JPS6183053A - Preparation of thermal head - Google Patents

Abstract

PURPOSE:To reduce the irregularity in the resistance value of the heat generating element of a thick film type thermal head, by reducing the resistance value by applying a voltage pulse to the heat generating resistor. CONSTITUTION:At first, the resistance value of each heat generating resistor is measured to be compared with an objective resistance value R0 and a voltage pulse is applied to a heat generating resistor having a resistance value larger than R0. A voltage pulse, wherein the initial setting of a peak value is V0, is applied at first to reduce the resistance value. The resistance value after reduction is measured and, if said value is equal to or more than R0, a voltage pulse with a pea value of V0+DELTAV is applied. Thereafter, the resistance value is measured and, if said value equal to or more than R0, a voltage pulse with a peak value of V0+2DELTAV is applied. As mentioned above, the peak value of the apply voltage pulse is gradually adjustment is stopped when the resistance value reaches R0 or less. By putting the resistance value in a definite range of R0 or less, the irregularity in the resistance value is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a method of manufacturing a thermal head used in facsimiles and printers as a dud i1H king.

[Conventional technology]

Thermal heads, which do not require development or fixing, are noiseless, free from matte/tenano, and have high reliability, are becoming popular as thermal recording paper improves. In thermosensitive recording, a recording current is applied to a resistor provided on a substrate.

The Joule heat generated by the current flowing through the resistor can be used to color the MA thermal paper that is in contact with the resistor, or the ink layer of the thermal transfer paper? This is a technology that prints and records recording signal information on transfer paper by melting it.

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

An insulating substrate (At, Au, etc. on 11) is attached to the thermal head.
A heating element is constituted by a lead part (2) made of a good electrically conductive material such as O by film-forming technology and a film-like element resistor (3) connected to both ends of the lead part (2).

An insulating substrate (the material for 11 is often an alumina ceramic substrate or an alumina ceramic substrate with a glaze layer). In the case of a thin film type, the material for the element resistor (3) is TaaN, Ta-8iOz, Ta-8i. ,
Ni-Cu.

A material such as Ti20+ is used. In the case of a thick film method, 1':t An oxide of a prize metal such as RuzO or PtO is mixed with a glass material, applied and sintered. Although not shown, after forming the element resistor (3), a glass film for holding the surface is fired.

When a constant viewing pressure 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 heating causes a delay of f'Lg to the N & thermal paper (6) in the A section of the recording device configured as shown in Figure 10.
is colored and printed on its surface.

Note that in FIG. 10, the same symbols as in FIG. 9 indicate corresponding parts. The direction of the pressing force of the push roll (4) is shown.

For example, in a facsimile thermal head, each head has approximately 200 width resistors arranged independently in parallel as one heating resistor. These heating resistors are heated to a surface temperature of about 250°C to 60σC by Joule heat, and an energy equivalent to reaching this temperature is applied, which varies depending on the resolution of each thermal head 6 or about 0.
．． 2mJ (joule) ~ 2m, T 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 resistance material, and the resistance material is printed or embedded using screen printing technology, and then fired as a post-process. A heating resistor is formed.

In the thin film type, a tantalum-based material is mainly vaporized or sputtered to form a basic pattern that can become a resistor, and then photo-etched to finish it into 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 generation from the P-N mating surface is utilized, and 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. Incidentally, although the manufacturing process for thin film molding is extensive, it has the great advantage that fine patterns can be formed with less variation in the resistance value of the heating resistor. On the other hand, the thick film type can be manufactured at low cost through a relatively short manufacturing process, but the resistance value of the heating resistor varies f!
! It faced the serious drawback of being a large edition. Thermal recording is not determined by the resistance value of the resistor, but uses the generated Joule hot metal, so variations in the resistance value naturally cause density unevenness in the image quality printed thereon.

@ Figure 11 shows the resistance 111 of each element resistor that makes up the thermal head, Rx, Ra, ......, R
An example of n is shown below.

Normally, the resistance value variation of thin film type is uniform within ±5% to ±15%, while that of thick film type is uniform between ±15% to ±15%.
Although it varies by 30%, it is inferior to the thin film type, but it continues to be used throughout its life, resulting in overload power.

This is because it has the great advantages of high reliability represented by wear resistance and low cost.

Recently, it has become possible to form fine patterns on thick film as well as on thin film. For example, when forming a conductor pattern, the thickness of the printed film, which conventionally required 3 μm or more, can be reduced to 3000 A or less. This advantage is due to the fact that the etching factor during photoetching is about the same as that of the thin film type, ie, zero, compared to the conventional etching factor of 20 fim f.

On the other hand, in addition to improvements in conventional screen printing technology, such as improvements in mesh screens and metal mask screens, there have also been efforts to improve the variation in resistance values of thick film types, as 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 as described in Japanese Patent Publication No. 57-18506, method of embedding a thick film resistor in a photoresist pattern as described in Japanese Patent Application Publication No. 54-99443. There are methods such as surface polishing treatment. moreover,
Japanese Patent Laid-Open No. 55-4759'7 has a thin film conductor printed with a thick film resistor.

Kowara was an attempt to make the shape of the heating resistor uniform and to improve the variation in resistance value caused by this effect.

In addition, progress has been made in improving materials for thick film resistors.

Suitable thick film resistive materials include, for example, ruthenium oxide, high-melting frit glass, zirconium oxide, etc., as described in JP-A-53-9544 and JP-A-53-9543. However, these improvements have mainly been made to maintain tilting of the thick film type thermal head, and have not improved the variation in heating resistance value.

By the way, if the shape of the thick film resistor is geometrically aligned with the thin film resistor, there is a question as to whether the variation in resistance value is really the same as that of the thin film resistor. Theoretically, the resistance value of the resistor is expressed by the following equation.

Here, ρ: Specific resistance of the resistor (Ω-am) t: Length of the resistor (cm) W: Width of the resistor (cm) t: Thickness of the resistor (am) The length of the heating resistor (4), the width (W), and the thickness (1) of the resistor usually vary slightly, but this ultimately becomes a problem.
This is the variation in the specific resistance of the resistor itself, which is caused by the difference in M degree that occurs during firing of 4-film resistance materials, such as fuzzy ruthenium, glass frit, and fuzzy zirconium, which basically maintain a certain particle size. This is the resulting variation in resistance value.

This problem cannot be solved by improving the strict screen printing and firing conditions of the floating knit manufacturing process, or even by improving the front and rear processes of manufacturing the heating resistors. This is because the particle size of ruthenium oxide, etc. is as large as 5 m, which is negligible as described in JP-A No. 53-9544, and also because it is difficult to determine the resistance value of thick film resistors. ruthenium oxide as raw material, and Me-s at the contact interface with the glass frit.
This is because the cause is ultimately due to the inhomogeneous bonding state of -Mθ (metal-insulator metal). Basically, if the resistance value of a thick film resistance material changes significantly even though the firing temperature, atmosphere, and firing speed are the same, it can be assumed that the bonding state of -Me rather than Me- changes. □ So what about the particle size of ruthenium oxide, glass frit, etc.? More dense thick film resistive materials have recently become commercially available. However, the desired effect c>h was not achieved.

From the above, it can be seen that unless the variation in thick film resistance due to non-uniformity of the contact interface is not improved, the variation in resistance value will not be improved. By the way, in order to improve variations in resistors, adjustment of resistance values has conventionally been carried out mainly on thick film circuit boards, thin film circuit boards, etc. by using a laser trimming method or the like. Also, JP-A-58-'73
In the liquid jet recording head described in No. 60 or JP-A-58-7360, 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 of the conventional methods for improving the variation in resistance values of thick film resistors are insufficient. Chemical trimming methods, which are susceptible to impact, cannot be used because of the mechanical vibration caused by the movement of a rotating roller located above the heating resistor and in contact with the thermal paper.

-Also, since a uniform m degree distribution is required, the shape of the heating resistor is also an important factor, so lasers.

Mechanical trimming methods such as diamond cutting and sandblasting could not be used because they deteriorated the performance of the thermal head due to burrs and changes in shape.

It is an object of the present invention to provide a method of fabricating a heat generating resistor of a thick film type thermal head by changing its resistance value without changing its shape.

[Means for solving problems]

According to the present invention, by applying a voltage pulse to the heating resistor of the thermal head, the resistance value is reduced and the variation in resistance is reduced.

[Effect]

In this invention, by utilizing the fact that the resistance value of the heating resistor decreases by applying a voltage pulse, it is possible to significantly reduce the variation in resistance value. As a result, density unevenness in the print quality of the thermal head can be significantly reduced.

[Examples of actual inventions]

After the main production process of the hair styling method of the thermal head according to the present invention, a process is carried out to completely reduce the resistance value of the heating resistor. That is, after forming the heat generating resistor, the lead wire, and the deep glass film on the substrate, the process of completely reducing the resistance value according to the present invention is carried out.

FIG. 1 shows the principle of the method for manufacturing a thermal head according to the present invention? FIG.

C's invention utilizes the phenomenon that when a full voltage is applied to a thick film resistor, the resistance value decreases. This current iid M engineering S
(Metal-Engin5ulator-8emico
It is also believed that this is because the insulation of the thick film resistor with the structure (N5U1ATOR) breaks through due to voltage. It is certain that the physical properties of the resistor change with the application of voltage.

FIG. 1 shows a case where the resistance values of heating resistors whose initial resistance values are R1, R2, and R3 are adjusted by Ro iC.

First, the resistance value of each heating resistor is measured and compared with the target resistance value RO. A voltage pulse cannot be applied to a thermal resistor such as R4, which has a resistance value r lower than RO. A voltage pulse is applied to a heating resistor having a resistance value R1°R21R3k greater than RO.

First, a voltage pulse whose peak value is initially set to Vo is applied to reduce the resistance value. The resistance value after the decrease is measured, and if the value is above [RoJ], a 4-pressure pulse gold with a peak value of Vo+ΔV is applied. When measuring the resistance value fe, if the value is above Ro, a voltage pulse having a peak value of vO+2Δ■ is applied. In this way, the peak value of the applied voltage pulse is gradually crystallized and decreased until the resistance value becomes less than Roa. When the resistance value does not become less than Roa, the entire adjustment is completed. and adjust the resistance value of the heating element to be within a certain range below RoJd.Since the purpose of this invention is to reduce the variation in resistance value, it is not good if the resistance value is below Roa. ,ROa
Is it within the certain range below? It takes.

Therefore, the resistance gi is decreased little by little and the process is stopped when the resistance becomes less than RO.

FIGS. 2C and 3 are diagrams showing the distribution of the resistance value of the heating resistor when the manufacturing method of the present invention is not implemented and when it is implemented. What is the maximum value of several heating resistors in one group? The white circle indicates the average value, the black circle indicates the average value, and the x mark indicates the minimum value.It can be seen that when the test is not carried out, there is a very large variation in the resistance, but when it is sharp, there is almost no variation.

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

(61t/'i thermal head to be adjusted +71 ic
Probing device that presses the probe ft (
81H is a relay network that guides the applied voltage pulse to the desired heating resistor, (ski! switch that switches between pressure application and resistance measurement, (101 is a pulse generation circuit that generates an adjustment voltage pulse, 1111H is a resistance meter, and 112+ is a calculation unit. , 13 is its input/output unit, 141 is a central processing unit (hereinafter referred to as CPU), 151 memories, 161 keyboards, and 171 (d printers).

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

A setting signal for the peak value of the applied voltage on the 7th from the calculation unit α21.

It is not possible to provide a setting signal for the number of pulses n included in one voltage application. Voltage application start signal 5T from calculation section port 2
When receiving ART 'i, pulse generation circuit +101 riE
NABLE @ issue? Return it to the calculation department. Also, switch (9
) or pulse generation circuit + KNABL switched to the OJ side
E is the f history of the peak value Vθ during the output period, and S
, TART is prohibited from occurring. While the voltage pulse is being applied, the peak value 8 should not be changed, and the start time of the next voltage pulse application should be issued just as the current voltage pulse application is about to end. This is because there is no such thing. 5TART When a certain period of time T1 has passed after applying the i signal, the pulse generation circuit (10) sends n pulses of wave high value force 'Vs to the switch (9) and the relay network +
81 fIr: Applied to the heating resistor of the thermal head (7). After 72 hours have passed after the application of the pulse voltage has ended, the switch <91 is turned off to the resistance meter III tgll. After 73 hours, the ENABLE signal is released and the next voltage can be applied. The resistance value was not measured during the time 3, and the measurement result was sent to the calculation unit 12.
Send to 1. In the calculation unit α2, the CPTT (I4) compares the measured value with the previous measured value.If the measured value is not within a certain range based on the previous measured value, it is determined that there is a V'ili contact failure. There are various setting methods, but the simplest method is to compare whether the value 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, t17+: then C! P.U.
(141fl, without adopting this measurement value, the reprobe sends out a signal to the probing device (6) to release the probe from the thermal head (7) to be measured and re-contact. Measure the value again.

As can be understood from Fig. 1, it is impossible for the resistance value to increase due to the application of a voltage pulse. It's because I can't think.

In this case, the probe re-contacts, but since it re-contacts the same spot as before, there is a possibility that the probe will again fail. Therefore, re-contact will be carried out not at the previous prison but at a prison a little further away. The probe is brought into fixed contact at a location called a band provided at the end of the lead wire, but re-contact is made at a slightly distant location within the same pad.

If the resistance measurement value is lower than the previous measurement value, Z041 adopts this measurement value and compares it with the adjustment target value RO. Ro
If it does not reach below a, CPTJ (141 is ENAB
After the LE signal is released, set value of pulse peak value (voltage applied) ■ Raise θ by ΔV to generate pulse I! 1l
After being applied to the IJ path (10), a start signal 5TART for applying the first 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 falls below the adjustment target value ROa, the adjustment of the resistance value of the heating resistor is completed.

Time limit T1. T2. Is it the effect of chattering in the switch (9) and relay network (8) that are installed in Ts f?
This is to avoid it. Even if a voltage pulse is generated from the pulse generating circuit (lO) before the switch (9) and relay network (8) are completely switched, the voltage 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 applied in the form of a single pulse, but it is easier to control it by applying it in a group of several pulses. Although it is not specified, if this becomes too large, the heating resistor will be destroyed. Therefore, when the energy of the voltage pulse is to a certain extent and there is a risk of destroying the heating resistor, it is necessary to Rather than adjusting the pulse width of a single pulse, the width of each pulse in a group of pulses, Δtf-!, must be adjusted to decrease.
The ratio △t/T of the pulse period T and the pulse width Δt is determined by the heating resistor according to the change in the peak value. Below a value that does not cause damage (it is easier to adjust).Alternatively, Δt/T may be kept constant and the number n of pulses constituting the pulse group may be changed according to changes in the peak value. If the light is small enough, the light may be applied either as a single pulse or as a group of pulses.

If the peak value of the applied voltage pulse is low, the phenomenon that the resistance value decreases no longer appears. Therefore, it is expected that the resistance value will decrease ^
Application of the first voltage pulse is started from a peak value such as that shown in FIG. vO in FIG. 1 shows the peak value of the applied voltage pulse.

Adjustment target resistance value Ro and pulse change n are changed using the keyboard (161).Resistance value after adjustment and C
The calculation result of PU (141) is printed on the printer i'71.

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 3, pulse conditions such as the wave island value V and the Hals number n are initialized. Next, in step 1211, the blowing device (6) blows the thermal head (7) and cuts the relay network (8).

After that, in step 4, @, set the wave height value n
A pulse train of 100 mm is applied and the resistance value is measured. Compare the current measurement value with the previous measurement value in step @,
Based on the previous measurement, the dog is blown again in step 4. [Previous control] If the value is smaller than the fixed value, a comparison with the adjustment target resistance value RO is performed in step (2). If the measured γ value is equal to or less than R, the adjustment for that heating resistor is completed.

If it does not fall below Roa, a pulse is applied with the wave quotient value ΔV of the applied voltage pulse increased (step).

In this way, adjustments are made in principle until the measured ROa is slightly below. However, there are some unique elements whose resistance value does not decrease no matter how much pulse voltage is applied. or,
There is a limit to the peak value of the pulse voltage that the pulse generating circuit (lO) can generate. Therefore, even if the resistance value does not fall below Ro Id, when the number of pulse voltage applications reaches a certain number, the adjustment is terminated. A step (to) is provided at the tth point.

It has already been described in FIGS. 2 and 3 that the resistance value of several heating resistors is measured as one group. When the adjustment for one group is completed, the CPU performs the calculation ΣR, printed.

After adjusting the total thermal resistance of the thermal head, CP
Calculate the standard deviation σ for the U circle. As a result, burp □ Rinta 1
Launched at 171.

Figure 71 shows the pulse generation L! of Figure 4! ! It is a pancreatic microscopic view of l tract t10+. In the figure, mount (in), ■ is a flip-flop circuit, clll (a), rock is a timer eJ path,
(to) σ pulse generator, (to) monostable multi-uog,
13I is a comparator.

When receiving the sweep start signal 5TART from the calculation unit 1121, the flip 70 is set to tmwlrw, ah.

71J block flop circuit to the calculation section F, NABL
I can't send an E signal. While the FiNABIJ function continues, changes to the d wave value word v8 and generation of the 5TART signal are prohibited. The coil (91) of the switch (9) is energized by the output of the flip-flop circuit (9), and the contact (9) is energized.
2), (93) is switched to the opposite side. After the flip-flop circuit (2) is set, the signal is output to the timer circuit 31) after l-lT1 time. When the flip-flop circuit (TO) is set by kneading, the gate 81 cannot be opened and the 7t pulse generated by the pulse generator cannot be applied to the monostable multi-circuit (TO). It is determined by the resistor and capacitor in the monostable multi-circuit □□□ which shapes the pulse width of the monostable multi-circuit pulse generator Q into a pulse having the desired pulse width Δt'l.

In Figure 8, pulse generation 4r,! Figure 3 shows the output pulse waveform of 3 and the output waveform of monostable multi@@(to).

The transistor (
Δt fl O
It becomes N state. Period V during which the transistor (7) is in the ON state
The output range pressure of the C voltage power supply is set by the switch (contact 91 (92)
), (93) are applied to the sample via the relay network t81.゛Volume height calculation unit 112 for 1-voltage power source
These wave height values are determined by 97 days.

Pulses passing through the gate bar are counted by a counter. The count value of the counter □□□ is compared with the value n given from the calculation unit (121) by the comparator (to).

When the count Ii1 or n is reached, the flip-flop circuit (to) is reset by the output of the comparator 44. The kneading closes the gate CA, completing one pulse voltage application to the sample.

The output of the comparator (to) is the timer l! l! IFIlrf41
) is also given.

After the time limit T2, the timer circuit (G) outputs an output, the flip-flop @3 is reset by kneading, and the switch (91
is switched to the resistance meter side. When the switch (9) is switched, the contacts (92) and (93) are switched to the positions shown, and the resistance value of the heating resistor of the sample is measured by the resistance meter (Il+).

Timer 1! ! When 13 hours have elapsed since the ENABLE signal was output, the timer outputs the ENABLE signal, which causes the flip-flop 1gl to be reset and the ENABLE signal to be output to the +H++ level. Konet/
This makes it possible to apply the next voltage pulse.

An example of the experimental results of resistance value changes according to the present invention is as follows:
In the case of L/-h without implementing the present invention, the absolute value is ±20% and the standard deviation σ is 5.6%, whereas when the present invention is applied, the absolute value is ±30% and the standard deviation - The variation in resistance values did not improve significantly, as it became the 10th and 4th section.

By doing this, you can completely eliminate the density unevenness of the print from the thermal head.

In order to adjust the resistance value (C, the initial setting value of the peak value of a certain pressure pulse to be applied (VO in Figure 1), tff 10 V, the increment of the applied pulse voltage every time Δvlxv or several V, 1
The resistance value of the heating element was adjusted by setting the pulse frequency n included in the voltage application once to 10 to 2 degrees, the width Δt of one pulse to 1 μ to several seconds, and the pulse interval to ten seconds.

Time Tl, 'l°td Around Ion seconds, time Tai
The inventors adjusted the resistance value by setting it to am seconds.

Resistance value a14'[f! It goes without saying that the specific numerical values of the parameters used for are not limited to the example described above, and that various numerical values can be obtained within the range that produces the effects of the present invention.

In step @ of Fig. 6, the magnitude is compared with the previous resistance measurement value, but instead of this, the resistance measurement value is compared to the previous resistance measurement value within a certain range, for example, 0.9 to 1. Check whether it is within the 0 times range, and if it is not within this range, remeasure the resistance value? You may also do this.

An example of the apparatus used to carry out the method of manufacturing a thermal head according to the present invention is shown in FIGS. 4 and 9, but the present invention is not limited to these.

Peak value v6 of pulse voltage and number of pulses n? Calculation part (12'
However, it is given to the pulse generation circuit (lO) on its own.

These can also be set manually.

This can be easily implemented by providing the pulse generation circuit with a switch for setting the peak value v6 and the number of pulses ni. Further, both automatic setting from the calculation unit i12' and manual operation may be used together.

In the example of FIG. 7, the switch (91ri) is a relay that energizes the coil (91) to drive the origins (92) and (93), but it is also possible to use a thyristor switch instead of the switch.

〔Effect of the invention〕

In the method for manufacturing a thermal head according to the present invention, voltage pulses are applied to the heating resistor to reduce the resistance value, so variations in the resistance value of the heating resistor of the thermal head are reduced, and the thermal head is Unevenness in print density can be significantly reduced.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the principle of the method of manufacturing a thermal head according to the present invention, Fig. 2, and Fig. 31 are distributions of resistance values when the method of manufacturing a thermal head according to the present invention is not adopted and when it is implemented. FIG. 4 is a configuration diagram showing an embodiment of an apparatus for carrying out the method of manufacturing a thermal head according to the present invention, FIG. 5 is a waveform diagram of the main part of FIG. 4, and FIG. Fig. 10 is a general configuration diagram showing the actual steps of the method for manufacturing a thermal head according to the invention. It is a figure showing an example of distribution. In the figure, fl+ is an insulating substrate, (2) cut-F line, (
3) is a heat generating resistor element, (6) a burrowing device, and (7)
) thermal head, (8) is a relay network, (9) is a switch, (lO) is a pulse generation circuit, [111 is a resistance meter, 121 is a calculation unit, (14) is OPυ, G1), chrysanthemum, (
6) timer circuit, (to) pulse generator, (to) monostable multi-circuit, gI) voltage power supply, (7) counter,
cll is a comparator. Note that the same reference numeral 8 in each figure indicates the same or equivalent part.

Claims (3)

[Claims] (1) A method for manufacturing a thermal head, which comprises applying a voltage pulse to a heating resistor of the thermal head to reduce the resistance value of the heating resistor. (2) The method for manufacturing a thermal head according to claim 1, wherein the voltage pulse is a single pulse. (3) The manufacturing method according to claim 1, wherein the voltage pulse consists of a plurality of pulses.