JPS61261066A - Thermal head - Google Patents

Abstract

PURPOSE:To provide a thermal head having a base which is not warped even under temperature variations, by a method wherein a dike is formed of a hardened adhesive along edges of a surface of a support, a base board is placed on the dike in a covering manner, and the support and the base board are adhered to each other by an adhesive at a substantially central part of the surface of the support. CONSTITUTION:On the surface of the support 2, the dike 4 formed of a hardened adhesive is provided along the edges of the surface, and the inside of the dike 4 is filled with a fluid filler 5, except a central part. The support 2 and the base board 3 are adhered to each other by an adhesive 6 at the central part. The base board 3 is placed on the dike 4 in the manner of covering the filler 5, and makes contact with the dike 4, but is not adhered to the dike 4. The dike 4 is provided for preventing outflow of the filler 5 and for maintaining a film thickness, and is adhered to the support 2, but is not adhered to the base board 3 although it makes contact with the latter. The filler 5 serves to secure a heat releasing property and absorb stress of thermal expansion. Accordingly, the base board is not warped due to temperature differences.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a thermal head, and particularly to a thermal head characterized by an adhesive structure between a substrate and a support.

(b) Prior Art Generally, in a thermal head, a substrate forming a printed portion such as a heating resistor and an electrode is attached with an adhesive to a support member forming a heat dissipating portion and the like. A sectional view of this type of thermal head is shown in FIG.

In the thermal head shown here, the substrate a and the support are entirely bonded with an adhesive C. A as the material of substrate a
f t 03 (alumina), A as the material of the support
Usually, 1, Fe is used, and as the adhesive, a room temperature curing adhesive or a thermosetting adhesive is used.

(c) Problems to be Solved by the Invention In the above-mentioned conventional thermal head, suppose that the A12o3 substrate a and the Al support are bonded together using a room temperature curing adhesive. The body is flat, but when heated, it turns into Al203 and AI! have different thermal expansion coefficients (A l1203 near, 2x 10
-' 1/”c, Al: 23.5x 10-b1/
℃), warpage occurs on the substrate a side.

Also, the substrate a of /1tO,! = Assuming that the AA support is bonded with a thermosetting adhesive, in this case the adhesive would be cured in an oven, etc., but the adhesive has not yet cured at the beginning of heating. , the substrate a and the support are stretched straight based on their respective expansion coefficients, and as time passes, the adhesive hardens, and the substrate a and the support are bonded together in a stretched state. After curing, when the substrate is cooled to room temperature, the substrate a and the support will shrink by the amount of elongation, but since the substrate a and the support have already been bonded and the degree of expansion is different, in this case, the support Warpage occurs toward the side.

In any of the above cases, when the thermal head is warped, there is a problem in that the printed portion on the surface of the substrate is not flush, resulting in uneven printing.

In view of the above, an object of the present invention is to provide a thermal head in which the substrate does not warp even if a temperature change occurs.

(d) Means and action for solving the problems The thermal head of the present invention has a structure in which a dike is formed by a hardened adhesive that goes around the edge of the surface of a support, and the inside of this dike is filled with fluidity. A substrate is placed on top of the substrate so as to close the embankment, and the support and the substrate are bonded to each other with an adhesive at a substantially central portion of the surface of the support.

In this thermal head, the support and the substrate are only bonded approximately at the center, so even if temperature changes occur due to heating or cooling, the edges are free from each other, so they expand and expand according to their respective expansion coefficients. Does not shrink or warp. Further, heat from the substrate is radiated to the support via the filler.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a plan view of a thermal head according to an embodiment of the present invention with the substrate omitted, and FIGS. FIG. 3 is a cross-sectional view including the substrate, taken along the line m.

The thermal head 1 of this embodiment is constructed by adhering a substrate 3 to a flat support 2.

A dike 4 is formed on the surface of the support 2 by a hardened adhesive so as to go around the edge, and the inside of the dike 4 is filled with a fluid filler 5 except for the central portion. Further, the support 2 and the substrate 3 are adhered to each other by an adhesive 6 at the central portion. The substrate 3 is superimposed on the embankment 4 so as to cover the filler 5, and is in contact with the embankment 4, but is not bonded.

The embankment 4 is provided to prevent the filler 5 from flowing out and maintain the film thickness, and is bonded to the support 2, but as described above, is only in contact with the substrate 3. The filler 5 is provided to ensure heat dissipation and absorb thermal expansion stress.

For the embankment 4 and the adhesive 6, silicone, epoxy, acrylic, etc. may be used. It does not matter whether it is a room temperature curing type or a thermosetting type. As the filler 6, silicone grease is used. These adhesives and fillers all have a thermal conductivity of lXl0-'cal/cInsec・℃~10
×1O-3ca1/cfflsec·°C is used. Although the layer thicknesses of the embankment 4, filler 5, and adhesive 6 may be arbitrary, it is preferable that the layer thickness be the same and that the layer thickness be 10 to 50 μm. Note that the support 2 is made of Al, and the substrate 3 is made of Al12.
Use o3.

The thermal head 1, in which the support 2 and the substrate 3 are bonded, expands and contracts at different degrees when there is a temperature change because the thermal expansion coefficients of the support 2 and the substrate 3 are different. The adhesive part is a small area in the center, and both ends are free, so they can expand and contract freely and will not warp.

Next, an example of a method for bonding the support 2 and the substrate 3 of the thermal held 1 will be described.

First, as shown in FIG. 4, an adhesive is applied to the edge of the surface of the support 2 by screen printing and hardened to form the embankment 4. Further, the filler 5 is filled inside the embankment 4 except for the central part by screen printing.

On the other hand, as shown in FIG. 5, an adhesive 6 is applied to the center of the back surface of the substrate 3 by screen printing. Then, the substrate 3 is turned upside down and placed on the support 2, and the adhesive 6 is cured to bond the support 2 and the substrate 3 together.

Adhesives and fillers can of course be applied and filled using methods other than screen printing, but if you use this method,
The bonding process can be simplified.

In the above embodiment, the pattern shape of the applied adhesive 6 for bonding the support 2 and the substrate 3 is rectangular, and the embankment 4
Although the adhesive 6 is applied to the support 2, the portion to which the adhesive 6 is applied may be approximately at the center of the support 2, and various shapes may be considered. For example, as shown in FIG. 6, it may be a rectangle extending from the long sides 4a to 4b of the embankment 4, or as shown in FIG. Rectangular adhesive portions 6a and 6b may be provided, or one of the adhesive portions 6a and 6b may be omitted (see FIG. 9). Alternatively, as shown in FIG. 8, a plurality of circular adhesive portions 5a, 5b, 5c,
6d may be provided.

(F) Effects of the Invention According to this invention, the support and the substrate are bonded only at the center, and the embankment at the edge and the substrate are not bonded, so even if thermal stress is applied, warping due to the difference in thermal expansion will not occur. It will never occur. For example, warping can be suppressed even by the difference in thermal expansion between AltOx and Al, and while printing quality is maintained, high heat dissipation and weight reduction of the thermal head can be achieved.

[Brief explanation of drawings]

FIG. 1 is a plan view of a thermal head according to an embodiment of the present invention with the board omitted; FIG. 2 is a cross-sectional view of the thermal head taken along line ■-■; FIG. 4 is a sectional view of the support body for explaining the bonding method of the thermal head, FIG. 5 is a sectional view of the same substrate, and FIGS. 8 and 9 are diagrams showing other examples of adhesive patterns of the present invention,
FIG. 10 is a sectional view for explaining a conventional thermal head. 1: Thermal head, 2: Support, 3: Substrate, 4: Embankment, 5: Filler, 6: Adhesive. Patent applicant ROHM Co., Ltd. agent
Patent Attorney Shigeru Nakamura 1J1 Figure 9 Figure ``0''

Claims (1)

[Claims] (1) forming an embankment with a hardened adhesive around the edge of the surface of the support, filling the inside of this embankment with a fluid filler, and superimposing a substrate so as to close the embankment; A thermal head characterized in that the support and the substrate are bonded to each other with an adhesive at a substantially central portion of the surface of the support.