JPH0229508B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for manufacturing thermal heads mainly used in facsimiles, printers, and the like.

[Conventional technology]

Thermal heads, which do not require development or fixing, are noiseless, maintenance-free, and highly reliable, are becoming popular as the performance of thermal recording paper improves. 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 layer of thermal transfer paper. This is a technology that prints and records recording signal information on transfer paper by melting it.

The general structure of the thermal head is shown in FIG. The thermal head consists of a heating element consisting of a lead part 2 made of a good electrical conductor material such as Al, Au, Cu, etc. by film-forming technology on an insulating substrate 1, and a film-like element resistor 3 connected to both ends of the lead part 2. do. 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 for the element resistor 3 is Ta ₂ N.Ta-SiO ₂ , Ta-Si, Ni-CuTi ₂ O ₂
Materials such as

In the case of a thick film method, a noble metal oxide 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 the section A of the recording apparatus constructed as shown in FIG. 10, and the thermal paper 5 develops color and is printed on its surface.
Note that in FIG. 10, the same symbols as in FIG. 9 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 due to the heat generated by the unit, and the applied energy equivalent to reaching this temperature is approximately 0.2 mJ, although it varies depending on the resolution of each thermal head.
(joule) ~2 mJ 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 is fired as a post-process to generate heat. A resistor is formed. The thin film type is mainly made by vapor depositing or sputtering tantalum-based materials to form a basic pattern that can be used as a resistor in advance.
After that, photoetching is performed to finish the desired pattern of independent resistors. 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 is 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, the thin film type has the great advantage that although the manufacturing process is extensive, there is little variation in the resistance value of the heating 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 utilizes the generated Joule heat, variations in resistance value naturally cause density unevenness in the image quality printed thereon.

FIG. 11 shows an example of the resistance values R ₁ , R ₂ , . . . , Rn of each element resistor constituting the thermal head.

Normally, the resistance value variation of thin film type is ±5% to ±15
%, whereas the thick film type has a variation of ±15% to ±30%, and although it is inferior to the thin film type, it is still the mainstream.
This is because it has the great advantages of high reliability, typified by overload power and wear resistance, and low cost.

Recently, it has become possible to form fine patterns with thick film types as well as with thin film types. For example, in the formation of conductor patterns, the printing film thickness was conventionally required to be 3 μm or more, but 3000 Å
It can also be configured with the following conductor film thickness. The advantage of this is that the etching factor during photoetching is about the same as that of the thin film type, compared to the conventional 20 μm.
In other words, the etching factor is approximately zero.

On the other hand, regarding improvement of the variation in resistance value of thick film type, in addition to improvement of conventional screen printing technology such as improvement of mesh screen and metal mask screen, there is also a method described in Japanese Patent Publication No. 59-22675. Photoetching of a thick film resistor, method of embedding a thick film resistor in a photoresist pattern described in Japanese Patent Publication No. 57-18506, and method of embedding a thick film resistor in a photoresist pattern as described in Japanese Patent Application Laid-open No. 54-99443. There are methods such as polishing the surface of the body. Further, Japanese Patent Application Laid-Open No. 55-47597 describes a thin film conductor with a thick film resistor printed thereon.

However, these methods require changing the shape of the resistor or using a complicated configuration;
This is difficult to apply to a thermal head consisting of a large number of minute resistors.

In addition, the chemical trimming method cannot be adopted because it is susceptible to shocks due to mechanical vibration caused by the movement of a rotating roller located above the heating element and pressing the thermal paper.

As for methods for improving variations in resistance values, adjustment of resistance values using laser trimming and the like has conventionally been carried out mainly on thick film circuit boards, thin film circuit boards, and the like. Also, JP-A-58
In the liquid jet recording head described in Japanese Patent Laid-Open No. 7360-7360 or Japanese Patent Application Laid-Open No. 58-7360, the thin film resistive element is laser trimmed to adjust the resistance value to match the electro-thermal conversion characteristics.

However, these conventional methods lead to changes in the shape of the resistor, tend to cause uneven print density in the thermal head, and cannot be used to improve variations in the resistance value of the thermal head.

In addition, as a conventional method for improving resistance value variations, Japanese Patent Publication No. 55-38812 describes a method for adjusting the resistance value of a Grace resistor made by sintering metal oxide powder such as ruthenium as a general thick film resistor. There is something.

Specifically, based on the action of a thick-film resistor under a high-voltage electric field, an overvoltage is applied to the Grace resistor across an insulating substrate, and the barrier insulation where the Grace resistor is thought to form a resistance is applied. The resistance value is corrected by decreasing the resistance value through destruction.

If an overvoltage is applied to a large number of microresistors such as a thermal head through an insulating substrate using this method, the shape of the resistor will likely change.
Furthermore, since an insulating substrate is used, adjusting variations in the resistance value of the thermal head becomes complicated.

Furthermore, Japanese Patent Publication No. 45-13145 discloses a method for manufacturing a microelectronic resistor having uniform and stable resistance value characteristics required for computers.

This involves passing an electric pulse through the resistor to apply a high electric field to the resistor to reduce its resistance value, but the resistor is made of a mixture of semiconductor, silver (or silver alloy), and glass. , it is stated that the change in resistivity of this mixture is attributable to the effect of the addition, that the additive enters the lattice of the semiconductor and adjusts the resistivity in proportion to the amount of additive added.

For example, monovalent silver ions are added to palladium oxide (semiconductor), one hole is generated per silver ion, and when an electric field is applied, silver jumps out of the palladium oxide lattice, resulting in As two holes are generated, the resistance value is lowered by increasing the number of holes.

However, if this method is applied to improve the variation in resistance value of a thermal head, the resistor material will be composed of a mixture of silver, semiconductor, and glass, and in this method, the semiconductor will change depending on the temperature. Since the mobility of holes changes, it is thought to lack thermal stability.

Therefore, this is not a preferable method for a thermal head in which the resistor generates heat to color the thermal paper.

On the other hand, progress has also been made in improving materials for thick film resistors.

Conventionally, noble metals such as silver-palladium (Ag/pd) have been used as conductive materials for thick film resistors, as described in the above-mentioned Japanese Patent Publication No. 13145/1983. However, this Ag/pd (PdO) system is affected by the firing atmosphere and lacks process stability, has relatively large current noise, cannot be fired at high temperatures due to problems with Pd oxidation and ring elements, and has sheet There were problems such as the inability to obtain a high resistance value and the large TCR (rate of change in resistance with respect to temperature), so it was not necessarily suitable as a thick film resistor material for thermal heads. Thick film resistive materials that improve these characteristics include ruthenium oxide described in Japanese Patent Application Laid-Open No. 53-9544 and Japanese Patent Application Laid-Open No. 53-9543,
Examples include high melting point fritted glass and zirconium oxide. Among these, the ruthenium oxide metal is Ag/pd.
It does not have the above-mentioned problems like other metals and is suitable as a thick film resistor material for thermal heads. In other words, ruthenium oxide metals can (a) cover a wide range of resistance values as heating elements for thermal heads; And high resistance values are achievable.

(b) It has good heat resistance properties, which are essential for thermal head heating elements.

(c) The particle size of the material can be made finer, making it possible to respond to finer dimensions of thermal head heating elements.

It has the following characteristics. However, the above JP-A-53
The ones described in Publication No.-9544 were mainly improved to maintain reliability as a thick-film thermal head, and there is no mention of whether they are suitable for improving variations in heating resistance values. Not yet.

[Problem to be solved by the invention]

Therefore, it is necessary to examine whether a bonding material of ruthenium oxide-based metal and glass is suitable as a thick film resistor material to improve the variation in resistance value of the heating resistor of a thermal head.

However, even if the shape of the thick film resistor is geometrically arranged to be the same as that of the thin film resistor, there is a question as to whether the variation in resistance value will be the same as that of the thin film resistor. Theoretically, the resistance value of the resistor is expressed by the following equation.

R=ρ・L/w, t (Ω) where, ρ: Specific resistance of resistor (Ω-cm) L: Length of resistor (cm) w: Width of resistor (cm) t: Resistor Thickness (cm) Screen-printed heating resistors usually vary slightly in length (L), width (w), and thickness (t) of the resistor, but this shape What ultimately becomes a problem rather than variations in resistance is resistance caused by differences in the degree of bonding that occur during firing of ruthenium oxide, glass, zirconium oxide, etc., in which thick film resistive materials basically maintain a certain grain size. It is thought that this is a variation in the specific resistance of the body itself, and as a result, variation in resistance value occurs.

This can be inferred from the fact that the problem cannot be solved even if strict screen printing and firing conditions are used in the thick film manufacturing process, and improvements are made in the pre-process and post-process of manufacturing the heating resistors. Furthermore, the particle size of ruthenium oxide, etc.
As stated in the publication, the size is 5 μm, which cannot be ignored, and the determination of the resistance value of thick film resistors is mainly based on the contact interface Me-Is-Me (metal-instrument) between ruthenium oxide and glass. This is because the heterogeneous bonding state of the metal (later metal) is thought to be the cause. The reason why the resistance value varies greatly even though the thick film resistor materials are basically the same and the firing temperature, atmosphere, and firing speed are the same is that
This is presumed to be due to a change in the bond state of Me-Is-Me.

In addition, thick film resistive materials such as ruthenium oxide and glass frit with finer grain sizes have recently become commercially available, but even when these are used, the desired effect has not been obtained. From the above, it is thought that variations in the heterogeneous bonding state at the contact interface between ruthenium oxide and glass in the thick film resistor are a factor that causes the resistance value to vary significantly.

In view of the above points, this invention has better process stability, higher sheet resistance, and TCR (rate of resistance change with temperature) than Ag/PD (pdO) based heat generating resistor materials for thermal heads. We adopted a ruthenium oxide-based material, which is suitable for heating resistors in thermal heads in various respects such as low heat resistance. It has good thermal stability without changing the shape of the heating resistor, and effectively improves the variation in resistance value of multiple heating resistors, thereby reducing uneven printing density of the thermal head. It is an object of the present invention to provide a new method for manufacturing a thermal head that can reduce costs.

[Means to solve the problem]

The thermal head manufacturing apparatus according to the present invention connects a conductive portion connected to a predetermined heating resistor selected from a plurality of heating resistors of a thermal head made of a bonding material of at least ruthenium oxide metal and glass paste. A pulse generating circuit that applies a voltage pulse by contacting a probe, a resistance meter that measures the resistance value of the heating resistor, a storage unit that stores a plurality of measured values measured by the resistance meter, and and a calculation section for calculating the average value or standard deviation value of the resistance value of the heating resistor, and the calculation section evaluates the variation in the resistance value of the heating resistor of the thermal head based on the average value or standard deviation of the resistance value of the heating resistor. It is something to do.

[Effect]

The thermal head manufacturing apparatus according to this invention includes:
Measure the resistance value of the heating resistor of the thermal head,
The present invention provides a method of manufacturing a thermal head with an average resistance value by applying a voltage pulse to reduce the resistance value and reducing the variation in the resistance value, and storing the resistance value of the heating resistor, based on the stored contents. be.

[Embodiments of the invention]

The method for manufacturing a thermal head according to this invention is to form a thick film resistor in a relatively short manufacturing process, after the main production process of firing a bonding material of ruthenium oxide metal and glass, the resistance value of the heating resistor is Implement processes to reduce 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 principle diagram showing that the resistance value of a heating resistor changes with voltage application according to the method of manufacturing a thermal head according to the present invention.

This invention utilizes the phenomenon that when a voltage is applied to a thick film resistor made of a resistor material in which ruthenium oxide metal particles are dispersed in glass, the resistance value decreases. This phenomenon is Me−Is−Me
This is thought to be due to the insulator of the thick film resistor having a (Metal-Insulator-Metal) structure breaking through when a voltage pulse is applied.

In detail, the thick film resistor material used here is one in which ruthenium oxide metal particles are dispersed in insulating glass, and microscopically, the ruthenium oxide metal particles are dispersed. The state is heterogeneous, and therefore the distances between each ruthenium oxide metal particle vary.

Therefore, before a voltage pulse is applied to this resistor material, the contact length (current path) of the metal particles is long, and a certain resistance value exists.

However, when a voltage pulse is applied to this resistor material, it is thought that if the distance between the metal particles is minute, a breakthrough will occur between these metal particles and electrical continuity will occur between them. It is presumed that as a result, the current path becomes shorter and the low resistance value decreases.

Furthermore, when a voltage pulse with a higher peak value is applied to this resistor material, breakthroughs are formed one after another between each metal particle as the peak value of the voltage pulse increases, and the resistance value gradually increases. It is thought that this decreases.

In this way, the method according to the present invention, in which the voltage pulse is applied to the resistor material at a higher peak value to lower the resistance value, is a conventional method in which an overvoltage is applied to the resistor across an insulating substrate. Alternatively, the number of holes is increased by applying electrical pulses to a counter material consisting of a mixture of silver, semiconductor and glass.

Since the method according to the present invention is aimed at a thermal head made of a microresistor, there is little risk of large cracks occurring on the surface of the resistor.
In addition, since the thermal stability causes a breakthrough between metal particles, it is stable against temperature changes.

Hereinafter, a method for manufacturing a thermal head according to the present invention will be explained with reference to the drawings.

FIG. 1 shows a case where the resistance values of the heating resistors, which have the initial resistance values 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 .

A voltage pulse is applied to the heating resistors having resistance values R ₁ , R ₂ , and R ₃ larger than R ₀ .

First, a voltage pulse whose peak value is initially set to V ₀ is applied to reduce the resistance value.

The resistance value after the decrease is measured, and if the value is R ₀ or more, a voltage pulse with a peak value of V ₀ +ΔV is applied. Thereafter, the resistance value is measured, and if the resistance value is R ₀ or more, a voltage pulse having a peak value of V ₀ +2ΔV is applied. In this way, the resistance value is gradually decreased while gradually increasing the peak value of the applied voltage pulse until the resistance value becomes R ₀ or less. 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.
FIG. 12 shows how the resistance change rate changes when the peak value of the pulse voltage is increased. As shown in FIG. 12, the resistance value of the resistor decreases regularly, and decreases almost linearly when the pulse voltage is about 100 [V] or more. The reason why the resistance value regularly decreases in this way is that although the distance between the metal particles contained in the resistor varies, breakthroughs occur one after another between each metal particle due to the increase in the peak value of the voltage pulse. It is thought that the resistance value decreases regularly. 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, the resistance value is gradually decreased until R ₀
Stop when the following occurs.

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. Several heating resistors 1
The maximum value in the group is indicated by a white circle, the average value by a black circle, and the minimum value 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 manufacturing method of the present invention. FIG. 5 is a waveform diagram of the main signals in FIG. 4.

Reference numeral 6 denotes a probing device that presses a probe into contact with the conductive part of the thermal head 7 to be adjusted, and generates an electric discharge between the conductive part of the thermal head 7 and the probe to touch the conductive part. It does not apply high voltage that may cause cracks. 8 is a relay network that guides the applied voltage pulse to a desired heating resistor; 9 is a switch that switches 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 unit;
13 is its input/output unit, 14 is a central processing unit (hereinafter referred to as CPU), 15 is a memory, 16 is a keyboard, and 17 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 sends the ENABLE signal back to the calculation section. Also, the switch 9 is switched to the pulse generation circuit 10 side.
During the period when the ENABLE signal is output, the peak value Vs
modification 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 T ₁ has passed after applying 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. Further, after ₃ hours T, the ENABLE 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 requests the probing device 6 to release the probe from the thermal head 7 to be measured and try again. Sends a reprobe signal to be contacted. Then, the resistance value is measured again. As can be understood from Figures 1 and 12, it is impossible for the resistance value to increase due to the application of voltage pulses, and if it does increase, it is due to poor contact of the probe. This is because it can be considered.

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 not at the previous point,
Do this at a location a little far 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 set value Vs of the peak value of the voltage pulse to be applied after the ENABLE signal is released is increased by ΔV and applied to the pulse generation circuit 10, 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 chattering of 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, if 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 Δt of each pulse in a pulse group consisting of multiple pulses is kept constant, and the ratio Δt/T of the pulse period T to the pulse width Δt is calculated as the change in the peak value. It is easier to adjust the heating resistor to a value below which will not destroy it.
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 application of the voltage pulse shown in FIG. 1 is started from a 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 output 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, in step (21), 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 , the peak value of the applied voltage pulse is increased by ΔV and a pulse is applied (step (27)).

In principle, adjustment is continued in this manner until the measured value becomes R ₀ or less. However, there are some unique elements whose resistance value does not decrease no matter how much pulse voltage is applied. Furthermore, 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 ends when the number of pulse voltage applications reaches a certain number. The 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, CPU14 becomes the average value,
Perform operations 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 generation circuit 10 of FIG. 4.

In the figure, 30, 32, 43 are flip-flop circuits, 31, 40, 42 are timer circuits, and 33 are flip-flop circuits.
is a pulse generator, 35 is a monostable multi-circuit, 36
is a transistor, 37 is a voltage power supply, 38 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 energizes the coil 91 of the switch 9, and the contacts 92 and 93 are switched to the opposite side as shown.

T ₁ after the flip-flop circuit is set
After a certain period of time, the timer circuit 30 outputs an output. As a result, when the flip-flop circuit 31 is set, the gate 34 is opened and the pulses generated by the pulse generator 33 are applied to the monostable multicircuit 35.

The monostable multicircuit 35 shapes the pulse width of the pulse generator 33 into a pulse having a desired pulse width Δt. Δt is determined by the resistor and capacitor in the monostable multicircuit 35. Figure 8 shows the output pulse waveform of the pulse generator 33 and the monostable multi-circuit 3.
The output waveform of No. 5 is shown.

The gate drive current of the transistor 36 is supplied by the pulse of the monostable multi-circuit 35, and the transistor 36 is ON for a period Δt when the pulse exists.
state. While the transistor 36 is in the ON state, the output voltage of the voltage power supply 37 reaches the contact 9 of the switch 9.
2,93, is applied to the sample via 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 given from the calculation section 12 by a comparator 39. When the count value reaches n, the flip-flop circuit 32 is set 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 the resistance meter side. 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 time _T3 has elapsed since the timer circuit 40 outputs an output, the timer circuit 42 outputs an output, which resets the flip-flop circuit 30, the Q terminal output becomes "H" level, and an ENABLE signal is sent to the calculation section 12. This allows the application of the next voltage pulse.

An example of the experimental results of the change in resistance value according to the present invention is that when the present invention is not implemented, the absolute value is ±20
While the % standard deviation σ was 5.6%, when the present invention was implemented, the variation was significantly improved, with the absolute value of ±3% standard deviation becoming 0.4%. As a result, it was possible to almost eliminate density unevenness in printing by the thermal head.

The inventors calculated the initial setting value (V ₀ in Figure 1) of the peak value of the voltage pulse applied to adjust the resistance value.
10V, each increment ΔV of applied pulse voltage is 1V
The number of pulses n included in one voltage application is 10 to 20, and the width Δt of one pulse is 1 μ to several μ.
The resistance value of the heating element was adjusted by setting the pulse interval to several tens of microseconds.

The inventors adjusted the resistance value by setting the time limits T ₁ and T ₂ 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, but instead of this, it is possible to compare the resistance value within a certain range, for example 0.9 to 1.0 times, compared to the previous resistance measurement value. Check whether it is within the range,
If it is not within this range, the resistance value may be remeasured.

An example of the apparatus implemented in 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 of pulses n are automatically given to the pulse generation circuit 10 from the calculating section 12, these can also be set manually. It is the peak value of the pulse generation circuit.
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 of FIG. 7, the switch 9 is a relay that energizes a coil 91 to drive contacts 92 and 93, but a semiconductor switch may be used instead.

〔Effect of the invention〕

The thermal head manufacturing apparatus according to the present invention includes:
Since it is equipped with a pulse generation circuit that applies a voltage pulse to the heating resistor to reduce its resistance value and a resistance meter that measures the resistance value of the heating resistor, the shape of the heating resistor of the thermal head does not change. It is possible to significantly reduce the unevenness of the print density of the thermal head by reducing the variation in resistance value without any problem.In addition, it is possible to significantly reduce the unevenness of print density of the thermal head. This makes it easier to understand whether the level has decreased.

[Brief explanation of drawings]

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 block diagram showing an embodiment of the apparatus implemented in 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. Flowchart diagram showing one implementation means of the method, FIG. 7 is a detailed configuration diagram of the pulse generation circuit of FIG. 4, FIG. 8 is a waveform explanatory diagram of FIG. 7, FIG. 9 is a general configuration diagram of the thermal head, 1st
Figure 0 is a diagram explaining how a thermal head is used in a thermal recording device, Figure 11 is a diagram showing an example of the resistance value distribution in a general thermal head,
FIG. 12 is a characteristic diagram of pulse voltage and resistance change rate according to the present invention. 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 Applying a voltage pulse by bringing a probe into contact with a conductive part connected to a predetermined heating resistor selected from among a plurality of heating resistors of a thermal head made of a bonding material of at least ruthenium oxide metal and glass paste. a resistance meter that measures the resistance value of the heat generating resistor; a memory unit that stores a plurality of measured values measured by the resistance meter; and a calculation section for calculating the average value or standard deviation value of the thermal head, and the variation in the resistance value of the heating resistor of the thermal head is evaluated based on the average value or standard deviation obtained by the calculation section. manufacturing equipment.