JPH022024A - Thermal head - Google Patents

Abstract

PURPOSE:To prevent the generation of warpage accompanied by a temp. change by adhering a compensation substrate composed of a material having a coefficient of thermal expansion smaller than that of a radiation plate to the surface, which is opposed to the surface loaded with an element board and a printed board, of the radiation plate. CONSTITUTION:In a thermal head, a ceramic element board 1 and a glass/epoxy type printed board 2 are adhered to the upper surface of an aluminum radiation plate 3 subjected to extrusion processing using an adhesive 5 and a compensation ceramic substrate composed of the same material quality as the radiation plate 3 is adhered to the rear of the radiation plate 3 at the position opposed to the ceramic element substrate by the adhesive 5. A current is supplied to the resistor 4 formed to the ceramic element substrate 1 to generate heat and hot press-bonding printing is performed between the thermal head and a platen roller but, since the compensation ceramic board 10 is adhered to the rear of the radiation plate 3, stress generated at high temp. by the difference between the coefficient of thermal expansion of the ceramic element substrate or glass/epoxy type printed board and that of the radiation plate is set off by the stress in the opposite direction generated by the difference between the coefficient of thermal expansion of the compensation board 10 and that of the radiation plate. Therefore, the bending and warpage of the thermal head can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a method in which a substrate divided into a ceramic element substrate and a glass epoxy printed wiring board (hereinafter abbreviated as glass epoxy printed wiring board) is mounted on a heat sink. Regarding the structure of the thermal head.

[Prior Art] Conventionally, this type of split-type thermal head, as shown in FIG. 2 are attached and mounted on a heat sink 3 made of metal such as aluminum using an adhesive 5 or the like. Then, the IC pellet 6 is mounted on the glass epoxy printed circuit board 2, and the IC pellet 6 is mounted using the gold wire 7.
The pellet 6 is connected to the corresponding electrode portions of the ceramic element substrate 1 and the glass-epoxy printed circuit board 2. Further, the IC pellet 6 is coated with a protective precoat resin 8, and parts such as a connector 9 are mounted on a part of the glass epoxy printed circuit board 2 by soldering.

[Problem to be solved by the invention]

In the conventional split-type thermal head described above, the ceramic element substrate 1 and the glass-epoxy printed circuit board 2 are mounted directly on the heat sink 3 with adhesive or the like, so the difference in coefficient of thermal expansion of each of them causes The following problems have arisen:

That is, since the ceramic element substrate l is usually made of alumina ceramic or the like, the coefficient of thermal expansion is approximately 6.5 x 10-h/''
It is C. Furthermore, since the glass-epoxy printed circuit board 2 is made of glass-epoxy resin, its thermal expansion coefficient is approximately 10XIO-/''C. Furthermore, the heat sink 3 is approximately 23XIO-6/''c when made of aluminum, and approximately 23XIO-6/''c when made of aluminum. Approximately 12X10-'/
"The coefficient of thermal expansion is C.

Therefore, due to the difference in thermal expansion coefficient between the substrate 1.2 and the heat sink 3, the entire thermal head is curved in the thickness direction due to a bimetallic effect caused by a difference in thermal stress at high temperatures. This means that the substrate may warp due to heating by the heater during the wire bonding connection of the gold wire 7 mentioned above.
This results in manufacturing problems that result in poor gold wire connections. Further, when printing with the completed thermal head, the heat generated by the resistor 4 causes the product to warp, and uneven contact with the opposing platen roller causes the problem of deterioration of print quality.

According to studies by the present inventors, warping of 100 to 200 μm has been confirmed in the past due to a temperature change of -20 to 70°C.

An object of the present invention is to provide a thermal head that suppresses the occurrence of warpage caused by the above-mentioned temperature changes.

[Means for Solving the Problems] The thermal head of the present invention has an element substrate and a printed circuit board mounted on a metal heat sink in which a ceramic element substrate on which a heating resistor is formed and a Galevo printed circuit board are bonded together. A compensation substrate made of a material having a coefficient of thermal expansion smaller than that of the heat sink is adhered to the surface opposite to the surface.

[Effect]

In the above configuration, the stress caused by the difference in the coefficient of thermal expansion between the ceramic element substrate or the glass-epoxy printed circuit board and the heat sink is offset by the stress in the opposite direction caused by the difference in the coefficient of thermal expansion between the compensation substrate and the heat sink. This prevents bending and warpage in the thermal head.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a longitudinal sectional view of a first embodiment of the present invention.

In the figure, 1 is a ceramic element substrate made of alumina ceramic or the like on which a resistor 4 and electrode conductors (not shown) are formed by sputtering and photolithography, and 2 is a printed copper foil formed on the surface. This is a glass epoxy printed circuit board 2 made of glass epoxy formed into a desired wiring pattern by a method. The ceramic element substrate 1 and the Gala Evo printed circuit board 2 are bonded using an adhesive 5 to the upper surface of an aluminum heat sink 3 that has been extruded into the cross-sectional shape shown.

Furthermore, an IC pellet 6 is mounted on the glass-epoxy printed circuit board 2 using paste, and this is connected between predetermined electrodes of the glass-epoxy printed circuit board 2 and the ceramic element substrate 1 using gold wires 7. . This IC pellet 6 and gold wire 7
is coated with a protective pre-coat resin 8. Further, mounted components such as a connector 9 are connected to a part of the glass epoxy printed circuit board 2 by soldering.

On the other hand, a compensating ceramic substrate 10 made of the same material is adhered to the back surface of the heat sink 3 at a position facing the ceramic element substrate 1 with an adhesive 5. In this embodiment, a ceramic element substrate 1 is bonded to the surface of a heat sink 3.
The width of the compensation ceramic substrate 10 and the width of the Gala Evo printed circuit board 2 are set at a dimensional ratio of 2=1.
The width dimension is set to 273.

According to this configuration, it is no longer possible to energize the resistor 4 formed on the ceramic element substrate 1 to generate heat, and to use this heat to perform thermocompression printing with a platen roller (not shown). It's the same.

In this configuration, by bonding the compensating ceramic substrate 10 to the back surface of the heat sink 3, it is possible to prevent bending at high temperatures due to the difference in thermal expansion coefficient between the ceramic element substrate l and the heat sink 3. In other words, ceramic element substrate 1
The amount of bending at high temperatures is different between the combination of the printed circuit board 2 and the heat sink 3, and the combination of the Gala Evo printed circuit board 2 and the heat sink 3. Curvature becomes dominant. However, by bonding the compensation ceramic substrate 10 having the same coefficient of thermal expansion as the ceramic element substrate 1 at opposite positions on the back surface of the heat sink 3 with the same width dimension, the ceramic element substrate 1 and the compensation ceramic Thermal stress generated between each of the substrates 10 and the heat sink 3 is canceled out, and bending in the thermal head can be prevented.

According to the inventor's study, the bending according to this embodiment is -
Maximum 10pm in the range of 20~-70″C,
It was confirmed that this was significantly improved compared to the conventional 100 to 200 μm.

FIG. 2 is a vertical sectional view of the second embodiment of the present invention, and
The same parts as in the figures are given the same reference numerals.

In this embodiment, the width ratio of the ceramic element substrate 1 and the glass-epoxy printed circuit board 2, which are bonded to the surface of the heat dissipation plate 3, is 1:2. The printed circuit board 2 becomes dominant. For this reason, here, a compensating glass epoxy substrate 11 having the same width as the glass epoxy printed circuit board 2 is adhered with an adhesive 5 on the back side of the heat sink 3 at a position facing the glass epoxy printed circuit board 2 .

In this embodiment, the thermal stress of the glass epoxy printed circuit board 2, which is dominant in bending at high temperatures, is offset by the compensating glass epoxy substrate 11, thereby making it possible to prevent the thermal head from bending.

Note that the compensation substrate bonded to the back side of the heat sink must have a smaller coefficient of thermal expansion than the heat sink for the effect of the present invention to be produced, and the material of the compensation substrate may be a ceramic substrate or Of course, it is not limited to the Gala Evo board.

[Effects of the Invention] As explained above, the present invention includes bonding a compensation substrate made of a material with a smaller coefficient of thermal expansion than the heat sink on the back side of the heat sink to which a ceramic element substrate and a glass-epoxy printed circuit board are bonded. Therefore, the stress generated at high temperatures due to the difference in the coefficient of thermal expansion between the ceramic element substrate or the glass-epoxy printed circuit board and the heat sink can be replaced by the stress in the opposite direction caused by the difference in the coefficient of thermal expansion between the compensating substrate and the heat sink. This cancels out bending and prevents warpage in the thermal head. As a result, it is possible to prevent warping of the gold wire during connection in the manufacturing process and warping of the head during printing operations, and it is possible to obtain a thermal head with high reliability and high printing quality.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a first embodiment of a thermal head according to the present invention, FIG. 2 is a vertical cross-sectional view of a second embodiment of the present invention, and FIG. 3 is a vertical cross-sectional view of a conventional thermal head. DESCRIPTION OF SYMBOLS 1... Ceramic element board, 2... Glass epoxy printed circuit board, 3... Heat sink, 4... Resistor, 5... Adhesive, 6... IC pellet, 7... Gold wire, 8...
Pre-coated resin, 9... Connector, 10... Compensation ceramic board, 11... Compensation Gala Evo board.

Claims (1)

[Claims] 1. In a thermal head having a configuration in which a ceramic element substrate on which a heating resistor is formed and a glass epoxy printed wiring board are adhered to a metal heat sink, the heat sink has the element substrate and the printed wiring board attached to the metal heat sink. A thermal head characterized by having a compensation substrate made of a material with a smaller coefficient of thermal expansion than a heat sink bonded to a surface opposite to the surface on which the substrate is mounted.