JPH05177859A - Production of thermal head - Google Patents

Abstract

PURPOSE:To enhance printing quality by preventing the curving of an insulating substrate and eliminating the irregularity in printing density. CONSTITUTION:After drive circuit elements are linearly arranged on an insulating substrate 23, the insulating substrate 23 is curved by predetermined curving quantity in a predetermined direction using a jig 40. Thereafter, a molding resin is applied to the insulating substrate so as to cover the drive circuit elements and, after heating, the jig 40 is detached to cool the resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thermal head used as a print output device such as a facsimile machine or a word processor.

[0002]

2. Description of the Related Art FIG. 6 is a sectional view of a typical conventional thermal head 1, and FIG. 7 is a perspective view of the thermal head 1. In the thermal head 1, an insulating substrate 3 made of ceramic is fixed on a heat dissipation plate 2 made of aluminum or the like,
A heat storage layer 4 made of glass is formed on the insulating substrate 3. The insulating substrate 3 is entirely covered to cover tantalum nitride Ta ₃ N ₄
A resistor layer 5 made of, for example, is formed by sputtering or the like, and a common electrode 6 made of aluminum or the like, an individual electrode 7, and a signal line 8 are patterned thereon. Resistor layer 5 sandwiched by common electrode 6 and individual electrode 7
6 is formed as the heat generating resistor 9, and a large number are formed in the direction perpendicular to the paper surface of FIG. A protective film 10 made of silicon nitride Si ₃ N ₄ or the like is formed including the array region of the heating resistors 9.

The signal line 8 includes a heat sink 2 and an insulating substrate 3
The print data and various control signals supplied from the external wiring substrate 11 fixed adjacent to are input to the drive circuit element 12 that drives each heating resistor 9 to generate heat. The drive circuit element 12 is connected by face-down bonding across the individual electrode 7 and the signal line 8. A large number of such drive circuit elements 12 are arranged in the direction perpendicular to the paper surface of FIG. After connecting the drive circuit elements 12, a thermosetting resin layer made of an epoxy resin or the like is used as a material on the insulating substrate 3 in the area where the drive circuit elements 12 are arranged. To be applied. After that, the insulating substrate 3 is heated at a temperature of 120 to 150 ° C. for 30 minutes to 1 hour to cure the resin layer, and the protective film 13 of the drive circuit element 12 is formed to form the thermal head 1.

[0004]

In such a conventional technique, the coefficient of thermal expansion of epoxy resin αr = 2.2 × 10 ^-5
℃ ^-1 , and the thermal expansion coefficient αb of the insulating substrate 3 = 0.7 × 10
It is known to be ^-5 ° C ^-1 . In the step of forming the protective film 13, a resin layer such as epoxy resin is applied to the flat insulating substrate 3 having a rectangular plate shape and then heated. In this heating step, the resin layer is cured in an equilibrium state within the above temperature range.
That is, the insulating substrate 3 maintains a flat state. After this,
Due to the difference in the coefficient of thermal expansion between the insulating substrate 3 and the protective film 13 at the time of cooling to room temperature, the amount of shrinkage of the protective film 13 is larger than the amount of shrinkage of the insulating substrate 3. Is convexly curved to the side opposite to the main surface side on which the drive circuit elements 12 and the like are formed.

The inventor of the present invention measured the bending state of the thermal head 1 having a total length L1 (232 mm) corresponding to the recording paper of Japanese Industrial Standard (JIS) A4, No. 4. The measurement result is shown by line C1 in FIG. That is, it was confirmed that the bending amount gradually increased in the longitudinal direction of the insulating substrate 3, that is, in the vicinity of the central portion from both ends in the main scanning direction, and the maximum bending amount d1 reached about 1.2 mm. When the insulating substrate 3 has such a curvature, the insulating substrate 3 has a different pressing force on the platen roller or the like used during the actual printing operation along the longitudinal direction thereof, which causes uneven printing density. have.

An object of the present invention is to solve the above technical problems and to provide a method of manufacturing a thermal head capable of eliminating the density unevenness in the print density and improving the print quality.

[0007]

According to the present invention, a plurality of heating resistors and a plurality of driving circuit elements for supplying driving power to the heating resistors are linearly arranged on a main surface of an insulating substrate. A method for manufacturing a thermal head, which is formed by coating the drive circuit element with a resin layer together with the following (A) to (C):
A method of manufacturing a thermal head, which comprises the steps of:

(A) The insulating substrate is curved so that the main surface side on which the drive circuit elements are arranged is convex, and a thermosetting resin is applied to the arrangement area of the drive circuit elements on the main surface.

(B) The thermosetting resin is cured by heating the insulating substrate in a curved state.

(C) Cool the insulating substrate.

[0011]

According to the present invention, the insulating substrate is curved in a convex shape on the main surface side on which the drive circuit elements are arranged, and the thermosetting resin is applied to the area where the drive circuit elements are formed. The insulating substrate is heated in a curved state to cure the thermosetting resin. Then, the insulating substrate is cooled. At this time, when the thermosetting resin is cured, the insulating substrate is in the curved state as described above, and the thermosetting resin is cured in the equilibrium state in this state. In this cooling step, the insulating substrate and the thermosetting resin shrink, but when the coefficient of thermal expansion of the resin is larger than that of the insulating substrate, the insulating substrate is bent in a direction convex to the side opposite to the main surface. At this time, the insulating substrate is curved in advance prior to cooling, and the bending due to cooling is offset to bring the insulating substrate into a substantially flat state.

[0012]

1 is a sectional view of a thermal head 21 according to an embodiment of the present invention, and FIG. 2 is an exploded perspective view of the thermal head 21. The thermal head 21 includes a heat dissipation plate 22 made of a metal material such as aluminum, on which an insulating substrate 23 made of alumina Al ₂ O ₃ based ceramic is fixed by an adhesive layer 30. A heat storage layer 35 is formed on the insulating substrate 23 by a thick film technique such as screen printing to have a layer thickness of 80 μm using silicate glass as an example, and the thick common electrode layer 27 is formed on the outer periphery of the insulating substrate 23. Formed along.

On the heat storage layer 35, for example, tantalum nitride T
A plurality of heating resistors 24 arranged in a straight line are formed by forming a resistor layer 34, a common electrode 36, a plurality of individual electrodes 37 and a signal line 29, which are obtained by forming a ₃ N ₄ to a film thickness of several hundred Å. Is configured. Each heating resistor 24 is covered and is made of, for example, silicon nitride Si ₃ N ₄ or the like, and a protective film 39 is formed by a thin film technique such as sputtering.

Each individual electrode 37 obtained by pattern-forming the aluminum or the like has a predetermined number of drive circuit elements 25.
And a signal line 2 to which data for printing operation and various control signals are externally input to the drive circuit element 25.
9 is connected. These drive circuit elements 25 are covered with a protective film 26 made of a synthetic resin material such as an epoxy resin having a coefficient of thermal expansion αr = 2.2 × 10 ^-5 ° C ^-1, for example.

The drive circuit element 25 is formed as a flip chip having solder bumps, and is connected to the insulating substrate 23 by face down bonding. An external wiring board 28 formed by fixing a flexible wiring board on a board made of glass epoxy resin is fixed to the plurality of signal lines 29 to which the drive circuit elements 25 are connected. The insulating substrate 2
3 and the external wiring board 28 are disposed on the heat dissipation plate 22 with the adhesive layer 3
Fixed by 0. Further, a cover 31 is provided to cover the formation region of the external wiring board 28 and the drive circuit element 25. A head substrate 33 is configured to include the insulating substrate 23 and the electrodes 36 and 37 formed thereon or the drive circuit element 25, and the head substrate 33 is fixed to the heat dissipation plate 22.

The thermal head 21 thus constructed
Performs thermal printing on the thermal recording paper 38 with the platen roller 32.

FIG. 3 is a process chart for explaining the manufacturing process of the thermal head 21 according to one embodiment of the present invention. In step a1, wiring patterns such as the heat storage layer 35, the resistor layer 34, the common electrode 36, the individual electrodes 37, and the signal lines 29 are formed on the insulating substrate 23, and the protective film including the formation region of the heating resistor 24 is formed. 39 is formed. In step a2, the drive circuit element 25 is bonded to each individual electrode 37 and the signal line 29 in the wiring pattern.

In step a3, the insulating substrate 23 is bent by the bending jig 40 shown in FIG. As shown in FIG. 5A, the jig 40 is bent when the length of the insulating substrate 23 is L1 (232 mm) corresponding to the thermal recording paper of Japanese Industrial Standard A No. 4, for example. 5 of the jig 40
The length L2 shown in (1) is selected to be the length L1.
The jig 40 is curved in a substantially arc shape along the longitudinal direction, and the curving amount d2 near the central portion in the longitudinal direction is selected to be about the maximum curving amount d1 (1.2 mm) described in the section of the prior art. Moreover, the direction of the curvature is convex in the main surface side direction on which the drive circuit element of the insulating substrate is mounted, which is based on the difference in the coefficient of thermal expansion between the insulating substrate and the protective film described with reference to FIG. Chosen to be.

As described above, the bending amount d2 of the jig 40 is based on the difference between the thermal expansion coefficients αb and αr of the insulating substrate 23 and the protective film 26, the temperature change width ΔT, and the total length L1 of the insulating substrate 23. Is defined as

[0020]

## EQU00001 ## d2 = (. Alpha.r-.alpha.b) .times..DELTA.T.times.L1 That is, in the present embodiment, when the materials of the insulating substrate 23 and the protective film 26 that constitute the thermal head 21 are clarified, the insulating substrate 23 is previously prepared. The determined bending amount d2 can be determined.

That is, using the jig 40 in such a curved state, the insulating substrate 23 is brought into contact with the insulating substrate 23 from the side opposite to the main surface on which the drive circuit element 25 is mounted, as shown in FIG.
The insulating substrate 23 is pressed from the side opposite to the jig 40. As a result, the insulating substrate 23 has a shape that follows the curve of the jig 40.

That is, while the insulating substrate 23 is curved using the jig 40 as described above, a mold resin such as epoxy resin or silicon resin is applied over the area where the drive circuit elements 25 are arranged in step a4. Process a
In the case of No. 5, the insulating substrate 23 coated with the mold resin is replaced with the jig 40
120 to 150 as an example with the lens attached to
The mold resin is solidified by baking at a temperature of C for 30 minutes to 1 hour. In step a6, the insulating substrate 23 is removed from the jig 40 and cooled to room temperature.

As described above, in the insulating substrate 23, in the step a4, the thermal expansion coefficient αr of the mold resin and the insulating substrate 23,
Regarding the amount of bending in the bending direction assumed based on the difference from αb, the bending amount is set to the same degree as the amount of bending assumed in the direction opposite to the assumed bending direction. Therefore, step a
5 and a6 are heated and solidified and then cooled, the thermal expansion coefficient αb of the insulating substrate 23 and the thermal expansion coefficient α of the protective film 26.
The insulating substrate 23 bends to the side opposite to the main surface based on the difference from r, but the curvature due to this temperature curing cancels the preset curvature of the insulating substrate, and the wiring board after cooling. 23 realizes a substantially flat state.

The inventor of the present invention measured the amount of bending of the insulating substrate 23 after cooling in the present example. The result is shown in Figure 5.
It is shown in line C2 of (2). That is, it was confirmed that the insulating substrate 23 after cooling was flattened to the extent that a curvature of about 0.1 mm was observed.

Therefore, in this embodiment, the thermal head 2
It is possible to make the insulating substrate 23 constituting No. 1 have significantly flatness as compared with the conventional technique. Accordingly, when performing the printing operation, the insulating substrate 23 can be brought into contact with the platen roller 31 with a uniform pressure contact force along the longitudinal direction, and uneven printing density can be eliminated.

[0026]

As described above, according to the present invention, the insulating substrate is curved so as to be convex on the main surface side on which the drive circuit elements are arranged, and the thermosetting resin is coated on the formation area of the drive circuit elements. The insulating substrate is heated in a curved state to cure the thermosetting resin. After that, the insulating substrate is cooled. At this time, when the thermosetting resin is cured, the insulating substrate is in the curved state as described above, and the thermosetting resin is cured in the equilibrium state in this state. In this cooling step, the insulating substrate and the thermosetting resin shrink, but the coefficient of thermal expansion of the resin is large, and the insulating substrate is bent in a direction convex toward the side opposite to the main surface. At this time, the insulating substrate is curved in advance prior to cooling, and the bending due to cooling is offset to bring the insulating substrate into a substantially flat state.

[Brief description of drawings]

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

FIG. 2 is an exploded perspective view of a thermal head 21.

FIG. 3 is a process drawing showing a manufacturing process of the thermal head 21 according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating a shape of a jig 40.

FIG. 5 is a diagram for explaining the operation of the present embodiment.

FIG. 6 is a cross-sectional view of a conventional thermal head 1.

7 is a perspective view of the thermal head 1. FIG.

FIG. 8 is a graph illustrating a problem of the conventional example.

[Explanation of symbols]

 21 Thermal Head 23 Insulating Substrate 25 Drive Circuit Element 26 Protective Film 40 Jig

Claims (1)

[Claims] 1. A plurality of heating resistors are provided on a main surface of an insulating substrate,
In a method of manufacturing a thermal head in which a plurality of drive circuit elements for supplying drive power to each of the heating resistors are arranged linearly and the drive circuit elements are covered with a resin layer, the following (A) to ( A method of manufacturing a thermal head, which comprises the step C). (A) The insulating substrate is curved so that the main surface side on which the drive circuit elements are arranged is convex, and a thermosetting resin is applied to the arrangement area of the drive circuit elements on the main surface. (B) The insulating substrate is heated in a curved state to cure the thermosetting resin. (C) Cool the insulating substrate.