JPH0159112B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal head for heat-sensitive recording, and in particular, a substrate forming a heating element and a substrate forming a multilayer wiring section of a semiconductor device for driving the heating element are separated. The present invention relates to an adhesive structure between a heating element substrate and a base of a heat-sensitive recording head in which these are integrated and held on one base.

As is well known, the thermal recording method is applied in various fields as a method for obtaining maintenance-free hard copies.

Among these various types of thermal heads, those with a large number of heating elements arranged in a row have become very popular in facsimile machines, but a very important problem with these types of heads is the low price of the heads. It is.

In a thermal head in which a large number of heating elements are arranged in a line, various semiconductor devices (semiconductor devices) are connected in series with the heating elements to facilitate driving of the heating elements. Currently, these semiconductor devices include ICs consisting of diodes, thyristors or shifters, registers, latches, and transistors.
etc. are used. In any of these semiconductor devices, multiple wirings are required for terminals other than the terminals connected to the heating element of the semiconductor device.

When using diodes as semiconductor devices, in the case of the so-called common diode method, one end of the diodes is commonly connected, so in this case, multilayer wiring is required for terminals that are not connected to the diode of the heating element. Become.

In order to reduce the price of these various thermal heads, approaches can be taken from various viewpoints, but in the case of so-called thin-film thermal heads, in which the heating element is formed using conventional thin film formation technology, A formation substrate and a multilayer wiring substrate are formed separately,
It has been proposed to reduce the cost of forming a heating element substrate by half or less by integrating and holding these two substrates on a thermal head base when semiconductor devices are mounted.

In a thermal head for heat-sensitive recording having such a configuration, the formation of a multilayer wiring board and the integral holding of the heating element board and the multilayer wiring board become factors that increase the manufacturing cost of the head.

However, compared to the method in which the heating element and multilayer wiring are formed on one substrate, the upper rail method reduces the heating element substrate size by half or less, so the heating element formation process, that is, the heating element, electrode The effect of more than doubling the capacity of each of the manufacturing equipment for thin film formation, heating element and electrode pattern formation, and wear-resistant layer formation has a significant cost reduction effect for the head as a whole.

The present invention provides a combination of a heating element substrate and a base that rationally solves the problem that occurs when the above-mentioned heating element substrate and multilayer wiring substrate are formed separately and then bonded to the base. This relates to adhesive configurations.

In order to facilitate understanding of the present invention, problems with conventional thermal heads for heat-sensitive recording will be explained below with reference to the drawings.

FIG. 1 is a wiring diagram of a heating element and a diode when a separate diode is used as a semiconductor device, where 1 is a heating element, 2 is a diode, and 3 is a multilayer wiring section.

FIG. 2 shows an example of the configuration of the head corresponding to FIG. 1.

In FIG. 2, 4 indicates the heating element 1 and the common electrode 6a,
The substrate 5 on which the individual electrodes 6b are formed is a multilayer wiring substrate, and on the multilayer wiring substrate 5, a multilayer wiring conductor 9 is formed. Generally, a wear-resistant layer is formed on the heating element 1, but this wear-resistant layer is omitted in FIG. 2. 2a is a semiconductor chip on which a plurality of diodes (five in the case of FIG. 2) are formed, and each diode is supported by flexible electrically insulating films 7a and 7b. Straight and L-shaped leads 8a and 8b are attached.

The semiconductor chip 2a is attached to the leads 8a, 8b held by the flexible films 7a, 7b as described above by a method known as a film carrier method. A thermal head corresponding to FIG. 1 is formed by connecting the other ends of the straight and L-shaped leads connected to the semiconductor chip to the individual electrodes 6b of the heating element and the multilayer wiring conductor 9, respectively.

However, this connection is made after the heating element substrate 4 and the multilayer wiring substrate 5 are integrated into the head base 10. As the heating element substrate, an alumina substrate or the like having a glass layer formed on the surface is suitable because of the properties required of the heating element, and a printed circuit board or the like which is cheaper than the alumina substrate is used as the multilayer wiring board 5. For the head base 10, a metal plate (iron plate, aluminum plate, etc.) is used in consideration of attachment to the head device.
When bonding the heating element substrate 4 and the head base 10 to manufacture the head shown in Fig. 2, the heating element forming surface (actually the wear-resistant layer surface) on the heating element substrate
It is surprisingly difficult to satisfy the requirement that the recording paper be as perfectly flat as possible (this requirement is necessary for perfect contact between the recording paper and the heating element).

Conventional thermal heads have attempted to achieve this objective by simply bonding or by a method as shown in FIG. 3 without attaching importance to this problem.

In FIG. 3, 13 is the same alumina substrate as the heating element substrate 4. As shown in FIG. 3, if the heating element substrate 4 and the flatness compensation substrate 13 are bonded to the upper and lower surfaces of the head base 10, regardless of the difference in thermal expansion coefficient between the head base 10 and the heating element substrate 4, The flatness of the surface of the abrasion resistant layer due to temperature rise during adhesion or use of the head can be maintained within a range that does not cause problems for thermal recording.
However, this configuration has drawbacks such as the fact that it is troublesome to add the flatness compensation board 13 during actual head manufacture, and the presence of the flatness compensation board 13 becomes an obstacle when fixing the head. There is.

In addition, by using a softer material than the heating element board for the multilayer wiring board, like a printed circuit board,
The influence on the flatness of the heating element can be reduced.

The present invention provides a thermal head that is divided into a heating element board and a multilayer wiring board as described above, and provides semiconductor element leads connected between the two boards.
Alternatively, there is a thermal head for heat-sensitive recording which has a bonding structure between a heating element base and a head base to ensure the flatness of the heating element substrate and less influence on the lead connection part (broken wire, lead separation, etc.). It provides:

That is, in the present invention, the central portion of the heating element substrate is adhered to the head base using a curable adhesive, and the peripheral portion thereof is adhered to the head base using an adhesive adhesive.

Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same numbers are given to the same parts as in the conventional thermal head for heat-sensitive recording.

FIG. 4 is a diagram showing a bonding structure between a heating element substrate and a head base according to an embodiment of the present invention, in which numeral 4 indicates a heating element substrate, and 5
1 is a multilayer wiring base, and 10 is a head base. However, on the heating element substrate 4 and the multilayer wiring board, if the semiconductor device connected to the heating element is a diode, there is a diode as shown in FIG. 2, and in the case of other semiconductor devices, each device is Suitable conductor patterns are formed, but since these conductor patterns are not directly related to the present invention, in FIG.
These are omitted.

In FIG. 4, a heating element substrate 4 and a multilayer wiring substrate 5 are adhesively held on surfaces 11 and 12 of a head base 10. As shown in FIG. In this example, this adhesion,
In particular, as shown in FIG. 4, the adhesive part 11 is divided into two parts 11a and 11b, and different adhesives are applied to these parts. That is, an adhesive (non-curing type) tape is applied to the adhesive part 11a, a curable resin is applied to the adhesive part 11b, and the heating element substrate 4 is adhesively held. With this adhesive configuration, the flatness of the heating element surface is
The flatness of the substrate 13 can be made to follow the flatness of the bonding surface 11 of the head base whose flatness has been secured in advance, and the flatness of the substrate 13 can be made to ensure the flatness as shown in FIG. 3 in the conventional example. It can be made unnecessary.

The area of the adhesive portion 11b at the center of the heating element substrate is determined by heat treatment during adhesion between the heating element base 4 and the head base 10 (particularly when adhering with curable resin), or when the heating element substrate and head are bonded during thermal recording. The size should be such that warping of the flatness of the heating element due to temperature changes such as a rise in the temperature of the base will not be a problem.

Due to these temperature changes, the difference in elongation between the heating element substrate and the base is as shown in Fig. 4 at the adhesive part 11a.
Although this is a deviation in the xy plane, this deviation is absorbed by the adhesive, and the flatness of the heating element is kept within a range that does not cause any recording problems.

On the other hand, when bonding the multilayer wiring board 5, even if the entire bonding surface 12 is bonded with a curable resin by using a printed circuit board, the effect on the flatness of the heating element is minimal. . If the same material as the heating element substrate is used as the multilayer wiring board 5, the effect on flatness can be avoided by adhesion similar to that of the heating element substrate in FIG.

In a head with an adhesive structure as shown in FIG. 4, the adhesive part 11b is resistant to shear stress in the y direction or in the x, y plane that is generated on the adhesive surface due to contact abrasion with paper during thermal recording. Providing the stopper 14 is effective for reinforcing the strength. The shape of this stopper 14 can be configured in various shapes depending on the actual shape of the head.

Although there are various variations in actual heads, the heating element substrate and the head substrate are generally connected by a hardening adhesive (e.g. epoxy) in the center of the heating element substrate and an adhesive adhesive (e.g. epoxy) around it. The basic idea of the present invention is to make the flatness of the heating element equal to the flatness of the base by adhering it to the head base using an adhesive (usually called adhesive tape), and to prevent this flatness from changing with temperature. be.

As explained above, the present invention is very useful for separating the heating element substrate and the multilayer wiring board to ensure the flatness of the heating element of a thermal head in which the heating element and the heating element driving device are integrated. This provides an adhesive structure between the heating element board and the head base.
Furthermore, it has the following effects.

(i) Freedom of choice of head base According to the present invention, the necessary flatness can be ensured even when there is a large difference in the coefficient of thermal expansion between the heating element substrate and the head base. That is, an inexpensive and lightweight board like A can be used as the head base, which helps to reduce the weight of the entire head.

On the other hand, if the A base is used in the conventional configuration as shown in FIG. 3, the substrate may peel off due to insufficient strength of the adhesive.

(ii) Rationalization of the head manufacturing process In actual thermal heads, various types of heat dissipation fins are often installed as a measure against the rise in head temperature during thermal recording.

In this case, if the heating element substrate and the multilayer wiring substrate are separated and these two substrates are directly bonded to a head base that also serves as a heat dissipation effect, it becomes difficult to design a device for connecting leads of a semiconductor device.

In contrast, in the present invention, the above-mentioned device design is facilitated by being able to remove various heat dissipation fins after the adhesion shown in FIG. 4 and the lead connection for mounting the semiconductor device on the head. . Of course, in the case of a head in which the heat generating board and the multilayer wiring board are not separated, it is easier to directly bond the heat generating board to the head base with heat dissipation fins. However, in the head that separates the heating element board and the multilayer wiring board, in order to connect the lead wires of the semiconductor device, the adhesion position accuracy of the heating element board and the multilayer wiring board is maintained, and the flatness of the heating element board is maintained. Because of this need, it is often useful to assemble the head in such a way that such heat dissipation fins are attached later.

Furthermore, the reliability of the lead connection of a semiconductor device in a head with an adhesive structure as shown in Fig. 4 is as follows.
It has also been experimentally confirmed that the case is almost the same as the case shown in the figure.

[Brief explanation of drawings]

FIG. 1 is a basic circuit diagram of a thermal head for heat-sensitive recording, FIG. 2 is a diagram showing the actual structure of the thermal head, and FIG. 3 is a perspective view showing the structure of a conventional thermal head for heat-sensitive recording. FIG. 4 is an exploded perspective view of a thermal head for heat-sensitive recording in one embodiment of the present invention. 4...Heating element board, 5...Multilayer wiring base, 1
0...Head base, 11, 11a, 11b, 12
...Adhesive part.

Claims (1)

[Claims] 1. In a thermal head for heat-sensitive recording, which is formed by fixing a heating element substrate on which a heating resistor is formed and a multilayer wiring board for a semiconductor device to a head base, the central part of the heating element substrate is fixed with a curable adhesive. , and its periphery is adhered to the head base with adhesive type adhesive, and the leads of the semiconductor device formed by the film carrier method are connected to the heating resistor and the conductor on the multilayer wiring board. A thermal head for heat-sensitive recording.