JP2003220721A - 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, and a plurality of signal 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 a flexible wiring board 7 having many wiring conductors 8 to be electrically connected via a solder 20 to the signal lines 6 are set together. At the same time, the driver ICs 5 and solder joining parts 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 solder joining parts 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 having a plurality of signal wirings 15 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 support plate 17 made of a glass cloth base epoxy resin, etc. There is known a structure in which a flexible wiring board 16 having a large number of wiring conductors 17 to be soldered to the signal wirings 15 is placed on the support body 17, and a recording medium such as thermal paper is used. A large number of heating elements 13 are transferred to the driver IC while being conveyed onto the heating elements 13.
A predetermined image is formed by selectively causing Joule heat to be generated as the drive unit 14 is driven and by transferring these heats to the recording medium.

The flexible wiring board 16 receives image data, print control signals, power, etc. from the outside.
1 is for supplying to the driver IC 14 and the like, and the connection portion with the head substrate 11 to which the solder joint is made contains epoxy resin as a main component in order to protect this portion from impact during use. A hard sealing material 19 is applied, and the sealing material 19 covers the solder joint between the head substrate 11 and the flexible wiring board 16 together with the driver IC 14.

The encapsulating material 19 is applied by applying a liquid epoxy resin precursor in a wide range from the mounting area of the driver IC 14 to the connecting area of the head substrate 11 and the flexible wiring board 16 by using a dispenser or the like. It was formed by heating and polymerizing this 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 flexible wiring board 16 and heated. -When polymerized, the head substrate 11 is accompanied by heat shrinkage of the sealing material 19.
-Alumina ceramics forming the base plate 12 between the flexible wiring boards 16 and the flexible wiring board 16
A large thermal stress is generated due to the difference in the linear expansion coefficient of the polyimide resin used as the base of the, and this causes a problem that the thermal head bends in an arch and warps. 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, resulting in “distortion” or “scratch” on the recording medium.
However, there is a defect that defective printing is formed.

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 wirings electrically connected to the signal wirings via solder. A thermal head in which a flexible wiring board having a conductor is provided side by side, and the driver IC and the solder joint are commonly covered with a sealing material containing epoxy resin as a main component. It is characterized in that the elastic modulus is set lower in the area on the solder joint 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 on the solder joint portion is larger than that on the driver IC. It is characterized by being set large in the area.

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 solder joint.

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 solder joint between the head substrate and the external wiring board in common is measured on the driver IC. Since the area above the solder joint is set lower than the area above, the epoxy resin liquid precursor is applied widely on the head substrate and external wiring board to form the encapsulant, and then 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 element on the recording medium is kept uniform.
It is possible to form a good and clear print.

Further, 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 solder joint. By setting it to be large, the thermal and mechanical properties of the encapsulant change stepwise according to the content of the elastic filler,
It is possible to effectively prevent cracks and the like from occurring inside the encapsulating material, and it becomes possible to satisfactorily cover the driver IC, the solder joint, and the like with the encapsulating material for a long period of time.

Further, according to the thermal head of the present invention, the hardness of the encapsulating material is improved by containing a predetermined amount of a hard inorganic filler made of alumina or silica in the encapsulating material on the driver IC. Is a driver IC
Since the height is appropriately increased only in the upper area, even when the recording medium is brought into sliding contact with the sealing material on the driver IC at the time of printing, abrasion of the sealing material due to sliding contact of the recording medium is prevented. The size of the driver IC can be kept small, and the driver IC can be well covered with the sealing material for a long period of time, whereby the reliability of the thermal head can be maintained high.

[0019]

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 a flexible wiring board. (External wiring board)
7 and 7.

The head substrate 1 has a large number of heating elements 3 and driver ICs 5 arranged linearly 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 having a surface 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 a ceramic material powder such as alumina, silica, magnesia, etc. to form a sludge, and this is formed by a conventionally known doctor blade. 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
The heating elements 3 are arranged linearly in the main scanning direction (longitudinal direction of the base plate 2) at a density of t per inch), and energizing 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 or TiSiO, it generates Joule heat when electric power is applied through the electrode 4 or the like, and a temperature necessary for forming a print on a recording medium, for example, 150 ° C. to 250 ° C. It reaches a temperature of ℃.

The electrode 4 connected to the heating element 3
Is formed of a conductive material such as aluminum or copper so as to form a predetermined pattern, and is commonly connected to all the heating elements 3 on one end side of the heating elements 3 to function as a common electrode. On the other end side, it functions as an individual electrode that connects each heating element 3 and an output terminal of a 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.

The plurality of driver ICs 5 mounted on the base plate 2 are arranged substantially parallel to 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.

The signal wiring 6 connected to the driver IC 5 has one end led out to the vicinity of the edge of the base plate 2 and is electrically connected to the wiring conductor 8 of the flexible wiring board 7 via the solder 20 at the lead-out portion. It is connected and image data, print control signals, electric power, etc. from the outside are supplied to the driver IC 5 through the plurality of signal wirings 6.

Incidentally, these signal wirings 6 are made of the same conductive material (aluminum etc.) as the above-mentioned electrodes 4, and by adopting a well-known thin film forming technique or the like, a pattern is formed simultaneously with the electrodes 4 and the like. It is formed.

Next to the above-mentioned head substrate 1, a supporting plate 9 made of a glass cloth base material epoxy resin or the like is provided.
A flexible wiring board 7 having a plurality of wiring conductors 8 soldered to the signal wirings 6 is further placed and fixed on the upper surface of the support plate 9.

In the flexible wiring board 7, a plurality of wiring conductors 8 made of a metal material such as copper are adhered on a base film made of a polyimide resin or the like, and the wiring conductors 8 are covered by a polyimide resin or the like. It has a structure partially covered with a film, and a connector (not shown) for connecting the thermal head to an electric circuit of the printer main body is attached to the rear end of the structure.

One end of the flexible wiring board 7 is superposed on the head substrate 1 and the wiring conductor 8 is soldered to the signal wiring 6 of the head substrate 1 at the superposed portion.
They are connected via 0, and serve to supply image data, print control signals, electric power, etc. from the outside to the heating element 3, the driver IC 5, etc. on the head substrate 1.

When the support plate 9 having the flexible wiring board 7 fixed on the upper surface is made of a glass cloth base material epoxy resin or the like, first, a glass cloth base material formed by using glass threads is impregnated with a liquid epoxy resin. -Support plate 9 obtained by curing and cutting it into a predetermined shape
The flexible wiring board 7 is fixed by placing the flexible wiring board 7 on the upper surface of the flexible wiring board 7 via an adhesive such as a double-sided tape.

Furthermore, the solder joint between the above-described head substrate 1 and flexible wiring board 7 and the above-mentioned head substrate 1
The upper driver IC 5 is commonly covered with a single encapsulant 10 whose main component is a thermosetting epoxy resin.

The sealing material 10 effectively prevents the driver IC 5 from corroding due to contact with moisture contained in the atmosphere by shutting off the driver IC 5 from the atmosphere, and also prevents the driver IC 5 from slidingly contacting a recording medium. The purpose of this is to protect the driver IC 5 and the solder joints from shocks applied together, and the connecting portion between the head substrate 1 and the flexible wiring board 7 is reinforced by the sealing material 10. , The positional relationship between the two is also kept substantially constant.

The encapsulant 10 contains a large number of elastic fillers made of silicone resin or the like and having a particle size of 0.1 μm to 100 μm.
The elastic fillers are distributed so as to be lower on the solder joint portion than on the driver IC 5 region and gradually larger from the region on the driver IC 5 to the solder joint portion.

The content of the elastic filler is larger on the solder joint portion than on the driver IC 5 area. Specifically, the content of the elastic filler is 50 wt% or less in the driver IC 5 area and 55 wt% in the solder joint portion. % To 95% by weight, respectively, whereby the head substrate 1 and the flexible wiring board 7 are set.
Appropriate elasticity is imparted to the encapsulating material 10 located at the boundary portion between and.

Therefore, when the liquid precursor of the epoxy resin is widely applied on the head substrate 1 and the flexible wiring board 7 to form the encapsulating material 10 and is heated and polymerized, the head substrate 1-flexible 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 solder joint, 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 coat the solder joints well over a long period of time.

Further, 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 commonly cover the driver IC 5 and the solder joint portion 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 having a small content of elastic filler is applied onto the driver IC 5, and a liquid precursor having a large content is applied onto the solder joint, This is performed by heating and polymerizing the liquid precursor and curing the epoxy resin after the two are mixed and integrated to some extent, whereby the encapsulating material 10 moves from the mounting area of the driver IC 5 to the head substrate 1 and the flexible wiring board. It is formed wide across the connection region 7.

Thus, the above-described thermal head of this 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 head substrate 1, the flexible wiring board (external wiring board) 7, the support plate 9 or the like is placed and fixed on a metal heat dissipation plate, or heat is generated on the head substrate 1. It goes without saying that the element 3 and the electrode 4 may be covered with a protective film made of silicon nitride, glass or the like, or a glaze layer may be interposed between the heating element 3 and the base plate 2.

[0047]

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 solder joint between the head substrate and the external wiring board in common is controlled by the driver. Since the area of the solder joint is set lower than the area of the IC, the liquid precursor of the epoxy resin is widely applied to the head substrate and the external wiring board to form the encapsulating material and heated. Even if thermal stress occurs due to the difference in linear expansion coefficient between the head substrate and the external wiring board during polymerization, the thermal stress is well relaxed by the deformation of the sealing material itself, and thermal It is possible to effectively prevent the warp of the head. Therefore, the linearity of the heating element array is maintained high, and the pressing force of the heating element on the recording medium is kept uniform.
It is possible to form a good and clear print.

Further, 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 solder joint. By setting it to be large, the thermal and mechanical properties of the encapsulant change stepwise according to the content of the elastic filler,
It is possible to effectively prevent cracks and the like from occurring inside the encapsulating material, and it becomes possible to satisfactorily cover the driver IC, the solder joint, and the like with the encapsulating material for a long period of time.

Further, according to the thermal head of the present invention, the hardness of the encapsulating material is improved by containing a predetermined amount of a hard inorganic filler made of alumina or silica in the encapsulating material on the driver IC. Is a driver IC
Since the height is appropriately increased only in the upper area, even when the recording medium is brought into sliding contact with the sealing material on the driver IC at the time of printing, abrasion of the sealing material due to sliding contact of the recording medium is prevented. The size of the driver IC can be kept small, and the driver IC can be well 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 (flexible wiring board), 8 ... Wiring conductor, 9 ... Support plate, 10.
..Sealing materials, 20 ... Solder

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. A head substrate having a plurality of signal wirings attached to the upper surface of a base plate located on the side and a flexible wiring board having a large number of wiring conductors electrically connected to the signal wirings by solder And the driver I
A thermal head in which C and a solder joint are commonly covered with an encapsulant having an epoxy resin as a main component, wherein the encapsulant has a flexural modulus higher than that of a region on the driver IC. The thermal head is characterized by being set low 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 encapsulant, and the content ratio of the elastic fillers is set to be larger in a region on a solder joint than in a region on a driver IC. The thermal head according to claim 1 or 2, characterized in that 4. The content of the elastic filler is Driver I
The thermal head according to claim 3, wherein the thermal head is gradually increased in size from a region on C to a region on the solder joint. 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.