JP2006334791A - Thermal printing head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-quality and high-durability thermal printing head which can reduce curving of a head substrate even when a hard thermosetting resin is used for a protection coating so as to protect a wire connecting part. <P>SOLUTION: In the thermal printing head, the long head substrate 13 of a ceramic with a plurality of heating resistors 12 arranged on a surface, and a driving circuit substrate 15 of a resin larger in coefficient of expansion than the head substrate with a wiring circuit 30 stationed thereon are arranged in parallel to each other. Moreover, the thermal printing head is equipped with the IC 14 for driving mounted on the head substrate 13 or the driving circuit substrate 15, and the protection coating 18 of a resin which coats the connecting part 17 of a bonding wire of the IC 14. The protection coating 18 is formed of the thermosetting resin. A first expansion control plate 32 and a second expansion control plate 33 smaller in coefficient of thermal expansion than the driving circuit substrate are bonded to both surfaces of the driving circuit substrate 15, thereby forming a compound plate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermal print head used for printing characters and images.

  Thermal print heads occupy an important position as recording devices in the field of office automation equipment and video printers. Thermal print heads record on thermal paper, ink ribbons, and plate-making film photographic paper by generating heat from a heating resistor placed on the substrate. Various developments have been made due to low noise and low cost. Has been done. FIG. 5 shows a conventional apparatus, in which the head substrate 101 is a long plate, and a glaze layer is formed on the surface so that convex portions are formed linearly, and a row of heating resistors 102 is formed on the convex portions on the glaze layer. Are also formed in a straight line. The head substrate 101 and the drive circuit substrate 103 are bonded to the support plate 100 with a double-sided tape, and a driving IC 104 is mounted on the head substrate 101 or the drive circuit substrate, and the head substrate 101, the drive substrate IC, and the drive circuit are bonded by bonding wires 105. The substrate 102 and the driving IC 104 are joined and encapsulated using a silicon-based resin or an epoxy resin 106 to protect the wire connection portion.

  When it protects with a silicon resin, since the hardness after hardening is low, there exists a problem that a wire is easy to be cut | disconnected by a heat stress and external pressure. In addition, when it is protected with an epoxy resin, it becomes a hard coat. However, since the linear expansion coefficients of the head substrate and the drive circuit substrate are different, there is a problem that the head substrate is bent when the epoxy resin is cured at a high temperature and then returned to normal temperature. .

Thus, in the case of using an epoxy resin that forms a hard coat, the epoxy resin is cured through a high temperature treatment from the viewpoint of high durability and the like. As shown in FIG. 6, the head substrate 101 and the drive circuit substrate 103 are butt-joined while maintaining linearity in a high temperature state. However, when returning to a normal temperature state, particularly in a thermal print head having a long print length, that is, a scanning direction. Due to the difference in linear expansion coefficient between the head substrate and the drive circuit substrate, the head substrate 101 warps in a bow shape in the surface direction, and the row R of the heating resistors 102 also warps as shown in the figure. The tendency becomes more prominent as the printing length is longer. Printing is performed by pressing the recording paper against the heating resistor row by the platen roller. Such an arcuate deformation is indicated by the arrow at the end or center of the row R of the heating resistor 102 from the nip line nip of the platen roller. Will result in a blurring of the print.
Japanese Patent Laid-Open No. 08-39856

  In consideration of arcuate deformation, it has been proposed that the heating resistor array is deformed in advance to form a pattern by warping in reverse (see Patent Document 1). However, it is inevitable that the deformation is uneven and the design is complicated.

The present invention has been made to solve the above disadvantages.

The present invention provides the above-mentioned head substrate in which a ceramic long head substrate having a plurality of heating resistors and electrode patterns connected to these heating resistors arranged on one surface and a wiring circuit connected to an external circuit are arranged. Mounted on the head substrate or the drive circuit board, a drive circuit board made of resin having a larger expansion coefficient, a support plate in which the head substrate and the drive circuit board are adjacently disposed on one surface. A driving IC connected via wire bonding between the electrode pattern of the head substrate and a wiring circuit of the driving circuit substrate, the driving IC, wire bonding, a part of the head substrate, and In a thermal print head comprising a resin protective film covering a part of the printed circuit board,
The protective coating is formed of a thermosetting resin, and a first expansion control plate and a second expansion control plate having a smaller thermal expansion coefficient than the drive circuit substrate are bonded to both sides of the drive circuit board. A thermal print head formed is provided.

  In the present invention, a drive circuit board is formed as a laminated composite board by means of an expansion control plate, and its combined linear expansion coefficient is made close to the linear expansion coefficient of the head substrate, so that, for example, an epoxy resin is used as a hard thermosetting resin for protecting the wire connection portion. Even if it is cured at a high temperature, it is possible to reduce the curvature of the head substrate, and it is possible to provide a thermal print head that is easy to design and has high quality and high durability.

  1 to 4 illustrate an embodiment of the present invention. A head substrate 13 in which a heating resistor 12 is formed on one surface of a long support plate 11 made of a metal such as aluminum Al and also serving as heat dissipation. And a driving circuit board 15 which is connected to an external circuit and supplies power to a driving IC (semiconductor integrated circuit) 14 and transmits its input / output signals. Here, the long length means a rectangular shape having a long side and a short side. The head substrate 12 and the drive circuit substrate 15 are arranged in contact with the long sides facing each other, and a plurality of driving ICs 14 are mounted in the vicinity of the contact side of the head substrate 13. A region in the vicinity of the contact side becomes the wire connection portion 17.

  As shown in FIG. 2, the head substrate 13 covers a glaze layer 21 on a long ceramic substrate 13a such as alumina, and a part of the glaze layer is raised in a convex shape along the long direction. A plurality of dot-like heating resistors 12 are arranged linearly in the same longitudinal direction. Electrode patterns 23a and 23b are connected to both ends of each heating resistor. One pattern 23a is arranged on the substrate as an individual electrode of each heating resistor and the other pattern 23b is a common electrode.

  The driving IC 14 is mounted on the head substrate so as to share and drive a part of the total number of heating resistor dots. For this reason, a plurality of ICs are arranged in a line along the longitudinal direction of the substrate. ing.

  The drive circuit board 15 is made of a resin material such as a glass epoxy plate in a long shape matching the head board, and has a wiring circuit 30 and an external circuit connection terminal 31 connected thereto on the surface. The glass epoxy plate is a glass fiber reinforced resin plate obtained by impregnating a glass fiber cloth with an epoxy resin and thermosetting it.

  3 and 4 show a composite plate of the drive circuit board 15 of the present embodiment. Thermal expansion control plates 32 and 33 made of alumina ceramic plates are bonded to both surfaces of the drive circuit board 15. In general, a resin material has a larger coefficient of linear expansion than a ceramic material and is rich in flexibility. By adopting a three-layer laminated composite plate structure as shown in the figure, the linear expansion coefficient of the composite plate structure can be brought close to the linear expansion coefficient of the thermal expansion control plates 32 and 33 bonded to both surfaces.

These thermal expansion control plates can be made of the same material as the ceramic material of the head substrate, and it is desirable that the drive circuit board 15 and the thermal expansion control plates 32 and 33 be firmly bonded. An epoxy adhesive having a tensile shear strength of 7.0 N / mm ² or more is suitable.

  As shown in FIG. 2, the head substrate 13 and the drive circuit substrate 15 are attached to the support plate 11 with double-sided adhesive tapes 34 and 35. The support plate 11 made of metal, the head substrate 13 made of ceramic, and the drive circuit substrate 15 made of resin have greatly different linear expansion coefficients, and the difference in thermal expansion coefficient between the support plate 11 and the head substrate 13 is different from that of the support plate 11. The difference in thermal expansion coefficient with the drive circuit board 15 is absorbed by this double-sided adhesive tape.

  A bonding wire 16 is used for wire connection between the electrode pattern 23 of the head substrate 13 and the driving IC 14 and between the wiring circuit 30 of the driving circuit substrate 15 and the driving IC 14. The wire connection portion 17 is a region extending over a part of the electrode pattern 23 region of the head substrate, a part of the driving IC 14, a region of the wiring circuit 30 of the driving circuit substrate 15, and a contact portion between the substrates 13 and 15. Further, a hard protective film 18 of a thermosetting resin such as an epoxy resin is coated as an encap for protecting the bonding wire 16 and the driving IC 14. The protective substrate 18 causes the head substrate 13 and the drive circuit substrate 15 to behave as an integrated substrate, and the difference in linear expansion coefficient between the two substrates affects the thermal expansion / contraction of each substrate. However, the thermal expansion control plates 32 and 33 bonded to the upper and lower surfaces of the drive circuit board 15 become composite plates with the drive circuit board 15 and lower the combined linear expansion coefficient to approach the coefficient of the head substrate 13.

  Further, finally, a protective cover 40 is attached on the protective film 18 with screws 41 provided on the drive circuit board to prevent damage due to external impacts such as a platen or recording paper.

  For example, an alumina substrate having a thickness of 0.8 mm and a linear expansion coefficient of 6.1 ppm is used for the head substrate 13, and a glass epoxy having a thickness of 0.9 mm and a linear expansion coefficient of 14.5 ppm is used for the drive circuit substrate 15. A substrate is used. The thermal expansion control plates 32 and 33 are made of an alumina substrate having the same material as the head substrate and having a thickness of 1 mm, and are bonded to the upper and lower surfaces of the drive circuit substrate 15 with an epoxy resin to form composite plates. The linear expansion coefficient of the composite plate varies depending on the linear expansion coefficient and thickness of the plates to be joined, but can be controlled below the expected value by selecting the thickness and characteristics of the plate, for example, to 11.5 ppm. Can do.

  As a result, the in-plane curvature of the head substrate can be reduced even when the wire connection portion is protected by high temperature thermosetting with an epoxy resin.

(Example)
Examples of the present invention will now be described. A glazed ceramic substrate holding a glazed layer 21 that keeps warm and smooth at a predetermined position on the ceramic substrate 13a is used as a head base 13, and the resistor layer 12 and the Al electrode patterns 23a and 23b are sequentially formed by a thin film forming method such as sputtering. Then, a photo-engraving process is performed on the substrate so that a plurality of pairs of heating resistors and electrodes are arranged in the same pattern. Thereafter, a protective film 18 was formed so as to protect at least the resistor portion, whereby the head substrate 13 was obtained. Here, the heating resistor array of the head substrate was 356 mm, and the outer shape of the head substrate 13 was 370 mm × 13 mm.

  Further, the first and second ceramic thermal expansion control plates 32 and 33 having a linear expansion coefficient of 6.1 ppm are formed on the upper and lower surfaces of the glass epoxy drive circuit board 15 on which the printed wiring 30 is formed with an epoxy adhesive. The drive circuit board 15 was made into a composite board. Here, the drive circuit board 15 is made of resin FR4 (trade name) and has a thickness of 0.9 mm and an outer shape of 370 mm × 30 mm. The thermal expansion control plate has a thickness of 1 mm on the upper surface side, an outer shape of 370 × 15 mm, and a lower surface side. The plate has a thickness of 1 mm and an outer shape of 370 × 20 mm, and the upper surface thermal expansion control plate of the drive circuit board 15 is shorter from the inner side in the longitudinal direction adjacent to the head board by 5 mm for wire connection between the head board and the wiring circuit 30. The exposed opening 36 in the wiring circuit region is formed by bonding. The expansion control plates on the upper surface and the lower surface both have a long side opposite to the head substrate adjacent portion protruding 10 mm from the edge of the support plate as a component connecting portion 37 such as an external signal or a connector for supplying power. The drive circuit board 15 and the expansion control plates 32 and 33 were connected by transferring an epoxy adhesive onto the ceramic substrate with a stamp tool, pressurizing the drive circuit board, and curing at high temperature.

  The drive circuit board composite and the head board 13 are joined to the Al support plate 11 with double-sided adhesive tape, the drive IC 14 is mounted on the head board 13, and the electrode pattern 23a of the head board and the drive IC 14 are mounted by the Au bonding wire 16. And the wiring circuit 30 of the driving circuit board and the driving IC 14 are joined. As the protective coating 18 of the wire connection portion 17, the head substrate 14 and the drive circuit substrate 15 were cured at a high temperature using an epoxy resin so as to bridge.

  In the above case, when the drive circuit board is not a composite board as in the prior art, the ceramic head board is curved in the plane direction by about 0.3 mm due to the difference in linear expansion coefficient. Printing is performed by pressing the recording paper against the heating resistor array by the platen roller, and the nip width of the platen roller is usually about 0.2 mm. Therefore, if the surface direction bend of 0.3 mm occurs, the heating resistance is generated from the nip of the platen roller. The end or center of the body row is disengaged and blurring of the print occurs.

  As a result of simulation, the composite plate of the present embodiment has a linear expansion coefficient of 7.3 ppm, and the curvature in the surface direction of the head substrate is 0.035 mm as an actually measured value.

  The thermal print head manufactured in this way has a drive circuit board made of a composite board with a ceramic board, so that the difference in thermal expansion coefficient between the head board and the drive circuit board composite is reduced, so that the straight line of the heating element array It became possible to maintain sex. Hard coat agent can be used even for thermal print heads with relatively long print lengths, which could not use hard coat agents such as epoxy as protective coatings due to the deformation of resistor rows. Thus, effects such as the extension of the product life and the improvement of the printing quality can be achieved.

  According to this embodiment, a drive circuit board having a linear expansion coefficient of 14.6 ppm or more is bonded to a plate material having a linear expansion coefficient of 6.1 ppm or less with an epoxy adhesive to form a composite board having a linear expansion coefficient of 7.3 ppm. Thus, a substantial difference in thermal expansion coefficient between the drive circuit board and the head board could be reduced. This makes it possible to manufacture thermal print heads that maintain the linearity of the heating element arrays, and it is possible to make hard coats with resin at the wire joints, which was not possible with thermal print heads with large print lengths. A great effect was obtained in terms of reliability and high durability.

  As described above, the epoxy resin is used as an example for the protective coating of the hard coat in the present embodiment, but the same effect can be obtained with another resin such as an acrylic resin.

  Further, polyimide, polymer liquid crystal, or the like can be used as the resin for the drive circuit board.

  Further, the present invention can be applied to a structure in which the driving IC is mounted on the driving circuit board instead of the head board.

Sectional drawing explaining one Embodiment of this invention FIG. 1 is an enlarged sectional view showing a part of FIG. The exploded perspective view explaining the drive circuit board of one embodiment of the present invention. The perspective view after the assembly explaining the drive circuit board of one embodiment of the present invention Sectional drawing explaining a conventional device Plan view explaining warpage of head substrate

Explanation of symbols

11: support plate 12: heating resistor 13: head substrate 14: driving IC
15: Drive circuit board 16: Bonding wire 17: Wire connection part 18: Protective film 21: Glaze layer 23a, 23b: Electrode pattern 30: Wiring circuit 32: First expansion control board 33: Second expansion control board

Claims (5)

A ceramic long head substrate having a plurality of heating resistors and electrode patterns connected to these heating resistors arranged on one surface;
A drive circuit board made of resin having a larger expansion coefficient than the head board on which a wiring circuit connected to an external circuit is arranged;
A support plate in which the head substrate and the drive circuit substrate are adjacently disposed on one surface; and
A driving IC mounted on the head substrate or the driving circuit substrate, connected to the electrode pattern of the head substrate, and a wiring circuit of the driving circuit substrate via a bonding wire;
In a thermal print head comprising the driving IC, a bonding wire, a part of the head substrate, and a resin protective film covering a part of the wired circuit board,
The protective film is formed of a thermosetting resin,
The drive circuit board is a thermal print head in which a first expansion control board and a second expansion control board having a smaller thermal expansion coefficient than the drive circuit board are bonded to each other to form a composite board. The thermal print head according to claim 1, wherein the first and second expansion control plates are expansion control plates having a linear expansion coefficient of 11.5 ppm or less. The thermal print head according to claim 1, wherein a thickness of the first and second expansion control plates is smaller than a thickness of the drive circuit board. The first expansion control board is bonded so that the wiring circuit area to be wire-bonded opens on the surface of the expansion control board on which the wiring circuit to be wire-bonded to the electrode pattern or the driving IC is disposed. Item 2. The thermal print head according to Item 1. 2. The thermal print head according to claim 1, wherein the adhesive that bonds the drive circuit board and the first and second expansion control plates is an epoxy adhesive having a tensile shear strength of 7.0 N / mm ² or more.

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