JP2006272851A - Thermal head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high durability thermal head in which densification can be dealt with. <P>SOLUTION: The thermal head comprises an insulating substrate 13, a plurality of heating resistor layers 14 arranged on the insulating substrate, an inorganic insulating protection layer 20 covering the heating part 15 of the heating resistor layer, and a plurality of wiring patterns 16 having one end connected with the heating resistor and the other end connected with an electrode pad 18, wherein the inorganic insulating protection layer 20 covers the wiring pattern 16 arranged around the electrode pad such that the electrode pad 18 is exposed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermal head, for example, a thermal head used for a facsimile, a printer, a card printer, a plate making machine, and the like.

  Due to the high image quality in the printing apparatus, it is required to increase the density of the thermal head. For this reason, in order to increase the density of the heating resistor and the wiring pattern, the distance between the wiring pattern and the electrode pad is reduced. Correspondingly, durability between wiring patterns is required, and further impact resistance and solvent resistance are required. Further, the high density increases the bonding connection between the electrode pad and the heating resistor driver IC, and the contact with the wiring pattern adjacent to the electrode pad becomes a problem due to the bonding position.

  As shown in FIG. 4, the conventional thermal head uses an insulating substrate in which a glaze layer 101 is disposed on an alumina substrate 100. A plurality of heating resistor layers 102, a wiring pattern 103 for supplying electric power thereto, and electrode pads 104 connected to the wiring pattern 103 are arranged on the glaze layer 101 with high density. Further, a SiON protective layer 106 is formed on the heat generating portion 105 of the heat generating resistor layer 102 by a thin film forming technique such as sputtering. The electrode pads 104 are arranged in a plurality of rows to increase the arrangement efficiency.

  However, when the electrode pads 104 and the wiring patterns 103 are arranged at high density, there is a possibility that the bonding wires 107 come into contact with other wiring patterns 103 or electrode pads 104 when wire bonding is performed. If the area of the electrode pad 104 is reduced, a margin for a bonding position shift of the wire 107 is reduced, and the adjacent wiring pattern is contacted to cause a short circuit defect. Further, when the bonding wire 107 is sealed with resin together with the driver IC 108, the bonding wire 107 and another electrode pad 104 may come into contact with each other.

In order to solve the above inconvenience, a thermal head (see Patent Document 1) in which only the electrode pad 104 is opened and the photosensitive polyimide resin film 109 is selectively formed on the surrounding wiring pattern 103 (see Patent Document 1), or photosensitive polyimide A thermal head for forming a dry film resist in place of the resin film 109 (see Patent Document 2) is disclosed to prevent wiring pattern protection and bonding wire contact failure.
JP-A-6-218969 JP 2000-135808 A

  However, photosensitive insulating films such as photosensitive polyimide resin and dry film resist have the following problems.

  (1) Peeling, scratching and chipping due to external force are likely to occur.

  (2) Low solvent resistance.

  The present invention solves the above-mentioned problems, and forms an extremely reliable insulating film, which has high impact resistance, durability, and solvent resistance, and facilitates bonding wire connection, resulting in short circuit failure and other disadvantages. It is providing the thermal head which prevents this.

  The thermal head according to one aspect of the present invention includes an insulating substrate, a plurality of heating resistor layers disposed on the insulating substrate, an inorganic insulating protective layer that covers a heating portion of the heating resistor layer, and the insulation. A plurality of wiring patterns disposed on the substrate and connected to the heating resistor layer; and a plurality of electrode pads connected to the wiring pattern, wherein the inorganic insulating protective layer generates heat from the heating resistor layer. The wiring pattern disposed around the electrode pad is covered so that the electrode pad is exposed while covering the portion.

    Furthermore, an insulating substrate, a plurality of heating resistor layers disposed on the insulating substrate, an inorganic insulating protective layer covering the heating portion of the heating resistor layer, and the heating portion disposed on the insulating substrate A plurality of wiring patterns connected to each other, a plurality of electrode pads connected to the wiring patterns, a driver IC disposed on the insulating substrate and driving the heat generating portion, and the electrode pads and the driver IC are connected to each other. In the thermal head including the bonding wire, the inorganic insulating protective layer is configured to expose the electrode pad and cover the wiring pattern disposed around the electrode pad.

  The inorganic insulating protective layer includes a first protective layer on the heat generating portion and the vicinity thereof, and a second protective layer provided on the wiring pattern near the electrode pad and having a layer thickness smaller than that of the first protective layer. It is a configuration.

    The thickness of the inorganic insulating protective layer is desirably 1 to 10 μm in terms of function, but the protective layer on the wiring pattern may be the same thickness as the protective layer on the heating resistor or can be formed thin. . It is desirable that the protective layer on the heat generating portion has a layer thickness of 1 μm to 10 μm from the viewpoint of wear resistance and thermal conductivity. On the other hand, the thinner the layer thickness on the wiring pattern near the electrode pad, the electrode pattern by photolithography It becomes easy to form the opening. However, if the thickness is 1 μm or less, reliability is lowered due to pinholes or the like, and therefore the protective layer on the wiring pattern near the electrode pad is preferably 1 μm to 5 μm.

  According to the present invention, the inorganic insulating protective layer is extended not only on the heating resistor but also on the wiring pad and the electrode pad region so as to cover the electrode pattern arranged around the electrode pad, and only the electrode pad is exposed. By doing so, even if the distance between the electrode pads and the distance between the electrode pads and the wiring pattern become narrow due to higher wiring density, the protective layer is not damaged by the connection work when bonding wires are connected. It is possible to avoid contact between the electrode pattern and the bonding wire arranged on the wire, and it is possible to prevent a wiring short circuit failure. In addition, since the durability and solvent resistance are excellent, the assembly process and the handling after commercialization are easy, and a reliable thermal head can be obtained.

    Further, according to the present invention, it is possible to cope with further higher density.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
1 and 2 schematically show a thermal head according to a first embodiment of the present invention. 1 is a plan view, and FIG. 1 is a cross-sectional view taken along line AA of FIG. Further, the drawing shows a case where the heat generating portion 15 of the heat generating resistor layer is disposed on the upper side, and the electrode pad 18 and the driver IC 21 are disposed on the lower side. The insulating substrate 13 includes an alumina ceramic support substrate 11 and a glaze layer 12 disposed on the support substrate 11. A plurality of heating resistor layers 14 are arranged on the glaze layer 12, and a wiring pattern 16 is connected to the heating resistor layers 14. The wiring pattern 16 is composed of a metal layer 17 such as Al of a highly conductive metal, and is laminated on the heating resistor layer 14, and the Al metal layer on the laminated structure is patterned to form a single layer portion of the heating resistor layer 14 alone. The heat generating part 15 is formed. Therefore, the actual wiring pattern 16 is a laminated structure in which the metal layer 17 is added to the heat generating resistor layer 14, and the drive current supplied to the heat generating part passes from the metal layer 17 through the heat generating part 15 to the metal layer 17 again. Configure a flowing series circuit.

  The inorganic insulating protective layer 20 covers the heating layer 15 of the heating resistor layer 14, the wiring pattern 16 including the periphery of the electrode pad, and the common electrode 19 so as to expose the electrode pad 18, and the same film layer on the glaze layer 12. Formed with.

  Further, a driver IC 21 that heats and drives the heat generating portion 15 of the heating resistor 14 is mounted, and the driver IC 21 is connected to the electrode pad 18 by a bonding wire 22.

The support substrate 11 is a flat inorganic substrate made of alumina ceramic. The glaze layer 12 is a glass glaze layer having a heat retaining function for storing heat generated from the heat generating portion 15 of the heat generating resistor layer 14 and a flat surface forming function such as the heat generating resistor layer 14, the wiring pattern 17, and the electrode pad 18. And formed on the entire surface of the support substrate 11. As a material for the glaze layer 12, SiO ₂ or the like is used.

The heating resistor layer 14 can be made of a metal nitride such as Ni, Cr, or Ta, or a cermet material such as Ta—SiO ₂ , Nb—SiO ₂ , or Ti—SiO ₂ .

  As a material of the wiring pattern 16, a highly conductive metal such as Al, Al—Si, Al—Si—Cu, or the like can be used. In addition, it is preferable to use a bondable metal such as Au or Au-Si.

The inorganic insulating protective layer 20 is preferably a wear-resistant Si—O—N-based layer. Si—Al—O—N, Ta ₂ O _{5 and} others can also be used. In the present embodiment, the inorganic insulating protective layer 20 is disposed not only on the heat generating portion 15 but also on the surrounding wiring pattern 16. The protective layer is a film that protects the vicinity of the heat generating portion from friction during printing and protects the wiring pattern 16 on the electrode pad side. The thickness of the protective layer 20 is suitably in the range of 1 μm to 10 μm when formed uniformly by sputtering or the like with the same thickness. If it is thinner than 1 μm, the uniformity of the film is impaired and pinhole defects are likely to occur, and if it is thicker than 10 μm, the heat radiation from the heat generating portion is lowered and the printing response is lowered, which is not practical.

  For the opening of the electrode pad opening, a dry film resist is stuck on the sputtered protective layer. The resist portion at the position where the electrode pad is opened is removed by photolithography, and the electrode pad surface is exposed by dry etching using this as a mask. The driver IC 21 for driving the heating resistor is bonded and mounted at a predetermined position on the insulating substrate 13 thus configured, and the electrode pads 18 and the IC 21 are bonded and connected by bonding wires 22 such as Au wires or Al wires.

  According to the present embodiment of the present invention, the thin and solid inorganic insulating protective layer 20 covers the wiring pattern 16 disposed around the electrode pad 18, and only the electrode pad 18 is exposed. There is no contact with the wiring pattern 16, and no chipping or cracking occurs even if the wire capillary at the time of bonding contacts the inorganic insulating protective layer at the electrode pad portion. In particular, even if the wiring pattern becomes finer and the electrode pad area is reduced as the density is increased, the protective layer functions as an insulating film that resists capillary displacement during bonding and deformation of the connecting portion of the bonding wire. The yield for defects can be improved, and a thermal head resistant to external impact suitable for high density can be obtained.

    Moreover, since the inorganic insulating protective layer is resistant to solvents, the layer does not peel off even when it comes into contact with the solvent during production or cleaning during use.

(Second Embodiment)
In the present embodiment, as shown in FIG. 3, the inorganic insulating protective layer 30 is formed with a first protective layer 31 that is thick near the heat generating portion and a thin second protective layer 32 that is near the electrode pad. That is, the protective layer forming step in the first embodiment is divided into two steps. First, a SiON layer is sputtered on the craze layer 12 in which the heat generating portion, the wiring pattern 16, the electrode pad 18, and the common electrode 19 are patterned in the first step. Deposit with. The other components (glaze layer 12, wiring pattern 16, electrode pad 18, IC 20, bonding wire 22) except for the protective layer are the same as those shown in FIGS.

  Next, in the second step, the vicinity of the heat generating portion is exposed, polyimide tape is bonded to the area on the wiring pattern 16, electrode pad 18, and common electrode 19 side as a mask, and a SiON layer is sputtered near the heat generating portion.

  In this step, the first protective layer 31 in the vicinity of the heat generating part and the second protective layer 32 in the vicinity of the electrode pad having different layer thicknesses are formed. According to this configuration, selection of the layer thickness can be greatly relaxed. In this example, the first protective layer is 5 μm thick, and the second protective layer is 1 μm thick. The first protective layer 31 is preferably set to a thickness of 1 μm to 10 μm, and the second protective layer 32 is preferably set to a thickness of 1 μm to 5 μm.

  Thereby, the inorganic insulating protective layer is rich in electrode pad processability by the photolithography method because the opening forming portion of the electrode pad portion is thin. On the other hand, the product functions sufficiently as a wear-resistant inorganic insulating protective layer for the heat generating part. In the wiring pattern and electrode pad region, a protective layer that is resistant to external impact and maintains solvent resistance and durability can be obtained.

  In the formation of the protective layer opening on the electrode pad, the thinner the protective layer, the more relaxed the conditions of the photoresist used as a mask. Instead of the dry film resist used in the first embodiment, a general photolithography is used. What formed the photosensitive polyimide film by application | coating can be used.

1 is a partial plan view of a thermal head according to a first embodiment of the invention. Sectional drawing which cut | disconnected FIG. 1 along the AA line and added IC mounting. The cross-sectional schematic of the thermal head which concerns on other embodiment of this invention. Sectional schematic drawing of a conventional thermal head.

Explanation of symbols

11: Support substrate 12: Glaze layer 13: Insulating substrate 14: Heating resistor layer 15: Heat generating portions 16, 16-1, 16-2: Wiring pattern 17: Metal layer 18: Electrode pad 19: Common electrodes 20, 30: Inorganic insulating protective layer 21: IC
22: Bonding wire 31: First protective layer 32: Second protective layer

Claims (4)

An insulating substrate; a plurality of heating resistor layers disposed on the insulating substrate; an inorganic insulating protective layer covering a heating portion of the heating resistor layer; and the heating resistor disposed on the insulating substrate. A plurality of wiring patterns connected to the wiring pattern and a plurality of electrode pads connected to the wiring pattern; and the inorganic insulating protective layer covers the heat generating portion of the heating resistor layer and A thermal head that covers the wiring pattern arranged around the electrode pad so that the electrode pad is exposed. An insulating substrate, a plurality of heating resistor layers disposed on the insulating substrate, an inorganic insulating protective layer covering the heating portion of the heating resistor layer, and disposed on the insulating substrate and connected to the heating portion A plurality of wiring patterns, a plurality of electrode pads connected to the wiring patterns, a driver IC that is disposed on the insulating substrate and drives the heat generating portion, and a bonding that connects the electrode pads and the driver IC A thermal head comprising a wire, wherein the inorganic insulating protective layer exposes the electrode pad and covers the wiring pattern disposed around the electrode pad. 3. The thermal head according to claim 1, wherein the inorganic insulating protective film is a SiON film. The thermal head according to claim 1, wherein the inorganic insulating protective layer has a thickness of 1 μm to 10 μm.

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