JP2003220723A - Thermal head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-quality thermal head which can form good and clear prints by effectively preventing printing failures. <P>SOLUTION: In the thermal head, a head board 1 where many heating elements 3 aligned in a straight line and driver ICs 5 are arranged on an upper face of a base plate 2 formed of a ceramic or the like, a plurality of signal distribution lines 6 are applied to the upper face of the base plate 2 positioned to the opposite side to the heating elements 3 with respect to the driver ICs 5, and an external wiring plate 7 formed of a resin having many wiring conductors 8 to be electrically connected via metal thin wires 9 to the signal distribution lines 6 are set together. Moreover, the driver ICs 5 and the metal thin wires 9 are coated in common by a sealing material 10 essentially consisting of an epoxy resin. A modulus of elasticity in bending of the sealing material 10 is set to be lower at a region on the metal thin wires 9 than at a region on the driver ICs 5. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

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]

2. Description of the Related Art Conventionally, a thermal head has been used as a recording device such as a facsimile.

As such a conventional thermal head, for example, as shown in FIG. 4, a large number of heating elements 13 linearly arranged on the upper surface of a base plate 12 made of alumina ceramics and a driver IC 14 for controlling the heat generation of these heating elements 13. And the driver I
A head substrate 11 in which a plurality of signal wirings 15 are attached to the upper surface of a base plate 12 located on the side opposite to the heating element 13 with respect to C14, and a resin-made external wiring board 16 having a large number of wiring conductors 17 Together with the head substrate 11
There is known a structure in which the signal wiring 15 and the wiring conductor 17 of the external wiring board 16 are individually bonded by the thin metal wires 18, and a number of recording media such as thermal paper are conveyed onto the heat generating element 13 while a large number of them are conveyed. A predetermined print is formed by causing the heating elements 13 to individually and selectively generate Joule heat as the driver IC 14 is driven and to transfer these heats to the recording medium.

The external wiring board 16 is for supplying image data, printing control signals, electric power, etc. from the outside to the head substrate 11, and is connected to the head substrate 11 to which the thin metal wires 18 are bonded. A hard encapsulating material 19 having an epoxy resin as a main component is adhered to the portion in order to protect this portion from impact during use, and the thin metal wire 18 is covered with the driver IC 14 by the encapsulating material 19. is doing.

Further, the encapsulating material 19 is formed from the mounting area of the driver IC 14 to the head substrate 11-external wiring board 1 by using a liquid epoxy resin precursor or the like.
It was formed by applying a wide coating to the connection region 6 and heating and polymerizing it at a high temperature.

[0006]

However, in the above-described conventional thermal head, when forming the encapsulating material 19, a liquid precursor of epoxy resin is widely applied on the head substrate 11 and the external wiring board 16 and heated. -Aluminum ceramics that forms the base plate 12 between the head substrate 11 and the external wiring board 16 due to heat shrinkage of the sealing material 19 when polymerized, and a glass cloth-based epoxy resin wire used as the base of the external wiring board 16. A large thermal stress is generated due to the difference in the expansion coefficient, which causes the thermal head to bend in an arch and warp. In that case, the linearity of the heating element array is significantly reduced, and the pressing force of the heating element 13 against the recording medium becomes non-uniform, so that printing defects such as "distortion" and "blurring" are formed on the recording medium. Had.

The present invention has been devised in view of the above-mentioned drawbacks, and an object thereof is to provide a high quality thermal head capable of effectively preventing the occurrence of printing defects and forming good and clear prints. To provide.

[0008]

In a thermal head of the present invention, a large number of linear heating elements and driver ICs for controlling the heating of these heating elements are arranged on the upper surface of a base plate made of ceramic or silicon. ,
A head substrate in which a plurality of signal wirings are attached to the upper surface of a base plate located on the side opposite to the heating element with respect to the driver IC, and a large number of electrically connected to the signal wirings via thin metal wires. A thermal head in which an external wiring board made of a resin having a wiring conductor is provided side by side, and the driver IC and the thin metal wire are commonly covered with a sealing material containing an epoxy resin as a main component. The bending elastic modulus is set to be lower in the area on the thin metal wire than in the area on the driver IC.

The thermal head of the present invention is characterized in that the driver IC is mounted on the base plate by face-down bonding.

Further, in the thermal head of the present invention, a large number of elastic body fillers are contained in the sealing material, and the content rate of the elastic body fillers is a region on the thin metal wire as compared with a region on the driver IC. It is characterized by being set large in.

Furthermore, the thermal head of the present invention is characterized in that the content of the elastic filler is gradually increased from the region on the driver IC to the region on the thin metal wire.

Furthermore, the thermal head of the present invention is characterized in that the elastic filler is made of a silicone resin.

Further, the thermal head of the present invention is characterized in that the elastic filler is contained in an amount of 50% by weight or less in a region on a driver IC and 55% by weight to 95% by weight in a region on a solder joint. To do.

Furthermore, the thermal head of the present invention is characterized in that the sealing material contains an inorganic filler made of either alumina or silica in a region above the driver IC.

Furthermore, the thermal head of the present invention is characterized in that the content of the inorganic filler is set to 60% by weight to 95% by weight.

According to the thermal head of the present invention, the flexural modulus of the epoxy resin encapsulant that covers the driver IC on the head substrate and the thin metal wire between the head substrate and the external wiring board in common is determined on the driver IC. Since it is set lower in the area on the thin metal wire than in the area, when the liquid precursor of epoxy resin is applied widely on the head substrate and the external wiring board to heat and polymerize when forming the encapsulating material. For example, even if thermal stress is generated between the head substrate and the external wiring board due to the difference in linear expansion coefficient between the two, the thermal stress is well relaxed by the deformation of the sealing material itself, and the thermal head is not warped. It can be effectively prevented from occurring. Therefore,
The linearity of the heating element array is maintained high, and the pressing force of the heating elements on the recording medium is kept uniform, so that a good and clear print can be formed.

According to the thermal head of the present invention, a large number of elastic fillers are contained in the sealing material, and the content ratio of these elastic fillers is gradually increased from the area on the driver IC to the area on the metal thin wire. By setting it so that the thermal characteristics and mechanical characteristics of the encapsulant change stepwise according to the content rate of the elastic filler, cracks etc. occur inside the encapsulant. Can be effectively prevented, and the driver IC, the thin metal wire, and the like can be satisfactorily covered with such a sealing material for a long period of time.

Further, according to the thermal head of the present invention, the elastic filler contained in the encapsulant is made of silicone resin, and the content of the elastic filler is controlled in the region on the thin metal wire. weight%~ By setting the weight%, the sealing material existing in the vicinity of the thin metal wire will be provided with appropriate flexibility. Therefore, it is applied along with the formation of the sealing material and the use of the thermal head. The external force can be satisfactorily relaxed by the sealing material, and it is also possible to reliably prevent disconnection of the thin metal wire.

Further, according to the thermal head of the present invention, a predetermined amount of a hard inorganic filler made of alumina or silica is contained in the sealing material on the driver IC, whereby Since the hardness is appropriately increased only in the area on the driver IC, even when the recording medium is slidably contacted with the sealing material on the driver IC at the time of printing, sealing accompanying the sliding contact of the recording medium is performed. The wear of the material can be suppressed to a small level, and the driver IC can be favorably covered with the sealing material for a long period of time, whereby the reliability of the thermal head can be maintained high.

[0020]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a plan 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. The thermal head shown in FIG. 1 generally has a head substrate 1 and an external wiring board. 7 and 7.

The head substrate 1 has a large number of linear heating elements 3 and driver ICs 5 arranged on the upper surface of a base plate 2 formed in a rectangular shape, and heats the driver ICs 5. It has a structure in which a plurality of signal wirings 6 are attached to the upper surface of the base plate 2 located on the side opposite to the element 3.

The base plate 2 is made of a ceramic material such as alumina ceramics or single crystal silicon whose surface is coated with an oxide film, and has an upper surface for supporting the heating element 3, the energizing electrode 4, the driver IC 5, and the like. Functions as a supporting base material.

When the base plate 2 is made of alumina ceramics, a suitable organic solvent or solvent is added to and mixed with ceramic material powder such as alumina, silica, magnesia, etc. to form a sludge shape, which is well known in the art. A ceramic green sheet is formed by adopting the method, and thereafter, the obtained ceramic green sheet is punched into a predetermined rectangular shape and then fired at a high temperature (about 1600 ° C.).

A large number of heating elements 3 provided on the upper surface of the base plate 2 are, for example, 600 dpi (do
They are arranged linearly in the main scanning direction (longitudinal direction of the base plate 2) at a density of t per inch), and electrodes 4 are connected to both ends of each heating element 3.

Each of the heating elements 3 is made of TaSi.
Since it is formed of an electric resistance material such as O and TiSiO, it generates Joule heat when electric power is applied through the energizing electrode 4, and a temperature necessary to form a print on the recording medium, for example, 150 ° C. It reaches a temperature of ~ 250 ° C.

The electrode 4 connected to the heating element 3
Is formed of a conductive material such as aluminum or copper in a predetermined pattern, is commonly connected to all the heating elements 3 at one end side of the heating elements 3 and functions as a common electrode, and the other end side of the heating elements 3 is Then, it functions as an individual electrode that connects each heating element 3 and the output terminal of the driver IC 5 described later.

The heating element 3 and the electrode 4 as described above are adhered to the upper surface of the base plate 2 in a predetermined thickness and in a predetermined pattern by adopting a conventionally known thin film forming technique, for example, a sputtering method, a photolithography technique, an etching technique or the like. ·It is formed.

A plurality of driver ICs 5 mounted on the base plate 2 are arranged substantially in parallel with the above-mentioned arrangement of the heating elements 3 with a predetermined space therebetween.

Such a driver IC 5 is for individually controlling the power supply to the heating elements 3 based on image data from the outside.
A flip-chip type driver IC is preferably used for this.

For example, a flip chip type driver I
When C5 is used, electronic circuits such as a shift register, a latch, and a switching transistor, and input / output terminals are provided on the lower surface of the C5, and conventionally known face-down bonding, that is, the input terminal is connected to the corresponding electrode 4 and the output terminal is connected. Is electrically connected to a signal wiring 6 to be described later via a brazing material such as solder, so that it is mounted at a predetermined position on the base plate 2.

Further, one end of the signal wiring 6 connected to the driver IC 5 is led out to the vicinity of the edge of the base plate 2, and the wiring conductor 8 of the external wiring board 7 is electrically connected to the lead-out portion through the thin metal wire 9. Connected to
Driver I receives image data and print control signals from the outside
It is designed to be supplied to C5.

These signal wirings 6 are made of the same conductive material (aluminum, etc.) as the above-mentioned electrodes 4, and are patterned at the same time as the electrodes 4 etc. by adopting a conventionally known thin film forming technique or the like. It is formed.

The signal wiring 6 of the head substrate 1 described above
An external wiring board 7 is provided side by side.

The external wiring board 7 has an image in which a plurality of wiring conductors 8 made of a metal material such as copper are attached in a predetermined pattern on the upper surface of a base 7a made of a glass cloth base material epoxy resin or the like. A connector (not shown) for connecting the thermal head to an electric circuit of the printer body is attached to one end of the printer.

The wiring conductor 8 of such an external wiring board 7 is provided with a bonding pad on the head substrate 1 side, and the pad and the signal wiring 6 of the head substrate 1 are bonded with a fine metal wire 9. By this, the image data, the print control signal, the electric power, etc. from the outside are supplied to the heating element 3, the driver IC 5 and the like on the head substrate 1.

When the base 7a of the external wiring board 7 is made of a glass cloth base material epoxy resin, a glass cloth base material formed by using a glass thread is first impregnated and cured with a liquid epoxy resin. The base 7a is formed by cutting into a predetermined shape, a metal foil such as a copper foil is attached to one main surface of the base 7a, and the base 7a is processed into a predetermined pattern by a conventionally known photolithography technique and etching technique. The wiring conductor 8 is formed.

A fine metal wire 9 for bonding the wiring conductor 8 of the external wiring board 7 and the signal wiring 6 of the head substrate 1 to each other.
Is formed in a loop shape so as to straddle the gap between the head substrate 1 and the external wiring board 7 by gold (Au) or the like, and conventionally known wire bonding is used to connect corresponding parts to each other. Is bonded to the signal wiring 6 and the wiring conductor 8.

Furthermore, the thin metal wires 9 and the driver IC 5 on the head substrate 1 described above are commonly covered with a single encapsulant 10 containing a thermosetting epoxy resin as a main component. Driver I by the sealing material 10
C5 is well shielded from the atmosphere, the driver IC5 is protected from corrosion due to contact with moisture contained in the atmosphere, and the driver IC5 and the thin metal wire 9 are protected from the impact applied due to the sliding contact of the recording medium. The connection between the head substrate 1 and the external wiring board 7 is reinforced so that the positional relationship between the head substrate 1 and the external wiring board 7 is maintained substantially constant.

Further, the encapsulating material 10 contains a large number of elastic fillers made of silicone resin or the like and having a particle diameter of 0.1 μm to 100 μm.
The elastic fillers are distributed so as to be lower in the area on the thin metal wire 9 than in the area on the driver IC 5, and gradually increase from the area on the driver IC 5 to the area on the thin metal wire 9.

The content of the elastic filler is larger in the region on the metal thin wire 9 than in the region on the driver IC 5, and specifically, 50% by weight or less in the region on the driver IC 5, on the metal thin wire 9. The area is set to 55% by weight to 95% by weight, respectively, whereby appropriate elasticity is given to the sealing material 10 located at the boundary between the head substrate 1 and the external wiring board 7.

Therefore, when the liquid precursor of the epoxy resin is widely applied on the head substrate 1 and the external wiring board 7 to form the encapsulating material 10 and is heated and polymerized, the head substrate 1-external wiring is used. Even if a thermal stress is generated between the plates 7 due to the difference in the linear expansion coefficient between them, the thermal stress is well relaxed by the deformation of the sealing material itself, and the thermal head is not warped. It can be effectively prevented. Therefore, the linearity of the heating element array is maintained high, the pressing force of the heating element 3 on the recording medium is kept uniform, and it is possible to form a good and clear print on the recording medium.

The content of the elastic filler is set so as to gradually increase from the region on the driver IC 5 to the region on the thin metal wire 9, and the thermal characteristics and mechanical characteristics of the sealing material 10 are also set. Since the elastic filler is changed stepwise in accordance with the content, it is possible to effectively prevent cracks and the like from occurring inside the sealing material 10. The sealing material 10 allows the driver IC 5 and It is also possible to satisfactorily coat the thin metal wires 9 and the like for a long period of time.

Further, the content ratio of the elastic body filler made of silicone resin present in the sealing material 10 is set to 55% by weight to 95% by weight in the region on the thin metal wire 9, and the vicinity of the thin metal wire 9 is set. Since the encapsulating material 10 is also provided with appropriate flexibility, the external force applied due to the formation of the encapsulating material 10 and the use of the thermal head is favorably relaxed by the encapsulating material 10. It is also possible to reliably prevent disconnection of the thin metal wire 10.

In this case, a hard inorganic filler made of either alumina or silica is contained in the sealing material 10 on the driver IC 5 in a predetermined amount, for example, 60% by weight to 95%.
If the content of the sealing material 10 is only wt%, the hardness of the sealing material 10 is appropriately increased only in the area on the driver IC 5, so that the recording medium is slidably contacted with the sealing material 10 on the driver IC 5 during printing. Also, the wear of the sealing material 10 due to the sliding contact of the recording medium can be suppressed to a small extent, and the driver IC 5 can be well covered with the sealing material 10 for a long period of time, thereby maintaining high reliability of the thermal head. It is also possible to do. Therefore, it is preferable that the sealing material 10 on the driver IC 5 contains a hard inorganic filler made of either alumina or silica in an amount of about 60% by weight to 95% by weight.

In order to cover the driver IC 5 and the thin metal wire 9 in common with the encapsulating material 10, first, two kinds of liquid epoxy resins (precursors) having different elastic filler contents are prepared. Next, as shown in FIG. 3, using two dispensers, a liquid precursor containing a small amount of elastic filler is applied on the driver IC 5, and a liquid precursor containing a large amount of the elastic filler is applied on the thin metal wire 9, respectively. After being mixed and integrated to some extent, the liquid precursor is heated and polymerized to cure the epoxy resin, so that the sealing material 10 is formed wide from the mounting area of the driver IC 5 to the bonding area of the fine metal wire 9.

Thus, the above-described thermal head of the present embodiment conveys a recording medium such as thermal paper onto the heating element array of the head substrate 1 while driving a large number of heating elements 3 in the driver I.
Along with the driving of C5, the Joule heat is selectively generated, and the generated heat is transmitted to the recording medium to form a predetermined image on the recording medium, thereby functioning as a thermal head.

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 resin-made external wiring board is formed of the glass cloth base epoxy resin, but instead of this, a plastic substrate made of another organic material or a polyimide resin is used. A flexible wiring board or the like using the above film may be used as the external wiring board, and in such a case, the same effect as that of the above-described embodiment can be obtained.

In the above-described embodiment, the head substrate 1 and the external wiring board 7 are placed and fixed on a metal radiator plate, and the heating element 3 and the electrodes 4 on the head substrate 1 are made of silicon nitride, glass or the like. Needless to say, a glaze layer may be provided between the heat generating element 3 and the base plate 2 or a protective film made of

[0050]

According to the thermal head of the present invention, the flexural modulus of the epoxy resin encapsulant that covers the driver IC on the head substrate and the thin metal wire between the head substrate and the external wiring board in common is determined by the driver IC. Since it was set lower in the area above the thin metal wire than in the area above, when forming the encapsulant, the epoxy resin liquid precursor was applied widely on the head substrate and external wiring board and heated and polymerized. Even when thermal stress is generated between the head substrate and the external wiring board due to the difference in linear expansion coefficient between the two, the thermal stress is satisfactorily relaxed by the deformation of the sealing material itself, It is possible to effectively prevent warpage. Therefore,
The linearity of the heating element array is maintained high, and the pressing force of the heating elements on the recording medium is kept uniform, so that a good and clear print can be formed.

According to the thermal head of the present invention, a large number of elastic fillers are contained in the sealing material, and the content ratio of these elastic fillers is gradually increased from the region on the driver IC to the region on the metal thin wire. By setting it so that the thermal characteristics and mechanical characteristics of the encapsulant change stepwise according to the content rate of the elastic filler, cracks etc. occur inside the encapsulant. Can be effectively prevented, and the driver IC, the thin metal wire, and the like can be satisfactorily covered with such a sealing material for a long period of time.

Further, according to the thermal head of the present invention, the elastic filler contained in the encapsulant is made of silicone resin, and the content of the elastic filler is 55% by weight in the region on the metal thin wire. By setting the content to 95% by weight, the encapsulating material existing in the vicinity of the thin metal wire is provided with appropriate flexibility. Therefore, the encapsulating material is applied along with the formation of the encapsulating material and the use of the thermal head. It is also possible to satisfactorily reduce the external force generated by the sealing material, and it is possible to reliably prevent disconnection of the thin metal wires.

Furthermore, according to the thermal head of the present invention, a predetermined amount of a hard inorganic filler made of alumina or silica is contained in the sealing material on the driver IC, whereby Since the hardness is appropriately increased only in the area on the driver IC, even when the recording medium is slidably contacted with the sealing material on the driver IC at the time of printing, sealing accompanying the sliding contact of the recording medium is performed. The wear of the material can be suppressed to a small level, and the driver IC can be favorably covered with the sealing material for a long period of time, whereby the reliability of the thermal head can be maintained high.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of the thermal head shown in FIG.

FIG. 3 is an enlarged sectional view of an essential part for explaining a method of forming a sealing material.

FIG. 4 is a sectional view of a conventional thermal head.

[Explanation of symbols]

1 ... Head substrate, 2 ... Base plate, 3 ...
・ Heating element, 4 ... Electrode, 5 ... Driver IC,
6 ... Signal wiring, 7 ... External wiring board, 8 ... Wiring conductor, 9 ... Metal thin wire, 10 ... Sealing material

Claims (8)

[Claims] 1. A large number of linearly arranged heating elements and a driver IC for controlling the heating of these heating elements are arranged on the upper surface of a base plate made of ceramic or silicon, and the heating element is opposite to the driver IC. Resin-made external wiring having a head substrate formed by coating a plurality of signal wirings on the upper surface of a base plate located on the side, and a large number of wiring conductors electrically connected to the signal wirings through thin metal wires. A thermal head in which a plate is provided side by side, and the driver IC and the thin metal wire are commonly covered with a sealing material containing an epoxy resin as a main component, and the bending elastic modulus of the sealing material is on the driver IC. The thermal head is characterized by being set lower in the area on the thin metal wire than in the area. 2. The thermal head according to claim 1, wherein the driver IC is mounted on the base plate by face down bonding. 3. A large number of elastic fillers are contained in the encapsulating material, and the content ratio of the elastic fillers is set to be larger in a region on the metal thin wire than in a region on the driver IC. The thermal head according to claim 1, wherein the thermal head is a thermal head. 4. The content of the elastic filler is Driver I
4. The thermal head according to claim 3, wherein the thermal head is gradually increased from the region on C to the region on the thin metal wire. 5. The thermal head according to claim 3, wherein the elastic filler is made of a silicone resin. 6. The elastic filler is 50% by weight or less in a region on a driver IC and 55% by weight in a region on a solder joint.
The content of ˜95% by weight is contained.
The thermal head described in. 7. The encapsulating material according to claim 1, wherein an inorganic filler made of alumina or silica is contained in a region above the driver IC. Thermal head. 8. The content of the inorganic filler is 60% by weight to.
The weight ratio is set to 95% by weight.
The thermal head described in.