JP2003220724A - Thermal head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-reliability thermal head which can form good prints by maintaining a linearity of a heating resistor array high. <P>SOLUTION: In the thermal head, a driver IC 5 where a plurality of terminal electrodes to be electrically connected to a circuit pattern 3 are set at a lower face is loaded by facedown bonding onto a head board 1 having many heating resistors 2 and the circuit pattern 3. At the same time, a head cover 9 having one end extending to the vicinity of the heating resistors 2 is set above the driver IC 5. An anisotropic conductive film 6 having a Shore hardness A of 60-70 is interposed between the driver IC 5 and the head board 1, and moreover an upper face of the driver IC 5 is pressed towards the head board 1 by an inner face of the head cover 9, thereby electrically connecting the terminal electrodes of the driver IC 5 and the circuit pattern 3 each other. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head incorporated as a recording device such as a facsimile or a video printer. [0002] Conventionally, thermal heads have been widely used as recording devices such as facsimile machines. As such a conventional thermal head, for example, as shown in FIG. 3, a head substrate 1 made of alumina ceramics on which a plurality of heating resistors 12, a circuit pattern 13 and a driver IC 14 arranged in a straight line are attached.
1 and a printed wiring board 15 made of a polyimide resin having a plurality of wiring conductors 16 are placed and provided side by side on a metal heat radiating plate 18, and wiring between the circuit pattern 13 on the head substrate 11 and the printed wiring board 15 is performed. Known is a structure in which the conductors 16 are electrically connected via solder, fine metal wires, or the like. The heating resistors 12 are individually selectively Joule-heated when the driver IC 14 is driven. Is transmitted to a recording medium such as thermal paper to form a predetermined print. As the driver IC 14, a flip-chip type driver IC in which electronic circuits and terminal electrodes are integrated on the lower surface is used.
The terminal electrode of C14 is soldered to the corresponding circuit pattern 13 on the upper surface of the head substrate to form a driver IC.
14 was mounted at a predetermined position on the head substrate 11. The head substrate 11 and the printed wiring board 15
A head cover 17 having one end extending to the vicinity of the heating resistor 12 is disposed on the connection portion with the head substrate 11 and the printed wiring board 15.
The connection between them and the driver IC 14 are protected from the application of external force. [0006] However, in the above-described conventional thermal head, the alumina ceramic forming the head substrate 11 and the single crystal silicon forming the driver IC 14 have a large difference in linear expansion coefficient. Therefore, when the temperature of the head substrate 11 and the driver IC 14 rises when the thermal head is used, a large thermal stress is generated between the two due to a difference in linear expansion coefficient. Therefore, when bonding between the circuit pattern 13 and the terminal electrode with a small amount of solder with the increase in the density of the circuit pattern 13 and the terminal electrode, there is a disadvantage that the solder joint is destroyed due to the large thermal stress described above. I was When the driver IC 14 is covered with a hard sealing material made of epoxy resin or the like, the thermal stress caused by the temperature rise of the thermal head is caused not only between the head substrate 11 and the driver IC 14 but also between the head substrate 11 and the driver IC 14. These thermal stresses cause the thermal head to bend greatly in the longitudinal direction, and the linearity of the heating resistor array (the arrangement of the heating resistors) is significantly lost. As a result, it becomes impossible to press all the heating resistors 12 against the recording medium with uniform strength, and the density unevenness,
A defect that causes printing failure such as a fray is induced. The present invention has been devised in view of the above-mentioned drawbacks, and has as its object to provide a high-reliability thermal head capable of forming a good print while maintaining a high linearity of a heating resistor array. To provide. A thermal head according to the present invention has a plurality of terminal electrodes electrically connected to the circuit pattern on a head substrate having a large number of heating resistors and circuit patterns. In a thermal head, a driver IC having a lower surface is mounted by face-down bonding, and a head cover having one end extending to the vicinity of a heating resistor is provided on the driver IC. Shore hardness A is 6 between
0 to 70 anisotropic conductive films are interposed, and the upper surface of the driver IC is pressed against the head substrate side by the inner surface of the head cover to electrically connect the terminal electrodes of the driver IC to the circuit pattern. It is assumed that. According to the thermal head of the present invention, the Shore hardness A is between 60 and 7 between the driver IC and the head substrate.
An anisotropic conductive film having an appropriate elasticity of 0 is interposed, and the upper surface of the driver IC is pressed against the head substrate by the inner surface of the head cover to electrically connect the terminal electrodes of the driver IC and the circuit pattern on the head substrate. The temperature of the thermal head rises when the thermal head is used, and the head substrate-driver I
Even if an attempt is made to generate a large thermal stress due to the difference in the coefficient of linear expansion between C, the thermal stress is applied to the head substrate-driver IC.
The connection between the head substrate and the driver IC can be maintained in a good state by absorbing and relaxing the anisotropic conductive film having a Shore hardness A of 60 to 70 which is interposed therebetween. Longitudinal bending due to stress can also be effectively prevented. Therefore, the linearity of the heating resistor row is maintained high, and a clear print can always be formed. Further, according to the thermal head of the present invention, pressure is applied to the anisotropic conductive film between the driver IC and the head substrate by a simple mechanism that only presses the driver IC toward the head substrate from the inner surface of the head cover. In this case, there is no need to separately attach a pressing member or the like in order to achieve conduction between the driver IC and the head substrate, and therefore, there is an advantage that the configuration of the thermal head can be simply maintained. The present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is an exploded perspective view of a thermal head according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of the thermal head of FIG. 1, where 1 is a head substrate, 2 is a heating resistor, and 3 is a circuit pattern. Reference numeral 5 denotes a driver IC, 6 denotes an anisotropic conductive film, and 9 denotes a head cover. The head substrate 1 is formed of an electrically insulating material such as alumina ceramics. A heating resistor 2 and a circuit pattern 3 are adhered on an upper surface of the head substrate 1 in a predetermined pattern, and function as a supporting base material for supporting these. I do. When the head substrate 1 is made of, for example, alumina ceramics, a ceramic material powder of alumina, silica, magnesia or the like is formed into a slurry by adding and mixing an appropriate organic solvent and a solvent. A ceramic green sheet is formed by employing a doctor blade method, and thereafter, the obtained green sheet is punched into a predetermined shape, and then subjected to high temperature (about 1600).
C). A plurality of heating resistors 2 are attached and formed on the upper surface of the head substrate 1, and a circuit pattern 3 is connected to each of the heating resistors 2. The heating resistor 2 is, for example, 600 dpi.
(Dots per inch), and are linearly arranged in the longitudinal direction (main scanning direction) of the head substrate 1, each of which is Ta.
Since it is made of an electrical resistance material such as a SiO-based or TiSiO-based material, Joule heat is generated when electric power is applied from the outside via the circuit pattern 3 or a driver IC 5 to be described later, and a print is formed on a recording medium. , For example, a temperature of 150 ° C to 250 ° C. The circuit pattern 3 connected to the heating resistor 2 is formed of a conductive material such as aluminum or copper so as to form a predetermined pattern. One end of the circuit pattern 3 is anisotropically connected to a terminal electrode of a driver IC 5 described later. It is electrically connected through the conductive film 6 and functions as a power supply wiring or a signal wiring for supplying external power or an electric signal to the driver IC 5 or the heating resistor 2. The heating resistor 2 and the circuit pattern 3
Employs, for example, a conventionally known thin film forming technique, for example, a sputtering method, a photolithography technique, an etching technique, etc., and deposits the above-described electric resistance material and conductive material on the upper surface of the head substrate 1 in a predetermined thickness and a predetermined pattern. Then, it is covered with a protective film 5 made of an inorganic material having excellent wear resistance such as silicon nitride or glass. A driver IC 5 is mounted on the upper surface of the head substrate 1 via an anisotropic conductive film 6. The driver IC 5 has a function of causing the plurality of heating resistors 2 to individually and selectively generate Joule heat,
More specifically, the driver IC 5 individually controls the energization of the heating resistor 2 based on image data or the like supplied via the printed wiring board 7. The driver IC 5 includes a shift register, a latch, and an output transistor. -Chip type driver I having an electronic circuit and terminal electrodes on its lower surface
C, the driver IC 5 is placed at a predetermined position on the head substrate 1 via the anisotropic conductive film 6, and
The terminal electrodes are selectively connected to the corresponding circuit patterns 3 by pressing the upper surface of the driver IC 5 toward the head substrate 1 with the inner surface of a head cover 9 described later. On the other hand, when a mechanical pressure is applied in the thickness direction, the anisotropic conductive film 6 interposed between the driver IC 5 and the head substrate 1 undergoes compression deformation (compression deformation ratio: 1).
0% to 15%), and has a characteristic of conducting in the thickness direction at a portion where the interval is reduced by the compression. As the anisotropic conductive film 6, for example, a base material made of silicone rubber or the like is used. A sheet-like anisotropic conductive film containing and dispersing therein a conductive filler made of Ni / Au or the like having a particle size of about 4 μm to 6 μm is preferably used. In that case, the content of the conductive filler is set to, for example, 80 wt% to 90 wt%. The anisotropic conductive film 6 has a Shore hardness A of 6
It has a moderate elasticity of 0 to 70, and the temperature of the head substrate 1 and the driver IC 5 rises when the thermal head is used, etc., and a large heat generated due to a difference in linear expansion coefficient between the head substrate 1 and the driver IC 5. Even if a stress is generated, the stress is favorably absorbed and reduced by the anisotropic conductive film 6 interposed between the head substrate 1 and the driver IC 5. Therefore, the head substrate 1-driver IC 5
It is possible to keep the connection between them in a good state, effectively prevent longitudinal bending caused by thermal stress, maintain a high linearity of the heating resistor row, and always keep clear A print can be formed. A printed wiring board 7 is provided adjacent to the above-described head substrate 1, and the head substrate 1 and the printed wiring board 7 are placed and fixed on a heat radiating plate 8 in a state where they are provided together. The printed wiring board 7 includes a plurality of wiring conductors 7 electrically connected to the circuit pattern 3 on the head substrate 1.
a, one end of the wiring conductor 7a is connected to the circuit pattern 3 of the head substrate 1, and the other end of the wiring conductor 7a is connected to the printer body via a connector attached to the rear end of the printed wiring board 7. By being connected, external power, image data, print control signals, and the like are transferred to the heating resistor 2 of the head substrate 1.
And the driver IC5. still,
As the printed wiring board 7, for example, a flexible wiring board in which a plurality of wiring conductors 7a are sandwiched between a base film made of a polyimide resin or the like and a cover film is suitably used. On the other hand, the heat radiating plate 8 supports the head substrate 1 and the printed wiring board 7 on the upper surface thereof, and absorbs a part of the heat of the head substrate 1 and radiates it to the atmosphere to thereby release the head substrate 1. Is made by effectively forming a metal such as aluminum or SUS into a predetermined shape by a conventionally known metal working method. The head substrate 1 and the printed wiring board 7 are bonded and fixed by placing the head substrate 1 and the printed wiring board 7 via an adhesive such as a tape. On the connection between the head substrate 1 and the printed wiring board 7, a head cover 9 having one end extended to the vicinity of the heating resistor 2 is provided. The head cover 9 is provided with a driver IC 5
And the connection between the head substrate 1 and the printed wiring board 7 is protected from the application of an external force, the running of the recording medium is supported on the outer surface thereof, and the guide member serves to guide the recording medium onto the heating resistor 2. It functions and is made of plastic, aluminum, stainless steel (SUS) or the like. As described above, the head cover 9 presses the upper surface of the driver IC 5 with its inner surface, and a moderate pressure, for example, 5 gf / mm ^{2 to} 30 g
A pressing force of f / mm ² is applied. In this case, the driver IC 5 is not damaged by the pressing force from the head cover 9 and the head cover 9 is not damaged.
Pressure can be applied to the anisotropic conductive film 6 between the driver IC 5 and the head substrate 1 by a simple mechanism that only presses the driver IC 5 toward the head substrate 1 on the inner surface of the substrate.
The structure of the thermal head can be kept simple compared to a case where a pressing member or the like is separately attached for achieving conduction between the driver IC 5 and the head substrate 1. When the head cover 9 is made of a plastic material, it is molded by employing a conventionally known injection molding method, and is attached and fixed to the heat radiating plate 8 by means of a conventionally known screw or the like. When the head cover 9 is formed of metal, an electrical connection between the driver IC 5 and the head cover 9 is made by applying an insulating process to a contact portion with the driver IC 5 or attaching an insulating sheet or the like. It is necessary to keep insulation. Thus, the above-described thermal head according to the present embodiment is provided with the heating resistor 2 in accordance with the driving of the driver IC 5.
And a predetermined power is applied to the heating resistor 2 to selectively and individually generate Joule heat based on the printing control signal.
The generated heat is conducted to a recording medium such as thermal paper, and a predetermined print is formed on the recording medium to function as a thermal head. It should be noted that the present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the gist of the present invention. For example, in the above-described embodiment, the head substrate 1 is formed of alumina ceramics. Instead, the head substrate 1 is formed of single-crystal silicon or the like whose surface is oxidized. No problem. According to the thermal head of the present invention, the Shore hardness A between the driver IC and the head substrate is 60 to 60.
70, the terminal electrode of the driver IC and the circuit pattern on the head substrate are electrically connected to each other by pressing the upper surface of the driver IC toward the head substrate with the inner surface of the head cover while interposing an anisotropic conductive film having appropriate elasticity. When the thermal head is used, for example, the temperature of the thermal head rises and a large thermal stress due to the difference in linear expansion coefficient between the head substrate and the driver IC is generated. The stress is applied to the head substrate-driver I
By favorably absorbing and relaxing the anisotropic conductive film interposed between C, the connection between the head substrate and the driver IC can be maintained in a good state, and the longitudinal direction due to thermal stress can be maintained. Curving can also be effectively prevented. Therefore, the linearity of the heating resistor row is maintained high, and a clear print can always be formed. Further, according to the thermal head of the present invention, pressure is applied to the anisotropic conductive film between the driver IC and the head substrate by a simple mechanism that only presses the driver IC toward the head substrate from the inner surface of the head cover. In this case, the driver IC is not damaged by the pressing force from the head cover, and compared with a case where a pressing member or the like is separately attached for achieving conduction between the driver IC and the head substrate. There is also an advantage that the configuration of the thermal head can be kept simple.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective view of a thermal head according to an embodiment of the present invention. FIG. 2 is a sectional view of the thermal head of FIG. FIG. 3 is a sectional view of a conventional thermal head. [Description of Signs] 1 ... Head substrate, 2 ... Heat generating resistor, 3 ... Circuit pattern, 4 ... Protective film, 5 ... Driver I
C, 6: anisotropic conductive film, 7: printed wiring board, 8.
..Heat radiators, 9 ... Head covers

Claims (1)

Claims: 1. A driver IC having a plurality of terminal electrodes on a lower surface which is electrically connected to a circuit pattern on a head substrate having a plurality of heating resistors and circuit patterns. A thermal head mounted by down bonding and having a head cover having one end extended to the vicinity of the heating resistor on the driver IC, wherein a Shore hardness A between the driver IC and the head substrate is provided.
Is that the anisotropic conductive film of 60 to 70 is interposed and the upper surface of the driver IC is pressed against the head substrate side by the inner surface of the head cover to electrically connect the terminal electrode of the driver IC and the circuit pattern. Characteristic thermal head.