JPH02145355A - thermal head - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head used in a thermal transfer recording device such as a video printer, and particularly to a thermal head suitable for recording video images.

[Conventional technology]

Conventionally, video images have been recorded using a method of performing density gradation recording by using sublimable dye ink paper and controlling the energization time of each dot of a thermal head in accordance with an image signal. for example.

By changing the energization time in 64 steps, halftone recording of 64 gradations for each color is performed.

The thermal head used for this transfers one line of data to the shift register according to the image data input to the external memory, and causes the heat generating resistor corresponding to each shift register to generate heat, for example, 512 dots. shift register (52 bits x 16 or 64 pits x
A thin film type head is used, which is equipped with 8 dots) and a 512 dot heating resistor.

In order to shorten data transfer time and print time, conventional video printers
As described in Japanese Patent No. 5955, a method is used in which a buffer memory for storing one line of image data is configured with a dual port memory, and output is performed at a higher speed than SAM (real access memory) output. According to this method, when controlling the energization at each gradation, there is no energization down time between each gradation due to the energization time required for color development being shorter than the time required for transfer, and it is efficient. Color development can be achieved and printing time can be shortened.

The RAM of the dual port memory has a configuration of 206 to 8, for example, usually 256 bits.

For example, two RAMs can be used in parallel and used as a 512-bit memory.

The thermal head used for this requires a shift register of 256 bits x 2 = 512 bits by two people, and for example, one in which eight 64-bit shift registers are mounted on a head substrate is used.

FIG. 9 is a plan view showing the structure of the conventional thermal head described above.

In FIG. 9, numeral 24 is a heat generating resistor array formed in a 512-dot array, and numeral 25 is a driving IC (hereinafter referred to as a shift register) in which a shift register, latch, and switch circuit are incorporated.

The heating resistor and the shift register are provided on the same lamic substrate 26. The shift register 25 is
It can be 32 bits or 64 bits.

The output from one shift register is wire bonded 27 in parallel to the heating element for 32 or 64 dots.
For example, shift register 6 is connected to 4C.
4, then 512÷64=8 shift registers are installed, and the fixed wiring pattern 2B connecting each shift register and the heating resistor is turned around 8 times to form 5.
It is wired to be connected to all 12 dots.

Needless to say, this wiring pattern 28 is designed so that the wiring resistance from the heating resistor 24 to the inside of the shift register is constant.

In such a conventional thermal head, the length Lr of the heating resistor array 24 is 1 due to constraints on shift register implementation.
The occupied length from the 8th (leftmost) shift register to the 8th (rightmost) shift register cannot help but become longer.

Also, unlike printing one character, printing one image requires coloring most of the area of the recording medium, so all dots of the thermal head must generate heat at the same time. For this reason, the current flowing through the thermal head becomes large9, and the voltage drop due to the resistance of the common electrode wiring cannot be ignored. If the common electrode resistance is large, density unevenness will occur on the printed screen and the quality of one image will be significantly degraded.

In order to sufficiently reduce the common electrode resistance, it is necessary to provide wide common electrodes 29 and 30 on both sides and above the heating resistor row 240. For this purpose, the width Lh of the ceramic substrate 26 must be changed.

Further, in the conventional thermal head, the shift register 25 is mounted on the same ceramic substrate 26 as the heating resistor 24. This ceramic board 26 has a configuration in which a flexible printed circuit board (abbreviated as FPC) 33 provided with a q input connector 51, 32 and a wiring section is connected to the wiring on the ceramic board 26 by pressure bonding from the outside.

For this reason, as shown in FIG. 9, the vertical width W of the ceramic substrate 26 is also required to be approximately 50 points, and coupled with the above-mentioned large Lh, the ceramic substrate becomes large and the material cost of the substrate itself increases. This is the biggest cause of the high cost of thermal heads due to reasons such as the decrease in the number of heads produced per thin film device. Since the electrode widths W, W4 have to be made smaller, the common wiring resistance increases, which causes the problem of deterioration of the print quality.

A thermal head is also known in which a common electrode is formed on the back surface and the upper end surface of the substrate in order to downsize the ceramic substrate. However, although this thermal head allows the substrate to be made smaller, it has a problem in that it has a complicated structure9 and the manufacturing process is complicated, which does not lead to cost reduction.

[Problem to be solved by the invention]

The conventional thermal head has 9 heat-generating resistors in a 512-bit shift register corresponding to the number of input data (512), and the heat-generating resistors and shift registers are arranged on - ceramic substrates. , the size of the ceramic substrate was unavoidable.

By the way, if you are planning to print an NTSC video image, the effective number of scanning lines is approximately 482, and the V
In order to avoid printing switching noise that occurs when printing 'l'Rm trenches, a number of pixels of about 468 is sufficient.

In view of this, an object of the present invention is to provide a low-cost, high-performance device that can sufficiently reduce the necessary and sufficient number of heating resistors, the shift resistance necessary for high-speed recording, and minimize the area of the ceramic substrate. Our goal is to provide a thermal head that provides high performance.

[Means to solve the problem]

In order to achieve the above object, the present application provides the following invention as a means for solving the problems.

The first invention provides a heat generating resistor array consisting of a plurality of dots of heat generating resistors and a common electrode adjacent to each end of the heat generating resistor array on a first substrate, and bits corresponding to the heat generating resistors. A shift register having a heat generating resistor is provided on a second substrate, and both substrates are butted together to form a heat generating resistor array;
In a thermal head configured to connect the output of a shift register by wire bonding, the number of heating resistors constituting the row of heating resistors is less than the number of bits of the shift register, and the number of heating resistors is reduced by the number of bits reduced. The common electrode is provided with a wide width.

A second invention is based on the first invention, wherein the first substrate has a heat generating resistor row constituted by N heat generating resistors, and a width W at each end thereof.
1 common electrode, and a shift register row having a number of bits of n bits×m (however, N < n×m) on the second substrate, and @W on both ends of this shift register row , and a common electrode for a pit from one end of the shift register row and a pit for b from the other end (
However, it is characterized in that a+b=n×m−N) are each not connected to the heating resistor, and the common electrode width is configured to be W, ≧W2.

Ninth, the present application provides the following third invention.

That is, in the third invention, the heating resistor array is provided on the first substrate, the shift register array is provided on the second substrate, and the length Lr occupied by the heating resistor array and its wiring pattern is determined by the shift register array. L1≦L with respect to the occupied length Ls, and the width W of the common electrode provided close to both sides of the heating resistor row is a W of the common electrode provided close to both sides of the shift register, It is characterized in that it is configured such that W, ≧W2.

Furthermore, the present application provides fourth to seventh inventions based on the above-mentioned inventions.

A fourth invention is based on the second or third invention, in which the first substrate is placed facing the output pad portions that are not connected to the heating resistor and are located at the left and right ends of the shift register array. It is characterized in that a common electrode is formed thereon so that W,>W2.

A fifth invention is based on the second or third invention, wherein the shift registers located at the left and right ends of the shift register row on the second substrate are provided offset to the inside of the thermal head. It is characterized by

A sixth invention is based on the first, second, and the like described above. 3rd, 4th or 5th
It is based on the invention of

The i@1 board and the second board are brought into contact with each other by placing the i@1 board and the second board together, taking care to avoid the difference in level, so that the top surface of the first board and the top surface of the shift register are approximately at the same height. It is characterized by connecting the shift register output and each common electrode.

A seventh invention is the above-mentioned first invention. Second. Third. 4th degree Based on the fifth or sixth invention, the first substrate is a ceramic substrate and the second substrate is a non-ceramic substrate.

More detailed embodiments of the invention described above are as follows.

A ceramic substrate is used as the first substrate, a heating resistor is provided on the ceramic substrate, and a non-ceramic substrate such as a glass epoxy substrate is used as the second substrate,
A shift register is provided on this board.The two boards are brought together and a head configuration is made in which each heating element and the shift register output are connected by wire bonding.The number of heating resistors is the number of bits of the shift register (for example, 512 ) with a smaller number of dots (for example, 468 to 480 dots),
The shift register is of a type in which an output pad is provided on one side parallel to the row of heating resistors (for example, a 32-bit or 64-bit one)'f: 16 or 8 shift registers are mounted. This makes the length of the heating resistor row shorter than the occupied length from the left end to the right end of the shift register row.

Further, the a bits of the leftmost shift register and the b pits of the rightmost shift register are configured not to be connected to the heating resistor, and only 468 to 480 dots are connected to the heating resistor.

On the other hand, for the common electrodes, a thin film common electrode is provided on a ceramic substrate close to both sides of the heat generating resistor row, and a thick film common electrode is provided on a glass epoxy substrate close to both sides of the shift register row. and connect the two.

By forming a thin film common electrode on a ceramic substrate so as to face the output pad area of the shift register without being connected to the heat generating resistor, it is possible to achieve a width that is wider than a thick film common electrode and has a sufficient resistance value with a minimum substrate width. Form a small thin film common electrode.

[Effect]

The number of heating resistors is kept to the necessary and sufficient number for printing one image, for example, 468 to 480 dots, and thin film common electrodes are provided on the first substrate in close proximity to both sides of the heating resistors, and a shift register is provided at a low cost. By mounting it on the second substrate and providing unconnected bits on the left and right sides, a wide thin film common electrode can be provided without increasing the width of the first substrate. ``Also, the vertical width of the first substrate can be reduced.Therefore, the resistance value of the thin film common electrode can be made sufficiently small.Furthermore, since the width of the thin film common electrode is connected to the thick film common electrode, the entire head The common electrode resistance of the head can be easily made smaller than that of a conventional thin film head, and the print quality can be improved.

Furthermore, the first substrate can be made smaller in both the vertical and horizontal directions, and the area of the first substrate can be reduced to 172 mm or less than the conventional substrate area, so that a significant cost reduction can be achieved.

- Since the shift register is provided for 512 bits, it is possible to use a conventional D-Arbort memory.
High-speed printing is possible.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing an entire embodiment of the thermal head of the present invention, FIG. 2 is a plan view showing an enlarged main part of the thermal head shown in FIG. 1, and FIG. 3 is a plan view showing the main part of the thermal head shown in FIG. 1. FIG. 3 is a cross-sectional view showing the AA cross section of the thermal head shown in FIG.

In Figures 1 to 3, 1 is a ceramic substrate, 2
Both substrates, which are non-ceramic substrates such as glass epoxy substrates, are butted and fixed on a heat sink 3 made of an aluminum plate or the like.

4 is a heating resistor row with a length Lr, in which heating resistors of 468 to 480 dots are formed in a row, and a width of about 111
It is formed on a partial glaze (glass layer) 5 having a semicylindrical cross section of 1 m. Note that the partial glaze 5 may be formed up to the side edges of the ceramic substrate 1, as shown in FIG.

Reference numeral 6 denotes a shift register (including latches, switches, etc.) provided close to one side of the non-ceramic substrate 20 parallel to the heating resistor array 4. The output pad is provided along one side 7 parallel to the heating resistor array 4.

8 is the wiring pattern on the ceramic substrate from each heating resistor to the connection part with the shift register output. 0The individual wiring resistance values, including the wiring resistance value inside the shift register, are designed to be almost constant. Needless to say, the output pad of the shift register and the wiring from each heating resistor are wire-bonded by the wire 4o so as to straddle the seam 9 of the board.

In the thermal head of the present invention, the shift register is provided with 512 bits so that data can be input from the 256-bit default port memory.For example, 16 32-bit shift registers are installed in the shift register. Since the resistor is 468 to 480 dots, as shown in FIGS. 1 and 2, a bit (for example, 16 bits) from the leftmost shift register and the rightmost shift register The b bits (for example, 16 bits) from the right end are output open and not connected to the heating resistor.

With this configuration, of the wiring pattern 8 from the heating resistor to the shift register, the left end a bit and the right end b bit become unnecessary. As a result, the length Lr occupied by the heating resistor array and its wiring pattern can be made shorter than the length occupied by the shift register array from the leftmost shift register to the rightmost shift register.

In the case of a thermal head for a video printer, as described above, since the current flowing through the thermal head is large, the voltage drop due to the resistance of the common electrode wiring within the thermal head cannot be ignored. This will be explained using FIG. 4.

In FIG. 4, 11 is a head power supply terminal, and the voltage v
h is applied. R1 is a glass epoxy substrate or F
The wiring resistance, R2, R, of the thick film common electrode 13 formed on the PC board 12 is the ceramic substrate 1 connected thereto.
4, R2 represents the resistance of the thin film common electrode 15 on both sides, and R5 represents the resistance of the upper thin film common electrode.
These are distributed resistances, but for convenience they are expressed as one resistance. Ro is the resistance value of the heating resistor 16, 17 is a switch that controls energization and de-energization according to the data of the shift register, and 18 is a ground terminal.

Now, if voltage vh is applied to head power supply terminal 11 and current Ih flows, then (R1 + R2) X due to common electrode resistance will reach the leftmost heating resistor.
A voltage drop of I h will occur. Before reaching the heating resistor in the center of the head, (R, +R2+R, /2)
A voltage drop of X Ih will occur (just in case, the IC
internal losses are ignored).

The head current Ih depends on the number of energized dots and varies from a pure white pattern to an eyelash black pattern, and a large current of up to 10 amperes flows.

Therefore, in order to keep the voltage applied to each heating element constant regardless of the number of energized dots, it is essential to make R5°R,,R, as small as possible (several tens of mΩ or less). Among the common electrode resistances, the thin film common electrode resistance R21R within the ceramic substrate 14 is particularly large.
In particular, the thickness of the common electrode 15 on the side where a large current flows is less than 10 μm, so in order to keep the common electrode resistance value on the order of 10 mΩ, it is necessary to make the width sufficiently wide (for example, 4 mm or more). be. However, since increasing the size of the ceramic substrate increases costs, it has usually been impossible to make the width of the thin film common electrode sufficiently large.

As is clear from FIGS. 1 and 2, in the thermal head of the present invention, the length Lr of the heating resistor row 4 is shorter than the length occupied by the shift register 60 row. By using the ceramic substrate part that faces the output pad area that is not connected to the heating resistor inside the resistor,
A wide thin film common electrode 19 with a width W can be formed immediately on both sides of the heating resistor row. In order to equalize the electrode width W on both sides, the number of non-connecting pads on the left and right sides should be set to a = b. In addition, by mounting the shift register 6 on a separate substrate, the vertical width W of the ceramic substrate 1 can be reduced to 1/2 or less of the conventional width (for example, 12 to I S m
+ ), the common electrode resistance value can be made sufficiently small without having to make W as wide as in the past.

On the other hand, a non-ceramic substrate 2 on which a shift register 6 is mounted
On the top, thick film common electrodes 20 are provided immediately adjacent to both sides of the shift register 60 at both left and right ends. Since the thick film common electrode can have a thickness of several tens of micrometers, the wiring resistance value can be made sufficiently small even if the width W2 is set to Wl greater than IJl (for example, "2=L/2").

The thin film common electrode 19 and the thick film common electrode 20 are wire-bonded by wires 41 (many) K so as to straddle both substrates. Note that the thick film common electrode 20 is connected to the head power supply terminal 21.

Further, 22 is a signal input terminal such as a data input terminal to the shift register 6, and is a 256-bit data input terminal.

It is constructed by two people on the premise of using Alport memory. When printing an image using the thermal head according to the present invention, it is sufficient to input image data into a portion of the 512-bit shift register corresponding to 468 to 480 dots connected to the heating resistor.

FIG. 5 shows the printing process using the thermal head of the present invention.
FIG. 3 is a diagram showing changes in print density depending on the number of energized dots.

As mentioned above, in conventional thermal heads, it is difficult to increase the width of the thin film common electrode and the electrode wiring resistance is high, so as the number of energized dots increases, the voltage applied to one heating resistor decreases, and the color density decreases. There was a drawback that the color level decreased by several gradations or more. For example, as shown in Figure 6, there is a pattern in which the entire screen is colored in the same color (corresponding to a state in which all dots are energized), and a pattern in which only a portion of the screen is colored in the same color (in a state in which a few dots are energized). This means that in an image in which there is a mixture of patterns (equivalent to 1), the color becomes darker when a small number of dots are energized, which is one of the causes of a significant deterioration in image quality.

In contrast, the thermal head of the present invention can sufficiently reduce the common electrode resistance by using the minimum necessary ceramic substrate, and even when all dots are energized, the concentration can be reduced to 1/2 of that of the conventional thermal head. It is possible to obtain high image quality without density unevenness.

The thermal head of the present invention uses a method of connecting the wiring from 468 to 480 heat generating resistors and the shift register output by wire bonding.The dot density of the heat generating resistors of the thermal head of the present invention is as follows. , based on the number of scanning lines of a video image and the print size, it is 5 to 6 dots/simplified, and the minimum wiring pitch may be at most 10 lines/square, which is not difficult based on the current wire bonding technology.

t7t, as shown in FIG. 5, if a small step is provided at the abutting portion 9 of the ceramic substrate 1 and the non-ceramic substrate 2, the top surface of the ceramic substrate 1 and the top surface of the shift register 6 can be placed at approximately the same height. It can also improve the workability, precision, and reliability of wire bonding.

In addition, in FIG. 5, 25 is a gap provided along the heat generating resistor row 4 and between it and the heat sink 5 directly below it. This gap 23 is provided for the purpose of reducing the escape of heat from the heating resistor to the heat sink 3 via the ceramic substrate 1 and improving the coloring efficiency.

The shape of the void portion 23 is not limited to that in this embodiment, and it is not necessarily necessary to provide it over the entire length of the heating resistor array 4. For example, the void portion 23 may be provided only at both left and right ends of the heating element array where the concentration tends to decrease. 1 may be provided as necessary for thermal design.

Further, in FIGS. 1 and 3, 34 is a thermistor for detecting head temperature, and 35 is a connection terminal between the wiring portion of the non-ceramic substrate 2 and the thermistor 34. Thermistor 3
Position 4 is provided at the center in the width direction of the head so that the representative temperature tube of the thermal head can be detected. In this embodiment, a hole is provided in the heat sink 3 and the thermistor 34 is embedded therein so that the thermistor 34 and the lead wire from the thermistor 34 do not need to protrude to the outside.

Note that the output part of the shift register 6 that is not connected to the heating resistor may be provided with a dummy pad 66, which may be wire-bonded to the end of the ceramic substrate, as shown in FIG. Also, up to the vicinity,
Since the thin film common electrode 19 having the width W1 can be formed in an extended manner, the same effect as described above can be obtained.

FIG. 7 is a plan view showing the main parts of another embodiment of the thermal head according to the present invention, and parts corresponding to those in FIG. 2 are given the same reference numerals.

In this embodiment, shift registers 6 located at both ends
is offset to the inside of the head, and the thick film common electrode width W2 provided close to the shift register is changed to the thin film common electrode width W,
It is constructed so that it is almost equal to . In this case, the portion of the wiring pattern from the heating resistor that corresponds to the offset portion needs to be a different pattern from other wiring patterns. However, since the thick film common electrode width W2 can be increased, there is an advantage that the overall common electrode resistance value of the thermal head can be further reduced.

Furthermore, although the above embodiment has been explained as a thin film head, the heat generating resistor and the common electrodes provided on both sides thereof are
It goes without saying that the present invention can also be applied to thick film type thermal heads formed by printing and baking, and similar effects can be obtained.

Furthermore, in each of the above embodiments, a ceramic substrate is used as the substrate on which the heating resistor is mounted, but a substrate made of other materials may be used as long as it can be used equally, or a non-ceramic substrate may be used. is a glass epoxy board, F
Although a PC board or the like is used, a board made of other materials that function equally well may be used.

〔Effect of the invention〕

According to the present invention, a ceramic substrate with a minimum area can be used to print a video image, and a heating resistor sufficient for printing a video image can be used.
Since it is possible to configure a shift register with the number of bits necessary for high-speed recording and a thin film common electrode with a sufficiently low resistance value, it is possible to realize significant cost reductions, obtain high image quality, and enable high-speed printing. It is possible to provide a high-performance thermal head that is capable of

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the overall configuration of an embodiment of the thermal head according to the present invention, and FIG. 2 is a plan view showing the main parts of the thermal head shown in FIG. 1. FIG. 5 shows the A-^ cross section of FIG. 1, FIG. 4 is a circuit diagram showing the common electrode resistance of the thermal head, and FIG. 5 is a graph showing changes in print density during printing by the thermal head of the present invention. FIG. 6 is an explanatory diagram showing an example of a print screen by a conventional thermal head, FIGS. 7 and 8 are plan views showing main parts of other embodiments of the present invention, and FIG. 9 is a diagram showing an example of a print screen by a conventional thermal head. FIG. 1...Ceramic substrate, 2...Non-ceramic substrate, 4...Heating resistor array, 6...Shift register, 8... Wiring pattern, 9...Board mating part. 11.21 Thin film common electrode for vIL source terminal 19, 20 Old thick film common electrode, 36 Dummy pad, 4 o + 41...・Wire. Fig. 1 Fig. 20 4 Ladder θ Shelf book row Ta... Difference between rice paddies, including p 2t
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Claims (1)

[Claims] 1. A heating resistor array consisting of a plurality of dots of heating resistors;
Common electrodes adjacent to both ends of the heat generating resistor array are provided on a first substrate, a shift register having bits corresponding to the heat generating resistors is provided on a second substrate, and both substrates are butted, In a thermal head having a configuration in which each of the heating resistors and the output part of the shift register are connected by wire bonding, the heating resistor array is provided with the heating resistors in a number smaller than the number of bits of the shift register. , a thermal head characterized in that the common electrode is widened to compensate for the reduction in the number of bits. 2. On the first substrate, the heat generating resistor array is formed of N heat generating resistors, and a width W_1 is provided at each end of the heat generating resistor array.
the common electrode, and the second substrate,
A shift register row having a number of bits of n bits×m (however, N<n×m) and common electrodes each having a width of W_2 are provided at both ends of the shift register row, and a Bits and b bits from the other end (a+b=n×m-N) are not connected to the heating resistor, respectively, and the width of the common electrode is set to W_1.
The thermal head according to claim 1, characterized in that the thermal head is configured so that ≧W_2. 3. The heating resistor array is provided on the first substrate, the shift register array is provided on the second substrate, and the length L_r occupied by the heating resistor array and its wiring pattern is determined by the shift register array. L_r≦L_s with respect to the length L_s occupied by the shift register, and the width W_1 of the common electrode provided close to both sides of the heating resistor row is the width of the common electrode provided close to both sides of the shift register. The thermal head according to claim 1, wherein the thermal head is configured such that W_1≧W_2 with respect to W_2. 4. Form a common electrode on the first substrate facing the output pad portions that are not connected to the heating resistor at the left and right ends of the shift register row, and
The thermal head according to claim 2 or 3, characterized in that 1>W_2. 5. The thermal head according to claim 2 or 3, wherein the shift registers located at the left and right ends of the shift register array on the second substrate are provided offset to the inside of the head. 6. Place the first substrate and the second substrate against each other with a step so that the top surface of the first substrate and the top surface of the shift register are approximately at the same height. 6. The thermal head according to claim 1, further comprising a connection between the heating resistor, the output section of the shift register, and each common electrode. 7. The first substrate is a ceramic substrate, and the second substrate is a ceramic substrate.
7. The thermal head according to claim 1, wherein the substrate is a non-ceramic substrate.