JPH04201575A - Thermal head - Google Patents

Abstract

PURPOSE:To bring a heat-generating part in improved contact with recording paper by a method wherein a recess coated with polyimide resin is formed to the underside of the heat-generating part of a copper-plated heat-resistant insulating resin substrate and, at the same time, a drive device is mounted by means of facedown bonding, and the polyimide resin is further applied to a solder dam. CONSTITUTION:Copper foils of a copper-plated heat-resistant insulating resin substrate 14 is formed in a radiating layer 16 by normal method for formation of wiring patterns, and an insulating layer 17 is made thereon with Ni Au plating and polyimide varnish coating applied. Film-forming with polyimide is applied only to a heat-generating part 22 of a heat-generating resistor 18 formed on the insulating layer, and a protruding part 25 is formed to the layer. An IC 9 for control, of the heat-generating resistor 18 is mounted to the layer 18 by means of facedown bonding, and polyimide is applied to form, together with the protruding part 25, a flow-prevention dam for reflow of solder bump at the time of the facedown bonding. As the heat-generating part of the heat-generating resistor is formed in a structure that projects above the surrounding parts, improving contact with recording paper an electricity-saving thermal head can be constructed therewith, making the best use of polyimide that is used as a heat-accumulating layer.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a thermal head used in thermal printing and recording devices such as facsimiles and printers.

[Conventional technology]

FIG. 4 shows the configuration around the heating resistor portion of a conventional thermal head using a ceramic substrate. In the figure, reference numeral 1 indicates a ceramic substrate made of alumina or the like, and reference numeral 2 indicates a glaze layer made of high melting point glass formed on the surface thereof. On the glaze layer 2, a heating resistor 3 made of Ta-8i02, RuO2, etc., a common electrode 4a and individual electrodes 4b made of A1, Au, etc., and a protective film 5 made of S1A1ON, SiON, amorphous glass, etc. are provided. It has a sequentially laminated structure. This thermal head is formed by vapor deposition or sputtering in the case of a thin film method, and by printing and baking in the case of a thick film method, but basically has the same structure. 5 to 7 show the overall structure of a conventional thermal head using a ceramic substrate. FIG. 5 shows an example in which a ceramic substrate 1 on which a heating resistor 3 is formed is combined with a hard printed wiring board 7. The electrical connection between both substrates 1 and 7 is made using an IC 9 for driving and controlling the heating resistor 3. It uses Au wire for wire bonding. 6 and 7 are examples in which a ceramic substrate 1 on which a heating resistor 3 is formed and an FPC (flexible substrate) 11 on which a reinforcing plate 10 is attached are combined, and the electrical connection between both substrates 1 and 11 is In FIG. 6, pressure bonding with rubber 12 is used, and in FIG. 7, thermocompression bonding with solder is used. Note that 13 in the figure is a heat sink. In the thermal head described above, it is necessary to apply heat of at least several hundred degrees during the manufacturing process to form the heating resistor portion, so an expensive ceramic substrate is used as an insulating substrate that can withstand this temperature. However, because ceramic substrates have poor workability, they are combined with hard printed wiring boards and FPCs, as mentioned above, which increases material costs and requires a large number of assembly steps. In order to solve these problems, the applicant of this application has developed a 300
We proposed a thermal head that electrically consists of a board, using a heat-resistant insulating resin board that has heat resistance of ~400°C or more and has workability similar to that of general hard printed wiring boards. For example, Japanese Patent Application No. 1-260529, Japanese Patent Application No. 2-2529
26, its structure is shown in FIG. In the figure, as the heat-resistant insulating resin substrate 14, a copper-clad board is used in which copper foil is stretched over a layer 15 of heat-resistant cloth impregnated with heat-resistant resin, and the copper foil is is etched using a normal pattern forming method, and a solid copper foil is left in the vicinity of the heating resistor to form the heat dissipation layer 16. An insulating film 17 is formed thereon as a heat storage layer using polyimide, for example.
Furthermore, the heating resistor 18, the common electrode 19a1, the individual electrode 19
b and the protective film 20 are sequentially laminated. In the thermal head with this configuration, as shown in FIG. 9, the heat generating resistor 18, its drive control circuit components (the drive control IC therein is indicated by 9), and the connector 21 for connection with an external circuit are also integrated. It can be mounted on two heat-resistant insulating resin substrates, and the connection wiring between them can be made using double-sided wiring with through holes or copper foil of a copper-clad board with two-layer wiring. The thermal head consists of

[Problem to be solved by the invention]

Figure 81 The thermal head with the configuration shown in Figure 9 uses a heat-resistant insulating resin substrate that can be processed in the same way as a normal hard printed wiring board, and can be fabricated with double-sided wiring or two-layer wiring using through holes. Including heating resistors,
The drive control circuit components, connector components for connection with external circuits, and connection wiring between these can be integrally formed and mounted on a single insulating substrate, and electrically the thermal head can be mounted on a single insulated substrate. will be formed. However, even though a material with excellent heat storage properties such as polyimide is used for the heat storage layer, as shown in FIG. Because its properties are not very good, its characteristics are not fully utilized. In view of the above, an object of the present invention is to provide a thermal head that uses a copper-clad heat-resistant insulated resin substrate and has a structure that allows the heat-generating portion to contact paper well.

[Means to solve the problem]

The problem solving means according to claim 1 of the present invention is a thermal head using a copper-clad heat-resistant insulating resin substrate as shown in FIGS. 25 was formed. Furthermore, the problem solving means according to claim 2 is to mount a heating resistor driving element on a copper-clad heat-resistant insulating resin substrate by face-down bonding, and to use polyimide resin as a solder dam to prevent the solder bumps from flowing. This is what I used.

[Function] In the problem solving means according to claim 1, the convex portion 25 made of polyimide is provided on the lower layer of the heat generating portion 22 of the heat generating resistor 18.
When provided, the heat-generating portion 22 protrudes from its peripheral portion, improving the paper contact property. Further, in the problem solving means according to claim 2, when the driving element 9 of the heating resistor 18 is mounted by face-down bonding, if polyimide is used as a dam for preventing the solder bump from flowing during reflow, this solder dam and Since the convex portion 25 on the lower layer of the heat generating portion 22 can be formed at the same time, the heat generating portion protrudes without adding a new process.

【Example】

Hereinafter, one embodiment of the present invention will be described based on the drawings. FIG. 1 shows an enlarged cross-sectional view of the vicinity of the heating resistor part of the embodiment of the present invention, FIG. 2 shows the overall configuration of the thermal head of the embodiment, and FIG. 3 shows the copper-clad heat-resistant insulating resin used in the embodiment. A cross-sectional view of the substrate is shown. First, the structure of the copper-clad heat-resistant insulating resin substrate used in this example will be explained based on FIG. 3. The copper-clad heat-resistant insulating resin board 14 is a double-sided copper-clad board (of course, only on one side), which has copper foils 16a and 16b on both sides of a layer 15 made of heat-resistant cloth (e.g., glass fiber) impregnated with heat-resistant resin (e.g., polyimide). A single-sided board covered with copper foil may be used), and the same processing method as for hard printed wiring boards such as ordinary glass epoxy boards can be applied. Moreover, since the copper-clad heat-resistant insulating resin substrate 14 uses heat-resistant cloth and heat-resistant resin, it has heat resistance that can withstand temperatures of 300 to 400° C. or higher. Next, the configuration around the heating resistor portion of this embodiment will be explained based on FIG. The heat dissipation layer 16 is formed by etching the copper foil of the copper-clad heat-resistant insulating resin substrate 14 having the structure shown in FIG. The heat dissipation layer 16 may be formed around the heating resistor shown by 26 in FIG. 2, taking into consideration the balance between heat dissipation performance and efficiency. At this time, a heating resistor 18 indicated by 27 in the figure is also added.
A part of the wiring pattern of the component mounting portion in which control circuit components for controlling energization, connector 21 for connection with an external circuit, etc. are mounted is also formed by etching. Next, Ni and Au are etched on this etched copper foil pattern.
Apply plating. Next, spin code the polyimide varnish,
The heat dissipating layer 16 is coated on the entire surface by roll coating, screen printing, etc., temporarily cured, etched, and then fully cured.
An insulating layer 17 is formed to cover the insulating layer 17. On top of that, another layer of polyimide is formed in the same manner only on the part corresponding to the heat generating part 22 of the heat generating resistor 18, and the convex part 2
form 5. A film of Ta-8i02 is formed thereon as a heating resistor 18 by sputtering. At this time, as shown in FIG. 1A, the end portion of the convex portion 25 made of polyimide has a gentle taper, so the step coverage of the heating resistor 18 does not pose a problem. Further, a layer of AI is formed as a common electrode 19a and individual electrodes 19b on the heating resistor 18 by vapor deposition or sputtering, and then etched into a desired pattern. At this time, a part of the wiring pattern of the component mounting portion where the control circuit component for controlling the energization of the heating resistor 18, the connector 21 for connection with an external circuit, etc., shown as 27 in FIG. After that, the heat generating resistor 18 is etched and separated into a desired pattern, and a protective film 20 is formed on the heat generating resistor 18 by etching and separating it into a desired pattern.
A film of iON or the like is formed by sputtering or vapor deposition. The polyimide varnish used to form the insulating layer 17 and the convex portions 25 may be, for example, Semico Fine or Trenice manufactured by Toshiku Co., Ltd., or PSI manufactured by Chisso Corporation.
-G series etc. Further, the drive control IC (indicated by 9 on tooth 2) of the heating resistor 18 is mounted by face-down bonding, and polyimide is used as a dam to prevent the solder bump from flowing during reflow. If there is
This solder dam and the convex portion 25 are formed at the same time. This eliminates the need to add a new process to form the convex portion 25 made of polyimide, which is particularly effective without increasing costs. That is, the thickness of the polyimide used as a dam to prevent solder flow is usually 3μ or less, while the thickness of the polyimide used as a heat storage layer is usually about 10 to 20μ.Since these two polyimides cannot be formed at the same time, they are formed twice. Therefore, by forming the convex portion 25 at the same time as forming the solder flow prevention dam, there is no need to add a new process. Next, the overall structure of the thermal head will be explained with reference to FIG. At the same time as the heating resistor 18 is formed on the heat-resistant insulating resin substrate on which the heating resistor portion shown in FIG. The connection wiring of the component mounting portion 27 on which connectors and the like are mounted can be formed as double-sided wiring using through holes or two-layer wiring using a polyimide insulating layer. Therefore, the drive control IC 9 for controlling the drive of the heating resistor 18 is mounted by face-down bonding (of course, wire bonding may also be used), and a connector for connection with other electrical components (not shown) and external circuits is mounted. By soldering and mounting 21 on the component mounting portion 27, a thermal head is completed on the -th board. The thermal head formed as described above is made of two substrates and has a structure in which the heat generating part protrudes from the peripheral part, so the paper contact property is significantly improved.
This is a power-saving thermal head that takes full advantage of the properties of the polyimide used as the heat storage layer. Although the thin film method has been described above, it goes without saying that this invention can also be applied to the thick film method if the firing temperature and the heat-resistant temperature of the heat-resistant insulating resin substrate become similar in the future. It is. It should be noted that the present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

【Effect of the invention】

As is clear from the above description, according to claim 1 of the present invention, the heat-generating portion of the heat-generating resistor has a structure that protrudes from its surrounding area, so that the paper contact property is improved and the polyimide used as the heat storage layer is A power-saving thermal head that takes full advantage of its characteristics can be realized. According to claim 2, when the driving element of the heating resistor is mounted by face-down bonding, if polyimide is used as a dam to prevent the solder bump from flowing during reflow, a new process is required to form the convex portion. The heat generating part can be made to protrude without adding anything else, which is extremely effective. In addition, the connection wiring of the component mounting area, which mounts the control circuit components that drive and control the heating resistor, connectors for connection with external circuits, etc., can be made using double-sided wiring using through holes or double-layer wiring using polyimide as an insulating layer. By doing so, it can be formed on the same substrate as the heating resistor, so it is possible to provide a thermal head consisting of -2 substrates.

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view of the vicinity of a heating resistor portion of a thermal head according to an embodiment of the present invention. FIG. 2 is an overall configuration diagram of a thermal head according to an embodiment of the present invention. FIG. 3 is a sectional view of a copper-clad heat-resistant insulating resin substrate. FIG. 4 is an enlarged cross-sectional view of the vicinity of the heating resistor portion of a conventional thermal head using a ceramic substrate. FIG. 5 is an overall configuration diagram of a conventional thermal head using a ceramic substrate. FIG. 6 is an overall configuration diagram of a thermal head in which a ceramic substrate and a flexible substrate are electrically connected using pressure bonding using rubber. FIG. 7 is an overall configuration diagram of a thermal head in which a ceramic substrate and a flexible substrate are electrically connected using thermocompression bonding of solder. FIG. 8 is an enlarged cross-sectional view of the vicinity of the heating resistor portion of the thermal head according to the prior art. FIG. 9 is an overall configuration diagram of a thermal head according to the prior art. 9 Drive element 14 Copper-clad heat-resistant insulating resin substrate 15 Layer 16a made of heat-resistant cloth impregnated with heat-resistant resin
, 16b copper foil 17 Insulating layer 18 Heat generating resistor 19a Common electrode 19b Individual electrode 20 Protective film 21 Connector 25 Convex portion 26 made of polyimide Heat generating resistor peripheral portion 27 Component mounting portion A Part of the tapered end of the convex portion

Claims (2)

[Claims] 1. A thermal head comprising, on a copper-clad heat-resistant insulating resin substrate, a heat storage layer made of polyimide resin, a plurality of heating resistors, a common electrode and individual electrodes for supplying power to the heating resistors, and a protective layer. A thermal head characterized in that a convex portion made of polyimide resin is formed in a lower layer of the heat generating portion of the heat generating resistor. 2. The thermal head according to claim 1, comprising:
A thermal head characterized in that a heating resistor driving element is mounted on a copper-clad heat-resistant insulating resin substrate by face-down bonding, and polyimide resin is used as a solder dam to prevent the solder bumps from flowing.