JPH04261872A - Method for trimming resistor for thin film thermal head - Google Patents

Abstract

PURPOSE:To provide a method for trimming a resistor for a thin film thermal head highly accurate toward the target resistance, capable of adjusting the resistance and good in operational efficiency. CONSTITUTION:In adjusting the resistance of a thin film resistance layer contained in a thermal head by applying thereto a predetermined electric power and trimming pulses for a predetermined time, the target range relatively close to the target resistance and an allowable range relatively wider than the target range are set. The resistance is adjusted so as to be within the target range. In a case where an excessive adjusting operation is required, however, the trimming is considered as a success, if the resistance is at least within the allowable range. Therefore, this can prevent the possibility of rejecting and discarding the thermal head having the resistance variations outside the target range but within the allowable range and free from other defects.

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 the resistance value of a heating resistor formed by thin film technology in a thermal head.

0002

2. Description of the Related Art A thermal head used in various printing output devices has a plurality of heating resistors formed on a head substrate, and the heating resistors are selectively energized with electric power to perform thermal printing. There are the following three types of resistance value variations that cause density unevenness during application in a thermal head.

(1) Variations among heads: Even if thermal heads are of the same standard, variations occur in the average resistance value of each head.

(2) Intra-head variation, ie, variation in the resistance value of the heating resistor within a single thermal head.

(3) Variation between adjacent dots, ie, variation between adjacent heating resistors within a single thermal head.

[0006] In the thick film thermal head, the heating resistor is formed by printing a paste-like resistor material on an electrically insulating substrate, so the variation in resistance value is most influenced by the printing accuracy, and therefore It is known that the variation within the head and between adjacent dots is large, and the variation between heads is relatively small because it is a variation in the average resistance value for each head. On the other hand, in the case of a thin film thermal head, a resistor material layer is formed by sputtering or vapor deposition, and then etched into a predetermined pattern shape to form a heating resistor. As a result, the variation in resistance value can be reduced to, for example, ±
It is known that it is as small as about 0.5%, and that the variation within the head is also 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 becomes relatively large.

[0007] In order to achieve the designed printing density at this time, the resistance value of each heating resistor must be uniform. However, the resistance value of the heating resistor using thick film technology is ±25%.
Because of the above-mentioned variations, a trimming technique is employed in which a voltage pulse is applied to the heat-generating resistor after the heat-generating resistor is formed to lower the resistance value, thereby suppressing the variation as much as possible.

As a first conventional example of performing such trimming, when the initial resistance value of the heating resistor is larger than the target resistance value, a trimming pulse of an initial voltage V0 is applied to lower the resistance value, and then the resistance value is lowered. A method is known in which a trimming pulse is applied in which the voltage is increased by an increment of ΔV until the resistance value becomes equal to or less than the target resistance value. However, with this method, in order to uniformize the resistance value of each heating resistor with high precision,
It is necessary to set the initial voltage V0 and the increase ΔV to relatively small values, which increases the number of trimming pulses to be applied to each heating resistor, which increases the time required for the trimming process and reduces production efficiency. The problem is that the

As a second conventional technique, the following trimming method is known. In other words, when manufacturing thermal heads, we focused on the phenomenon that within the same lot or on the same board, there is regularity and reproducibility in the state of change in resistance value when the same trimming pulse is applied to each heating resistor. , the voltage value of the applied trimming pulse and the rate of change Δ of the resistance value R
A correlation between R/R, that is, a calibration curve, is determined in advance, an initial voltage V0 is determined according to this calibration curve, and the resistance value is brought as close to the target resistance value as possible by applying this initial voltage V0. . Thereafter, a pulse is applied in which the voltage is increased by an increment of ΔV to gradually decrease the resistance value.

0010

According to the second conventional example, the resistance value of a thick film thermal head conventionally manufactured by thick film technology such as printing can be adjusted relatively satisfactorily. When the resistance value is adjusted using the second conventional example, the degree of approach to the target resistance value, 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 in resistance value of thick film thermal heads after trimming is ±1.5% between thermal heads and ±1.5% within a thermal head. 5%,
The difference between adjacent heating resistors is ±3%. Considering that the initial resistance value variation of thick film thermal heads is usually ±25% or more, this can be said to be a sufficient technique for improving the variation.

On the other hand, in recent years, thin film thermal heads manufactured by thin film techniques such as vapor deposition and sputtering have been used. In the case of this thin-film thermal head, the initial resistance value variation between adjacent heating resistors is around ±1%, and in a thin-film thermal head for images that can display halftones without causing density unevenness, adjacent heating thin-film resistors The variation in resistance value between bodies is required to be approximately ±0.5%. For this reason,
The second conventional example is extremely inadequate as a trimming technique for a thin film thermal head.

[0012] Furthermore, even if it is assumed that the second conventional technique is applied to trimming a thin film thermal head, the following three problems will occur, and the controllability to the target resistance value will be extremely poor. .

(1) Although the conventional technology is based on the assumption that the resistance value decreases by applying a trimming pulse with a gradually increased voltage, as will be explained in the examples, the present inventor It was confirmed that the resistance value does not necessarily decrease depending on the pulse conditions used. Therefore, if the applied voltage is gradually increased because the resistance value after pulse application has not decreased from the resistance value before application, the actual resistance value will move away from the target resistance value, and the heating resistance There are also cases where the body is destroyed.

(2) Even if a trimming pulse of a constant voltage level V0 is applied, it is impossible to create a calibration curve because the rate of change in resistance value varies greatly depending on the resistance value of each head or heating resistor.

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

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

[0017]

[Means for Solving the Problems] The present invention provides a method for trimming a plurality of heating resistors arranged linearly on an electrically insulating substrate of a thin film thermal head, in which a voltage pulse is applied to the heating resistors. Then, based on the measurement results, a voltage pulse is applied to each heat generating resistor to increase the resistance. If the resistance value after the change is within a predetermined narrow target resistance value range, trimming of the heating resistor is finished, and if it deviates from the target resistance value, the heating resistor is trimmed again. A method for trimming a resistor of a thin film thermal head is characterized in that trimming is performed to bring the resistance value within an allowable range.

[0018]

According to the present invention, a predetermined narrow target resistance value range and a permissible resistance value range larger than the target resistance value range are determined for the predetermined target resistance value of each heating resistor. A voltage pulse is applied to the heating resistor, and a change in the decrease or increase in the resistance value of the heating resistor corresponding to the pulse width of the applied voltage pulse and the applied power is measured.

Based on this measurement result, a voltage pulse is applied to each heating resistor to lower or increase the resistance value, and if the resistance value after the change is within the target resistance value range, the heating resistor is trimmed. Finish and continue trimming the remaining heating resistor. When the resistance value after the change is outside the target resistance value range and the resistance value after the change is increasing when a voltage pulse that further lowers the resistance value is applied, or when a pulse that increases the resistance value is applied. When the resistance value rises above the target resistance value range, the resistance value after the change is compared with the allowable resistance value range and trimming is completed.

[0020] This makes it possible to prevent the heating resistor from being destroyed when trimming the heating resistor, thereby making it possible to improve workability and trimming efficiency.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view for explaining the structure of a thin film thermal head (hereinafter abbreviated as "thermal head") 21 manufactured using the trimming method of the present invention. The thermal head 21 includes a heat sink 22 made of a metal material such as aluminum, and a head substrate 23 is fixed thereon with an adhesive layer 32. On the head substrate 23, a large number of heating resistors 24 are formed in a straight line in a direction perpendicular to the paper plane of FIG. A plurality of drive circuit elements 25 connected by electrodes are arranged. These drive circuit elements 25 are covered with a protective layer 26 made of synthetic resin material.

A heat storage layer 35 is formed on the head substrate 23 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. A heating resistor layer 34, a common electrode layer 36, and a plurality of individual electrodes 37 are formed on the heat storage layer 35, and a plurality of linear heating resistors 24 are configured. The heat generating resistor 24 performs thermal printing on the thermal paper 32 between the heat generating resistor 24 and the platen roller 31 via a wear-resistant layer 39 formed by a thin film technique such as sputtering. Also, this heating resistor 2
4 is controlled by a drive circuit element 25 realized as an integrated circuit element. The individual electrodes 37 covered with an insulating layer 28 are connected to the drive circuit element 25, and signals for driving the heating resistor 24 are input to the drive circuit element 25, and external connections covered with the insulating layer 28 are connected to the drive circuit element 25. Terminals 29 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 surroundings.

In the present invention, at the stage when the heating resistor layer 34, the common electrode 36, and the plurality of individual electrodes 37 are formed on the head substrate 23, the resistance value of each of the plurality of heating resistors 24 defined by these is determined. This is an attempt to make it uniform by trimming it. As a result of conducting experiments on the above thermal head 21, the following facts were found.

(1) Before forming the wear-resistant layer 39, a trimming pulse is applied in the atmosphere. At this time, by appropriately selecting the pulse width, the resistance value of the heating resistor 24 can be increased as well as lowered. 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 in resistance value ΔR/of the heating resistor 24.
It was confirmed that when R is taken, the obtained characteristic curve changes greatly by changing the pulse width of the applied trimming pulse. Lines L1, L2 shown in FIG.
L3 indicates a case where the pulse widths are different from each other, and when the corresponding pulse widths are expressed as WL1, WL2, and WL3 (collectively referred to as WL when necessary), the relationship between these is as follows.

002
5]

[Math 1] WL1>WL2>WL3 It is.

That is, when the pulse width WL is relatively long, the resistance value increases as the applied power increases, as shown by line L1. On the other hand, when the pulse width WL is relatively short, the resistance value does not change in range A below the threshold power Pth, as shown by line L3;
When the applied power is increased to about the above range B, the resistance value decreases. Also, the pulse width W is between the pulse widths WL1 and WL3.
At L2, as shown by line L2, both an increase phenomenon and a decrease phenomenon of the resistance value appear depending on the degree of applied power P. In other words, in the range A of applied power below the threshold power Pth, the resistance value gradually decreases as the applied power increases, but the rate of decrease gradually decreases to 0.
becomes. In the range of applied power P equal to or higher than threshold power Pth,
As the applied power P increases, the resistance value gradually increases.

In this way, the pulse width W of the trimming pulse
The phenomenon in which the resistance value of the heating resistor 24 can change in either an upward or downward direction depending on L will be explained as follows with reference to FIG. That is, the resistance value of the heating resistor 24 changes due to the application of the trimming pulse due to the annealing effect due to the heat generated by the heating resistor layer 34 itself, that is, the crystallization of the heating resistor layer 34, and the heat generation of the heating resistor layer 34 itself. This is due to oxidation. Among these, the annealing effect appears as a decrease in resistance value due to the progress of crystallization of the heating resistor layer 34, and oxidation appears as an increase in resistance value.

When the pulse width WL1 of the applied trimming pulse is set to be relatively long and the applied voltage is set to be low as shown in FIG. does not show a rapid or significant rise, and on the other hand, since the pulse width WL1 is relatively long, the relatively low temperature continues for a long time. The progress state of the annealing effect in the heating resistor layer 34 is determined by the temperature, and in this case, the temperature T1 has not reached the temperature Ta at which the annealing effect occurs, and the resistance value decreases due to the annealing effect. does not occur. However, since the temperature is higher than the temperature Tox at which an oxidation phenomenon occurs, and this state continues for a relatively long time, oxidation progresses in the heating resistor layer 34 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 results in the state shown in FIG. 4(2). That is, the heating resistor layer 34 rapidly increases in temperature 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 progresses 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 oxidation temperature Tox is exceeded is relatively short, 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 aforementioned annealing effect and oxidation is the dominant phenomenon. That is, control can be performed to increase or decrease the resistance value of the heating resistor layer 34.

(2) As shown in FIG. 4(1), when applying a trimming pulse with a pulse width WL3 that causes only a decrease in the resistance value in the heating resistor layer 34, the pulse width WL3 of the trimming pulse is fixed. If this is done, even if the resistance values before application of the trimming pulse are different for each heat generating resistor 24, each heat generating resistor 24 exhibits a substantially constant rate of change in resistance value by applying the same applied power. on the other hand,
The same is true when applying a trimming pulse with a pulse width WL1 that causes only an increase in the resistance value as shown in FIG. Even if it differs from time to time, it shows a nearly constant rate of change in resistance value.

Taking all of this into account, it can be concluded that the characteristic curves of lines L1 and 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 mentioned above, the progress of the annealing effect and oxidation, which are factors that change the resistance value of the heat generating resistor layer 34, changes depending on the state of the heat generating resistor layer 34 itself corresponding to the state of the trimming pulse applied. ) and the temperature change characteristics as shown in FIG. 4(2). Therefore, if the pulse width WL and the applied power P are the same, even if the resistance values of the heating resistors 24 are different from each other,
The characteristics of the temperature change over time for each heating resistor 24 are the same for each heating resistor 24, and as described above, a substantially constant rate of change in resistance value can be obtained.

(3) The annealing effect that causes the aforementioned resistance value drop in the heat generating resistor layer 34 advances rearrangement and recrystallization of constituent molecules within the heat generating resistor layer 34. Therefore, the durability of the heating resistor 24 against applied pulses (trimming pulses, driving pulses accompanying use, etc.) is improved. On the other hand, the oxidation phenomenon that causes an increase in resistance value is
The range of the predetermined resistance value of the heating resistor 24 is narrowed, and therefore the actual film thickness is reduced. For this reason, durability against applied pulses deteriorates. That is, the process of significantly increasing the resistance value of the heat generating resistor 24 deteriorates the heat generating resistor 24, resulting in a shortened lifespan.

Based on the above conditions, a method of applying the above-described resistance value increase and decrease phenomenon to adjustment of the resistance value of the heating resistor 24 will be explained. Figure 4 (1
), when a trimming pulse with a relatively short pulse width WL3 is applied, if the pulse width WL3 is kept constant, the relationship between the applied power and the rate of change in resistance value changes as described above. Although the resistance value does not depend on the resistance value, the rate of change in resistance value actually varies due to unevenness of the heat storage layer 35, variation in dimensions of the heating resistor 24, and the like.

Therefore, the applied power P and the resistance change rate ΔR
As shown in FIG. 5, the graph showing the relationship between /R and line L4a shows the ideal correspondence relationship.
, L4b. Therefore, as explained as the second conventional technique, when manufacturing a thermal head, a trimming pulse is applied to the head substrate 23 in the same lot and the heating resistor 24 in the same head substrate 23, and Even if a calibration curve is obtained, the pulse width and applied power of the trimming pulse are determined based on this calibration curve, and such a trimming pulse is applied to each heat generating resistor 24, the line L4a, shown in FIG.
Due to the variation between L4b, highly accurate control of the resistance value change rate is impossible.

For example, in order to change the resistance value by -n%, data on the corresponding applied power P0 (-n%) was obtained from the calibration curve of line L4 in FIG. 5, and a trimming pulse having this applied power was applied. In this case, the rate of change in resistance value actually varies within the range of width δ shown in FIG. Therefore, the resistance value change rate obtained is -n-d2% at the lower limit and -n+ at the upper limit.
It will vary between d1% (d1+d2=δ).

Therefore, when trimming the heating resistor 24, it is necessary to apply a trimming pulse once and then apply another trimming pulse to increase or decrease the resistance value. It was confirmed that such processing can be realized by the following method.

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

In order to further reduce the resistance value, the trimming pulse may be applied by further increasing the applied power ΔP. Since the pulse width is set relatively short at this time, the above-mentioned oxidation phenomenon hardly occurs, but if the applied power ΔP is too small, the oxidation phenomenon cannot be ignored, and on the contrary, the resistance value may increase. Therefore, the predetermined applied power ΔP is determined by comprehensively considering such conditions.

When the resistance value is increased after the first trimming pulse is applied, it is only necessary to allow the aforementioned oxidation phenomenon to proceed, and the characteristic shown in FIG. 3 (1) as shown in line L1 in FIG. 2 is obtained.
A trimming pulse with a relatively long pulse width WL1 as shown in the figure is applied. As a result, the temperature of the heating resistor 24 basically decreases from the temperature after the first trimming pulse is applied, 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 in resistance value for each application of the trimming pulse can be reduced, for example, by approximately +0.1 to 0.2%.
The resistance value of the heat generating resistor 24 can be controlled with high precision because it can be changed in minute increments.

FIG. 6 is a block diagram of a trimming device 41 according to the present invention. The head substrate 23 of the thermal head 21 is attached to the trimming device 41, and the resistor layer 51 is attached to the trimming device 41.
A probing device 42 is provided that brings probes into contact with the upper common electrode 36 and the individual electrodes 37 individually for each heating resistor 24. Pulse generator 45
connected to. The resistance value measured by the resistance value meter 44 is input to a calibration curve creation section 47 that creates and stores a calibration curve within the control device 46 . The head substrate 23 is mounted on an XY stage 52, and the XY stage 52 positions the substrate 23 by a positioning mechanism 53 under the control of the control device 46.

The trimming pulse generating section 45 includes a reference pulse generating section 48, and the generated reference pulse passes through a pulse width adjusting section 49 and a voltage adjusting section 50, and is outputted as a trimming pulse as described later. Via the switching circuit 43 and probing device 42,
The voltage is applied to the selected heating resistor 24.

FIG. 7 is a process diagram illustrating the entire process of manufacturing the thermal head 21. As shown in FIG. In step a1 of FIG. 7, a thick film common electrode layer 27 and a heat storage layer 35 are formed on the thermal head 21. In step a2, a heating resistor layer 34 is formed on the thermal head 21, and in step a3, the common electrode 36 and individual electrodes 37 are formed on the heating resistor layer 34. In step a4, a trimming process, which will be described in detail later, is performed to adjust the resistance value of each heating resistor 24 to be uniform, and then in step a5, a wear-resistant layer 39 is formed. Thereafter, the thermal head 21 is completed through other processing.

FIG. 8 is a process diagram illustrating the process of setting various conditions for trimming pulses necessary for trimming according to an embodiment of the present invention. In this embodiment, if the head substrate 23 to be trimmed is from the same lot, or if the heating resistor 24 is from the same head substrate 23, regularity and reproducibility will appear in the resistance value change. Apply this fact. That is, a sample head substrate is set in the same lot with the same specifications as the head substrate 23 to be trimmed, and a trimming pulse application test is performed on this using the trimming device 41 shown in FIG. 6 under the following pulse conditions 1 to 3. Let's find out.

(Condition 1) A pulse width WLd at which the resistance value decreases when one pulse is applied is determined in step d1, and in the pulse width WLd, a test pulse is applied while changing the applied power variously. The rate of change in resistance value due to the application of this test pulse is measured, and a calibration curve shown as line L4 in FIG. 5 is obtained. From this calibration curve, at the relevant pulse width WLd, the resistance value change rate ΔR/R is -1%, -2%, ..., -n%.
The applied power P0 (-1%), P0 (-2%), ...,
P0 (-n%) is determined in step d2.

(Condition 2) Pulse width W obtained under Condition 1 above
After lowering the resistance value by applying one pulse in Ld, the increased power ΔP required to further lower the resistance value by d1% (for example, 2 to 3%) is determined in step d3.

(Condition 3) The pulse width WLu at which the resistance value increases when one pulse is applied is determined in step d4, and test pulses with various applied powers are applied at the pulse width WLu, and the rate of change in resistance value due to this is determined. Measure. In this way, a calibration curve of line L5 shown in FIG. 9 is obtained. From this calibration curve L5, the applied power P1 required to increase the resistance value by d2% (for example, 0.2 to 0.3%) at the pulse width WLu is determined in step d5.

In step d6, when actually trimming, the target resistance value is divided into a first resistance value range that is considered to approximately match the target resistance value, and a target resistance value range that is smaller than this target resistance value range. A second tolerance range, which is a more moderate resistance value range, is set and stored in the control device 46. Here, if the target range is ±δ1% and the tolerance range is ±δ2%, the resistance value R of each heating resistor 24 obtained by trimming is as follows:

[0050]

[Math 2]

When [0051], it is determined that the resistance value is within the target resistance value range,

[0052]

[Math 3]

When [0053], it is determined that the resistance value is within the allowable resistance value range.

FIG. 12 is a flowchart illustrating details of the trimming process according to the embodiment of the present invention. Step e1
Now, as explained with reference to FIG.
In step e2, the probing device 42 is attached to the head substrate 23 to be trimmed, and the initial resistance value R0 of the heating resistor 24 is measured. In step e3, the required change amount -DR
Calculate. That is, the target resistance value Rf is preset in the specifications of the thermal head 21,

[0055]

[Formula 4]-DR=(Rf-R0)/R0*100[%]
Calculate.

In step e4, in order to lower the resistance value by the required amount of change DR, condition 1 determined in step e1 is applied.
The pulse width WLd and the applied voltage P0 (-DR%) are determined. In step e5, the pulse width WLd and the applied power P0
and the applied voltage V0

[0057]

[Math 5]

After the reference pulse generated by the reference pulse generator 48 is adjusted by the pulse width adjuster 49 and the voltage adjuster 50 based on these data, the reference pulse is transmitted via the switching unit 43 and the probing device 42 heating resistor 2
4.

At step e6, the switching means 43 is switched to the resistance value meter 44 side, and the resistance value R after the first pulse application is measured by the resistance value meter 44. step e
In step 7, it is determined whether this resistance value R is within a range that is considered to match the target resistance value Rf, that is, whether the second equation is satisfied. Measurement point P in Figure 13
If 1 is established, the trimming process for the heat generating resistor 24 is completed, and the process moves on to the trimming process for other heat generating resistors 24. When the process for all the heat generating resistors 24 is completed, the trimming process for the next thermal head is started. Move.

If the judgment at step e7 is negative, then FIG.
If it is necessary to further reduce the resistance value of the heating resistor 24 as at measurement point P2 of No. 3, the process proceeds to step e8.
Next, set new pulse conditions and apply this pulse. The pulse width of this pulse is the same pulse width WLd as the trimming pulse applied last time, and the applied power P0+iΔP (i=1, 2,...) to which the increased power ΔP obtained under condition 2 is added from applied voltage V1

[
0061

[Math 6]

is determined and applied to the heating resistor 24 via the probing device 42.

After that, the process moves to step e9, where the resistance value is measured and the resistance values before and after the pulse application are compared. That is, when the resistance value after applying the trimming pulse in step e8 is Ra and the resistance value before applying the trimming pulse is Rb, the resistance value Ra becomes the resistance value Rb in step e10.
Determine whether it is greater than If this determination is affirmative, that is, if measurement points P3 and P4 in FIG. 11 are obtained, then the trimming pulse applied in an attempt to lower the resistance value has conversely increased the resistance value. At this time, the process moves to step e11, and the resistance value Ra at this time
It is determined whether or not satisfies the third equation. Figure 1
If the resistance value of the heating resistor 24 at this time is satisfied as in measurement point P3 of 1, it is determined that the resistance value is within the allowable range, the trimming is completed as a good product, and the processing moves on to other heating resistors. . If the resistance value of the heating resistor 24 is not within the allowable range and is not satisfied as shown at measurement point P4 in FIG. is determined to be defective and the trimming process is terminated.

[0064] If the judgment in step e7 is negative,
If the obtained resistance value needs to be increased relative to the target resistance value, as at measurement point P5 in FIG. Voltage V2

[0065]

[Math 7]

A trimming pulse is generated and applied to the heating resistor 24. After this, the process moves to step e13, and the resistance value after the pulse application is measured again. Next, the process moves to step e14. Here, similar to step e7,
It is determined whether the resistance value is within a range that is considered to match the target resistance value Rf, that is, whether the second equation is satisfied. If the measurement point P6 in FIG. 13 is established, the process for the heat generating resistor 24 ends and the process moves on to trimming the other heat generating resistors 24.

If the judgment in step e14 is negative and the resistance value is still low and needs to be further increased as at the thirteenth measurement point P7, the process returns to step e12 and the pulse width WLu and voltage level are changed again. The application of the trimming pulse of V2 and the measurement of the resistance value are repeated, and when the judgment in step e14 becomes affirmative, the process ends as described above.

During this repetition, if the judgment at step e14 is negative and the resistance value has risen above the target resistance value range as at measurement point P8 in FIG. 12, the process moves to step e11. As described above, it is determined here whether the resistance value is within the allowable range, that is, whether the above equation 3 is satisfied. If this judgment is affirmative, the trimming is completed as a non-defective item as described above, and the processing moves on to other heating resistors. If negative, it is determined that the product is defective and the trimming process is terminated. In this way, the trimming process for all heating resistors is completed.

In the above embodiment, in the process of increasing the resistance value while applying a trimming pulse, if the resistance value Rb before the pulse application is larger than the resistance value Ra after the pulse application, that is, trimming to increase the resistance value is performed. There are cases where the resistance value decreases due to the pulse. In such a case, the rate of increase in resistance value due to each pulse application is actually about +0.1 to +0.2%, which is a maximum of ±
This is because approximately 0.5% is often smaller than the measurement error of a certain resistance value meter 44, and it has been confirmed that the resistance value reliably increases by applying a plurality of trimming pulses. Therefore, in such a case,
Continue the trimming process.

In the above embodiments, when the resistance value increases due to the application of the trimming pulse to lower the resistance value, or when the trimming pulse to increase the resistance value is applied, the change in the resistance value becomes excessive. , when the resistance value becomes higher than the target resistance range, if the trimming pulse application is continued, the resistance value may move away from the target resistance value or the heating resistance value 24 may be destroyed. This embodiment avoids such a situation, prevents undesirable situations such as the destruction caused by trimming, and even when the resistance value is difficult to fall within the target resistance value range, the allowable resistance value If it is within this range, it is judged to be a good product, and a trimming method with excellent usability has been realized.

As explained in Condition 3 above, the rate of change in the resistance value due to the applied voltage V2 for increasing the resistance value is:
It is selected to be about 0.2 to 0.3%, which is extremely small. Therefore, even if the controllability required for the target resistance value in the thin film thermal head 21 is, for example, about ±0.3%, the resistance value can be trimmed with high precision. If such processing is performed on all the heating resistors 24 of the head substrate 23, the resistance value variation between the head substrates 23 will be ±0.3%, and the resistance value variation within the head substrate 23 will be ±0.3%. , it is possible to realize a thermal head 21 in which the resistance value is adjusted with high precision so that the variation in resistance value between adjacent heating resistors 24 is ±0.6%.

In the trimming process of this embodiment, the pulse conditions are set so that the first trimming pulse in step e5 brings the resistance value Ri as close to the target resistance value Rf as possible. 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 productivity can be improved.

In the above-mentioned embodiment, the trimming process was performed for each heating resistor 24, but by providing a plurality of resistance value meters 44 and trimming pulse generators 45 each, a plurality of heating resistors 24 can be trimmed. The trimming process may be performed in parallel. Also, heating resistor 2
The means for changing the resistance value of No. 4 is not limited to the application of the trimming pulse, but may also include, for example, irradiation with laser light to obtain the calibration curves shown in FIGS. 5 and 11 based on the laser light intensity and irradiation time. Good too.

[0074]

As described above, according to the present invention, there is a predetermined narrow target resistance value range for the predetermined target resistance value of each heating resistor, and an allowable resistance value range that is larger than the target resistance value range. Establish. A voltage pulse is applied to the heating resistor, and a change in the decrease or increase in the resistance value of the heating resistor corresponding to the pulse width of the applied voltage pulse and the applied power is measured.

Based on this measurement result, a voltage pulse is applied to each heating resistor to lower or increase the resistance value, and if the resistance value after the change is within the target resistance value range, the heating resistor is trimmed. Finish and continue trimming the remaining heating resistor. When the resistance value after the change is outside the target resistance value range and the resistance value after the change is increasing when a voltage pulse that further lowers the resistance value is applied, or when a pulse that increases the resistance value is applied. When the resistance value rises above the target resistance value range, the resistance value after the change is compared with the allowable resistance value range and trimming is completed.

[0076] This makes it possible to prevent the heating resistor from being destroyed when trimming the heating resistor, thereby improving workability and trimming efficiency.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a thermal head 21 that is a subject of the present invention.

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

FIG. 3 is a graph showing the waveform of a trimming pulse with a relatively long pulse width and the change in temperature of the heating resistor 24 over time.

FIG. 4 is a graph showing the waveform of a trimming pulse with a relatively short pulse width and the temperature change of the heating resistor 24 over time.

FIG. 5 is a graph showing the relationship between applied power and resistance change rate when the pulse width is kept constant.

FIG. 6 is a block diagram of the trimming device 41.

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

FIG. 8 is a process diagram illustrating pulse condition setting processing.

FIG. 9 is a graph showing the relationship between applied power and resistance change rate when the pulse width is kept constant.

FIG. 10 is a process diagram illustrating trimming processing.

FIG. 11 is a graph showing a case where the resistance value disappears from a certain step and does not decrease to the target value in the process of lowering the resistance value.

FIG. 12 is a graph showing a case where the resistance value increases too much beyond the target resistance value range in the process of increasing the resistance value.

FIG. 13 is a graph when the resistance value is normally controlled within the target resistance range.

[Explanation of symbols]

21 Thermal head 23 Head board 24 Heating resistor 41 Trimming device 44 Resistance value meter 45 Trimming pulse generator 47 Calibration curve storage section 49 Pulse width adjustment section 50 Voltage adjustment section

Claims (1)

[Claims] 1. A method for trimming a plurality of heating resistors arranged linearly on an electrically insulating substrate of a thin film thermal head, in which a voltage pulse is applied to the heating resistors and the pulse width of the voltage pulse is Measure the change in the resistance value of the heating resistor corresponding to the applied power and the decrease or increase in the resistance value,
Next, based on this measurement result, a voltage pulse is applied to each heating resistor to lower or increase the resistance value, and if the resistance value after the change is within a predetermined narrow target resistance value range, the heating resistor A method for trimming a resistor of a thin film thermal head, characterized in that when trimming of the body ends and the resistance value deviates from a target resistance value, the heating resistor is trimmed again so that the resistance value falls within an allowable range.