of 250 V at the maximum.

The high-voltage pulse generator 54 is not limited to the configuration shown in FIG.
With high precision and attention, such as to prevent the pulse waveform from dulling due to the stray capacitance of the printed wiring board where the printed circuit board is provided, and to prevent other circuits from malfunctioning due to electromagnetic noise generated by high voltage and high speed switching operation Designed.
Therefore, as described above, the configuration is extremely complicated and the cost is high.

The pulse voltage adjusting section 50 of the low voltage pulse generating section 45 has a circuit configuration shown in FIG. 15 as an example. As described above, the low-voltage pulse generating section 45 outputs a pulse having a relatively low pulse voltage and a long pulse width, so that a low-speed and low-voltage switching operation can be performed. Unnecessary bipolar transistors 70 and 71 are used. A pulse having a relatively long pulse width from the pulse width adjusting unit 49 is connected to the resistor 7 at the base of the transistor 70.
2 and a capacitor 73 are input through a parallel circuit.
The collector of the transistor 70 is connected via a resistor 74 to a power supply of, for example, +12 V, and the emitter is connected to a resistor 7.
5, and is connected to the base of the transistor 71 via a parallel circuit of a resistor 76 and a capacitor 77. The base of the transistor 71 is connected via a resistor 78 to a potential of, for example, -5 V, the emitter is grounded, and the collector is via a load 79, for example, up to 70 V
Is connected to the power supply potential.

The switching circuit 43 includes a switch circuit S1,
S2 and S3. The switch circuit S1 connects the n input lines 59 of the probing device 42 to the common terminals c11 and c11.
, C1n connected to the respective switches S11, S12,..., S1n. Individual contacts a11, a12, a1 of the individual switches S11 to S1n
, A1n are the individual contacts a21 of the switch circuit S2,
a22, a23,..., a2n, and individual contacts b11, b12, b1 of the individual switches S11 to S1n.
, B1n are the n sets of low-voltage pulse generators 45
Connected to each other. On the other hand, the switch circuit S2 has a common contact c2, and the common contact c2 is connected to the common contact c3 of the switch circuit S3. The switch circuit S3 has individual contacts a3 and b3. The individual contact a3 is connected to the resistance meter 44, and the individual contact b3 is connected to the high-voltage pulse generator 54.

That is, using the probing device 42,
When measuring the resistance value of each heating resistor 24 of the thermal head 21, the common contacts c11 to c11 of the switch circuit S1 are measured.
c1n is switched to the individual contacts a11 to a1n, and the switch circuit S3 is switched to the individual contact a3. In this state, the common contact c2 of the switch circuit S2 is changed to the individual contacts a21 to a2n.
Are sequentially connected. Such a process is performed on all the heating resistors 24 on the insulating substrate 23, and the heating resistors 24
Is measured.

On the other hand, in order to apply a high-voltage trimming pulse having a short pulse width as shown in FIG. 4A to lower the resistance value of each heating resistor 24, the switch circuit S1 needs to have a low resistance value. A connection state similar to that at the time of measurement is established, and the switch circuit S3 is switched to the individual contact b3 side. In this state, when the individual contacts a21 to a2n are sequentially selected by the switch circuit S2, a trimming pulse for lowering the resistance value is applied to each heating resistor 24. At this time, only a single set of high voltage pulse generators 54 is used. Therefore, a trimming pulse is applied to each heating resistor 24. However, this trimming pulse has a relatively short pulse width, and Even if the voltage is sequentially applied to each heating resistor 24, the trimming processing time can be kept low.

When a low-voltage trimming pulse having a relatively long pulse width as shown in FIG. 3A is applied to the heating resistor 24, the switch circuit S1 is connected to the individual contacts b11 to b1.
By switching to the n-side, a trimming pulse is applied to n heating resistors 24 simultaneously. That is, FIG.
Although the trimming pulse of (1) has a relatively long pulse width,
By applying the voltage in parallel to the plurality of heating resistors 24,
The trimming processing time can be remarkably reduced.

FIG. 16 is a process chart for explaining the entire process of manufacturing the thermal head 21. In step a1 of FIG. 16, a thick film common electrode layer 27 and a heat storage layer 35 are formed on the thermal head 23. In step a2, the heating resistor layer 34 is formed on the thermal head 23. 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, 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 processing, the thermal head 21 is completed.

FIG. 17 is a process chart for explaining a process for setting various conditions of a trimming pulse necessary for performing the trimming process. In this embodiment, if the insulating substrate 23 to be trimmed is an insulating substrate 23 in the same lot or a heating resistor 24 in the same insulating substrate 23, regularity and reproducibility appear in the resistance value change. Apply the fact that That is, a sample insulating substrate is set in the same lot with the same standard as the insulating substrate 23 to be trimmed, and a trimming pulse application test is performed on the sample insulating substrate using the trimming device 41 shown in FIG. Ask for.

(Condition 1) When one pulse is applied, a pulse width WLd (for example, 10 μsec) at which the resistance value decreases is obtained in step b1, and a test pulse is applied by changing the applied power variously in the pulse width WLd. . The rate of change of the resistance value 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.

(Condition 2) The pulse width W obtained under the above condition 1
In Ld, after one pulse is applied to lower the resistance value, the increase power ΔP required to further reduce the resistance value by d2% (for example, 2 to 3%) is obtained in step b3.

(Condition 3) A pulse width WLu (for example, 100 msec) at which the resistance value increases when one pulse is applied is obtained in step b4, and a test pulse in which the applied power is variously changed in the pulse width WLu is applied. Measure the rate of change of the resistance value. Thus, the calibration curve of the line L5 shown in FIG. 18 is obtained. From the calibration curve L5, the applied power P1 required to increase the resistance value by d1% (for example, 0.2 to 0.3%) in the pulse width WLu is obtained in step b5.

FIG. 19 is a flowchart illustrating details of the trimming process. In step c1, as described with reference to FIG. 17, the pulse conditions 1 to 3 are obtained and stored in the calibration curve storage unit 47. In step c2, the probing device 42 is mounted on the insulating substrate 23 to be trimmed. , N sets of probes 58 are brought into contact with each other to measure the initial resistance value R0i (i = 1 to n) of each heating resistor 24. Step c
In step 3, the required change amount -DRi of each heating resistor 24 is calculated. That is, in the specification of the thermal head 21, the target resistance value Rf is set in advance,

[0061]

-DRi = (Rf-R0i) * 100 / R0i [%] is calculated.

In step c4, the required change amount-DR
In order to reduce the resistance value by i, the pulse width WLd and the applied power P0 (-DR%) of the condition 1 obtained in step c1 are obtained. In step c5, the applied voltage V0 is calculated based on the pulse width WLd and the applied power P0.

[0063]

(Equation 3)

After the reference pulse generated by the reference pulse generation unit 55 is adjusted by the pulse width adjustment unit 56 and the pulse voltage adjustment unit 57 based on these data,
The voltage is applied to the heating resistor 24 via the switching circuits S3, S2, S1 of the switching circuit 43 and the probing device 42.

In step c6, in the switching circuit 43, the switching circuit S3 is switched to the individual contact a3 side, that is, to the resistance value measuring unit 44 side, and the resistance value R1i (i = 1 to n) after the first pulse application is applied. It is measured by the resistance meter 44. In step c7, it is determined whether or not the resistance value R1i is within a range ε considered to be equal to the target resistance value Rf, that is,

[0066]

It is determined whether or not | R1i−Rf | ≦ ε holds. If the condition is satisfied, the trimming process for the heating resistor 24 ends, and the process proceeds to the trimming process for another heating resistor 24.

If the determination in step c7 is negative, the process proceeds to step c8, where it is determined whether or not the resistance value R1i is lower than the target resistance value Rf. If not, the pulse width WLd is the same as the pulse width of the previously applied trimming pulse, and the applied voltage V1 is obtained from the applied power P0 + ΔP to which the increased power amount ΔP obtained under the condition 2 is added.

[0068]

(Equation 5)

Is obtained and applied to the heating resistor 24 via the probing device 42.

Thereafter, the processing shifts to step c6, where the resistance value is measured and the processing as described above is repeated. That is, the power is increased by ΔP until the determination in step c7 or step c8 becomes positive, and the application of the trimming pulse and the measurement of the resistance value are repeated.

If the determination at step c8 is affirmative, the process proceeds to step c10, where the pulse width WL obtained under condition 3 is determined.
u, from applied power P1 to applied voltage V2

[0072]

(Equation 6)

The trimming pulse is generated and applied to the heating resistor 24 at the same time. Thereafter, the process returns to step c6, and the application of the trimming pulse having the pulse width WLu and the voltage level V2 and the measurement of the resistance value are repeated, and step c6 is performed.
When the determination in step 7 is affirmative, the process ends as described above. Since step c10 takes time as described above, all of the heating resistors 2 that have become affirmative in step c8.
4 at the same time.

As described in Condition 3, the rate of change of the resistance value by the applied voltage V2 for increasing the resistance value is as follows.
It 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 Rf of the thin-film thermal head 21 is strict, for example, about ± 0.3%, the resistance value can be trimmed with high accuracy. Such processing is performed on the insulating substrate 23.
For all of the heating resistors 24, the insulating substrate 2
± 3% variation in resistance value between the three, insulating substrate 2
The thermal head 21 whose resistance value is adjusted with high accuracy can be realized in which the variation of the resistance value within 3 is ± 0.3% and the variation of the resistance value between the adjacent heating resistors 24 is ± 0.6%.

As described above, in this embodiment, the heating resistor 2
The adjustment of the resistance value of No. 4 is performed by combining the application of the trimming pulse for decreasing the resistance value and the application of the trimming pulse for increasing the resistance value. In addition, the resistance value is greatly reduced at first, and the resistance value is slightly increased, so that the resistance value can be adjusted with high precision. Also, the application of the trimming pulse for increasing the resistance value performed many times has a long pulse width,
In order to avoid a situation in which the processing speed is reduced by repeating this, the voltage is applied to the plurality of heating resistors 24 at the same time. As a result, the time required for the trimming process is significantly reduced, and workability is greatly improved.

In the trimming process of this embodiment, pulse conditions are set so that the resistance value R1i is made as close as possible to the target resistance value Rf by the first trimming pulse in step c5. Therefore, the number of pulses required for the entire trimming process of the thermal head 21 can be reduced, the processing speed of the entire trimming process can be improved, and the productivity can be improved.

FIGS. 20 and 21 are flow charts for explaining the second embodiment of the present invention. This embodiment is similar to the above-described embodiment, particularly the processing shown in FIG. 19, but can perform trimming processing with higher precision. Step d1
Then, in addition to the pulse conditions 1 to 3 described with reference to FIG. 17, condition 4 is also obtained.

(Condition 4) From the calibration curve of the line L5 shown in FIG. 18 created when obtaining the condition 3, the resistance value is reduced by d3% (0.01 to 0.05% as an example) smaller than the condition 3. An applied power P2 required to increase the power is obtained. The pulse conditions 1 to 4 thus determined are stored in the calibration curve storage unit 47.

In step d2, the probing device 42
Is mounted on the insulating substrate 23 to be trimmed, and n sets of probes 58 are brought into contact with each other to make the initial resistance value R0i of each heating resistor 24.
(I = 1 to n) is measured.

In step d3, the required change amount -DRi '
Is calculated. That is, the lines L4a and L4 in FIG.
In consideration of the degree of variation in the rate of change of the resistance value described with reference to FIG. 4b, the required change amount -DRi 'is determined so that the measured value falls below the target resistance value Rf as much as possible.

In step d4, the required change amount -DR
In order to lower the resistance value by i ', the pulse width WLd of condition 1 and the applied power P0 (-DRi'%) are obtained. In step d5, the applied voltage V0 calculated by the above equation (3) is calculated from the pulse width WLd and the applied power P0, and the reference pulse generated by the reference pulse generator 48 based on the data is used as the pulse width adjuster. After being adjusted by 49 and the pulse voltage adjustment unit 50, the voltage is sequentially applied to each heating resistor 24 via the switch circuit S <b> 1 of the switching circuit 43 and the probing device 42.

At step d6, the resistance Ri is measured.
In step d7, it is determined whether or not the measured resistance value Ri has fallen below the target resistance value Rf. If this determination is negative, the process returns to step d5 and pulse application is performed again, but the power at this time is increased by ΔP. That is, the pulse voltage is as shown in Equation 5 above.

This process is repeated, and when the determination in step d7 is affirmative, the process proceeds to step d8, where it is determined whether the trimming is completed. That is, it is determined whether Equation 4 is satisfied. If this judgment is affirmative, this resistor 2
The trimming process of No. 4 is completed, and no pulse is applied to the resistor 24 hereinafter.

If not, the process proceeds to step d9 where the resistance Ri is changed to the reference resistance Rf '.

[0085]

## EQU7 ## Rf '= Rf.times. (100-d) / 100 d; It is determined whether or not the deviation is equal to or more than a predetermined deviation (%) from the target resistance value Rf. If this determination is affirmative, the routine proceeds to step d10 in FIG. In step d10, the pulse width WL of the condition 3 determined in step d1
u, the pulse of the applied power P1
Apply from In step d11, the resistance value is measured again,
Returning to step d8, a series of processing is repeated.

If the determination in step d9 is negative, the process proceeds to step d12. In Step d12, Step d1
The pulse width WLu and the applied power P2 of the condition 4 obtained in
Is applied from the low-voltage pulse generator 45. In step d13, the process waits until a predetermined time Tp elapses until the temperature rise of the heating resistor 24 due to the trimming pulse applied in step d12 decreases to, for example, about room temperature. That is, immediately after the application of the trimming pulse,
This is because the temperature of the heating resistor 24 is high and a correct resistance value cannot be measured. By measuring the resistance value after cooling to about room temperature, the measurement accuracy of the resistance value can be improved.

That is, in such a state, step d1
At 4, the resistance value Rik is measured. In step d15, it is determined whether or not the number k of times of measurement of the resistance value is equal to or greater than a predetermined maximum number K of times. If this determination is negative, the resistance value Rik is kept up to the maximum number K of times of measurement in step d14.
Is measured. In step d16, the average resistance value Ria of the resistance values Rik measured over the maximum number of times K is measured.

[0088]

(Equation 8)

Is calculated. The measurement is repeated many times in this manner, and the average value is used as the resistance value of the heating resistor 24. In other words, by setting Ri = Ria, it is possible to eliminate variations between measurements and improve measurement accuracy.

Thereafter, the processing returns to step d8 again.
A series of processing is repeated until the determination here becomes affirmative.

As described above, the trimming process with improved measurement accuracy allows the resistance value of the heating resistor 24 to be adjusted with high accuracy.

In particular, the rate of change of the resistance value due to the pulse of condition 4 is selected to be about 0.01 to 0.05%. Since the pressing is performed within the range of 01 to 0.05, it is possible to realize the thermal head 21 in which the resistance value is adjusted with high accuracy and the variation of the resistance value in the insulating substrate 23 is ± 0.05%.

Steps d10 and d12 of applying a pulse with a pulse width WLu are performed on the heating resistor 24 using a plurality of low voltage pulse generating means. As shown in FIG. 9, the pulse application and the multiple measurement of the resistance value under the condition 4 requiring a long processing time are after the resistance value exceeds Rf ′. Therefore, if −d% is made small, the processing speed does not decrease so much. .

According to the experiment conducted by the inventor of the present invention, the increase in the measurement accuracy due to the multiple measurements of the resistance value was caused by the dispersion of the measurement on the vertical axis and the number of measurements on the horizontal axis as shown in FIG. Was obtained. This property is

[0095]

(Equation 9)

It has been confirmed that the function is defined by the following function.

In FIG. 12, the individual contacts b11, b12,..., B1n of the switch circuit S1 may be connected in parallel to a single set of low-voltage pulse generators 45.

[0098]

As described above, according to the present invention, at least a part of the heating resistor is oxidized to reduce the electrical resistance by annealing the first pulse for increasing the electrical resistance or annealing the heating resistor. The resistance value of each heating resistor can be adjusted by increasing or decreasing the resistance value of the heating resistor by switching and applying the second pulse for causing the resistance to increase. In other words, the so-called calibration curve can be measured by measuring the decrease or increase in the resistance value of the heating resistor from the pulse width of the previously applied voltage pulse and the applied power and performing trimming to measure a so-called calibration curve. Significantly improved. The resistance value can be reduced or increased by appropriately selecting the pulse width of the applied voltage pulse, so that the workability and the controllability with respect to the target resistance value are remarkably improved. One more
The operation of applying the first pulse, which requires a relatively long time for pulse application, is performed simultaneously and in parallel with the plurality of heating resistors, so that the time required for the trimming process can be significantly reduced. The workability is also 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 in the temperature of the heating resistor 24;

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

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

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

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

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

FIG. 10 is a graph showing the relationship between the applied power and the rate of change in resistance when the pulse width is constant.

FIG. 11 is a graph showing a distribution of a variation in a resistance value change rate when a pulse width is fixed.

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

FIG. 13 is a cross-sectional view of the vicinity of the thermal head 21 in the trimming device 41.

FIG. 14 is a block diagram showing a configuration of a high-voltage pulse generator 54.

FIG. 15 is a block diagram showing a configuration of a low-voltage pulse generator 45.

FIG. 16 is a process chart for explaining the entire manufacturing process of the thermal head 21.

FIG. 17 is a process diagram illustrating a pulse condition setting process.

FIG. 18 is a graph showing the relationship between the applied power and the rate of change in resistance when the pulse width is constant.

FIG. 19 is a flowchart illustrating a trimming process according to an embodiment of the present invention.

FIG. 20 is a flowchart illustrating a trimming process according to a second embodiment of the present invention.

FIG. 21 is a flowchart illustrating a trimming process according to a second embodiment of the present invention.

FIG. 22 is a graph illustrating the relationship between the number of measurements and the magnitude of variation in the measurement results.

FIG. 23 is a graph showing a relationship between a true resistance value and a measured resistance value including variation.

FIG. 24 is a graph showing a relationship between a true resistance value and a measured resistance value including variation.

[Explanation of symbols]

 21 Thermal Head 23 Insulating Substrate 24 Heating Resistor 41 Trimming Device 42 Probing Device 43 Switching Circuit 45 Low Voltage Pulse Generator 47 Calibration Curve Storage 49 Pulse Width Adjuster 50 Pulse Voltage Adjuster 54 High Voltage Pulse Generator 59 Input Line S1-S3 Switch circuit

Claims (2)

(57) [Claims] An apparatus for trimming a plurality of heating resistors arranged on an electrically insulating substrate of a thermal head, comprising: a power supply unit for individually supplying power from a plurality of input lines to the same number of heating resistors; A low-voltage pulse generating means for generating a first pulse having a relatively low voltage and a long duration for oxidizing at least a part of the heating resistor to increase the electric resistance value; A high-voltage pulse generating means for generating a second pulse having a relatively high voltage and a short duration for reducing the resistance value; and simultaneously connecting the outputs of the low-voltage pulse generating means to a plurality of input lines of the power supply means. Switching means for switching the output of the high-voltage pulse generating means to be sequentially connected to each of the input lines. 2. An apparatus according to claim 1, wherein a plurality of said low voltage pulse generating means are used.