JP2000246936A - Thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal head capable of preventing occurrence of a crack of an insulation film that protects a conductive pattern on a printed wiring board substrate and preventing the breaking of the conductive pattern. SOLUTION: A head substrate having heaters provided thereon and a printed wiring board are fixed to a support board. A driving IC for driving heating resistors is provided on the head substrate and the driving IC is sealed by a resin 8. A part 13a of a conductive pattern on a printed wiring board substrate 5b at a portion below an external profile section 8a of the resin 8 is removed and an insulation film 12a, 12 is formed on a printed wiring board substrate 5a and a conductive pattern 13. As the printed wiring board substrate 5b and the insulation film 12a hardly adhere to each other, it is possible to prevent occurrence of a crack of the insulation film 12 at the portion below the external profile section 8a of the resin 8 and in the vicinity thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a thermal head.

[0002]

2. Description of the Related Art As shown in the sectional view of FIG. 3, a conventional thermal head 1 has a head substrate 4 provided with a heating element 3 on a support plate 2 and a printed wiring board 5 fixed with an adhesive 6.
A driving IC 7 for driving the heating element 3 is mounted on the printed wiring board 5. A resin 8 is applied on the drive IC 7 for the purpose of protection. The drive IC 7 may be mounted close to the printed wiring board 5 on the head substrate 4. The printed wiring board 5
Has a connector 9 for making an electrical connection with an external control device.
Is attached.

FIG. 2A shows a state in which a resin 8 is applied to the surface of a substrate 5a of a printed wiring board in a conventional thermal head, and FIG. 2B shows FIG. 2A.
AA ′ section of FIG. As a thermal head, there is a method of changing the driving IC to a multi-bit driving IC in which more transistor circuits are built in one driving IC chip for the purpose of cost reduction. In the case of performing this method, and in order to increase the noise margin in the thermal head circuit, that is, the tolerance for circuit noise, the conductor pattern on the printed wiring board base material reduces the conductor resistance value as one circuit pattern. Therefore, it is necessary to form the pattern with a wide width.

[0004] To secure a wide pattern width,
As shown in FIG. 2, the place where the conductor pattern 10 is formed inevitably covers the area where the resin 8 is applied,
A case occurs in which they are arranged so as to hang on a. In this case, the printed wiring board 5 includes a resin 8 and an insulating film 1 from the upper layer.
1, the conductive pattern 10, and the printed wiring board base material 5a are arranged in this order, and the back side of the printed wiring board has the same structure.

The thermal head having such a structure prints on thermal paper by heating the heating element 3 (FIG. 3) by energization during actual operation, and the temperature of the thermal head as a whole is about 70 to 70%. Increase to 80 ° C. In addition, there is a cooling time between the energizations, and the temperature is repeatedly increased and decreased. Due to the difference in the coefficient of thermal expansion between the resin 8, the insulating film 11, the conductor pattern 10, and the printed wiring board base material 5a due to the heating and cooling, at the joints of the constituent members, depending on the amount of temperature change, The dimensions of the member change. The dimensional change has an adverse effect on the laminated portion of each member. For example, a difference in thermal expansion coefficient between the resin 8 and the insulating film 11 and a difference in the amount of dimensional change between the insulating film 11 and the conductor pattern 10 causes a stress between the members.

Here, the thermal expansion coefficient of each member generally used for a thermal head is 2.4 × 10 ⁻⁵ / ° C. for the resin 8, 15.0 × 10 ⁻⁵ / ° C. for the insulating film 11, and the conductor pattern ( Copper) 1
0 is 1.7 × 10 ⁻⁵ / ° C., and the printed wiring board base material 5a is 1.4 × 10 ⁻⁵ / ° C.

Also, there is a difference in the adhesion between the above-mentioned members, and the insulating films 11 and the conductive patterns 10, the resin 8 and the insulating films 11, the conductive patterns 10 and the printed The wiring board base 5a, the insulating film 11, and the printed wiring board base 5a are in this order.

Due to the stress generated by the difference in the coefficient of thermal expansion, the insulating film 1 is formed in a portion where the adhesion between the members is weak.
1 has cracks. The places where the cracks are most likely to occur are below and around the resin outer contour 8a where the insulating film 11 is formed on the conductor pattern 10 and the resin 8 is applied on the insulating film 11.

[0009]

As described above, the conductor pattern 10 is widened in order to increase the noise margin, and the insulating film 1 is formed on the conductor pattern 10 in a stacked state.
1. The area where the resin 8 is formed in the upper layer of the insulating film 11 is widened, and the area where cracks in the insulating film 11 occur is also increased.

In the conductor pattern 10 formed on the printed wiring board base material 5a, if an insulating film 11a for protecting the conductor pattern 10 exists under and in the vicinity of the resin outer peripheral portion 8a, thermal expansion during heating and cooling occurs. Cracks occur in the insulating film portion 11a due to the difference in coefficient and the difference in adhesion. A part of the conductor pattern at the place where the crack occurs is exposed and comes into contact with the outside air, and oxidization and corrosion progress with the lapse of time to cause disconnection. The present invention has been made in view of the above problems, and proposes a thermal head capable of suppressing occurrence of cracks in the insulating film and preventing disconnection of a conductor pattern.

[0011]

According to the thermal head of the present invention, a head substrate provided with a heating element on a support plate and a printed wiring board are fixed, and a driving IC for driving the heating element is sealed with resin. A part of the pattern of the conductor pattern on the printed wiring board substrate located under the outer peripheral portion of the resin of the thermal head is deleted.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. Here, FIG. 1A is a top view of a main part, and FIG. 1B is a cross-sectional view taken along the line BB ′ of FIG.
As shown in FIG. 1, a resin 8 is applied to an upper part of an insulating film 12 for protecting a conductor pattern 13 on a printed wiring board base material 5a. By applying the resin 8, the resin outer contour portion 8 is formed.
a will be formed on the upper part of this laminated portion. Then, the conductor pattern 1 corresponding to the lower layer of the resin outer contour portion 8a
Part of pattern 3 is deleted. In the removed portion 13a of the conductor pattern, the insulating film portion 12a is directly laminated on the printed wiring board base material 5a, and the resin 8 is applied on the upper portion thereof.
As a result, the adhesion to the printed wiring board substrate 5b under the insulating film portion 12a increases.

By the increase in the adhesion, it is possible to prevent cracks in the insulating film 12 and the insulating film 12a below and around the resin outer contour. This is because the adhesive force between the insulating film 12 and the printed wiring board substrate 5a is stronger than the stress caused by the dimensional change due to the difference in the thermal expansion coefficient between the resin 8 and the insulating film 12. The strength of this adhesive force depends on the insulating film 1
No. 2 is mainly composed of an epoxy resin material, and the printed wiring board base material 5a also uses the same type of material.

Hereinafter, the shape of the deleted portion of the conductor pattern 13 will be described in detail. Similarly, as shown in FIGS. 1 and 2, a part of the conductor pattern corresponding to the lower layer of the resin outer contour portion 8a is deleted. Deleted portion 13 of the conductor pattern at this time
The size of a is intermittently deleted in order to avoid increasing the conductor resistance value of the deleted portion, and the insulating film 12 is directly laminated on the printed wiring board base material 5a in the deleted portions. . If the conductor resistance value does not increase as a result, the deletion region may be continuously increased.
The removal dimension in the direction perpendicular to the resin outer contour 8a is determined in consideration of the variation in the position of the resin outer contour.

Here, in the case where a wide conductor pattern is disposed below the resin outer contour portion 8a in the conductor pattern 13 of the printed wiring board 5, a part of the conductor pattern is widely removed as described above. The occurrence of cracks in the insulating film 12 can be more effectively prevented, and thereby the disconnection of the conductor pattern 13 can be eliminated.

[0016]

According to the present invention, a part of a conductor pattern on a printed wiring board base material located under or around a resin outer contour portion of a resin applied to protect a drive IC and under the resin outer contour portion is eliminated. And, since an insulating film was formed on the printed wiring board base material and the conductor pattern,
Since the printed wiring board base material and the insulating film are firmly adhered to each other, it is possible to prevent the occurrence of cracks in the insulating film at the outer peripheral contour of the resin.

[Brief description of the drawings]

FIG. 1 is a plan view and a sectional view of a main part of a thermal head according to the present invention.

FIG. 2 is a plan view and a sectional view of a main part of a conventional thermal head.

FIG. 3 is a sectional view of a conventional molding apparatus.

[Explanation of symbols]

5 Printed wiring board 5a Printed wiring board base material
8 Resin 8a Resin outer peripheral part 13 Conductor pattern 13a Conductor pattern deleted part

Claims (4)

[Claims] 1. A head substrate provided with a heating element on a support plate and a printed wiring board are fixed, and a driving IC for driving a heating resistor is mounted on the head substrate or the printed wiring board. In a thermal head in which is sealed with a resin, a part of the conductor pattern on the printed wiring board substrate located below the outer peripheral contour portion of the resin is deleted, and the insulating is provided on the printed wiring board substrate and the conductor pattern. A thermal head formed by forming a film. 2. The thermal head according to claim 1, wherein a part of the conductor pattern is intermittently deleted. 3. A head substrate provided with a heating element on a support plate and a printed wiring board are fixed, and a driving IC for driving a heating resistor is mounted on the head substrate or the printed wiring board. In a thermal head obtained by sealing with a resin, a part of a conductor pattern on a printed wiring board base material located under the outer peripheral contour part and near the lower part of the outer peripheral contour part of the resin is removed, and the printed wiring board base material and A thermal head comprising an insulating film formed on the conductor pattern. 4. The thermal head according to claim 3, wherein a part of the conductor pattern is intermittently deleted.