JP2820870B2 - Thermal head and manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head and, more particularly, to a thermal head having improved electrical connection failure by wire bonding.

[0002]

2. Description of the Related Art A thermal head is an electronic component for printing on thermal paper or the like by heat. It is used for a facsimile or a print output unit of a printer. With the miniaturization and portability of these devices, the thermal head is required to be further miniaturized and to have improved reliability and quality.

FIG. 9 is a cross-sectional view of a conventional thermal head disclosed in Japanese Patent Publication No. 5-5668. In FIG. 9, 1 is a heating resistor, 2 is a first substrate, 3 is a second substrate, 4 is an integrated circuit (IC), 5 is a bonding wire,
6 is a protective resin and 7 is a heat sink. FIG.
3 is a process flowchart for explaining a conventional thermal head manufacturing process.

In a conventional thermal head, first, a first substrate 2 made of ceramic or the like having a plurality of heating resistors 1 is made of a printed wiring board (PCB) such as a glass cloth base epoxy resin copper-clad laminate. And so on, on a second substrate 3 made of the same. According to the structure of the conventional thermal head, the integrated circuit 4 for driving the heating resistors 1 is mounted on the second substrate 3, and the output of the switching circuit to each heating resistor 1 is connected to the bonding wire 5A. Through integrated circuit 4
It is connected to a pattern (not shown) on the first substrate 2. Further, a control signal from an external CPU or the like is input to the integrated circuit 4 from a pattern (not shown) of the second substrate 3 via the bonding wires 5B.

A bonding wire 5 used in a conventional thermal head is made of gold (Au) or aluminum (A).
1) (approximately 25 μm). On the other hand, since the second substrate 3 is made of a printed wiring board or the like, the glass transition point (also referred to as “glass transition temperature”) is about 130 ° C. Therefore, when the integrated circuit 4 is mounted, the bonding wire 5B is wire-bonded to the integrated circuit 4 and the second substrate 3 and to the integrated circuit 4 and the first substrate 2 at a temperature of 130 ° C. or less. ing.

[0006] The mounted integrated circuit 4 is sealed and protected by a protective resin 6. Generally, the coefficient of linear expansion of the first substrate 2 made of ceramic or the like is different from the coefficient of linear expansion of the second substrate 3 made of a printed wiring board or the like. For this reason, as the protective resin 6, a silicone resin having a low hardness is used to alleviate the middle shrinkage caused by the difference in the linear expansion coefficient.

[0010] The manufacturing process of a conventional thermal head will be described in detail. As shown in FIG. 10, first, a pattern, a heating resistor 1 and a protective film are formed on a first substrate 2 (S201). Next, the first substrate 2 is divided (S20).
2). Next, the first substrate 2 and the second substrate 3 are joined (S203). IC die bonding is performed on the second substrate 3 (S204). Then, the first substrate 2 and the integrated circuit 4
Are bonded by bonding wires 5A, and the second substrate 3 and the integrated circuit 4 are bonded by bonding wires 5B (S205). At this time, as described above, the wire bond connection is performed at about 130 ° C. or lower of the glass transition point of the second substrate 3. Thereafter, the protective resin 6 is coated on the integrated circuit 4 and its vicinity (S206).

[0008]

However, as described above, since the second substrate is formed of a printed wiring board (PCB) such as a glass cloth base epoxy resin copper-clad laminate or the like, the second substrate is When the integrated circuit and the second substrate and the integrated circuit are connected by wire bonding, if the glass transition temperature (Tg) of the second substrate is 130 ° C. or more, the printed wiring board and the like are softened, and a stable wire is formed. There is a problem that the bonding strength of bonding cannot be obtained. This causes a reduction in the reliability of the thermal head.

For example, in the case of an A4 size thermal head, since it has a heating resistor of 1728 bits (bits), wire bonding between the first substrate and the integrated circuit at 1728 or more places and the second board at about 200 places or more are made. Bonding between the substrate and the integrated circuit is performed. In general,
In order to connect at a high speed a total of 2,000 or more wire bondings, a gold ball bonding method is used. According to this method, it is generally known that stable wire bonding can be performed by setting the substrate temperature to about 200 ° C. to 250 ° C.

On the other hand, the gold wire bonding temperature in the conventional thermal head is the glass transition temperature (T
The temperature was 130 ° C. or lower due to the influence of g). Therefore, the preferable bonding temperature of gold wire bonding is 200 ° C. to 250 ° C.
Bonding must be performed at a temperature lower than ℃, and there has been a problem that defective wire bonding frequently occurs.

In practice, the surface temperature of the second substrate is set to 130
When the temperature is set so as to be set to about 110 ° C., the surface temperature of the first substrate provided thereon becomes about 110 ° C. Therefore, A
More than 1728 wire bond bonds in four sizes are actually performed at extremely low temperatures.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to stably perform wire bonding between a substrate and an integrated circuit, and to provide a highly reliable, high quality, and miniaturized thermal. Is to provide a head. Another object of the present invention is to provide a thermal head having a function integrated with a system such as a facsimile or a printer.

[0013]

Means for Solving the Problems In order to solve the above problems, the thermal head according to the present invention has the following features.

(1) First where a plurality of heating resistors are formed
And a second substrate on which a detection element for detecting the presence or absence of thermal paper or an operation instruction mark including an end mark and a start mark is mounted. When an integrated circuit for driving a body is formed and the integrated circuit is electrically connected to the first substrate, wire bonding is performed at a temperature equal to or higher than the glass transition temperature of the second substrate. When electrically connecting to the substrate, wire bonding is performed below the glass transition temperature of the second substrate.

(2) First where a plurality of heating resistors are formed
And a second substrate on which a detection element for detecting the presence or absence of thermal paper or an operation instruction mark including an end mark and a start mark is mounted. When an integrated circuit for driving a body is formed and the integrated circuit is electrically connected to the first substrate, wire bonding is performed at 200 ° C. to 250 ° C. to electrically connect the integrated circuit and the second substrate. In the case of the connection, the wire bonding is performed at 130 ° C. or less.

(3) First where a plurality of heating resistors are formed
And a second substrate mounted with a detection element for detecting the presence or absence of thermal paper or an operation instruction mark including an end mark and a start mark, wherein the first substrate is provided on the second substrate. An integrated circuit for driving the heating resistor is formed on the first substrate, and when the integrated circuit is electrically connected to the first substrate, the integrated circuit is connected to the second substrate. When the integrated circuit is electrically connected to the second substrate at a temperature higher than the glass transition temperature, the wire bonding is performed at a temperature lower than the glass transition temperature of the second substrate.

(4) First where a plurality of heating resistors are formed
And a second substrate mounted with a detection element for detecting the presence or absence of thermal paper or an operation instruction mark including an end mark and a start mark, wherein the first substrate is provided on the second substrate. An integrated circuit for driving the heating resistor is formed on the first substrate, and when the integrated circuit is electrically connected to the first substrate, the integrated circuit is connected to the second substrate. When wire bonding is performed at a temperature equal to or higher than the glass transition temperature and the integrated circuit is electrically connected to the second substrate, wire bonding is performed at a temperature equal to or lower than the glass transition temperature of the second substrate, and the second substrate dissipates heat. It is arranged on a heat sink.

(5) First where a plurality of heating resistors are formed
And a second substrate mounted with a detection element for detecting the presence or absence of thermal paper or an operation instruction mark including an end mark and a start mark, wherein the first substrate is provided on the second substrate. An integrated circuit for driving the heating resistor is formed on the first substrate, and when the integrated circuit is electrically connected to the first substrate, the integrated circuit is connected to the second substrate. When wire bonding is performed at a temperature equal to or higher than the glass transition temperature and the integrated circuit is electrically connected to the second substrate, wire bonding is performed at a temperature equal to or lower than the glass transition temperature of the second substrate, and the second substrate dissipates heat. The heat sink has arms at both ends so as to sandwich a platen roller in contact with the heating resistor.

That is, in the thermal head according to the present invention, an integrated circuit (IC) is mounted on a first substrate, and the integrated circuit and the first circuit are mounted before the step of bonding the first substrate and the second substrate.
And a heat sink having a mechanism for positioning the heat-sensitive paper detecting element and the center of the platen roller with the heating resistor.

The method for manufacturing a thermal head according to the present invention has the following features.

(1) A heating resistor forming step of forming a plurality of heating resistors on the first substrate, and a detection of detecting presence or absence of thermal paper or an operation instruction mark including an end mark and a start mark on the second substrate. A mounting step of mounting an element, an integrated circuit mounting step of mounting an integrated circuit for driving the heating resistor on the first substrate, and a glass transition of the second substrate to the first substrate. A first connection step of electrically connecting by wire bonding at a temperature equal to or higher than a temperature, a bonding step of bonding the first substrate and the second substrate,
A second connection step of electrically connecting the second substrate and the integrated circuit by wire bonding at a temperature equal to or lower than the glass transition temperature of the second substrate.

(2) A heating resistor forming step for forming a plurality of heating resistors on the first substrate, and detection for detecting presence or absence of thermal paper on the second substrate or an operation instruction mark including an end mark and a start mark. A mounting step of mounting an element, an integrated circuit mounting step of mounting an integrated circuit for driving the heating resistor on the first substrate, and wire-bonding the first substrate and the integrated circuit at 200 ° C. to 250 ° C. A first connection step of electrically connecting by bonding, a bonding step of bonding the first substrate and the second substrate, and a wire bonding of the second substrate and the integrated circuit at 130 ° C. or less by wire bonding. A second connection step of making electrical connection; and a coating step of coating the integrated circuit with a protective resin.

[0023]

In the thermal head of the present invention constructed as described above, the integrated circuit for driving the heating resistor is mounted on the first substrate, and the first substrate is bonded to the second substrate before the first substrate is joined to the second substrate. Suitable temperature (200 ° C to 250 ° C) for gold wire bonding because the substrate 1 and the integrated circuit are wire bonded.
Can be done with For this reason, the failure rate of wire bonding between the first substrate and the integrated circuit is reduced, and the reliability of the thermal head is improved.

Further, by mounting an integrated circuit for driving the heating resistor on the first substrate, the area of the second substrate can be reduced. Therefore, the size of the thermal head can be reduced.

Further, by disposing a heat sink for heat radiation below the second substrate, heat radiation of the thermal head is improved. Arms for sandwiching a platen roller in contact with the heat generating resistor are provided at both ends of the heat sink. Thus, the arrangement of the bracket for positioning the center of the platen roller and the heating resistor can be omitted. Therefore, the size of the thermal head can be reduced.

In the method of manufacturing a thermal head according to the present invention, after the integrated circuit mounting step of mounting the integrated circuit for driving the heating resistor on the first substrate, the first substrate and the integrated circuit are bonded by wire bonding. Performing a first connection step of electrically connecting, and thereafter performing a step of joining the first substrate and the second substrate, and performing a second connection for electrically connecting the second substrate and the integrated circuit; I decided to do the process. Therefore, wire bonding between the first substrate and the integrated circuit can be performed at a temperature suitable for wire bonding (equal to or higher than the glass transition temperature of the second substrate, for example, 200 ° C. to 250 ° C.). When wire bonding the second substrate and the integrated circuit, the wire bonding can be performed at a temperature equal to or lower than the glass transition temperature of the second substrate (130 ° C. or lower). For this reason, the failure rate of wire bonding between the first substrate and the integrated circuit is reduced, and the reliability of the thermal head is improved.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

First Embodiment FIG. 1 is a sectional view of a first embodiment of a thermal head according to the present invention. FIG. 2 is a perspective view of the first embodiment of the thermal head according to the present invention. FIG. 3 is an enlarged perspective view of a main part of the first embodiment of the thermal head according to the present invention.
FIG. 4 is a process flowchart illustrating a method for manufacturing the thermal head according to the first embodiment of the present invention. The same or equivalent parts as those of the conventional one are denoted by the same reference numerals,
Description is omitted.

1 to 3, reference numeral 4 denotes a heating resistor 1;
Is an integrated circuit (IC) die-bonded on the first substrate 2 having 1 and 3, 5A
Are bonding wires connected from the integrated circuit 4 to the bonding pads 10A in the pattern wired on the first substrate 2. 5B is the integrated circuit 4
To the bonding wires connected to the bonding pads 10B in the pattern on the second substrate 3. Reference numeral 8 denotes an adhesive resin for joining the first substrate 2 and the second substrate 3, and usually a double-sided tape or an elastic adhesive is used. Reference numeral 9 denotes a connector provided at the lower end of the second substrate 3 and serving as an interface with an external circuit.

The thermal head of this embodiment is manufactured by the steps shown in FIG.

First, a pattern, a plurality of heating resistors and a protective film are formed on the first substrate 2 (S101). Normal,
The first substrate 2 is designed to manufacture a plurality of thermal heads. A feature of the present invention is that the integrated circuit 4 is mounted on the first substrate 2 while maintaining the original substrate size including the plurality of units, and the bonding pads 10B and the integrated circuit 4 in the pattern on the first substrate 2 Is connected by wire bonding. That is, the integrated circuit 4 is die-bonded on the first substrate 2 (S102). Then, the first substrate 2 is heated at 250 ° C., which is a temperature suitable for gold wire bonding.
The bonding pads 10A in the upper pattern and the integrated circuit 4 are wire-bonded (S103). Then, the first substrate 2 is divided, and the first substrate 2 and the second substrate 3 are joined with the adhesive resin 8 (S104). Then, a printed wiring board (PC such as glass cloth base epoxy resin copper clad laminate)
B) or lower (1)
At 30 ° C. or lower), wire bonding is performed from the integrated circuit 4 to the bonding pad 10B in the pattern wired on the second substrate 3 (S105). afterwards,
The protective resin 6 is coated on the integrated circuit 4 and its vicinity (S
206).

The following advantages are obtained by having the above configuration and manufacturing process. That is, the first
After the substrate 2 and the integrated circuit 4 are wire-bonded,
Since the first substrate 2 and the second substrate 3 are joined together, the preferable temperature for gold wire bonding is 200 ° C.
At 250 ° C., the integrated circuit 4 can be wire-bonded to the first substrate 2 made of ceramic or the like. Thereby, the bonding strength between the bonding wires 5A and the bonding pads 10A in the pattern on the first substrate 2 can be stabilized.

According to the experiment of the present inventors, it was found that the gold pattern formed on the glazed ceramic substrate
When a gold bonding wire having a purity of 99.9% of 5 μm is mounted by wire bonding, the thermal head obtained by the conventional configuration and manufacturing process (that is, wire bonding at 130 ° C. or lower) has an average value of 2 to 2 in the bonding pull test. It has been confirmed that the average value is improved to about 9 g in the case of the thermal head of the present invention, while it is about 3 g. This is considered to be because the chemical reaction between the gold wire bonding 5A and the bonding pad 10A was promoted by heat.

Further, the first substrate 2 is divided into individual units, and the first substrate 2 and the second substrate 3 are joined together.
And the bonding pads 10B of the second substrate 3 are wire-bonded, so that the softening point of the second substrate 3 made of a printed wiring board (PCB) such as a glass cloth base epoxy resin copper-clad laminate or the like is lower than the softening point. That is, wire bonding can be performed at a glass transition temperature or lower (130 ° C. or lower).

Usually, the number of wire bondings on the entire surface of the thermal head is [1728 bits + about 200 bits] as described above, which is about 2000 bits or more in total. The number of wire bonds to the first substrate 2 accounts for about 90% of the whole.

Therefore, according to the present invention, the defective rate of wire bonding is greatly reduced, and the reliability of the thermal head is also improved.

Second Embodiment Next, a description will be given of a second embodiment of the thermal head according to the present invention.

FIG. 5 is a sectional view of a second embodiment of the thermal head according to the present invention. FIG. 6 is a perspective view of a second embodiment of the thermal head according to the present invention. The same reference numerals are given to the same or corresponding portions as those of the conventional one, and the description is omitted.

Reference numeral 11 denotes a detecting element for detecting the size of the thermal paper, the presence / absence of the thermal paper, or the end mark / start mark. The detection element 11 is mechanically and electrically joined to the second substrate 3 by an adhesive or soldering. Thus, an electrical signal with a photosensor or a detection element such as a limit switch can be output to the outside via the connector 9 of the second substrate 3.

Third Embodiment Next, a third embodiment of the thermal head according to the present invention will be described.

FIG. 7 is a side view of a third embodiment of the thermal head according to the present invention. FIG. 8 is a perspective view of a third embodiment of the thermal head according to the present invention. The same reference numerals are given to the same or corresponding portions as those of the conventional one, and the description is omitted.

Reference numeral 7 is a heat sink for radiating heat of the thermal head. Thereby, the heat of the thermal head can be released. The feature of this embodiment is that this heat sink 7 has arms protruding from both ends of the thermal head as shown at 7A in FIGS. This arm
It has a role of a positioning mechanism for sandwiching the outer diameter of the platen roller 12 and positioning the platen roller 12 and the heating resistor 1.
This eliminates the need for a positioning bracket separately attached to the conventional thermal head, and can further reduce the size of the thermal head.

In the above embodiment, the platen roller 1
Although the mechanism for sandwiching the outer diameter of the platen roller in positioning the center of the heating resistor 2 and the heating resistor 1 has been described, the heating resistor 1 and the pins already positioned are arranged from both ends of the heat sink 7 of the thermal head. The same effect can be obtained by positioning the center of the platen roller 12 and the heating resistor 1 via the head housing.

[0044]

As described above, in the thermal head of the present invention, the integrated circuit for driving the heating resistor is mounted on the first substrate, and the first substrate is bonded to the second substrate before the first substrate is joined to the second substrate. 1
Since the substrate and the integrated circuit are bonded by wire, the bonding can be performed at a preferable temperature (200 ° C. to 250 ° C.) for gold wire bonding. Thereby, the defect rate of wire bonding between the first substrate and the integrated circuit is reduced, and the reliability of the thermal head can be improved.

Further, by mounting an integrated circuit for driving the heating resistor on the first substrate, the area of the second substrate can be reduced. Therefore, the size of the thermal head can be reduced.

Further, by disposing a heat sink for heat radiation below the second substrate, heat radiation of the thermal head is improved. Arms for sandwiching a platen roller in contact with the heating resistor are provided at both ends of the heat sink. Thus, the arrangement of the bracket for positioning the center of the platen roller and the heating resistor can be omitted, and the thermal head can be reduced in size.

In the method of manufacturing a thermal head according to the present invention, after the integrated circuit mounting step of mounting the integrated circuit for driving the heating resistor on the first substrate, the first substrate and the integrated circuit are bonded by wire bonding. Performing a first connection step of electrically connecting, and thereafter performing a step of joining the first substrate and the second substrate, and performing a second connection for electrically connecting the second substrate and the integrated circuit; The process was performed. Therefore, wire bonding between the first substrate and the integrated circuit can be performed at a temperature suitable for wire bonding (equal to or higher than the glass transition temperature of the second substrate, for example, 200 ° C. to 250 ° C.). When wire bonding the second substrate and the integrated circuit, the wire bonding can be performed at a temperature equal to or lower than the glass transition temperature of the second substrate (130 ° C. or lower). Thereby, the defect rate of wire bonding between the first substrate and the integrated circuit is reduced, and the reliability of the thermal head can be improved.

As described above, a small and high quality thermal head can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of a thermal head according to the present invention.

FIG. 2 is a perspective view of a first embodiment of the thermal head according to the present invention.

FIG. 3 is an enlarged perspective view of a main part of the first embodiment of the thermal head according to the present invention.

FIG. 4 is a process flowchart illustrating a method for manufacturing a thermal head according to a first embodiment of the present invention.

FIG. 5 is a sectional view of a second embodiment of the thermal head according to the present invention.

FIG. 6 is a perspective view of a second embodiment of the thermal head according to the present invention.

FIG. 7 is a side view of a third embodiment of the thermal head according to the present invention.

FIG. 8 is a perspective view of a third embodiment of the thermal head according to the present invention.

FIG. 9 is a sectional view of a conventional thermal head.

FIG. 10 is a process flowchart illustrating a conventional thermal head manufacturing process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating resistor 2 1st board 3 2nd board 4 Integrated circuit 5, 5A, 5B Bonding wire 6 Protective resin 7, 7A Heat sink 8 Adhesive resin 9 Connector 11 Detection element 12 Platen roller

Claims (7)

(57) [Claims] A first substrate 1. A plurality of heating resistors are formed, in a thermal head and a second printed circuit board, on the first substrate, an integrated circuit for driving the heating resistor Is formed, and when the integrated circuit is electrically connected to the first substrate, wire bonding is performed at a temperature equal to or higher than the glass transition temperature of the second substrate, and the integrated circuit and the second substrate are electrically connected. When connecting, the thermal head is wire-bonded below the glass transition temperature of the second substrate. A first substrate 2. A plurality of heating resistors are formed, in a thermal head and a second printed circuit board, on the first substrate, an integrated circuit for driving the heating resistor When the integrated circuit is electrically connected to the first substrate, wire bonding is performed at 200 ° C. to 250 ° C. When the integrated circuit is electrically connected to the second substrate, A thermal head which is wire-bonded at 130 ° C. or lower. A first substrate 3. A plurality of heating resistors are formed, in a thermal head and a second printed circuit board, the first substrate is disposed on the second substrate, the first An integrated circuit for driving the heating resistor is formed on the first substrate. When the integrated circuit is electrically connected to the first substrate, a wire is formed at a temperature equal to or higher than the glass transition temperature of the second substrate. A thermal head, wherein, when the integrated circuit is electrically connected to the second substrate, wire bonding is performed at a temperature equal to or lower than a glass transition temperature of the second substrate. A first substrate 4. A plurality of heating resistors are formed, in a thermal head and a second printed circuit board, the first substrate is disposed on the second substrate, the first An integrated circuit for driving the heating resistor is formed on the first substrate. When the integrated circuit is electrically connected to the first substrate, a wire is formed at a temperature equal to or higher than the glass transition temperature of the second substrate. When the integrated circuit and the second substrate are electrically connected, wire bonding is performed at a temperature equal to or lower than the glass transition temperature of the second substrate, and the second substrate is disposed on a heat sink for heat radiation. A thermal head, which is provided. A first substrate wherein the plurality of heating resistors are formed, in a thermal head and a second printed circuit board, the first substrate is disposed on the second substrate, the first An integrated circuit for driving the heating resistor is formed on the first substrate. When the integrated circuit is electrically connected to the first substrate, a wire is formed at a temperature equal to or higher than the glass transition temperature of the second substrate. When the integrated circuit and the second substrate are electrically connected, wire bonding is performed at a temperature equal to or lower than the glass transition temperature of the second substrate, and the second substrate is disposed on a heat sink for heat radiation. A thermal head, wherein the heat sink is provided with arms at both ends so as to sandwich a platen roller in contact with the heating resistor. 6.No.Forming multiple heating resistors on one substrate
Heating resistor forming process,  An integrated circuit for driving the heating resistor on the first substrate
An integrated circuit mounting step of mounting the first substrate and the integrated circuit on a glass of a second substrate
Electrical connection by wire bonding above the transition temperature
A first connecting step, and a joining step of joining the first substrate and the second substrate
And the second substrate and the integrated circuit are glass of a second substrate.
Electrical connection by wire bonding below the transition temperature
A method for manufacturing a thermal head, comprising: 7.No.Forming multiple heating resistors on one substrate
Heating resistor forming process,  An integrated circuit for driving the heating resistor on the first substrate
Mounting the first substrate and the integrated circuit at 200 ° C. to 250 ° C.
The first connection electrically connected by wire bonding at
A continuation step; and a bonding step of bonding the first substrate and the second substrate.
And bonding the second substrate and the integrated circuit at 130 ° C. or less.
Second connection step of electrically connecting by wire bonding
And a coating step of coating the integrated circuit with a protective resin.