JPH0624943U - Thermal head - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent damage to the wire bonding part due to heat during wire bonding work and to prevent the heat sink from warping due to the temperature rise of the heating resistor during printing. A metal plate having a coefficient of thermal expansion substantially equal to or close to a coefficient of thermal expansion of the ceramic substrate 1 between the ceramic substrate 1 and the printed circuit board 3 provided with the heating resistor 2 and the aluminum alloy radiator plate 4. 20 is interposed.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a thermal head used in a printer or the like.

[0002]

[Prior art]

A thermal head used in a printer or the like has a large number of heating resistors arranged in an array on a ceramic substrate made of Al ₂ O ₃ or the like in a direction orthogonal to the feeding direction of the thermal recording paper, and these heating resistors are connected to each other by a voltage. Is applied to selectively generate heat to cause a color reaction on the thermosensitive recording paper to print information. Therefore, heat generation during circuit connection and printing becomes a problem, and a heat dissipation structure is required.

FIGS. 3A and 3B show a conventional example of such a thermal head. FIG. 3A is a sectional view of a thermal head using a composite substrate system and FIG. . Briefly explaining this, 1 is a ceramic substrate on which a heating resistor 2 and lead electrodes are printed, 3 is a printed circuit board as a circuit board, 3'is a flexible printed circuit board as a circuit board, and 4 is an aluminum alloy. A heat sink made of aluminum, 5 a pressing cover made of an aluminum alloy, 6 a set screw, 7 a driver IC, 8 an elastic member such as silicon rubber, 9 a thermal recording paper, and 10 a platen roller. In the composite board method shown in FIG. 1A, the ceramic board 1 and the printed board 3 are bonded and fixed to the heat sink 4 with double-sided tape, and then the lead electrodes of the ceramic board 1 and the control circuit of the printed board 3 are processed by wire bonding. However, in the joining method shown in FIG. 2B, the ceramic substrate 1 and the flexible printed circuit board 3'are placed on the heat sink 4 and the control circuit portion of the flexible printed circuit board 3'is ceramic. It is constructed such that it is superposed on the lead electrode portion of the substrate 1, and the overlapping portion is pressed by the pressing cover 5 via the elastic member 8 to be electrically connected.

[0004]

[Problems to be solved by the device]

However, in the above-described conventional thermal heads, since the ceramic substrate 1 and the radiator plate 4 having different thermal expansion coefficients are directly bonded to each other in any of the systems, the radiator plate 4 with the temperature rise is There is a problem that various inconveniences occur due to thermal deformation. That is, in the case of the composite substrate method shown in FIG. 3A, the wire bonding work for electrically connecting the ceramic substrate 1 adhered and fixed to the heat sink 4 and the printed circuit board 3 uses heat and ultrasonic waves. Since the heat treatment is performed by high temperature, the ceramic substrate 1 and the heat dissipation plate 4 thermally expand during this treatment, but the thermal expansion coefficients of these members are different, and the thermal expansion coefficient (Al ₂ O ₃ ; 7 ×) of the ceramic substrate 1 is different. 10 ^-6 / ° C) is small and hardly thermally expands, whereas the heat dissipation plate 4 has a larger coefficient of thermal expansion (Al; 23.2 × 10 ^-6 / ° C) than the ceramic substrate 1 and Try to grow greatly. Therefore, the entire thermal head is curved in a convex shape on the side opposite to the platen roller 10, as shown in FIG. As a result, there has been a problem that the bonding portion between the ceramic substrate 1 and the printed circuit board 3 is displaced and the wire bonding portion is damaged. On the other hand, in the case of the pressure contact method shown in FIG. 3B, the heat dissipation plate 4 tends to expand much more than the ceramic substrate 1 due to the temperature rise of the heat-generating antibody 2 during the recording operation, so that the entire thermal head has been described above. Similarly, it is convexly curved on the side opposite to the platen roller 10. As a result, there is a problem in that the gap between the heat generating resistor 2 and the platen roller 10 is enlarged, causing a print fading phenomenon.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to prevent the heat sink from warping due to thermal expansion, to prevent damage to the wire bonding portion, and to print. It is to provide a thermal head capable of preventing scratches and the like.

[0006]

[Means for Solving the Problems]

 In order to achieve the above object, a thermal head according to the present invention comprises a ceramic substrate having a heating resistor, electrodes, etc. and a circuit substrate having a control circuit, which are disposed on a heat sink made of aluminum. In the thermal head to which the control circuit is electrically connected, a metal plate having a coefficient of thermal expansion substantially equal to or close to the coefficient of thermal expansion of the ceramic board is interposed between the heat dissipation plate and the ceramic board and circuit board. It is a thing.

[0007]

[Action]

 Since there is a thermal expansion difference of more than 3 times between the ceramic board and the heat sink, in the thermal head of the composite board type, if the heat sink expands and warps due to the temperature rise during the wire bonding work, the ceramic board or the circuit board. Although the wire bonding part may be damaged due to misalignment, if a metal plate with a coefficient of thermal expansion that is approximately equal to or close to that of the ceramic board is placed between the ceramic board and circuit board and the heat sink, heat dissipation The heat transfer to the plate is reduced, and the thermal expansion of the heat sink is reduced and prevented. In addition, in the thermal head of the joint type, the thermal expansion of the heat sink due to the heat generation of the heat generating resistor is reduced, and the warp of the heat sink is reduced and prevented.

[0008]

【Example】

Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. FIG. 1 is an exploded perspective view showing an embodiment of a thermal head according to the present invention, and FIG. 2 is a sectional view. The same components as those of the conventional head shown in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted. In these drawings, the present embodiment shows a case where the present invention is applied to a composite substrate type thermal head, and a metal plate 20 having an appropriate thickness is interposed between the ceramic substrate 1, the printed circuit board 3 and the heat dissipation plate 4. Is different from the conventional structure shown in FIG. 3 (a), and other structures are the same. As a material of the metal plate 20, a metal having a coefficient of thermal expansion substantially equal to or close to the coefficient of thermal expansion of the ceramic substrate 1 made of Al ₂ O ₃ or the like, for example, iron, stainless steel or the like is used. The thermal expansion coefficients of iron and stainless steel are Al 11.7 × 10 ⁻⁶ / ° C and 10.0 × 10 ⁻⁶ / ° C, respectively.

In manufacturing the thermal head having the above structure, first, the ceramic substrate 1 and the printed circuit board 3 are bonded and fixed on the metal plate 20 by a double-sided tape, and then the ceramic substrate 1 and the printed circuit board 3 are fixed to each other. The plate 20 is bonded and fixed onto the heat dissipation plate 4 with a double-sided tape, and then the lead electrode of the ceramic substrate 1 and the control circuit of the printed circuit board 3 are electrically connected by a wire bonding process. In addition, 21 is a screw hole and 22-24 is a screw mounting hole.

In the thermal head according to the present invention, the metal plate 20 having a coefficient of thermal expansion substantially equal to that of the ceramic substrate 1 is interposed between the ceramic substrate 1, the printed circuit board 3 and the heat dissipation plate 4 as described above. Therefore, it is possible to prevent the heat from being transferred to the heat dissipation plate 4 during the wire bonding work for electrically connecting the ceramic substrate 1 and the printed circuit board 3. Therefore, it is possible to prevent the heat dissipation plate 4 from warping due to thermal expansion. Further, it is possible to prevent the heat dissipation plate 4 from warping due to the heat generation of the heat generating resistor 2 during printing.

Although the above embodiment has been described with respect to the case of being applied to the thermal head of the composite substrate type, the present invention is not limited to this, and may be applied to the thermal head of the joining type. .

[0012]

[Effect of device]

 As described above, in the thermal head according to the present invention, a metal plate having a coefficient of thermal expansion which is substantially equal to or close to that of the ceramic substrate is interposed between the ceramic substrate, the circuit substrate and the heat dissipation plate made of aluminum alloy. Therefore, in the case of a composite substrate type thermal head, it is possible to prevent and reduce the warp of the heat sink due to heat during wire bonding work. Therefore, the ceramic substrate or the circuit substrate will not be displaced, and damage to the wire bonding portion can be prevented. Even during printing, the heat of the heating resistor does not transfer to the heat sink, and the heat sink can be prevented from warping. Therefore, it is possible to improve print quality without causing print blur. Further, in the joint type thermal head, the heat of the heat generating resistor is not transferred to the heat radiating plate during printing, so that the warp of the heat radiating plate can be prevented. Therefore, even in the case of the joining method, print blurring does not occur and print quality can be improved.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing an embodiment of a thermal head according to the present invention.

FIG. 2 is a side sectional view of the head.

3A and 3B are side cross-sectional views of a conventional thermal head, respectively.

FIG. 4 is a diagram showing thermal deformation of a thermal head.

[Explanation of symbols]

 1 Ceramic Board 2 Heating Resistor 3 Printed Circuit Board 3'Flexible Printed Circuit Board 4 Heat Sink 5 Presser Cover 6 Set Screw 10 Platen Roller 20 Metal Plate

Claims (1)

[Scope of utility model registration request] 1. A thermal head in which a ceramic substrate provided with a heating resistor, electrodes and the like and a circuit substrate provided with a control circuit are disposed on a heat sink made of aluminum, and the electrodes are electrically connected to the control circuit. The thermal head, wherein a metal plate having a coefficient of thermal expansion substantially equal to or close to the coefficient of thermal expansion of the ceramic substrate is interposed between the heat dissipation plate and the ceramic substrate and the circuit board.