JPH0584946A - Thermal printing head substrate and production thereof - Google Patents

Abstract

PURPOSE:To achieve cost reduction by reducing the use amount of gold by forming a fine wiring pattern using gold and forming other wiring pattern using a silver material if necessary. CONSTITUTION:Gold paste is applied only to a region where fine wiring patterns 8 must be formed by screen printing and baked to form a gold film 9. Continuously, wiring patterns other than the fine wiring patterns among the respective wiring patterns to be formed on a material substrate, that is, a common wiring pattern 5 and signal wiring patterns 6 are formed by a screen printing method using silver paste. As the silver paste, one containing only silver may be used or silver/palladium paste containing silver and palladium may be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal print head substrate and a method of manufacturing the same, and more particularly to a thermal print head substrate which is manufactured by following the same manufacturing steps as before and reducing the amount of gold used.

[0002]

2. Description of the Related Art A so-called line type thermal print head is usually constructed such that a linearly extending heating resistor formed on a substrate is driven by a dedicated drive IC for each predetermined number of dots. is there. The drive I disposed on one side of the heating resistor is disposed on the head substrate.
A fine wiring pattern for connecting C and the heating element,
Various wiring patterns are formed, such as a wiring pattern for connecting the external connection terminal and the drive IC, and a common wiring pattern routed from the external connection terminal to the other side of the heating resistor.

Conventionally, these wiring patterns are usually formed as follows. First, a gold film is formed on the entire surface or almost the entire surface of the material substrate by a so-called thick film printing method, and then unnecessary portions are removed by a photo-etching method, thereby forming the respective wiring patterns at once. Then, in order to increase the thickness of the common wiring pattern and reduce the voltage drop, in some cases,
A gold or silver pattern is further overlaid on the common wiring pattern to form a print.

Next, a heating resistor is formed in the heating resistor forming portion on the wiring pattern by a thick film printing method consisting of screen printing and firing, and a protective glass is formed in a necessary portion on the material substrate by the thick film printing method. To do. Thus, on the head substrate on which the basic wiring pattern is formed, bonding of the driving IC and wire bonding between the pad on the driving IC and a predetermined wiring pattern are performed, and further, the driving IC is arranged. A resin coat is applied to the exposed portion in order to protect the IC surface and the bonding wire.

[0005]

By the way, the wiring pattern formed between the heating resistor and the driving IC has a dot length of 1 mm and a ratio of 8 dots. Since it is for driving, it is extremely fine, and since a relatively large current flows, it is indispensable to use gold that is not only strong against electrical corrosion such as so-called migration but also strong against oxidation. Conventionally, since it is necessary to form such a fine wiring pattern with gold, all the wiring patterns to be formed on the material substrate, including the other wiring patterns, are formed with gold. Therefore, the amount of gold used is relatively large, which is one of the reasons for increasing the manufacturing cost of the thermal print head substrate.

As a conductive material resistant to migration,
Attempts have been made to reduce the cost of forming wiring patterns using copper, but in this case, it is necessary to perform pattern formation using copper in a nitrogen atmosphere so that oxidative corrosion does not occur before the protective glass printing firing step. However, this rather increases the cost of the entire manufacturing process and cannot be adopted suddenly.

By the way, of the various wiring patterns to be formed in the material substrate, it is substantially essential to use gold as described above for the fine pattern to be formed between the heating resistor and the drive IC. The condition is that it is between the external connection terminal of the substrate and the drive IC or each drive I
Regarding wiring patterns provided to electrically connect between Cs, currents flowing through these wirings are logic currents, and particularly in a C-MOS type IC, almost no current flows on the signal wiring side and migration or the like occurs. I have almost no worries. The wiring pattern to be formed between the external connection terminal and the driving IC includes a wiring for power ground in addition to the wiring pattern for signal wiring in which almost no current flows as described above. Although a large current flows, there is a relatively large space between the drive IC and the external terminal, so that the wiring pattern itself can be formed wide.

The invention of the present application was conceived based on the above knowledge, and the thermal printing capable of reducing the amount of gold used and reducing the cost while following the steps similar to the conventional ones. It is an object of the present invention to provide a head substrate and a manufacturing method thereof.

[0009]

In order to solve the above problems, the present invention takes the following technical means. That is, the thermal printhead substrate according to claim 1 of the present application is a drive that is to be mounted on the surface of the substrate from the placement portion of the heating resistor to be formed in a straight line to one side of the heating resistor placement portion. A fine wiring pattern formed up to the IC placement portion, a common wiring pattern routed from the external connection terminal portion to the other side of the heating resistor placement portion, an external connection terminal portion and the drive IC Control signal input
In a thermal print head substrate provided with a signal wiring pattern formed to achieve electrical connection with an output section and signal connection between each driving IC, among the above wiring patterns,
At least the fine wiring pattern is formed of gold, and the other wiring patterns are formed of a silver-based material as needed.

According to a second aspect of the present invention, there is provided a method of manufacturing a thermal print head substrate, wherein the heating resistor arranging portion, which is to be formed in a straight line on the surface of the substrate, is disposed on one side of the heating resistor arranging portion. IC to be mounted on
A fine wiring pattern formed while reaching the placement portion of
A common wiring pattern that is routed from the external connection terminal to the other side of the heating resistor arrangement section, conduction between the external connection terminal and the control signal input / output section of the drive IC, and a signal between each drive IC. A method of manufacturing a thermal printhead substrate including a signal wiring pattern formed for connection, wherein a step of forming a gold film is limited to a region where the fine wiring pattern is formed, and the gold film is etched. By the step of forming a fine wiring pattern,
Forming a wiring pattern other than the fine wiring pattern by screen printing and firing using a silver-based material; forming a heating resistor in the heating resistor placement portion on the fine wiring pattern by screen printing and firing; It is characterized by including.

[0011]

According to the present invention, of various wiring patterns to be formed on the thermal print head substrate, fine pattern formation is required and the conduction current is large. Only the fine wiring pattern extending to the heat generating resistor arranging portion or the drive IC arranging portion, which is required to be resistant to corrosion, is subjected to pattern formation using gold and a photoetching method. The other wiring patterns are formed by using a silver-based material instead of using gold, and by a pattern forming method including screen printing and firing. Therefore, the area to be patterned with gold is significantly smaller than that of the conventional method, so the cost of silver-based material is sufficient compared to gold, even if the area where silver-based material is used instead of gold is increased. Therefore, the material cost of the wiring pattern is reduced as a whole.

In addition, the present invention does not add a special process as compared with the conventional one, but follows the same process as the conventional one. That is, in the related art, there is a pattern forming step using a silver-based material by screen printing and firing to reinforce the common wiring pattern. In the present invention, a thick film using such a silver-based material is used. It only widens the area for pattern formation by the printing method. Therefore, when implementing the present invention, the number of steps does not increase, and a special method is not adopted. Therefore, there is no factor that raises the cost for the pattern formation, and eventually the manufacturing cost of the thermal print head substrate according to the present invention is reduced as compared with the conventional one.

Wiring patterns other than the above-mentioned fine wiring pattern to be formed by gold have a large pattern forming area even though there is a portion where a relatively large amount of current flows. Therefore, a wide pattern is sufficient. Therefore, the deterioration of electrical characteristics due to the practice of the present invention does not occur.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 schematically shows a typical configuration example of a head substrate 1 on which a line type thermal print head is to be formed.

On one side of the surface of a rectangular strip-shaped material substrate 2 made of ceramic, a heating resistor 3 extending linearly in parallel with the side edge is formed. On one side of the heating resistor 3, a plurality of drives are provided to drive the heating resistor 3 divided into blocks each having a predetermined number of dots (usually 128 dots) in the longitudinal direction. The ICs 4 ... Are arranged in a row at a position deviated from the heating resistor 3 by a certain distance in the width direction of the substrate.
On the other side of the heating resistor 3, a common wiring pattern 5 is provided.
Have been routed around. Further, the area between the arrangement area of the drive ICs 4 ... Etc. above each drive IC4
A wiring pattern (for convenience, this is referred to as a signal wiring pattern) for electrically connecting to each other is formed. Further, the ends of the common wiring pattern 5 are connected to the terminal portions 7 provided on the other side edge 2 a of the substrate at both ends in the longitudinal direction of the material substrate 2.

Wirings for the logic power supply (VDD), strobe signal, clock pulse signal, power ground, logic ground, etc., which should be conducted to the signal system pads of the drive IC 4 may be commonly connected to the corresponding pads of each drive IC. In the configuration example shown in FIG. 1, a so-called flexible substrate for external connection in which such common connection is superposed and connected to the external connection terminal portion 7 arranged on the other side edge 2b of the material substrate 2. It is of the type achieved by. In addition, the data signal may be substantially cascade-connected between the data-in pad and the data-out pad in each drive IC.
In the configuration example shown in (1), this is achieved by temporarily moving the external connection terminal portion 7 to the flexible connection board side.

However, by devising a wiring pattern to be formed in a band-shaped region having a predetermined width between the arrangement region of the drive ICs 4 ... And the other side edge 2b of the material substrate 2,
Even without the help of the flexible external connection board,
The common connection described above can also be achieved. For this purpose, for example, a wiring pattern of a signal, such as a strobe signal pattern and a logic power supply pattern, which can be commonly connected to the corresponding pad of each drive IC 4, is formed in the above-mentioned strip-shaped region so as to extend in the longitudinal direction of the substrate. Wire bonding between the wiring pattern and the pad on the drive IC may be performed.

In any case, the area between the arrangement area of the drive ICs 4 ...
A pattern for supplying a signal or electric power to C4 and further for connecting a ground is formed, so that it is possible to form a wide pattern with a relatively large margin. The same is true for.

On the other hand, the heating resistor 3 and each drive I
In the area between the arrangement area of C4 ..., From the dot corresponding portion to the vicinity of the output pad arrangement side of the drive IC 4 in order to individually drive each of the dots divided in the longitudinal direction of the heating resistor 3 to generate heat. A fine comb-tooth-shaped wiring pattern 8 that extends is formed. As well shown in FIG. 2, in the portion where the heating resistor 3 is to be formed, the control-side comb tooth-shaped patterns 8a extending in parallel from the drive IC 4 side and having a parallel shape.
Between the unit patterns 8b, ..., Common patterns 5a, 5b ,.
Is in. In the figure, these fine patterns 8a, 8b, ..., 5a, 5b,
Although the intervals of ... are shown widened, in reality, the pitch of these patterns 8a, 8b, ... is 8 within a length of 1 mm.
When forming dots, the intervals are as small as 125 μm. Therefore, each pattern 8a, 8
The pattern widths of b, ..., 5a, 5b, ... Are too small to be formed by screen printing.

If the individual pattern indicated by reference numeral 8a is turned on among the control side fine patterns 8, two individual common patterns 5a located on both sides of the individual pattern 8a in the heating resistor 3 are sandwiched. , 5b, a substantially rectangular area defined by the distance between the two ends of the line 5b, 5b generates heat.

Conventionally, the fine wiring pattern 8 is used.
(Including the comb-teeth-shaped common patterns 5a, 5b ...), the common wiring pattern 5 routed along the arrangement area of the heating resistor 3, and the arrangement area of the drive IC 4 and the other side edge 2b of the material substrate. All of the various signal wiring patterns 6 formed between them were formed by a photo-etching method using gold as a material. That is, the gold paste is printed and applied on the entire surface of the material substrate 2, and the gold paste is baked to form a gold film, and then unnecessary portions are removed by a photoetching method, and all of the above wiring patterns 5, 6, 8 are formed. Had formed.

In the present invention, each of the above wiring patterns is
It is formed as follows. First, as shown in FIG. 3, the gold wiring 9 is screen-printed using a gold paste in a region where the fine wiring pattern 8 shown in FIG. .. In this embodiment, in addition to the area where the fine pattern 8 is to be formed, the gold coating is also formed on the area of a predetermined width along the other side edge 2b of the material substrate 2. This is because it is preferable to form the external connection terminal portion 7 with gold in order to reduce the situation where the external connection terminal portion 7 has poor conduction. Then, the gold film 9 formed by limiting the area as described above
On the other hand, by applying a photo-etching technique, unnecessary portions are removed to form a fine pattern 8 as shown in FIG. At this time, the external connection terminal portion 7 is also formed at the same time.

Then, as shown in FIG. 5, among the wiring patterns to be formed on the material substrate, wiring patterns other than the fine wiring pattern 8 described above, that is, the common wiring pattern 5 and the signal wiring pattern 6, are formed. It is formed by a screen printing method using a silver paste. That is, the pattern itself is formed by the screen printing method. The molding method by such printing is the same as the conventional thick film printing method. As a silver paste,
It may contain only silver, or may be a so-called silver-palladium paste containing silver and palladium. These common wiring pattern 5 and signal wiring pattern 6
Unlike the fine wiring pattern 8 as described above, since it can be formed as a wiring pattern having a sufficient width, it can be formed without problems by a so-called thick film printing method. Further, even if the pattern is made of silver, since the pattern width is sufficient, there is no adverse effect on the electrical characteristics of the thermal print head as a whole.

After the wiring patterns 5, 6 and 8 are formed in this manner, a heating resistor 3 is formed by thick film printing in the heating resistor forming region of the fine pattern 8 as shown in FIG. Further, a glass protective film (not shown) is formed in a predetermined region on the substrate by using a thick film printing method.

Then, the drive IC 4 is bonded to a predetermined portion, the pad on the IC 4 and the signal wiring pattern 6 are wire-bonded, and the position is adjacent to the drive IC 4 of the fine wiring pattern 8. The respective end portions of the drive IC 4 and the output pads on the drive IC 4 are wire-bonded. The drive IC 4 and the area bonded by wire bonding are often covered with a resin coat (not shown).

As described above, in the thermal print head substrate of the present invention, the portion where the pattern is formed by the photo-etching method using gold extends from the arrangement area of the heating resistor 3 to the arrangement area of the drive IC. Since it is limited to only the fine wiring pattern formation part between,
It is possible to significantly reduce the amount of gold used as compared with the conventional method in which all the wiring patterns are made of gold.

On the other hand, although the range in which the pattern should be formed is increased by the silver-based material, the cost of silver is much lower than the price of gold, so that the cost can be reduced as a whole. Further, even in the conventional case, since it is usual to form the common reinforcing pattern using the silver paste in order to reduce the voltage drop of the common wiring pattern 5, the number of steps is also the same as the conventional case, and therefore, There is no additional step in carrying out the present invention, and it is possible to manufacture at a low cost by directly following the conventional pattern forming method of the head substrate.

Of course, the scope of the present invention is not limited to the above embodiments. In particular, as to the arrangement configuration of the patterns, as described in the first half of the description of the embodiment, as a mode of the signal wiring pattern 6,
As a method for substantially common connection (parallel connection) of pads between ICs, as shown in the illustrated example, when the flexible circuit board is used, the common connection may be achieved by a pattern on the flexible board. In the area where the signal wiring pattern 6 is formed, a pattern for supplying a signal or electric power that allows parallel connection between the respective driving ICs is arranged so as to extend in the longitudinal direction of the substrate, and a predetermined portion of the pattern corresponds to the IC. The pads may be connected by wire bonding.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing a typical configuration example of a thermal printhead substrate.

FIG. 2 is a partially enlarged plan view of the thermal print head substrate shown in FIG.

FIG. 3 is a plan view showing one step of the manufacturing method of the present invention, showing a state in which a gold coating is formed in a limited region.

FIG. 4 is a diagram showing one step of the manufacturing method of the present invention, and is a plan view showing a state in which a fine wiring pattern is formed by subjecting the gold film shown in FIG. 3 to photoetching.

FIG. 5 is a diagram showing one step of the manufacturing method of the present invention, in which a common wiring pattern and a signal wiring pattern are further formed from the state shown in FIG. 4 by screen printing and firing using a silver-based material. FIG.

[Explanation of symbols]

 1 Thermal Print Head Substrate 2 Material Substrate 3 Heating Resistor 4 Drive IC 5 Common Wiring Pattern 6 Signal Wiring Pattern 7 External Connection Terminal 8 Fine Wiring Pattern 9 Gold Film

Claims (2)

[Claims] 1. A surface of a substrate is formed between a heat generating resistor arranging portion to be formed in a straight line and a drive IC arranging portion to be mounted on one side of the heat generating resistor arranging portion. A fine wiring pattern, a common wiring pattern drawn from the external connection terminal portion to the other side of the heating resistor arrangement portion, conduction between the external connection terminal portion and the control signal input / output portion of the drive IC, and In a thermal print head substrate including a signal wiring pattern formed for signal connection between drive ICs, at least the fine wiring pattern is formed from gold among the wiring patterns, and a wiring pattern other than the above is required. A thermal print head substrate, characterized in that it is formed of a silver-based material. 2. The surface of the substrate is formed between the placement portion of the heating resistor to be formed in a straight line and the placement portion of the drive IC to be mounted on one side of the heating resistor placement portion. A fine wiring pattern, a common wiring pattern drawn from the external connection terminal portion to the other side of the heating resistor arrangement portion, conduction between the external connection terminal portion and the control signal input / output portion of the drive IC, and A method of manufacturing a thermal printhead substrate, comprising: a signal wiring pattern formed for signal connection between drive ICs; a step of forming a gold film only in a region where the fine wiring pattern is formed; To form a fine wiring pattern by etching, wiring patterns other than the fine wiring pattern are screen-printed and baked using a silver-based material. And a step of forming a heating resistor on the heating resistor arrangement portion on the fine wiring pattern by screen printing and firing.