JPH0547961B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates primarily to a resistive material for a thermal head used in facsimiles and printers, and a method for manufacturing a thermal head using this material.

[Conventional technology]

Thermal heads, which do not require fixing, are noiseless, maintenance-free, and highly reliable, have become popular as thermal recording paper has improved. In thermal recording, a recording current is applied to a resistor provided on a substrate, and the heat generated by the current flowing through the resistor is used to color the thermal paper in contact with the resistor, or to color the ink on thermal transfer paper. This is a technology that prints and records recording signal information on transfer paper by melting the layer.

A general structural diagram of the thermal head is shown in FIG.

The thermal head is made of Al, Au, and Cu on an insulating substrate 1.
A heating element is composed of a lead part 2 made of a good electrically conductive material such as the above by film-forming technology, and a film-like element resistor 3 connected to the lead part 2 at both ends thereof.

As the material of the insulating substrate 1, an alumina ceramic substrate or an alumina ceramic substrate with a glaze layer is often used. In the case of a thin film method, the material of the element resistor 3 is Ta ₂ N, Ta-Sio ₂ , Ta-Si,
Materials such as Ni-CuTi ₂ O ₃ are used.

In the case of a thick film method, an oxide of a noble metal such as Ru ₂ O or Pto is mixed with a glass material, coated, and sintered.

Although not shown, after forming the element resistor 3, a glass film for protecting it is fired.
When a constant voltage is applied to both ends of the lead portion of this thermal head for a certain period of time, heat is generated in the resistor portion due to Joule heat. This heat is transferred to the thermal paper 5 in a section A of the recording apparatus constructed as shown in FIG. 14, and the thermal paper 5 develops color and an image is printed on its surface. In addition,
In FIG. 14, the same symbols as in FIG. 13 indicate corresponding parts. P indicates the pressing direction of the roll 4.

Generally, in a thermal head for facsimile, for example, about 2000 resistors are independently arranged in parallel as heating resistors per head. The surface temperature of these heating resistors is heated to about 250°C to 600°C by the heat generated by the heat generator.The applied energy equivalent to reaching this temperature is about 0.2 mj, although it varies depending on the resolution of each thermal head.
(Jyur) ~2mj is required.

Conventionally, this thermal head has been available in thick film type, thin film type, and semiconductor type, depending on the manufacturing process and material of the resistor. For the thick film type, a desired pattern is formed in advance on a screen or photoresist film using a paste-like resistive material, and the resistive material is printed or embedded using screen printing technology, and then baked as a post-process. A heating resistor is formed. For the thin film type, a tantalum-based material is mainly vapor-deposited or sputtered to form a basic pattern that can become a resistor, and then photo-etched to create an independent resistor with a desired pattern. In the semiconductor type, for example, resistance is diffused in a part of a silicon base material to form a resistor, and heat generated at the P-N junction surface is utilized, and almost the same means as in the semiconductor manufacturing process are used.

Of the above three manufacturing methods, the ones that have been put into practical use are the thick film type and the thin film type. By the way, although the manufacturing process of the thin film type is large, it has the great advantage that there is little variation in the resistance value of the heat generating resistor and a fine pattern can be formed. On the other hand, the thick-film type can be manufactured at low cost through a relatively short manufacturing process, but it has the serious drawback of large variations in the resistance value of the heating resistor. Since thermosensitive recording is determined by the resistance value of a resistor and uses the generated Joule heat, variations in resistance value naturally cause density unevenness in the quality of the image printed thereon.

FIG. 15 shows an example of the resistance values R ₁ , R _{2 .} . . , R of each element resistor constituting the thermal head.

Normally, the variation in resistance value of thin film type is ±5% to ±
While it is uniform within 15%, the thick-film type has a variation of ±15% to ±30%, and although it is inferior to the thin-film type, it is the main cause of overload power. This is because it has the great advantages of high reliability represented by wear resistance and low cost. Recently, even with thick film type, it has become possible to form fine patterns as well as with thin film type. For example, when forming a conductor pattern, a printed film thickness of 3 μm or more was conventionally required, but a conductor film thickness of 3000 Å or less can also be formed. This advantage is that the etching factor during photoetching is
Compared to the 20 μm required, the etching factor is the same as that of the thin film type, that is, almost zero.

On the other hand, in order to improve the variation in resistance value of thick film types, in addition to improving conventional screen printing technology such as improving mesh screens and metal mask screens, for example, the thick film method described in Japanese Patent Publication No. 59-22675 Photoetching of resistors, methods of embedding thick film resistors in photoresist patterns as described in Japanese Patent Publication No. 18506/1982, and method of embedding thick film resistors in photoresist patterns as described in Japanese Patent Publication No. 54-99443. There is a method of surface polishing. Furthermore, as described in Japanese Patent Application Laid-Open No. 55-47597, there is one in which a thick film resistor is printed on a thin film conductor. These attempts are to make the shape of the heating resistor uniform and to improve the variation in resistance value caused by this effect.

Improvements in thick film resistor materials have also been made. As a thick film resistor material, for example, Japanese Patent Application Laid-Open No. 53-9544
Ruthenium oxide, high melting point fritted glass, zirconium oxide, etc., as described in No. 1998 and Japanese Patent Publication No. 53-9543, are suitable. However, these improvements have been made primarily to maintain reliability as a thick film thermal head, and have not improved the variation in heating resistance value. By the way, if the shape of a thick film resistor is geometrically arranged to be the same as that of a thin film resistor, there is a question as to whether the variation in resistance value will really be the same as that of a thin film resistor. Theoretically, the resistance value of the resistor is expressed by the following equation.

R = ρ・/w, t (Ω) Where, ρ = Specific resistance of the resistor (Ω-cm) = Length of the resistor (cm) w = Width of the resistor (cm) t = Thickness of the resistor (cm) Screen-printed heating resistors usually have slight variations in the length (), width (w), and thickness (t) of the resistor, but this ultimately becomes a problem. This is due to the variation in the specific resistance of the resistor itself, which is caused by the difference in the degree of bonding that occurs during firing of ruthenium oxide, glass frit, zirconium oxide, etc., which basically maintain a certain particle size in thick film resistor materials. This is the resulting variation in resistance value. This problem cannot be solved even by improving the strict screen printing and firing conditions of the thick film manufacturing process, and even by improving the pre-processes and post-processes for manufacturing these heating resistors. This is because the grain size of ternium oxide, etc. is 5 μm, which cannot be ignored, as stated in JP-A No. 53-9544, and also because the determination of the resistance value of thick film resistors is mainly based on oxidation. This is because the ultimate cause is the heterogeneous bonding state of Me-Is-Me (metal-insulator-metal) at the contact interface of the ruthenium glass frit. Basically, the reason why the resistance value of thick film resistive materials changes significantly even though the firing temperature, atmosphere, and firing speed are the same can be presumed to be because the bonding state of Me-Is-Me changes.

Therefore, thick film resistive materials such as ruthenium oxide and glass frit with finer grain sizes have recently become commercially available. However, the desired effect could not be obtained.

From the above, it can be seen that unless the variation in thick film resistance due to non-uniformity of the contact surface is not improved, the variation in resistance value will not be improved. by the way,
In order to improve variations in resistors, laser trimming and the like have been used to adjust resistance values mainly for thick film circuit boards, thin film circuit boards, and the like. Further, in the liquid jet recording head described in Japanese Patent Application Laid-open No. 58-7360 or 1987-7360, the thin film resistive element is laser trimmed to adjust the resistance value to match the electric-heat exchange characteristics.

[Problem that the invention seeks to solve]

All conventional methods for improving the variation in resistance values of thick film resistors have been insufficient. Chemical trimming methods, which are susceptible to impact, cannot be used because mechanical vibrations occur due to the movement of the rotating roller, which is located above the heating resistor and presses against the thermal paper. In addition, since uniform temperature distribution is required, the shape of the heating resistor is also an important factor. Mechanical trimming methods such as laser, diamond cutting, and sandblasting can deteriorate the performance of the thermal head due to changes in shape. It was unusable.

Therefore, the present invention relates to a method for correcting variations in resistance value by applying a voltage pulse to a heating resistor made of a bonding material of ruthenium oxide, glass frit, and zirconium oxide to lower its resistance value. The variation in resistance value when no voltage pulse is applied to the bonded material of glass frit and zirconium oxide is ±15 to ±30% compared to ±5 to ±15% for the thin film type. Since applying a voltage pulse would lead to destruction of the heating resistor, this was done in order to not apply too large a voltage pulse and to increase the rate of decrease in resistance value to the same level or less as in the case of a thin film type. It is.

That is, when applying a voltage pulse that is not very large to a heating resistor, the present invention is capable of applying a voltage pulse by changing the blending ratio of ruthenium oxide and glass frit, the blending ratio of ruthenium oxide and glass frit, and the particle size of ruthenium oxide. In view of the fact that the rate of decrease in resistance value varies, the resistance value is reduced by applying a voltage pulse to a heating resistor in which the compounding ratio of ruthenium oxide and glass frit and the particle size of ruthenium oxide are set within a predetermined range. To provide a novel method for manufacturing a thermal head, which makes it possible to reduce the variation in resistance value of a heating resistor to less than the variation in a thin film, thereby correcting the variation in resistance value and reducing uneven printing of the thermal head. It is.

[Means to solve the problem]

The method for manufacturing a thermal head according to this invention includes:
A probe is brought into contact with the conductive part connected to the heating resistor of the thermal head, which is made of a thick film resistor material made of an engaging material of at least ruthenium oxide, glass frit, and zirconium oxide, and a voltage pulse is applied to the heating resistor. The resistance value is measured, and when the measured resistance value is greater than or equal to a predetermined value, a voltage pulse having a higher peak value than the voltage pulse is applied via the probe to lower the resistance value, and the resistance value is reduced. In the method for manufacturing a thermal head, the application of the voltage pulse with increased peak value is stopped when the peak value is below a predetermined value, the component ratio between the ruthenium oxide and the glass frit is such that the ruthenium oxide is 30 to 50% by weight and the glass frit is 50% by weight. 70% by weight, and the particle size of the ruthenium oxide is 0.3 to 1.0 μm.

[Effect]

In this invention, the component ratio between ruthenium oxide and glass frit is 30 to 50% by weight for ruthenium oxide and 50 to 70% by weight for glass frit, and the particle size of ruthenium oxide is 0.3 to 1.0 μm. By applying the voltage, it is possible to correct the variation in the resistance value of the heating resistor to the same level or less as in the case of a thin film.

[Embodiments of the invention]

The present invention employs a resistive material with a certain composition, and the method for manufacturing the thermal head implements a process to reduce the resistance of the heating resistor after the main production process. That is, after forming the heating resistor, lead wire, and protective glass film on the substrate, the process of reducing the resistance value according to the present invention is performed.

FIG. 1 is a diagram showing the principle of a method for producing a thermal head according to the present invention.

This invention utilizes the phenomenon that when a voltage is applied to a thick film resistor, the resistance value decreases. This phenomenon is thought to be due to voltage breakthrough in the insulator of the thick film resistor with a MIN (Metal-Insulator-Metal) structure.
In any case, it is certain that the physical properties of the resistor change due to the application of voltage.

FIG. 1 shows a case where the resistance values of the heating resistors whose initial resistance values are R ₁ , R ₂ , and R ₃ are adjusted to R ₀ .

First, the resistance value of each heating resistor is measured and compared with the target resistance value R ₀ . No voltage pulse is applied to a heating resistor having a resistance value lower than R ₀ , such as R ₄ . Resistance values R ₁ , R ₂ , larger than R ₀ ,
Apply a voltage pulse to a heating resistor with R ₃ .

First, a voltage pulse whose peak value is initially set to V ₀ is applied to reduce the resistance value. Measure the resistance value after the decrease, and if the value is R ₀ or more, V ₀ + △V
A voltage pulse with a peak value of is applied. After that, measure the resistance value, and if the value is R ₀ or more, V ₀ +2△V
A voltage pulse with a peak value of is applied. In this way, the peak value of the applied voltage pulse is gradually decreased until the resistance value reaches R ₀ or more. When the resistance value becomes R0 _or less, the adjustment ends there. In this way, the resistance value of the heating element is made to be within a certain range of R ₀ or less. Since the purpose of the present invention is to reduce the variation in resistance value, it is not only necessary that the resistance value be less than or equal to R ₀ , but it is necessary that the resistance value be within a certain range of less than or equal to R ₀ . Therefore, reduce the resistance value little by little, and stop when it reaches R ₀ or less.

FIGS. 2 and 3 are diagrams showing the distribution of resistance values of the heating resistor when the manufacturing method of the present invention is not implemented and when it is implemented. A number of heating resistors are grouped into one group, and the maximum value is indicated by a white circle, the average value is indicated by a black circle, and the minimum value is indicated by an x.

It can be seen that the variation in resistance values is very large when the test is not carried out, but when the test is carried out, the variation is almost eliminated.

FIG. 4 is a configuration diagram showing an example of an apparatus used in the production method of the present invention. FIG. 5 is a waveform diagram of the main signals in FIG. 4.

6 is a probing device that presses a probe against the thermal head 7 to be adjusted; 8 is a relay network that guides the applied voltage pulse to the desired heating resistor;
9 is a switch for switching between voltage application and resistance measurement, 10 is a pulse generation circuit that generates an adjusted voltage pulse, 11 is a resistance meter, 12 is a calculation section, 13 is an input/output section thereof, and 14 is a central processing unit (hereinafter referred to as CPU).
), 15 is a memory, 16 is a keyboard, 1
7 is a printer.

The procedure for reducing the resistance value according to the present invention will be explained.

A setting signal for the peak value Vs of the applied voltage and a setting signal for the number n of pulses included in one voltage application are provided from the calculation unit 12. Upon receiving the voltage application start signal START from the calculation unit 12, the pulse generation circuit 1
0 returns an ENABLE prohibition signal to the calculation section. or,
The switch 9 is switched to the pulse generation circuit 10 side. During the period when the ENABLE prohibition signal is output, changes in the peak value Vs and generation of the START signal are prohibited. This is because the peak value Vs should not be changed while the voltage pulse is being applied, and the start signal START for applying the next voltage pulse should not be issued until the application of the current voltage pulse is finished. When a certain period of time _T1 has elapsed after the application of the START signal, the pulse generating circuit 10 applies n pulses having a peak value of Vs to the heating resistor of the thermal head 7 via the switch 9 and the relay network 8. After T ₂ hours have passed after the application of the pulse voltage is finished, the switch 9 is switched to the resistance meter 11 side. And even more
T After ₃ hours, the ENABLE prohibition signal is released and the next voltage application becomes possible. The resistance value is measured during time T ₃ and the measurement result is sent to the calculation section 12 . In the calculation unit 12, the CPU 14 compares the measured value with the previous measured value. If the measured value is not within a certain range based on the previous measurement value, it is determined that there is a contact failure. There are various ways to set a certain range, but the simplest method is to compare the value to see if it is higher than the previous measured value.

The case of this method will be described below as an example.

If a value higher than the previous measurement value is obtained, the CPU 14 does not adopt this measurement value and causes the proping device 6 to release the probe from the thermal head 7 to be measured and re-contact it. A probe signal is sent to the destination. Then, the resistance value is measured again. As can be understood from Figure 1, it is impossible for the resistance value to increase due to the application of a voltage pulse, and if it does increase, it is thought to be due to poor contact of the probe. This is because it will be done.

In this case, if the probe contacts the same point again, there is a possibility that the probe will contact again. Therefore, re-contact is performed not at the previous location but at a location a little further away. The probe makes contact at a point called a pad provided at the end of the lead wire, but makes contact again at a slightly distant location within the same pad.

If the resistance measurement is lower than the previous measurement, the CPU
14 employs this measured value and compares it with the adjustment target value R ₀ . If R does not reach ₀ or less, the CPU14
After the ENABLE prohibition signal is released, the set value Vs of the peak value of the voltage pulse to be applied is increased by △V and given to the pulse generation circuit 10, and then a start signal START for application of the next voltage pulse is generated. .

In this way, the resistance value of the heating resistor is decreased while gradually increasing the peak value of the applied voltage pulse. When the resistance value becomes equal to or less than the adjustment target value R ₀ , the adjustment of the resistance value of the heating resistor is completed.

The reason for providing the time limits T ₁ , T ₂ , and T ₃ is to avoid the influence of chatter in the switch 9 and the relay network 8 . Even if a voltage pulse is generated from the pulse generating circuit 10 before the switch 9 and the relay network 8 are completely switched, the pulse will not be applied to the thermal head 7. Also, switch 9,
Even if the resistance value is measured before the relay network 8 is completely switched, accurate measurement cannot be made.

The voltage pulse to be applied may be a single pulse, but it is easier to control it if it is applied as a group of several pulses. The energy of the voltage pulse is defined by the peak value and the pulse width Δt, but if this becomes too large, the heating resistor will be destroyed. Therefore, when the voltage pulse has a certain amount of energy and there is a risk of destroying the heating resistor, the pulse width must be adjusted to decrease in accordance with the peak value of the voltage pulse. Rather than adjusting the pulse width of a single pulse, the width △t of each pulse in a pulse group is kept constant, and the ratio △t/T of the pulse period T to the pulse width △t is varied. It is easier to adjust the heating resistor to a value below which will not destroy the heating resistor in response to a change in the high value.
Alternatively, Δt/T may be kept constant and the number n of pulses constituting the pulse group may be changed in accordance with changes in the peak value. If the energy of the voltage pulse is sufficiently small, it may be applied either as a single pulse or as a group of pulses.

When the peak value of the applied voltage pulse is low, the phenomenon that the resistance value decreases is no longer observed. Therefore, the first voltage pulse application is started from a peak value at which a decrease in resistance value can be expected. V ₀ in FIG. 1 indicates the peak value of the first applied voltage pulse.

The adjustment target resistance value R ₀ and the number of pulses n are changed using the keyboard 16. The adjusted resistance value and the calculation result of the CPU 14 are outputted to the printer 17.

FIG. 6 is a flowchart of a method for adjusting the resistance value of a heating resistor using the apparatus shown in FIG. 4.

In step 20, pulse conditions such as the peak value Vs and the number of pulses n are initialized. Next, step 21
In this step, probing of the thermal head 7 by the probing device 6 and switching of the relay network 8 are performed. Thereafter, in steps 22 and 23, n pulse trains having a set peak value are applied, and the resistance value is measured. The current measurement value is compared with the previous measurement value in step 24, and if it is larger than the previous measurement value, probing is performed again in step 25. If it is smaller than the previous measured value, a comparison with the adjusted target resistance value _R0 is performed in step 26. If the measured value is less than or equal to R ₀ , the adjustment for that heating resistor is completed. If R is not below ₀ , increase the peak value of the applied voltage pulse by △V and apply a pulse (step
27).

Adjustment continues in this manner as a deceleration until the measured value is below R ₀ . However, there are some unique elements whose resistance value does not decrease no matter how much pulse voltage is applied. Further, there is a limit to the peak value of the pulse voltage that the pulse generating circuit 10 can generate. Therefore, even if the resistance value does not become less than R ₀ , the adjustment is terminated when the number of pulse voltage applications reaches a certain number. Step 28 is provided for this purpose.

It has already been described in FIGS. 2 and 3 that the resistance value is measured using several heating resistors as one group.

When the adjustment for one group is completed, the CPU14 becomes the average value.
Perform calculations ΣR and ΣR ² to find the standard deviation. Then, the printer 17 prints the maximum value, average value, and minimum value of one group as shown in FIG. After adjusting the total heating resistance of the thermal head,
The CPU 14 calculates the standard deviation σ. The results are printed on printer 17.

FIG. 7 is a detailed explanatory diagram of the pulse generating circuit 10 of FIG. 4. In the figure, 30, 32, 43 are flip-flop circuits, 31, 40, 42 are timer circuits, 33 is a pulse generator, 35 is a monostable multi-circuit, 36 is a transistor, 37 is a voltage power supply, 3
8 is a counter, and 39 is a comparator.

When the start signal START signal is received from the calculating section 12, the flip-flop circuits 30 and 43 are set. From the flip-flop circuit 30 to the calculation section
ENABLE inhibit signal is sent. While the ENABLE prohibition signal continues, the peak value signal Vs cannot be changed,
Generation of the START signal is prohibited. The output of the flip-flop circuit 43 causes the coil 9 of the switch 9 to
1 is energized, and the contacts 92 and 93 are switched to the opposite side as shown in the figure. Timer circuit 31 outputs _T1 hours after flip-flop circuit 30 is set. As a result, when the flip-flop circuit 32 is set, the gate 34 is opened, and the pulse generator 3
The monostable multi-circuit 35 changes the pulse width of the pulse generator 33 to a desired pulse width Δt.
Shape the pulse into a pulse with . Δt is determined by the resistor and capacitor in the monostable multicircuit 35. FIG. 8 shows the output pulse waveform of the pulse generator 33 and the output waveform of the monostable multi-circuit 35.

The gate drive current of the transistor 36 is supplied by the pulse of the monostable multi-circuit 35, and the period Δt during which the pulse exists is
It becomes ON state. While the transistor 36 is in the ON state, the output voltage of the voltage power source 37 is applied to the sample via the contacts 92 and 93 of the switch 9 and the relay network 8. The peak value of the voltage power supply 37 is determined by the peak value signal Vs from the calculation section 12.

Pulses passing through gate 34 are counted by counter 38. The count value of the counter 38 is compared with the number n provided from the calculation section 12 by a comparator 39. When the count value reaches n, the flip-flop circuit 32 is reset by the output of the comparator 39. This closes the gate 34 and ends the application of one pulse voltage to the sample.

The output of comparator 39 is also given to timer circuit 40. After the time limit _T2 , the timer circuit 40 outputs an output, which resets the flip-flop 43 and switches the switch 9 to resistance measurement. When the switch 9 is switched, the contacts 92 and 93 are switched to the illustrated positions, and the resistance value of the heat generating resistor of the sample is measured by the resistance meter 11.

When the time _T3 has elapsed since the timer circuit 40 outputs, the timer circuit 42 outputs an output, which resets the flip-flop circuit 30 and the terminal output goes to "H" level, the ENABLE inhibit signal is reset, and the next voltage is reset. It becomes possible to apply pulses.

An example of the experimental results of resistance value changes according to the present invention is that for approximately 2000 heating resistors (A4 size 1728 bits, B4 size 2048 bits), when the present invention is not implemented, the absolute value is ±20%, Standard deviation σ is 5.6
%, when the present invention was implemented, the variation in resistance values was significantly improved, with an absolute value of ±3% and a standard deviation of 0.4%. As a result, it was possible to almost eliminate density unevenness in printing by the thermal head.

The inventors set the initial setting value of the peak value of the voltage pulse applied to adjust the resistance value (V ₀ in Figure 1) as a number + V, and the increment △V for each pulse voltage applied.
Adjust the resistance value of the heating element by setting 1 V to several V, the number of pulses n included in one voltage application to 10 to 20, the width of one pulse △t to 1 μ to several μ seconds, and the pulse interval to several + μ seconds. I went.

The inventors adjusted the resistance values by setting the time limits T ₁ and T ₃ to around 10 msec and the time limit T ₂ to several msec.

The specific numerical values of the parameters used to adjust the resistance value are not limited to the example mentioned above.
It goes without saying that various numerical values can be taken within the range that produces the effects of this invention.

In step 24 of FIG. 6, a comparison is made with the previous resistance measurement value.
You may check whether it is within the range of ~1.0 times or not, and if it is not within this range, you may re-measure the resistance value.

An example of an apparatus for carrying out the method of manufacturing a thermal head according to the present invention is shown in FIGS. 4 and 7.
This invention is not limited to these.

Although the peak value Vs of the pulse voltage and the number n of pulses are automatically given to the pulse generation circuit 10 from the calculating section 12, they can also be set manually. The peak value of those pulse generation circuits
This can be easily implemented by providing a switch for setting Vs and the number of pulses n. Further, both automatic setting from the calculation unit 12 and manual operation may be used together.

In the example shown in FIG. 7, the switch 9 is a relay that energizes a coil 91 to drive contacts 92 and 93.
It is also possible to use a semiconductor switch instead.

In order to effectively perform the above-described method of applying a voltage pulse to reduce the resistance value and thereby reduce variations in resistance, it is necessary to select a material for the heating resistor that is suitable for this method. The thick film resistor material used for the heating resistor of the thermal head is mainly composed of ruthenium oxide as its conductive material.
By using other platinum group elements or their oxides and mixing them with glass frit such as borosilicate glass or lead borosilicate glass, a resistance paste having an arbitrary sheet resistance value can be derived.
However, an important point in carrying out the invention described above is that in the process of applying a voltage pulse to reduce the resistance value, the rate of decrease in the resistance value differs depending on the type of resistor paste, and depending on the type, the resistance value may decrease. In some cases, there is almost no decrease. That is, the rate at which the resistance value decreases with respect to the voltage pulse differs mainly due to the difference in the blended amounts of ruthenium oxide and glass frit. The smaller the amount of ruthenium oxide blended than the glass frit, the greater the rate of decrease in resistance value. This will be explained below using figures.
In addition, in FIG. 9, FIG. 10, FIG. 11, FIG. 12, FIG. 16, FIG. 17, FIG. This figure shows the component ratio between two types of materials, ruthenium oxide and glass frit, without considering materials such as ruthenium oxide and glass frit.
That is, it does not indicate the respective blending ratios of ruthenium oxide and glass frit in a material consisting of three or more types of ruthenium oxide, glass frit, and other materials. FIG. 9 shows data obtained by applying voltage pulses to resistance pastes containing different amounts of three types of ruthenium oxide R and glass frit G known from material analysis, and measuring the rate of decrease in resistance value. From Figure 9, it can be seen that when the proportions of ruthenium oxide and glass frit are the same (R50, G50), the rate of decrease in resistance value (△R ₃ ) is only expected to be 10%. As the resistance value decreases, the rate of decrease in the resistance value increases, and when the glass frit is 70% (R30, G70), the raw material ratio (ΔR ₁ ) of the resistance value reaches 50% or more. The reason for this is that when there are many glass frits in the Me-Is-Me layer region shown in the schematic diagram (Fig. 10), there will be more breakthroughs, and as a result, it is presumed that the rate of decrease in resistance value will be higher. However, this mechanism is currently unknown. So far, it has not been clarified. In another experiment, the rate of decrease in resistance value varied by changing the particle size of ruthenium oxide in response to the application of a voltage pulse. The particle size of ruthenium oxide is determined by sizing using a centrifuge, but since uniform particle sizes cannot always be obtained, the particle size is determined using the particle size distribution curve shown in Figure 11 at the 50% value of the curve. stipulate. Figure 12 shows 40% ruthenium oxide,
FIG. 3 is a characteristic diagram showing the results of measuring the rate of decrease in resistance value by varying the particle size of ruthenium oxide with a glass frit content of 60%. Ruthenium oxide particle size
When the thickness is 0.6 μm or more, the rate of decrease in resistance value increases and is effective. However, when the particle size is 1.0 μm,
Although the resistance value increases even with a relatively small voltage pulse, this means that the resistor has been destroyed, so the peak value of the voltage pulse must be limited to a fairly low value.

Normally, the resistance value of the heating resistor is determined by the content of ruthenium oxide, but from the perspective of correcting the variation in the resistance value of the heating resistor of the thermal head,
When ruthenium oxide is less than 30% by weight, the initial resistance value becomes high as shown in Figure 9, for example, 10×10 ²
It is undesirable for the initial resistance value to be too high because it is unsuitable for practical use because it exceeds Ω, and the resistance value does not stabilize after voltage pulse is applied.Inversion and the rate of decrease in resistance value become large. .

On the other hand, as shown in Figure 12, if the particle size of ruthenium oxide is reduced to 0.3 μm, the rate of decrease in resistance is small; if the particle size is set to 1.0 μm, the rate of decrease in resistance is large; The resistance value begins to rise at a voltage lower than that in the case, leading to destruction of the resistor.

Furthermore, from FIG. 9, when ruthenium oxide is 50% by weight or more, the initial resistance value is low, but the rate of decrease in resistance value becomes small.

Therefore, in order to prevent the resistor from being destroyed by a voltage pulse that is not too large, the particle size of the ruthenium oxide should be 1.0 μm or less, and in order to prevent the initial resistance value from being too high, the blending amount of ruthenium oxide should be 30 μm or less.
It is preferable to set it to % by weight or more.

Here, if we focus on the magnitude of the rate of decrease in resistance value from Figures 9 and 12, we can see that the lower the amount of ruthenium oxide (wt%), the greater the rate of decrease in resistance value due to the application of voltage pulses; It can be said that the larger the particle size of ruthenium oxide, the greater the rate of decrease in resistance value.

However, in this embodiment, the resistance value is reduced by applying a voltage pulse to a higher resistance value based on the initial low resistance value, and the variation in resistance value of the conventional thin film type is reduced by ± To make it equivalent to 15%, the reduction rate (ΔR) should be 30%.

Figures 16, 17, and 18 show that ruthenium oxide is 50% by weight, 40% by weight, and 30% by weight, respectively.
In the case where the particle size of ruthenium oxide is 0.3μ,
It is a characteristic diagram showing how the resistance value decreases for 0.6μ and 1.0μ. From Figure 16, ruthenium oxide is 50
The reduction rate (△R) of the resistance value when the particle size is 1.0 μ% by weight is approximately 53%, and the ruthenium oxide is 30% by weight,
When the particle size is 0.3μ, the rate of decrease in resistance (△R) is approximately
60%, which is greater than the variation in thin film shape (30%) in both cases.

Therefore, in these cases, by applying a voltage pulse, it is possible to correct the variation in the resistance value of the heating resistor to a degree greater than the variation in the case of a thin film type.

〔Effect of the invention〕

The method for manufacturing a thermal head according to this invention includes:
A voltage pulse was applied to a heating resistor in which the component ratio between ruthenium oxide and glass frit was 30 to 50% by weight of ruthenium oxide, 50 to 70% by weight of glass frit, and the particle size of ruthenium oxide was 0.3 to 1.0 μm. Since the resistance value is reduced, the resistance value is not destroyed, the initial resistance value is not increased too much, and the reduction rate of the resistance value is increased. It is possible to reduce the variation to less than ±3%, thereby reducing the variation in resistance value and the unevenness in print density of the thermal head.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the principle of the thermal head manufacturing method according to the present invention, and FIGS. 2 and 3 show the distribution of resistance values when the thermal head manufacturing method according to the present invention is not implemented and when it is implemented. Figure shown, 4th
The figure is a configuration diagram showing an embodiment of the apparatus for carrying out the method for manufacturing a thermal head according to the present invention, FIG. 5 is a waveform diagram of the main part of FIG. 4, and FIG. A flowchart showing one implementation procedure of the method, FIG. 7 is a detailed configuration diagram of the pulse generation circuit of FIG. 4, FIG. 8 is a waveform explanation diagram of FIG. 7, and FIG. 9 is a material component of the thick film resistor paste Fig. 10 is a schematic diagram showing the internal structure of the heating resistor, Fig. 11 is a particle size distribution curve defining the particle size of ruthenium oxide, Fig. 12 is a characteristic diagram showing the rate of decrease in resistance value due to the difference in Characteristic diagram showing the rate of decrease in resistance value depending on the particle size of ruthenium oxide according to the present invention, No. 13
Figure 14 is a diagram illustrating the general configuration of a thermal head, Figure 14 is a diagram explaining how the thermal head is used in a thermal recording device, Figure 15 is a diagram showing an example of the distribution of resistance values in a general thermal head, and Figure 16 is a diagram showing an example of the distribution of resistance values in a general thermal head.
Figures 17 and 18 show that ruthenium oxide is 50% by weight, 40% by weight, and 30% by weight according to the practice of the present invention.
It is a characteristic diagram showing how the resistance value decreases when the particle size is 0.3μ, 0.6μ, and 1.0μ in the case of weight%. In the figure, 1 is an insulated substrate, 2 is a lead wire, and 3
1 is a heating resistance element, 6 is a probing device, 7 is a thermal head, 8 is a relay network, 9 is a switch, 1
0 is a pulse generation circuit, 11 is a resistance meter, 12 is a calculation unit, 14 is a CPU, 31, 40, 42 are timer circuits, 33 is a pulse generator, 35 is a monostable multi-circuit, 37 is a voltage power supply, 38 is a counter 39 is a comparator. Note that the same reference numerals in each figure indicate the same or equivalent parts.

Claims (1)

[Claims] 1. After applying a voltage pulse by bringing a probe into contact with the conductive part connected to the heating resistor of a thermal head made of a thick film resistor material made of a bonding material of at least ruthenium oxide, glass frit, and zirconium oxide, The resistance value is measured, and when the measured resistance value is greater than or equal to a predetermined value, a voltage pulse having a higher peak value than the voltage pulse is applied via the probe to lower the resistance value, and the resistance value is reduced. In the method for manufacturing a thermal head, in which the application of the voltage pulse with an increased peak value is stopped when the peak value is below a predetermined value, the component ratio between the ruthenium oxide and the glass frit is such that the ruthenium oxide is 30 to 50% by weight, and the glass frit is 30 to 50% by weight. A method for producing a thermal head, characterized in that the content of the ruthenium oxide is in the range of 50 to 70% by weight, and the particle size of the ruthenium oxide is 0.3 to 1.0 μm.