JPH04298360A - Method for trimming resistor of membrane thermal head - Google Patents

Abstract

PURPOSE:To perform the trimming treatment of a membrane thermal head at a high speed with high controllability. CONSTITUTION:A large number of the heating resistor elements 24 of a thermal head 21 are arranged in a direction vertical to a paper surface and divided into groups at every two or more items. On the basis of the deviation between the calibration curve at the time of the trimming of the heating resistors 24 of the first group and the change quantity of an actual resistance value, the aforementioned calibration curve is corrected to perform the trimming treatment of the next group.

Description

[Detailed description of the invention]

0001

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

0002

2. Description of the Related Art A thermal head used in various printing output devices has a plurality of heating resistors arranged in a straight line on an electrically insulating head substrate, and the rows of heating resistors are selectively energized with electric power. , thermal printing is performed. At this time, in order to achieve the designed print density, the resistance value of each heating resistor is
It needs to be uniform, and for this reason, a pulse trimming technique is employed in which the resistance value is adjusted by applying a voltage pulse to the heating resistor after the heating resistor is formed.

A typical conventional example is, for example, Japanese Patent Application Laid-Open No. 1-1
20363. In this conventional example, a plurality of heating resistors serving as samples are selected from within the thermal head to be trimmed in a thick film thermal head, and voltage pulses are sequentially applied to them starting from a relatively low voltage one. At this time, a calibration curve showing the relationship between the applied voltage and the change in resistance value is created, and an approximate expression representing the curve is calculated. Next, the applied voltage of the test pulse is determined based on this approximate expression, and the test pulse is applied to the sample resistor.

[0004] The obtained resistance value change is measured to determine whether the approximation formula is acceptable or not. If the approximation formula is acceptable, pulse conditions are determined using the approximation formula as is, and trimming processing is performed over all the heating resistors. If the judgment result of the approximation formula is negative, the approximation formula is corrected based on the measurement result of the change in resistance value due to the application of the test pulse, or another sample resistor is selected separately, and the process is performed as described above. The approximation equation is recalculated by sequentially applying voltage pulses starting from relatively low voltage pulses.

[0005] In this way, after calculating an approximate expression with as high precision as possible, actual trimming processing is performed. In addition, considering the situation where the obtained optimal approximation formula changes locally even within the same head board, a single thermal head is divided into multiple blocks, and the approximation formula is corrected for each block. Various trimming methods have also been proposed.

[0006] Such a conventional example is based on the following premise.

(1) When a trimming pulse of a specific voltage is applied once, and when a trimming pulse with a voltage increased sequentially from a relatively low voltage is applied once until the specific voltage is reached. are equivalent with respect to the amount of change in resistance value.

(2) When a trimming pulse is applied, the resistance value of the heating resistor changes from the initial resistance value R0 to the resistance value R, but the resistance value change rate (R-R0)/R0 is Regarding the boundary value V0 of the applied voltage and the incremental voltage ΔV, which is independent of the value R0 and at which the resistance value starts to change,

[0009]

[Math 1]

α, β: Approximate by equations determined by voltage V, like constants determined by the structure of the thermal head.

[0011]

[Problems to be Solved by the Invention] However, the present inventor has developed a thin-film thermal head manufactured by thin-film technology, that is, a resistor layer constituting a heat-generating resistor by thin-film technology such as sputtering or vapor deposition to a layer thickness of several 100 Å. It has been confirmed that in the case of a thermal head formed by the above, the premises of the first and second terms do not hold true. That is, in the thin film thermal head, even when the applied pulse voltage is the same, the amount of change in resistance value after trimming differs depending on the initial resistance value R0.

[0012] Also, by increasing the voltage sequentially from a relatively low voltage,
It was confirmed that the resistance value changes do not match when a trimming pulse is applied once until a specific voltage is reached and when a trimming pulse of the specific voltage is applied only once. Therefore, the above-mentioned conventional example cannot be applied to the thin-film thermal head, and there is a desire for a trimming processing technique for the above-mentioned thin-film thermal head that can perform trimming processing with high controllability and in a relatively short time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for trimming a thin film thermal head, which solves the above-mentioned technical problems and allows for high controllability and high-speed trimming processing.

[0014]

[Means for Solving the Problems] The present invention provides a method for trimming a plurality of heating resistive elements linearly arranged on an electrically insulating substrate of a thin film thermal head. A voltage pulse is applied to the heating resistor element, and the relationship between the decrease or increase in the resistance value of the heating resistor element corresponding to the pulse width of the voltage pulse and the applied power is memorized in advance as a calibration curve. In a method for trimming a resistor of a thin film thermal head in which the applied power of a trimming pulse is determined based on a calibration curve, the heating resistive element is divided into a plurality of groups, and the amount of change in resistance value due to the applied power of the trimming pulse is determined for each group. In addition to calculating the amount of deviation from the above calibration curve, the power to be applied to the group to be trimmed from now on is determined based on the calibration curve corrected based on the amount of deviation in the group that has already been trimmed. This is a method for trimming a resistor of a thin film thermal head, which is characterized by trimming.

[0015]

[Operation] According to the present invention, a trimming pulse is applied to the heating resistive element of a thermal head of the same standard as the thermal head to be trimmed, and the change in resistance value corresponding to the pulse width and applied power is memorized as a calibration curve. . Next, the heating resistive elements of the thermal head to be trimmed are divided into a plurality of groups, a trimming pulse based on the calibration curve is applied to one group, and the amount of change in resistance value and the amount of deviation from the calibration curve are calculated. . For subsequent groups, a new calibration curve is determined by correcting the applied power of the trimming pulse to the calibration curve used during trimming of the previous group by the amount of deviation in the previous group, and a new calibration is performed. get a curve. This determines the applied power of the trimming pulse to be applied. Thereafter, similar processing is repeated.

In this way, in the present invention, when trimming each heat generating resistor element to adjust its resistance value, the calibration curve is corrected for each block to be trimmed and the trimming is repeated, so that the thin film thermal head to be trimmed is Depending on the characteristics of the image, it is possible to perform a good trimming process. Additionally, since the calibration curve corrected for each block is basically close to the characteristics of the thin film thermal head, the number of trimming pulses applied in subsequent blocks can be reduced, resulting in faster trimming processing. It is possible to contribute to the development of

[0017]

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 heat generating resistive elements 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 2 made of synthetic resin material.
6.

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 resistance element 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 resistance elements 24 are formed. The heating resistor element 24 is connected to the platen roller 31 via a wear-resistant layer 39 formed by a thin film technique such as sputtering.
Thermal printing is performed on the thermal paper 32 between the two. Further, this heating resistor element 24 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 element 24 are input to the drive circuit element 25, and external connections covered with an insulating layer 28 are connected to the drive circuit element 25. terminal 2
9 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. The present invention provides a heating resistor layer 34 on the head substrate 23,
At the stage where the common electrode 36 and the plurality of individual electrodes 37 are formed, the plurality of heating resistance elements 2 defined by these
The purpose is to trim the resistance values every 4 to make them uniform. 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 resistive element 24 can be increased as well as lowered. A summary of the experimental results is shown in the graph of FIG. In other words, the horizontal axis represents the applied power, and the vertical axis represents the resistance change rate Δ of the heating resistor element 24.
It was confirmed that when R/R is taken, the obtained characteristic curve changes greatly by changing the pulse width of the applied trimming pulse. Lines L1 and L shown in Figure 2
2 and L3 indicate the 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.

0
020]

[Equation 2] WL1>WL2>WL3.

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 direction of change in the resistance value of the heating resistor element 24 can either rise or fall depending on L will be explained as follows with reference to FIG. 3. That is, the reason why the resistance value of the heating resistor element 24 changes due to the application of the trimming pulse is due to the annealing effect due to the heat generation of the heating resistor element layer 34 itself, that is, the crystallization of the heating resistor element layer 34, and the heat generation of the heating resistor element 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.
Oxidation also appears as an increase in resistance.

When the pulse width WL1 of the applied trimming pulse is set relatively long and the applied voltage is set low as shown in FIG. 3(1), the heating resistive element layer 34
Since the pulse width WL1 is relatively low, the temperature does not rise rapidly or significantly, and on the other hand, the pulse width WL1 is relatively long, so the relatively low temperature continues for a long time. The progress state of the annealing effect in the heat generating resistive element 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 that causes the oxidation phenomenon, and this state continues for a relatively long time, the heating resistor element layer 3
4, oxidation 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 3
The temperature change in step 4 results in the state shown in FIG. 4(2). That is, the heat generating resistive element layer 34 rapidly rises 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 temperature T
2, the annealing effect progresses and the heating resistor element layer 3
The resistance value of 4 decreases. On the other hand, the temperature T at which the oxidation occurs
Since the period in which the temperature exceeds ox is relatively short, oxidation hardly occurs and no increase in resistance value occurs. That is, by appropriately selecting the pulse width WL of the trimming pulse 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 heat generating resistive element layer 34.

(2) As shown in FIG. 3(1), when applying a trimming pulse with a pulse width WL1 that causes only an increase in the resistance value in the heating resistive element layer 34, the pulse width WL1 of the trimming pulse is fixed. If this is done, even if the resistance value before the application of the trimming pulse is different for each heat generating resistor element 24, by applying the same applied power, each heat generating resistor element 24 will exhibit a substantially constant rate of change in resistance value. On the other hand, the same applies when applying a trimming pulse with a pulse width WL3 that causes only a decrease in the resistance value as shown in FIG. 4(1), and if the applied power is the same, the resistance value before the trimming pulse is Although the resistance value varies from element to element 24, it exhibits a substantially constant rate of change in resistance value.

[0026] The inventor of the present invention has developed the heating resistor element 2 shown in FIG.
4, the length in the left-right direction in FIG. 1 is 151 μm, the width in the direction perpendicular to the plane of FIG. was measured. The relationship between the applied voltage and the change in resistance value is shown in lines L6 and L7 in FIG. 5(1). It is thus understood that the state of change in resistance value differs significantly in relation to the applied voltage.

On the other hand, the relationship between applied power and resistance value change is shown in lines L8 and L9 in FIG. 5(2). As shown in the figure, it is understood that if the applied power is the same, the resistance value changes will be the same regardless of the difference in the initial resistance value before trimming. Putting these together, the line L shown in Figure 2
It can be concluded that the characteristic curve of 1.L3 does not depend on the resistance value of each heating resistor element 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 element layer 34, changes depending on the state of the heat generating resistor layer 34 itself corresponding to the state of the applied trimming pulse (Fig. 3 (2)). ) 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 resistive elements 24 are different, the temperature time conversion characteristics of each heating resistive element 24 are as follows.
The resistance value is the same between each heating resistor element 24, and as described above, a substantially constant rate of change in resistance value can be obtained.

(3) After applying a trimming pulse of a predetermined applied power P0 to the heating resistor element 24, from the second time onwards, by applying a trimming pulse with the applied power increased by an increment ΔP of the applied power, the trimming pulse is gradually applied. The resistance value can be lowered. Regarding the heating resistor element 24 shown in FIG. 1, the inventor of the present invention has determined that the heating resistor element 24 having a length of 151 μm in the horizontal direction in FIG. After applying a pulse to lower the resistance value, the change in resistance value was measured when the applied power was increased by an increment ΔP from the second time onwards. The results are shown in lines L10 and L11 in FIG. As described above, although the manner in which the resistance value decreases differs depending on the applied power of the first pulse, the resistance value decreases in any case.

(4) In the explanation of item 3 above, by making the second and subsequent trimming pulses a trimming pulse with a relatively long pulse width as shown in FIG.
The resistance value can be gradually increased. The inventor of this case is
With respect to the plurality of heat generating resistive elements 24 having mutually different resistance values as described in the third section, changes in resistance values were measured when a trimming pulse with a pulse width of, for example, 50 ms was applied from the second time onward. This state is shown in Figure 7 line L.
12, L13. As shown in FIG. 7, it is understood that the resistance value can be gradually increased. At this time, line L12 indicates a case where the applied power is higher than line L13. Furthermore, as shown in line L13 when the applied power is set to a low value, the change in resistance value upon application of one trimming pulse can be set to be relatively small. Thereby, the resistance value of the heating resistor element 24 can be controlled with extremely high precision by trimming.

(5) The annealing effect that causes the above-described decrease in the resistance value of the heat generating resistor element layer 34 advances the rearrangement and crystallization of the constituent molecules within the heat generating resistor element layer 34. Therefore, the durability of the heating resistive element 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 the resistance value narrows the region of the predetermined resistance value of the heating resistive element 24, thereby reducing the actual film thickness. For this reason, durability against applied pulses deteriorates. In other words, the process of significantly increasing the resistance value of the heat generating resistor element 24 deteriorates the heat generating resistor element 24, resulting in a shortened lifespan.

(6) When the heating resistance element 24 is made of tantalum Ta, the inventor has confirmed that the resistance value can be reduced to about -70% with a pulse width of 1 ms or less. However, if the resistance value is excessively reduced, the heating resistance element 24 may aggregate, and the heating resistance element 24 may
A situation arises in which the heat storage layer 35 directly below is destroyed due to the heat. Considering these points, the inventor of the present invention determined the maximum trimming amount -D which is the limit that can maintain the reliability of the thermal head 21.
It was confirmed that R1 was, for example, about -40% as shown in FIG.

(7) As described above, when trimming is performed by increasing or decreasing the resistance value, if the resistance value decreases excessively due to the application of the trimming pulse, the trimming pulse having a relatively long pulse width as described above is applied. Then, it becomes necessary to oxidize the heating resistive element 24 and increase its resistance value. This oxidation causes the heating resistor element 24 to
reliability decreases. Moreover, when attempting to perform control to further reduce the resistance value by increasing the applied power, if the resistance value change is excessive in the downward direction due to the first trimming pulse application, a trimming pulse that further reduces the resistance value is applied. However, it has been confirmed that even when the resistance value does not decrease, the resistance value may actually increase, or may decrease by far exceeding the pre-calculated amount of decrease. In such a case, the heating resistor element 24 may be destroyed. When performing the above-mentioned resistance increase or decrease control through such an experiment, the resistance value change is, for example, a limit value of -D of about -30%.
It was confirmed that it cannot be made higher than R2.

(8) Regarding the heat generating resistor element 24, it has been confirmed that when trimming is not performed, the resistance value decreases, for example, by about 2 to 3% as the thermal head 21 is used. This is heating resistor element 2 which has been trimmed.
In No. 4, reliability with respect to applied pulses is improved due to the above-mentioned annealing effect, and therefore the resistance value does not decrease during use. On the other hand, the heating resistor element 24 that has not been subjected to the trimming process does not have the above-mentioned annealing effect, and therefore its resistance value decreases. Therefore, within a single thermal head 21, the amount of heat generated varies with use, resulting in uneven density. Therefore, all the heating resistance elements 24 of the thermal head 21 are
For example, it is necessary to perform trimming processing by a minimum trimming amount DR4 of about -3%.

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 heat generating resistor element 24 will be explained. Figure 4 (
As shown in 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 of the heating resistor element 24 changes as described above. Although the state 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 element 24, and the like.

Therefore, the applied power P and the resistance change rate ΔR
As shown in FIG. 9, the graph showing the relationship with
, L4b. Therefore, as explained in the prior art, when manufacturing a thermal head, a trimming pulse is applied to the head substrate 23 in the same lot and the heating resistor element 24 in the same head substrate 23, and the calibration curve of line L4 in FIG. 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 the heating resistor element 2.
Even if the voltage is applied every 4, the lines L4a and L shown in FIG.
4b, it is impossible to control the resistance change rate with high precision.

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. 9, 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 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 element 24, after applying a trimming pulse once,
Furthermore, it is necessary to increase or decrease the resistance value by applying a trimming pulse. 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 resistive element 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 is applied. As a result, the temperature of the heating resistive element 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 element 24 can be reliably increased. In addition, by selecting the applied power P1 at this time to be relatively small, it is possible to change the rate of increase in the resistance value every time a trimming pulse is applied, for example, by about +0.1 to 0.2%, and the heating resistance element 24
The resistance value of can be controlled with high precision.

FIG. 10 shows a trimming device 41 according to the present invention.
FIG. The trimming device 41 is attached to the head substrate 23 of the thermal head 21 and trims the resistive element layer 5.
The heating resistor element 2 is connected to the common electrode 36 and the individual electrodes 37 on 1.
A probing device 42 is provided which brings probes into contact with each of the four probes individually, and the probing device 42 is connected to a resistance value meter 44 and a trimming pulse generator 45 via a switching means 43. 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 board 23 is
The XY stage 52 is mounted on a Y stage 52, and the XY stage 52 is mounted on the substrate 2 by a positioning mechanism 53 under the control of the control device 46.
Perform positioning in step 3.

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, so that
It is output as a trimming pulse as described later, and applied to the selected heat generating resistor element 24 via the switching circuit 43 and the probing device 42.

FIG. 11 is a process diagram illustrating the entire process of manufacturing the thermal head 21. As shown in FIG. In step a1 of FIG. 11, a thick film common electrode layer 27 and a heat storage layer 35 are formed on the thermal head 21. In step a2, the thermal head 2
1, and in step a3, the common electrode 36 and the individual electrodes 3 are formed on the heat generating resistor layer 34.
form 7. In step a4, a trimming process, the details of which will be described later, is performed to adjust the resistance value of each heating resistor element 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. 12 is a process diagram illustrating a trimming processing method according to an embodiment of the present invention, and FIG. 13 is a process diagram illustrating a calibration curve creation and other pulse condition determination processing methods in the process of FIG. 12. It is. In step b1 of FIG. 12, a sample head in which heating resistive elements 24 are arranged as shown in FIG. 1 is prepared, and the pulse conditions as described above are determined.

The details of this process will be explained with reference to the process chart for creating a calibration curve shown in FIG. That is, a sample head substrate is set up, and a trimming pulse application test is performed using the trimming device 41 shown in FIG. 10 to determine the following pulse conditions 1 to 3.

(Condition 1) A pulse width WLd at which the resistance value decreases when one pulse is applied is determined in step c1, 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. 9 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 c2.

(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 c3.

(Condition 3) The pulse width WLu at which the resistance value increases when one pulse is applied is determined in step c4.

(Condition 4) In this way, the pulse width W
In Lu, the resistance value is set to d2% (for example, 0.2 to 0.
3%) is determined in step c5.

In step b2 of FIG. 12, the calibration curve correction value Ph
= 0. In step b3, the plurality of heat generating resistive elements 24 arranged linearly on the head substrate 23 are divided into a plurality of groups. In this embodiment, for example, FIG. 15(1)
As shown in FIG. 1, a heat generating resistor element array 55 formed from a plurality of heat generating resistive elements 24 is divided into, for example, 11 blocks B0, B1, . . . , B10.

After that, the proping device 42 is attached to the heating resistor element 24 of the block B0 shown in FIG. 15 on the head substrate 23 to be trimmed, and the initial resistance value R is set.
Measure 0. In step b4, the required resistance value change amount -DR is calculated from the initial resistance value R0 and the predetermined target resistance value Rf.

[0053]

[Math 3]

Calculate . In step b5, the pulse width WLd corresponding to the required resistance value change amount DR is determined, and the required applied power P0 (-DR%) is determined from the calibration curve L4 in FIG. In step b6, the determined applied power P0(-DR
%) is corrected using the calibration curve correction value Ph. That is,

[
0055

[Equation 4] As shown by P0(-DR%)=P0(-DR%)+Ph, the applied power P0(-DR%) obtained in step b5 is replaced with P0(-DR%)+Ph. The rationale for the possibility of such correction processing of the calibration curve will be explained in the following embodiments.

In step b7, the applied voltage V0 is determined from the pulse width WLd and the applied power P0 (-DR%).

[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 is applied to the heating resistor element 24.

In step b8, 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. In step b9,
Actual resistance value change amount from the initial resistance value R0 - DR1

[0060]

[Math 6]

[0061] and the corresponding applied power P0(-DR
1%) is determined from line L15 in FIG. Process b11
Now, the amount of deviation Ph from the calibration curve L15 in the heating resistor element 24 to which the proping device 41 is currently connected.
i (i=0,1,2...)

[0062]

[Formula 7] Phi = P0i (-DR%) - P0i (-DR1%) is calculated, and the calculation result is used as the calibration curve correction value by the control device 46.
to be memorized. In step b12, it is determined whether the resistance value R measured in step b8 is within a range that is considered to match the target resistance value Rf, that is,

[0063]

[Equation 8] |R-Rf|/Rf≦εε: It is determined whether a predetermined minute amount is established.

If the judgment in step b12 is affirmative, step b1
Move on to 7. If negative, the process moves to step b13, and it is determined whether the measured resistance value R is larger than the target resistance value Rf. If this judgment is negative, the process moves to step b14,
The voltage is calculated as shown in the fifth equation using the relatively long pulse width WLμ as described above for increasing the resistance value, and the applied power P1, and a trimming pulse for increasing the resistance value with low applied power is applied to perform the process. The process moves to step b15, the resistance value is measured again, and the process returns to step b12.

If the judgment in step b13 is affirmative, the process moves to step b16, where a trimming pulse for reducing the resistance value is applied in which the applied power is increased by the incremental power ΔP with the aforementioned pulse width WLd for reducing the resistance value. Then, return to step b12.

If the determination in step b12 is affirmative, the process moves to step b17, where it is determined, for example, whether trimming of all the heating resistive elements 24 in block B0 in FIG. 15 has been completed. If the process has not been completed, the process returns to step b3 and the above-described process is repeated for the remaining heating resistive elements 24 in this block. If the judgment is positive, the process proceeds to step b1.
8, the average Ph of the deviation amount Phi of all the heating resistance elements 24 in this block is calculated.

[0067]

[Math. 9]

The average deviation amount Ph is set as the deviation amount Ph of block B0, for example.

If the judgment in step b17 is negative, it means that there is a heating resistor element 24 whose resistance value is not within the target resistance value range in block B0, and the process returns to step b3 and repeats the above-mentioned process. .

In this way, for example, block B0 shown in FIG. 15 performs trimming based on the calibration curve L15 shown in FIG. 16 so that all the heating resistive elements 24 fall within the target resistance value range.

In step b19, it is determined whether trimming has been completed for all blocks B0 to B10 as shown in FIG. 15, and if it has been completed, the trimming process is completed. If it has not been completed, the process moves to another subsequent block, for example block B1, in step b20, returns to step b3, and repeats the above-described process. At this time, step b6
Now, the deviation amount Ph obtained in step b18 with respect to the calibration curve corrected during trimming of block B0 in FIG.
The calibration curve is further corrected as shown in the fifth equation. Trimming of block B1 is performed using this further corrected calibration curve.

[0072] Thereafter, as the blocks B2, .

[0073] In this way, blocks B0,...,B10
As the trimming process progresses, the calibration curve matches the characteristics of the thermal head to be trimmed, and the resistance value of each heating resistor element 24 can be easily adjusted. Further, as the trimming for each block progresses, the number of times the trimming pulse is applied decreases. This makes it possible to speed up the trimming process.

[0074] If the number of heating resistive elements 24 constituting each of the blocks B0 to B10 is too small, there is no point in performing an average calculation, and if it is too large, there is no point in correcting the calibration curve. According to experiments, about 16 to 64 dots is appropriate. Of course, this number of dots does not need to match the number of probes of the probing device 41.

FIG. 17 is a process diagram illustrating a trimming method according to a second embodiment of the present invention. Figure 17 process d1
, d2, and d3 are the same as steps b1 to b3 in FIG. In step d4 of FIG. 17, it is determined whether or not the measurement of the initial resistance value R0 has been completed over all the heating resistive elements 24, and the measurement is continued until the measurement is completed. Once completed, the process moves on to step d5, where, for example, as shown in FIG.
is divided into blocks B0 to B10, the average resistance value is calculated for each block Bi (i=0 to 10). Now, when the resistance value distribution of the thermal head is shown by line L16 in FIG. 18(1), the average resistance value distribution for each block Bi is obtained as shown by line L16a.

In step d6, the block having the minimum average resistance value is determined. In the example of FIG. 18(1), the fifth block B5 corresponds to this. In step d7, the probe of the probing device 41 is moved to block B5. The subsequent steps d8 to d21 correspond to steps b3 to b17 in FIG. 12, and perform the same processing as described above. At this time, the trimming order for each block Bi in the heating resistance value sequence 55 progresses from the fifth block B5 to block B6, etc., as shown in FIG. 18(2).

In this way, when the judgment in step d21 becomes affirmative regarding the trimming process within each block, the process moves to step d22, and the trimming processing in the heating resistor element array 55 in the rightmost or leftmost block in FIG. Determine whether or not. If this determination is negative, it means that the trimming process can be further advanced to the blocks on the right or left side as the trimming progresses, and the process moves to step d23, where the same process as step b18 in FIG. 12 is performed.

In the subsequent step d24, the block currently being trimmed is the fifth block B.
5, etc., it is determined whether the block is the first to be trimmed. If this determination is affirmative, the calibration curve correction value Ph is stored as the correction value Ph0 in step d25. Thereafter, the process moves to step d26, in which the probe is moved to, for example, the sixth block B6 adjacent to the right side. After this, the process moves to step d8, and the above-described process is repeated.

If the determination in step d22 is affirmative, the process moves to step d27, where it is determined whether or not the trimming process has been completed for all blocks. If the trimming process has been completed, the trimming process for the thermal head is completed and the process moves on to the next thermal head. If this judgment is negative, for example, in FIG. 18(2), the sixth block B in the trimming order
This means that the trimming process in step 10 has been completed. At this time, in step d28, the first trimmed block B
Probing device 42 to the fourth block B4 next to the left side of No. 5
move. In step d29, the calibration curve correction value Ph is set to Ph0 stored in the step d25, and the process is moved to step d8, where the trimming process proceeds to the left in FIG. 19 for the remaining blocks B0 to B4 shown in FIG. .

As described above, in this embodiment, trimming is started from the block with the smallest average resistance value. That is, in the first embodiment, the second and subsequent blocks to be trimmed are trimmed using a calibration curve obtained by correcting the calibration curve obtained with the sample head using the characteristics of the sample head to be trimmed. , the first block B5 is subjected to trimming processing based on the calibration curve obtained with the sample head. At this time, if the deviation between the calibration curve and the trimming characteristics of the thermal head to be trimmed is large, and the resistance value of the first block is considerably higher than the target resistance value, the resistance value change obtained by applying the first trimming pulse However, there is a possibility that a large error may occur from the required amount of change in resistance value, or that the heating resistor element 24 may be destroyed due to application of an overpower pulse.

As described in the above embodiment, if the resistance value change amount is larger than the required resistance value change amount and an error occurs, the resistance value can be controlled within the target resistance value range by applying a subsequent trimming pulse. Therefore, it is necessary to prevent the heating resistor element from being destroyed, and for this purpose, as explained in the second embodiment, starting from the block with the minimum average resistance value. In other words, since this block is closest to the target resistance value, the required resistance change amount is the smallest. Therefore, even when trimming processing is performed based on the calibration curve obtained from the sample head, the applied power obtained from the calibration curve is also the smallest. Therefore, even if the resistance value change characteristics of the thermal head to be trimmed deviate greatly from the calibration curve, and therefore the applied power of the first pulse becomes overpower,
Therefore, the possibility that the heat generating resistor element is destroyed can be reduced as much as possible.

As a modification of the trimming process procedure of the second embodiment, as shown in FIG. 18(3), the trimming process is started from block B5 where the trimming process is performed first toward the left side of FIG. However, when the leftmost block is reached, the process may move to block B6 on the right side of block B5, and the trimming process may proceed from there to the right in FIG.

In the first and second embodiments, when performing trimming processing, for example, when emphasis is placed on shortening the processing time for correcting the amount of deviation from the calibration curve, the method of the first embodiment is preferable; Further, in the case where emphasis is placed on preventing the above-mentioned heating resistor element from being destroyed when correcting the amount of deviation from the calibration curve, the method of the second embodiment is suitable.

[0084]

As described above, according to the present invention, when adjusting the resistance value by trimming each heating resistor element, the calibration curve is corrected for each block to be trimmed and trimming is repeated, so that the trimming target can be adjusted. Depending on the characteristics of the thin film thermal head, it is possible to perform a good trimming process. Additionally, since the calibration curve corrected for each block is basically close to the characteristics of the thin-film thermal head, the number of trimming pulses applied to subsequent blocks can be reduced, and the trimming process It can contribute to speeding up.

Furthermore, in the present invention, the resistance values of all heating resistive elements of the thermal head to be trimmed are measured, the average resistance value is calculated for each set block, and the trimming process is started from the block with the lowest average resistance value. do. According to this, since the average resistance value of the block to which trimming processing is performed first is the lowest, the required resistance change amount with respect to the target resistance value of this block is the smallest, and the applied power calculated from the calibration curve obtained in advance is also the smallest. Therefore, even if the deviation between the trimming characteristics of the thermal head to be trimmed and the calibration curve is large, when a trimming pulse is applied based on this calibration curve, overpower may occur and the characteristics of the resistive element may deteriorate or be destroyed. It is possible to prevent such situations from occurring.

[Brief explanation of drawings]

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 element 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 element 24 over time.

FIG. 5 is a graph explaining the effect of the present invention.

FIG. 6 is a graph showing a calibration curve for explaining the operation of this embodiment.

FIG. 7 is a graph explaining the effect of the present invention.

FIG. 8 is a graph explaining the effect of the present invention.

9 is a plan view of the heating resistor element 24. FIG.

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

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

FIG. 12 is a process diagram illustrating trimming processing.

FIG. 13 is a process diagram illustrating a calibration curve creation process.

FIG. 14 is a graph showing the relationship between applied power and resistance change rate when the pulse width is kept constant.

FIG. 15 is a diagram showing an example of block divisions of the heating resistor element array 55.

FIG. 16 is a graph explaining the effect of the present invention.

FIG. 17 is a process diagram illustrating a trimming method according to a second embodiment.

FIG. 18 is a graph explaining the operation of this embodiment.

FIG. 19 is a diagram showing an example of block division in this embodiment.

[Explanation of symbols]

21 Thermal head 23 Head board 24 Heating element 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. When trimming a plurality of heat generating resistive elements linearly arranged on an electrically insulating substrate of a thin film thermal head, a voltage pulse is applied to the heat generating resistive elements of a thermal head of the same standard as the thin film thermal head. The relationship between the decrease or increase in the resistance value of the heating resistor element corresponding to the pulse width of the voltage pulse and the applied power is stored in advance as a calibration curve, and the trimming pulse is calculated based on this calibration curve. In a resistor trimming method for a thin-film thermal head that determines the applied power, the heating resistor is divided into a plurality of groups, and for each group, the deviation between the amount of resistance change due to the applied power of the trimming pulse and the calibration curve is calculated. In addition to the calculation, the power to be applied to the group to be trimmed from now on is determined based on a calibration curve corrected based on the deviation amount in the already trimmed group, and each group is trimmed in sequence. How to trim the resistor of a thin film thermal head.