JPS62281402A - Method of trimming thick film resistance array - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] This invention relates to a trimming method for setting each resistor of a resistor array to a predetermined resistance value without changing its shape, and in particular, More specifically, the present invention relates to a method of controlling voltage values when applying high voltage pulses to a resistor array for trimming.

[Technical background of the invention]

For example, in a thermal printer, when a head is constructed of seven thick-film resistors, trimming is performed to set the resistance to a predetermined value without changing the shape of each resistor in the resistor array. That is, in a resistor array used in a thermal print head, heat generation temperature such as maximum temperature and heat generation area is a problem, so a trimming method such as laser trimming that changes the shape of the resistor cannot be adopted.

Generally, a trimming method is used to lower the resistance value by applying a high voltage pulse to cause electrostatic breakdown of the glass barrier between the conductive particles of the thick film resistor and causing a short circuit. This method is difficult to specify uniformly because its trimming characteristics and subsequent resistance stability vary depending on the thick film resistor paste, conductive paste, and firing conditions used6. As the number of resistors increases, many resistor arrays have a density of 8 resistors/Im or more. For example, an A4 size sheet has a resistor array with a density of 1700 resistors or more. By the way, the initial resistance value varies by about ±15%.

To keep this within ±3%, 170 mm per head is required.
It is necessary to trim zero or more resistive elements.

Now, to explain the conventional trimming method with reference to FIGS. 1 and 2, each resistor element 2 of the resistor array 1 of the thermal print head is connected to a common electrode 4 provided on a substrate 3 and a drive circuit, etc. The probe 6 which is provided between the electrode 5 and the common electrode 4 and the probe 7 which is applied to the electrode 5 first
Measure the initial resistance value. This measurement is performed using selector switch 8.
This is done by switching to the resistance measuring device 9 side. What are the measurement results?

The data is sent to the control device 10, and the control device 10 receives the program voltage.
g11 and the pulse generation circuit 12 to first set the high voltage A. Here, the changeover switch 8 is switched to the pulse application side, and the voltage A pulse is applied to the first resistance element via the probe 6.7. Switch the selector switch 8 to the resistance measuring device 9 side again.

The resistance value of the first resistance element 2 is measured, the measurement result is sent to the control device 10, and the control device 10
Then, the pulse generating circuit 12 is driven to set the high voltage B. The voltage pulse B caused by this high voltage B is applied again to the first resistance element 2 by switching the changeover switch 8. Then, the resistance value of the first resistance element 2 is measured again, and the voltage pulse C of the high voltage C is applied to the first resistance element 2 again based on the measurement result. Thereafter, the same operation is generally repeated six or more times by increasing the applied voltage step by step until the resistance value reaches the desired value. When the desired resistance value is reached, the second resistance element 2 is connected to the probe 6°. This basic procedure of moving 7 is shown in Figure 2.

This method takes too much time to trim more than 1,700 resistive elements. Therefore, a method of performing parallel processing using a large number of probes has also been proposed. Parallel processing methods can be broadly classified into the following two methods.

The first method is to prepare a large number of steps in advance, corresponding to each step in FIG. For example, high voltage A, B, C
... are separated into separate probes, that is, separate processes, and when voltage pulse A (e.g., 350 V) has been applied, the stage is moved one step and voltage pulse B (e.g., 400 V) is applied. . After the application of voltage pulse B is completed, the stage is moved one step further to apply voltage pulse C (for example, 450 V), and then moved to voltage pulse D. In this case, when the stage moves, each probe moves at the same time, so if one moves the high voltage setting from A to B, the other steps can also move the high voltage setting from B to C, for example. It can be moved to D. This method has the advantage of making the system hardware single-function, such as using a fixed-voltage power supply for each process rather than a programmable high-voltage pulse power supply. Since time-consuming probe movement time is required for each processing step, the trimming time cannot be reduced as much as expected. Furthermore, since the initial resistance values in the array vary, it becomes difficult to develop software for controlling the resistance value, which is the absolute value, rather than the resistance change, in separate resistance measurement steps. Furthermore, due to variations in initial values, it is necessary to increase the number of high voltage setting stages.

The second method for parallel processing is to extend the system based on FIGS. 1 and 2 to include adjacent resistive elements, and install n resistive elements. According to this method, although there is a cost increase in that n devices other than the control device 10, that is, a changeover switch 8, a resistance measuring device 9, a program power source 11, and a pulse generation circuit 12 are prepared, one Since trimming of one resistive element can be completed at the probe position, n probes can be moved in one stage movement, resulting in the shortest trimming time.
4Also, since it is a parallel system of n pieces,
The contents of the system are simplified and easy to manufacture. When trimming is performed using this method, conventionally a method is used in which high voltage pulses are applied at regular intervals to obtain a target resistance value.

That is, 300V, 350V, 450V/750V,
800V, 850V (7), change the high voltage path) L/pass (7) size and set the target resistance value (for example, ±3%).
). Therefore, a large number of high voltage setting steps are required, and many time-consuming steps such as pulse generation, measurement waiting time, and high voltage setting are required, and furthermore, many repetitive steps are required.

The time required for trimming was increasing.

[Objective of the Invention] The object of the present invention is to focus on the fact that, as mentioned above, the conventional trimming method using parallel processing applies a large number of pulses each having a different voltage value, so that the overall trimming time cannot be shortened. An object of the present invention is to provide a method for trimming a thick film resistor array, which can significantly reduce the number of pulse applications compared to the conventional method, shorten the overall trimming time, and set a desired resistance value.

[Structure of the Invention] The method for trimming a thick film resistor array of the present invention includes measuring the rate of change in the resistance value of a resistor element in advance by applying high voltage pulses having different voltage values to each resistor element, The initial resistance value of the resistance element to be processed is measured to determine the target resistance change rate to achieve the desired resistance value, and first, a plurality of high voltage pulses corresponding to a first resistance change rate that is approximately half of the target resistance change rate are applied. A high voltage pulse is applied multiple times, and then a high voltage pulse corresponding to a second resistance change rate obtained by adding the first resistance change rate to a resistance change rate that is approximately half the difference between the target resistance change rate and the first resistance change rate is applied multiple times. The feature is that the resistance element is trimmed so that the resistance change rate approaches the target resistance change rate by applying the voltage.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 and 3.
, 4 will be explained. One resistor element 2 is taken out of the plurality of resistor elements 2 constituting the resistor array 1, and a high voltage pulse with a constant pulse width is applied within the range of 0 to 1000 V, for example, as shown in FIG. The voltage is applied to this resistance element 2 with various changes. Curve data indicating the change in resistance value of the resistance element 2 at this time is obtained in advance. That is, for example 20
Data on the percentage change in the resistance value of the resistance element 2 when a high voltage pulse of 0V is applied is obtained in advance.

Specifically, the initial resistance value of the resistance element 2 of the resistance array 1 to be trimmed is measured using the probes 6 and 7 and the resistance measuring device 9. As a result, it is assumed that the target resistance value of the resistance element 2 is 127% of this initial resistance value. First, this -2
The voltage value required to lower the voltage to -13.5%, which is half of 7%, is determined based on the curve data shown in FIG. According to FIG. 3', 400 high voltage pulses are required to reduce the voltage to -13.5%. Therefore, a high voltage pulse of 400V is applied twice to the resistance element 2 by the control device 10, the program power supply 11, and the pulse generation circuit 12, and -13,
Trim to 5%. Then -13,5% of the current
-6.75%, which is half of -13.5%, which is the difference between the target value and the target value of -27%, is added to the current -13.5%, which is -20.
The third voltage is 510V, which is the voltage value required to lower the voltage to 25%.
This high voltage pulse of 510 V is similarly applied to the resistance element 2 twice to trim it to -20 and 25%. The percentage at this time is - 20.2
The difference between 5% and the target percentage of -27%, which is -6.75%, is half of -3.37%, which is the current -2
600V, which is the voltage value required to lower the voltage to -23.62% added to 0.25%, is determined from Figure 3, and this 600V
Similarly, a high voltage pulse of 2 is applied to the resistance element 2 twice to trim it to -23.62%. Finally, -27
-1 which is half of -3.8% which is the difference between % and -23.62%
. Through these four trimmings, the target value has almost been reached.

In this example, three different high voltage pulses are applied twice each, as shown in Figure 4.
The rate of change in resistance value when the same voltage pulse (400V in this case) is applied to a resistive element multiple times is that most of the trimming effect is obtained when the first high voltage pulse is applied, and saturates after that. The focus is on Therefore, to ensure safety, two pulses are applied to a high voltage that has been set once to completely saturate the trimming, and any subsequent irregular changes in trimming are removed.

In order to select a pulse voltage, determine the number of pulses, and control a series of sequences in accordance with the curve shown in FIG. 3, a microcomputer may be provided in the control device 10, and the control may be performed using the microcomputer.

[Effects of the Invention] As described above, the thick film resistor array trimming method of the present invention applies high voltage pulses with different voltage values to each resistor element to adjust the rate of change in the resistance value of the resistor element. Measure the initial resistance value of the resistance element to be processed in advance to find the target resistance change rate to achieve the desired resistance value. The voltage value is determined from the above measurement data, and a high voltage pulse of that value is applied to perform the first trimming.
Next, the high voltage value corresponding to the resistance change rate obtained by adding approximately half the difference between the resistance change rate due to this first trimming and the target resistance change rate to the resistance change rate due to the first trimming is calculated using the above measured data. By applying a high voltage pulse of that value and performing the second trimming, trimming is performed to or near the target resistance change rate. Therefore, the number of times of trimming can be reduced compared to conventional trimming methods, and the time required for trimming the entire thermal terint head can be significantly reduced. Furthermore, an apparatus for carrying out this method can be used by simply modifying a conventional apparatus by changing its sequence.

[Brief explanation of drawings]

Figure 1 is a diagram schematically showing the basic trimming system, Figure 2 is a diagram showing the basic trimming procedure, and Figure 3 is a diagram showing the basic trimming procedure.
The figure is a graph showing a curve of the rate of change in resistance value with respect to high voltage pulses, and FIG. 4 is a graph showing the change in resistance value with respect to the number of applied pulses. In the drawing, 1 is a resistor array, 2 is a resistor element, 6.7 is a probe, 9 is a resistance measuring device, and 12 is a pulse generation circuit. Patent Applicant/Fujitsu General Co., Ltd. Representative Patent Attorney Takuya Ohara Figure 1

Claims (1)

[Claims] In a trimming method in which a predetermined resistance value is set by applying a high voltage pulse to each of the resistance elements of a thick film resistance array in which a plurality of resistance elements are provided on a substrate by thick film printing, one of the resistance elements is set to a predetermined resistance value. The rate of change in the resistance value of the resistance element is measured in advance by applying high voltage pulses with different voltage values to the resistor element, and the initial resistance value of the resistance element to be processed is measured to achieve a desired resistance value. The resistance change rate is determined, and the first resistance change rate is approximately half of the target resistance change rate.
A high voltage pulse corresponding to the resistance change rate is applied multiple times,
Next, a high voltage pulse corresponding to a second resistance change rate obtained by adding a resistance change rate that is approximately half the difference between the target resistance change rate and the first resistance change rate to the first resistance change rate is applied multiple times. A method for trimming a thick film resistor array, characterized in that the resistor element is trimmed so as to approach the target resistance change rate.