JPH04292954A - Thermal head device - Google Patents

Abstract

PURPOSE:To make a heating value constant for every heating resistor of a thermal head to print dots of a uniform shape by a method wherein the heating value of the heating part of the thermal head part is determined in accordance with a voltage drop value existing for every output terminal of a drive circuit. CONSTITUTION:A thermal head 20 provided with a resistor array having the same resistivity as that of an actual thermal head is provided with drive ICs having resistors r1-rn and drive circuits t1-tn for driving these resistors r1-rn. An IC drop measuring device is connected to the thermal head 20. A pulse voltage is applied to the resistor array having the same resistivity as that of the actual thermal head from a pulse generation circuit 90. A probe 100 is applied to an output electrode pad of the connected IC for every bit. An IC drop is read from the resistivity indicated on an oscilloscope 80. An adjusting value per bit is found for correcting a variation of a heating value caused by the variation of the IC drop.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head device used in facsimile machines and printers, and more particularly to a thermal head device capable of obtaining good image quality without density unevenness.

0002

[Prior Art] Thermal head head devices, which are one type of recording element, have low operating noise and do not require processing steps such as development and fixing, so they are widely used in facsimile printing units and various printers. . 7 to 9 are explanatory diagrams of an example of the structure of this type of thermal head device, in which a first board on which a thermal head section is mounted and a second board on which a drive circuit section such as an IC is mounted are placed on a heat dissipation board. A bonded type thermal head device is shown. FIG. 7 is a cross-sectional view of the head board.
1 is an insulating substrate made of a substrate made of ceramic material coated with an underglaze layer of glass-based material; 2 is a resistor layer forming a heating section (heating resistor); 3 is a common electrode; 4 is an individual electrode; is a wear-resistant layer (overglaze layer), which will hereinafter be referred to as substrate A.

FIG. 8 is a side view of a thermal head device, and 6 is a heat dissipation board on which a head board A and a drive circuit board (hereinafter referred to as B board) on which a drive IC is mounted are adhered. The individual electrodes 4 on the A substrate and the IC wiring on the B substrate are connected by bonding wires 8 such as gold wires. A connector 9 for electrical connection with an external circuit is connected to the B board, and the external circuit and IC wiring are connected to this connector 9.
are connected via. FIG. 9 is a top view of the thermal head, in which the A substrate on which the heat generating part is formed extends in the main scanning direction A necessary number of connectors 9 for connection with an external circuit are arranged.

The heat generating section of the A substrate generates heat by Joule heat caused by the current flowing between the selected individual electrode 4 and the common electrode 3 via the IC 7, and directly heats the thermosensitive recording paper to develop color, or the ink on the ink sheet. is melted and transferred to recording paper,
Alternatively, recording is performed by heating the ink donor film to sublimate the dye onto the sublimation recording paper to develop color. By the way, if the resistance value of this resistor is not uniform over the entire area, a difference will occur in the temperature of the heating element when it generates heat, and density unevenness will occur in the recorded result. In order to make the resistance value of this resistor uniform for all dots, a so-called trimming process has been conventionally performed. This trimming includes pulse trimming, which utilizes the property that the resistance value of a resistor decreases due to an electric field and adjusts the resistance value of the resistor individually by applying a voltage pulse through a common electrode and individual electrodes. By partially processing the resistor or electrode with a laser beam or changing the resistance value by heating, the resistance value or current value is adjusted, and as a result, the amount of heat generated by the resistor is adjusted uniformly between dots. It is known as laser trimming.

FIG. 10 is a conventional process diagram for manufacturing a thermal head. First, metal organic deposition (MOD) is performed on an insulating substrate 1 by screen printing or the like.
) A step of forming a resistor layer 2 by coating and drying a resistor material (P11), a step of forming a layer of conductor (for example, gold (Au)) on the resistor layer 2 by screen printing (
P12), Step of patterning the conductor layer by photolithography to form the common electrode 3 and individual electrodes 4 (P13), Step of etching the resistor layer 2 using the electrode as a mask to form the required heat generating part An A substrate having a thermal head formed in step (P14) and step (P15) of forming the overglaze layer 5 is obtained. And A
The resistance value of the thermal head formed on the substrate is adjusted by laser trimming (P2). Next, A board and IC
and the B board, which is a wiring board on which the connector is mounted, are glued onto the heat dissipation board 1 (P3), and the IC is mounted on the B board (P3).
4) Connect the common electrode 4 of the A board to the IC using wire bonding.
(P5) and perform an IC mounting inspection (
P6). After completing the IC mounting inspection, the exposed electrode parts including the IC and its terminal parts are sealed with resin (P
7), connect the connector 9 (P8), and then glue the thermal head cover (P9) to complete the process.

FIG. 11 is a side sectional view of the completed thermal head device, in which 10 is the resin layer for sealing, and 11 is a cover. To trim the resistance value of the resistor in the above step P2, touch the probe (measuring probe) of the resistance meter to the common electrode 3 individual electrode 4 connected to each resistor (corresponding to 1 dot) forming the heat generating part. A laser trimming method is used in which the resistance value of the resistor portion is adjusted by adjusting the resistance value of the resistor portion by irradiating the resistor with laser light. In conventional pulse trimming and laser trimming, after trimming, the resistance value of the heating resistor bit of the thermal head is adjusted to a certain constant resistance value, and the wiring resistance value is also trimmed to be constant to eliminate density unevenness. Some are reducing the incidence. Further, the laser trimming methods disclosed in Japanese Patent Laid-Open No. 54-79457 and Japanese Patent Laid-Open No. 54-132758 provide a method for adjusting the resistance value without damaging the protective film of the resistor.

[Problem to be solved by the invention]

[0007] In the above-mentioned conventional technology, the occurrence of density unevenness is attempted to be reduced by keeping the resistance value of the thermal head and the resistance value of the wiring formed on the A substrate constant and equalizing the heat capacity of each heat generating part. , No consideration is given to density unevenness caused by causes on the B substrate side. Figure 12 shows the IC for driving the thermal head.
is an explanatory diagram of the positional relationship of terminals (referred to as pads herein), in which 7 is an IC, 71 is an output pad, and 72 is a ground pad (GND pad). As shown in the figure,
The output voltage of the IC is determined by the distance between the output pad 71 and the GND pad 72. Figure 13 shows the I shown in Figure 12.
This is an explanatory diagram of an example of the measured value of the output voltage drop (IC drop) of each output pad of C, and as shown in the figure, each drive output terminal (output pad: bit terminal) of the IC
The voltage drop (IC drop) due to the internal resistance of is for each bit (for each drive bit corresponding to 1 dot of heat generation)
There are variations in internal resistance, and the amount of IC drop for each bit is different due to this difference in internal resistance, so even if the resistance values on the thermal head side are precisely aligned, the amount of heat generated will vary from dot to dot. As a result, there is a problem in that density unevenness occurs. In this figure, the horizontal axis represents the bit terminal numbers of ICs having bit terminals from 0 to 64, and the vertical axis represents the drop voltage (V) of each IC. An object of the present invention is to solve the problems of the prior art and to
By adjusting the heat generation amount of each print dot and making the dot shape uniform, taking into account drops, it is possible to achieve excellent print quality and record more gradations of density than conventional thermal head devices. An object of the present invention is to provide a thermal head device with the following features.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a thermal head section in which a heat generating section is formed on a heat dissipation substrate, and an I.
In a thermal head device equipped with a drive circuit section mounting elements such as C, etc., the heat generating section is set according to the voltage drop amount for each drive output terminal due to the difference in internal resistance such as 1C that constitutes the drive circuit. The IC drop voltage is measured in advance, or the internal resistance value is taken into account during trimming to determine the resistance value of the heating resistor, the resistance value of the electrode bridged by the resistor, or both. By trimming, the amount of heat generated by the resistor that prints each dot is adjusted to be uniform, thereby obtaining a thermal head device with no density unevenness. That is,
By adjusting the resistance value of the resistor of the corresponding heat generating part to a constant value according to the amount of output voltage drop for each bit of the drive circuit such as IC, or according to the amount of voltage drop for each bit of the above-mentioned drive IC. By adjusting the resistance value of the electrode of the corresponding heat generating part to a constant value, or by adjusting the resistance value of both the resistor and the electrode to a constant value, the amount of heat generated by the heat generating part is made to be equal to a constant value. The resistance value of the resistor is adjusted by pulse trimming or laser trimming. The resistance value of the above resistor can be adjusted by changing the resistance value by changing the resistance characteristics by pulse trimming or laser trimming, or by changing the size and shape by laser trimming.The resistance value of the electrode can also be adjusted by laser trimming. This is done by changing their size and shape by trimming.

[Effect]

In a thermal head device equipped with a head substrate in which a heat generating part is formed on a heat dissipation board and a drive circuit board on which an IC or the like is mounted, the heat generating part is set according to the amount of voltage drop for each output terminal of the drive circuit. By having the
It is possible to eliminate density unevenness depending on the output voltage of the drive circuit and density unevenness in the heat generating portion driven by each IC when a plurality of ICs are used as the drive circuit. Adjustment of the resistance value of a resistor by pulse trimming or laser trimming (heating action) can increase the resistance value without changing the shape or size of the resistor. The resistance value of the electrode is adjusted by changing the shape of the resistor or electrode. By adjusting each of the resistance values described above, the amount of heat generated (heat capacity) for each dot can be set uniformly, and the print density becomes uniform.

【Example】

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Below, as a drive circuit, I
A method using C will be explained. FIG. 1 is a block diagram illustrating an example of an IC drop measuring device for obtaining a thermal head device according to the present invention, and 20 is a thermal head having a resistor array having the same resistance value as an actual thermal head. , r1 , r2 , ... rn
is the resistance of each resistor, 70 is the drive IC and T1, T2, T
3,...Tn are the resistors r1, r2,...
. . . A drive circuit that drives each rn.
Involved in dot printing. Further, 80 is an oscilloscope, 90 is a pulse generation circuit, and 100 is a probe. A pulse voltage is applied from the pulse generation circuit 90 to the resistor array 20 having the same resistance value as the actual thermal head, and each bit (resistors r1, r2, . . .
...rn), and apply the probe 100 to the output electrode pad of the IC connected to the terminal, and read the IC drop by observing the resistance value with an oscilloscope. The above measuring device produces an IC as shown in FIG. 13 above.
Obtains drop properties. The amount of resistance adjustment is calculated as follows. That is, the voltage applied when the probe is applied is V, the lowest voltage drop is Vn, and the difference between the drop voltage for each bit and Vn is ΔV(n). Next, calculate the target resistance value of each bit as follows. Let R be the resistance value to be made equal, and let ΔR(n) be the adjustment amount for each bit to correct the variation in heat generation due to variation in IC drop.
shall be. In order to keep the calorific value constant, (V-Vn-ΔV(n))2/(R-ΔR(n)
)=(V-Vn)2/R=const.

...The adjustment amount for each bit is determined using the equation (1).

FIG. 2 is a block diagram showing an example of the configuration of a pulse trimming device, in which 201 is a control device (computer), 202 is a pulse generator that generates trimming pulses, 203 is a resistance measuring device, and 204 is a resistance array. 205 is a switch for switching between resistance measurement and trimming pulse application;
06 is a measuring device (prober), and 207 is a thermal head device to be adjusted. Note that the laser trimming device has a configuration including a laser oscillator in place of the pulse generator in FIG. 2. Specifically, the results shown in FIG. 3 were obtained by subjecting a thick-film lift-off thermal head with a resolution of 8 dots/mm to high-precision pulse trimming using the apparatus shown in FIG. 2. FIG. 3 is an explanatory diagram of the resistance value of the resistor array after pulse trimming, and shows that the resistance was adjusted to a maximum of 12.8Ω with respect to the average resistance value of 1000Ω.

FIG. 4 is a resistance characteristic diagram showing the results of adjusting the resistance value of the resistor by laser trimming using an 8 dot/mm thin film thermal head. We were able to resolve this problem and obtain good image quality. Each of the above specific examples is for trimming and adjusting the resistance value of a resistor, and next, a specific example for adjusting the resistance value will be explained. FIG. 5 is an explanatory diagram of a thermal head in which the resistance value is adjusted by changing the width (main scanning direction) of the resistor of the heat generating part, and shows 2-1, 2-2, 2
-3,...2-i,2-j,...2-62
, 2-63 and 2-64 are resistors. Here, the width of the mask was designed by adjusting the width of the resistor of a thin film thermal head of 8 dots/mm so that the above resistance value was achieved. Specifically, the conventional line width is 100μ
Since resistor 2-i is set to 987Ω, it is designed to be 98.7 μm, and resistor 2-63, which is set to 988Ω, is designed to be 98.8 μm. As a result, it was possible to eliminate the unevenness of each IC. In addition, by adjusting the wiring width of the 8 dot/mm thin film thermal head, the wiring resistance of the thermal head was adjusted to ΔR(
n) was designed. The following formula was used as the basic formula for calculation. Rw=L/W×ρ
...(Formula 2
) However, Rw is the wiring resistance, L is the wiring length, W is the wiring width, and ρ is the sheet resistance. Specifically, we used aluminum with a sheet resistance of 5 mΩ/□ and wired approximately 12 mm, so the maximum wire It had a resistance of 8Ω when the width was 100μm. Therefore, by transforming the above formula, (Formula 3) W(n)=Rw/(Rw+ΔR(n))×W
(Formula 3) However, the wiring width for each bit was calculated and designed using Rw=8Ω and W=100μm.

FIG. 6 is an explanatory diagram of a thermal head in which the width of the individual electrodes in the main scanning direction is trimmed to adjust the amount of heat generated by the heat generating section, and shows 4-1, 4-2, 4-3, . . .
・4-i ,4-j ...4-62 ,4-63
, 4-64 are individual electrodes. In this case, the width of electrodes 4-i and 4-j is 38 μm, and the width of electrodes 4-62
The width of 4-64 was 42 μm, and the minimum line width was 38 μm as shown in the figure.

【Effect of the invention】

As explained above, the thermal head device according to the present invention can print uniform dot shapes by keeping the amount of heat generated by each resistive element of the thermal head constant even if the internal resistance of the drive circuit (IC, etc.) varies widely. can do. Incidentally, when the thermal head device of the present invention was installed in a dye-sublimation printer to perform recording, it was found that multi-gradation recording of 32 or more gradations was not possible with conventional thermal head devices due to unevenness in the internal resistance of the IC. Compared to the previous example, good recording without unevenness was obtained up to 256 gradations.

[0015]

[Brief explanation of drawings]

FIG. 1 is a block diagram illustrating an example of an IC drop measuring device for obtaining a thermal head device according to the present invention.

FIG. 2 is a block diagram showing an example of the configuration of a pulse trimming device.

FIG. 3 is an explanatory diagram of the resistance value of the resistor array after pulse trimming.

FIG. 4 is a resistance characteristic diagram showing the result of adjusting the resistance value of a resistor by laser trimming using an 8 dot/mm thin film thermal head.

FIG. 5 is an explanatory diagram of a thermal head in which the resistance value is adjusted by changing the width (main scanning direction) of the resistor of the heat generating part.

FIG. 6 is an explanatory diagram of a thermal head in which the amount of heat generated by the heat generating portion is adjusted by trimming the width of the individual electrodes in the main scanning direction.

FIG. 7 is a cross-sectional view of the head substrate.

FIG. 8 is a side view of the thermal head device.

FIG. 9 is a top view of the thermal head.

FIG. 10 is a conventional process diagram for manufacturing a thermal head.

FIG. 11 is a side sectional view of the completed thermal head device.

FIG. 12 is an explanatory diagram of the positional relationship of terminals of an IC for driving a thermal head.

13 is an explanatory diagram of an example of a measured value of the output voltage drop of each output pad of the IC shown in FIG. 17. FIG.

[Explanation of symbols] 1...Insulating substrate, 2...Resistor, 3...Common electrode, 4...Individual electrode, 5...Overglaze layer, 6...・Heat dissipation board, 7...IC, 8...
...Bonding wire, 9...Connector, 20
... Thermal head, 70 ... Drive IC, 80
...Oscilloscope, 90...Pulse generator,
100...probe.

Claims (1)

[Claims] 1. A thermal head device in which a thermal head part constituting a heat generating part and a drive circuit part driving the heat generating part are mounted on a heat dissipation board, wherein the heat generation amount of the heat generating part of the thermal head part is controlled by the drive circuit part driving the heat generating part. A thermal head device characterized in that settings are made according to the amount of voltage drop present at each output terminal of a circuit.