JP2004322448A - Thermal head and thermal printer using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable thermal head by making connection between a head substrate and an external wiring board sure and firm, and to provide a thermal printer. <P>SOLUTION: The thermal head includes the head substrate 1 with heating elements 3 and connection pads 5 electrically connected to the heating elements 3, and the external wiring board 8 with wiring pads 10 connected via an electroconductive material 6 to the connection pads 5. Grooves 5a are formed at the connection pads 5, and a part of the electroconductive material 6 is filled inside the grooves 5a. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a thermal head and a thermal printer for forming an image on thermal paper, recording paper, and the like using heat generated by a heating element.
[0002]
[Prior art]
Conventionally, a thermal head has been used as a recording device such as a facsimile or a video printer.
[0003]
As such a conventional thermal head, for example, as shown in FIG. 5, a head substrate having a plurality of heating elements 23 and connection pads 25 electrically connected to the heating elements 23, and a conductive material 26 provided on the connection pads 25 And an external wiring board 28 having a wiring conductor 29 electrically connected thereto via a thermal head or a thermal paper or an ink ribbon using a platen roller provided on a thermal head. While transporting a recording medium such as recording paper onto the heating elements 23, the heating elements 23 are selectively and individually heated based on an external printing signal, and the generated heat is transferred to the heating elements 23. The heat is conducted to the recording medium, and a predetermined print is formed on the thermal paper or the recording paper by the conducted heat.
[0004]
By the way, in various thermal heads such as a facsimile thermal head, cost reduction and miniaturization of the thermal head are more demanded, and accordingly, the area of the connection pad 25 is required to be further reduced. (For example, see Patent Document 1).
[0005]
[Patent Document 1]
JP-A-8-230224 (paragraph number on page 2)
[0006]
[Problems to be solved by the invention]
However, when the area of the connection pad 25 is reduced, the mechanical strength between the connection pad 25 and the conductive material 26 is reduced, and a part of the conductive material 26 may be peeled off by applying a slight force during handling. Therefore, there arises a problem that the reliability of the electrical connection is reduced and the operation of the thermal head is abnormal. In other words, when handling such a thermal head, care must be taken so that no mechanical stress is applied to the conductive material 26 connecting the head substrate 21 and the external wiring board 28. Induces the problem of poor sex.
[0007]
The above-mentioned problem is that when the head substrate and the external wiring board having different linear expansion coefficients are electrically connected by soldering, the head substrate and the external wiring board are connected to the solder as the conductive material 26 due to thermal stress caused by the difference between the two. This is particularly problematic because the electrical connection with the pad 25 is likely to decrease.
[0008]
The present invention has been devised in view of the above problems, and an object of the present invention is to provide a reliable and reliable thermal head and a thermal printer in which the connection between a head substrate and an external wiring board is reliably and firmly made. It is in.
[0009]
[Means for Solving the Problems]
A thermal head according to the present invention includes a head substrate having a heating element and a connection pad electrically connected to the heating element, and an external wiring having a wiring pad connected to the connection pad via a conductive material. A groove in the connection pad, and a part of the conductive material is filled in the groove.
[0010]
The thermal head according to the present invention is characterized in that the width of the groove is larger on the opening side than on the bottom side.
[0011]
Further, in the thermal head according to the present invention, a plurality of the grooves are provided in the connection pad.
[0012]
Further, a thermal printer according to the present invention includes the above-described thermal head and a driving unit for driving the thermal head.
[0013]
According to the present invention, the connection pad on the head substrate is provided with a groove, and the inside of the groove is filled with a part of the conductive material for electrically connecting the connection pad and the wiring pad. The contact area with the material can be increased, and the joining strength between the two can be increased. Therefore, it is possible to reduce the problem caused by reducing the area of the connection pad, that is, the problem that the conductive material is separated from the connection pad due to mechanical stress or thermal stress applied when handling the thermal head. It is possible to maintain high electrical reliability with the wiring board. This also increases the reliability of the thermal printer.
[0014]
Such effects can be further enhanced by providing a plurality of the grooves in each connection pad.
[0015]
Further, according to the present invention, by setting the width of the groove to be larger on the opening side than on the bottom side, the conductive material for electrically connecting the connection pad and the wiring pad can easily enter the inside of the groove. . Therefore, the productivity of the thermal head and the thermal printer can be improved.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
[0017]
FIG. 1 is a cross-sectional view of a thermal head according to an embodiment of the present invention, and FIG. 2 is a plan view (not shown) of a head substrate constituting the thermal head of FIG. 1. The thermal head shown in FIG. The head substrate 1 and the external wiring board 8 are electrically connected to each other by a conductive material 6.
[0018]
The head substrate 1 has a glaze layer 2, a heating element 3, a circuit conductor 4, and a connection on the upper surface of a base plate 1 a formed in a rectangular shape by using various materials such as alumina ceramics, single crystal silicon, and Fe—Ni alloy. It has a pad 5, a protective film 7, and the like, and functions as a supporting base material that supports the glaze layer 2, the heating element 3, the circuit conductor 4, the connection pad 5, the protective film 7, and the like on its upper surface.
[0019]
When the base plate 1a constituting the head substrate 1 is made of alumina ceramics, an appropriate organic solvent / solvent is added to and mixed with a ceramic raw material powder of, for example, alumina, silica, magnesia, etc. to form a slurry. A ceramic green sheet is obtained by employing a well-known doctor blade method, a calendar roll method, or the like, and thereafter, the ceramic green sheet is punched into a rectangular shape and fired at a high temperature.
[0020]
On the upper surface of the base plate 1a, a glaze layer 2 made of glass is adhered.
[0021]
The glaze layer 2 has a structure in which a protruding portion 2a arranged in a band shape along one long side of the substrate 1 is partially formed on a base portion 2b which is applied to the base plate 1a with a substantially uniform thickness over the entire upper surface. Have.
[0022]
In the glaze layer 2, the thickness of the base 2b is set to 50 μm to 250 μm, and the thickness of the top of the projection 2a is set to 20 μm to 80 μm. A plurality of heating elements 3 are provided near the top of the projection 2a. Has been adhered.
[0023]
Since the glaze layer 2 is formed of, for example, glass having a thermal conductivity of 0.7 W / m · K to 1.0 W / m · K, the glaze layer 2 stores a part of the heat of the heating element 3 therein. In this case, the thermal responsiveness of the thermal head is maintained satisfactorily, specifically, as a heat storage layer for raising the temperature of the heating element 3 to a predetermined temperature required for printing in a short time.
[0024]
The glaze layer 2 is formed by printing and applying a predetermined glass paste obtained by adding and mixing an appropriate organic solvent to glass powder on the entire upper surface of the substrate 1 by a conventionally known screen printing or the like. It is formed by processing into a predetermined pattern by a well-known etching method or sandblasting method and baking it at a high temperature (850 ° C. to 950 ° C.).
[0025]
The heating elements 3 are linearly arranged at a density of, for example, 600 dpi (dot per inch), and are each made of an electric resistance material such as TaSiO, TiSiO, or TiCSiO. When electric power is supplied from the outside via the circuit conductor 4 to be produced, Joule heat is generated, and a temperature required for forming an image on thermal paper or melting the ink of the ink ribbon, for example, 150 ° C. Heat is generated at a temperature of 400 ° C.
[0026]
The circuit conductors 4 connected to both ends of each of the heating elements 3 function as power supply wiring for supplying predetermined power to the heating elements 3, and are made of a metal material such as aluminum (Al) or copper (Cu). Thus, one end thereof is led out to the vicinity of the other long side of the substrate 1 (a position separated from the end of the substrate by 100 μm to 300 μm) to form the connection part as the connection pad 5.
[0027]
The plurality of connection pads 5 are for electrically connecting to the wiring conductors 9 of the external wiring board 8 via conductive materials 6 (solder in this embodiment) such as solder and bonding wires on the upper surface. , Are arranged along the other long side of the substrate 1.
[0028]
Such a connection pad 5 has a structure in which, for example, a Ni layer and an Au layer are sequentially adhered to a lead-out portion of the circuit conductor 4 serving as a base, and each connection pad 5 has the other long side of the substrate 1. A single or a plurality of grooves 5a substantially parallel to the above are formed (single in this embodiment).
[0029]
The groove 5a has a width of 5 μm to 150 μm and a depth of 2.5 μm to 5.0 μm, and is formed such that a part of the glaze layer 2 is exposed from the bottom surface of the groove 5a. A part of the conductive material 6 is filled in the inside of 5a to increase the bonding strength between the connection pad 5 and the conductive material 6.
[0030]
The heating element 3 and the circuit conductor 4 are formed by sequentially forming a resistive film such as a TaSiO based film and a metal film such as Al into a predetermined thickness (resistive film 0) by a conventionally known sputtering method or vapor deposition method. (0.015 μm to 0.02 μm: metal film 0.9 μm to 1.2 μm), and the laminate is formed in a predetermined pattern by employing a conventionally known photolithography technique and etching technique. Reference numeral 5 denotes that a Ni layer and an Au layer are sequentially laminated on a predetermined region of the circuit conductor 4 by using, for example, a conventionally known electroless plating method, and that a conventionally known photolithography technique and an etching technique are employed for the laminate. This is formed by providing the groove 5a.
[0031]
A protective film 7 is provided on the upper surfaces of the heating element 3 and the circuit conductor 4, and the heating element 3 and the circuit conductor 4 are commonly covered with the protective film 7.
[0032]
The protective film 7 is made of an inorganic material having excellent wear resistance, such as silicon nitride (Si ₃ N ₄ ), silicon oxide (SiO ₂ ), and sialon (Si—Al—O—N). It functions to protect the circuit conductors 4 and the like from wear due to sliding contact of the recording medium and corrosion due to contact with moisture or the like contained in the atmosphere.
[0033]
The protective film 7 is formed by a conventionally known thin film forming technique, for example, a CVD (Chemical Vapor Deposition) method, a sputtering method, or the like, and is made of silicon nitride (Si ₃ N ₄ ), silicon oxide (SiO ₂ ), sialon (Si— It is formed by applying an inorganic material such as Al-ON) on the upper surface of the heating element 3 or the circuit conductor 4 in a thickness of 5 μm to 10 μm.
[0034]
On the other hand, the external wiring board 8 electrically connected to the head substrate 1 includes, for example, a plurality of wiring conductors 9 formed of a metal material such as copper or aluminum and a pair of relatively soft resin materials such as a polyimide resin. By connecting one end to the head substrate 1 and the other end to an external electric circuit, the heating element 3 is connected from the external electric circuit via the connection pad 5 and the circuit conductor 4. To supply a predetermined electric power.
[0035]
The external wiring board 8 is provided with an opening in one of the films on one end side to expose a part of the wiring conductor to form the exposed portion as the wiring pad 10, and to connect the wiring pad 10 and the connection pad 5 with each other. By joining via the material 6, the connection pads 5 of the head substrate 1 and the wiring pads 10 of the external wiring board 8 are individually electrically connected.
[0036]
Here, as described above, the connection pad 5 is provided with the groove 5a and the region formed inside the groove 5a is partially filled with the conductive material 6, so that the connection pad 5 and the conductive material 6 And the joint area of the two can be increased. Therefore, it is possible to reduce the problem caused by reducing the area of the connection pad 5, that is, the problem that the conductive material 6 is separated from the connection pad 5 due to mechanical stress or thermal stress applied when handling the thermal head. The electrical reliability between the substrate 1 and the external wiring board 8 can be kept high.
[0037]
When the external wiring board 8 is formed of a flexible wiring board, for example, a copper foil is adhered on a film made of a polyimide resin, and the copper foil is formed by employing a conventionally known photolithography technique and etching technique. It is manufactured by processing into a predetermined pattern and then coating the processed copper foil with a film made of polyimide resin.
[0038]
When the external wiring board 8 and the head substrate 1 are joined together, when the conductive material 6 is made of solder, for example, the solder is applied to the connection pads 5 of the head substrate 1 in a state where solder is previously provided on the exposed portions of the wiring conductors 9. This is performed by overlapping one end of the external wiring board 8 with the head substrate 1 so as to be positioned above, and pressing and heating the overlapped portion with a heater bar or the like. When the conductive material 6 is a bonding wire, the connection pad 5 of the head substrate 1 and the wiring conductor 9 of the external wiring board 8 are electrically connected by employing a conventionally known wire bonding method.
[0039]
Here, in order to fill the inside of the groove 5a with the solder which is the conductive material 6, the solder may be heated at a temperature of about 230 ° C. for 10 seconds or more. At this time, if the width of the groove 5a is set to be larger on the opening side than on the bottom side, the conductive material 6 can easily enter the inside of the groove 5a easily, and the productivity of the thermal head can be improved. Can be provided to In order to make the width of the groove 5a larger on the opening side than on the bottom side, the etching time may be longer than usual.
[0040]
As shown in FIG. 3, a thermal printer incorporating the above-described thermal head includes a driving unit C for driving the thermal head T and a transport unit for transporting the recording medium onto the heating element 3 of the thermal head T. , A platen roller 11, transport rollers 12a, 12b, 12c, 12d, and the like.
[0041]
The driving means C includes a driver IC in which shift registers, latches, switching transistors, and the like are integrated at high density, and a control circuit that supplies control signals such as strobe signals and latch signals to the driver IC. By switching on / off the switching transistor in the driver IC based on the control signal, the heat generation of the heating element 3 is controlled.
[0042]
On the other hand, the platen roller 11 as a conveying means is a cylindrical member in which butadiene rubber or the like is wound around a shaft core made of metal such as SUS to a thickness of about 3 mm to 15 mm. The recording medium is conveyed in a direction perpendicular to the arrangement of the heating elements 3 (the direction of the arrow in the figure) while pressing the recording medium against the heating elements 3.
[0043]
The transport rollers 12a, 12b, 12c, and 12d have their outer peripheral portions formed of metal, rubber, or the like, and are disposed separately from the thermal head T on the upstream side and the downstream side in the recording medium transport direction. The transporting of the recording medium is supported by the transport rollers 12a, 12b, 12c, and 12d and the platen roller 11 described above.
[0044]
At the same time, a large number of heating elements 3 are selectively caused to generate Joule heat in accordance with the driving of the driving means C, and the heat is transmitted to the recording medium, whereby a predetermined print is formed.
[0045]
Note 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.
[0046]
For example, in the above-described embodiment, the glaze layer 2 is applied to the entire upper surface of the base plate 1a. Instead, a band-like glaze layer having a mountain-like cross section is partially formed on the upper surface of the base plate 1a. It may be made to adhere to. Further, the glaze layer 2 having a substantially uniform thickness may be formed over the entire surface of the base plate 1a without providing the protrusion 2a of the glaze layer 2 in the above-described embodiment.
[0047]
In the above embodiment, if the groove 5'a is provided at least in the vicinity of the edge of the connection pad 5 (in a region up to 100 μm from the edge) as shown in FIG. The strength near the edge of the connection pad 5, which tends to be insufficient, can be reliably increased, and the reliability of the thermal head can be further improved.
[0048]
Further, in the above-described embodiment, if an electroless plating layer such as a Ni layer or an Au layer constituting the connection pad 5 is led out to the inner surface of the groove 5, the conductive material 6 such as solder is provided inside the groove 5. Filling becomes easier, and the adhesion between the inner surface of the groove 5 and the conductive material 6 can be further increased, so that the productivity and reliability of the thermal head can be further improved.
[0049]
Further, in the above-described embodiment, a groove is formed in the wiring pad 10 of the external wiring board 8 in the same manner as the connection pad 5, and the conductive material 6 is filled in the groove. There is also an advantage that the bonding strength between the wiring pad 10 and the wiring pad 10 can be increased.
[0050]
【The invention's effect】
According to the present invention, the connection pad on the head substrate is provided with a groove, and the inside of the groove is filled with a part of the conductive material for electrically connecting the connection pad and the wiring pad. The contact area with the material can be increased, and the joining strength between the two can be increased. Therefore, it is possible to reduce the problem caused by reducing the area of the connection pad, that is, the problem that the conductive material is separated from the connection pad due to mechanical stress or thermal stress applied when handling the thermal head. It is possible to maintain high electrical reliability with the wiring board. This also increases the reliability of the thermal printer.
[0051]
Such effects can be further enhanced by providing a plurality of the grooves in each connection pad.
[0052]
Further, according to the present invention, by setting the width of the groove to be larger on the opening side than on the bottom side, the conductive material for electrically connecting the connection pad and the wiring pad can easily enter the inside of the groove. . Therefore, the productivity of the thermal head and the thermal printer can be improved.
[Brief description of the drawings]
FIG. 1 is a sectional view of a thermal head according to an embodiment of the present invention.
FIG. 2 is a plan view of a head substrate constituting the thermal head of FIG. 1 (a protective film is not shown).
FIG. 3 is a schematic side view of a thermal printer configured by incorporating the thermal head of FIG. 1;
FIG. 4 is a sectional view of a thermal head according to another embodiment of the present invention.
FIG. 5 is a sectional view of a conventional thermal head.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Glaze layer 3 ... Heating element 4 ... Circuit conductor 5 ... Connection pad 5a, 5'a ... Groove 6 ... Conductive material 7 ... Protective film 8 external wiring board 9 wiring conductor 10 wiring pad 11 platen rollers 12a, 12b, 12c, 12d transport roller

Claims (4)

A thermal board comprising: a head substrate having a heating element and a connection pad electrically connected to the heating element; and an external wiring board having a wiring pad connected to the connection pad via a conductive material. In the head,
A thermal head, wherein a groove is provided in the connection pad, and a part of the conductive material is filled in the groove. 2. The thermal head according to claim 1, wherein the width of the groove is larger on the opening side than on the bottom side. The thermal head according to claim 1, wherein a plurality of the grooves are provided in the connection pad. A thermal printer comprising: the thermal head according to any one of claims 1 to 3; and driving means for driving the thermal head.

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