JPS5926277A - Production of thermal head - Google Patents

Abstract

PURPOSE:To prevent a plated metal layer from being delaminated, by a method wherein a pattern of a photoresist layer is provided in a region including an abrasion-resistant layer and excepting a bonding part of an electrode, and the electrode is plated with gold by using the photoresist pattern as a mask. CONSTITUTION:A tantalum nitride layer 10, a nichrome layer 11, a gold layer 12 and the plated gold layer 13 are provided in four layers on a ceramic substrate 1 by appropriate means, thereafter the layers are patterned to produce a heating resistor and the electrode. Then, a silicon dioxide layer 14 as a protective layer and a tantalum pentoxide layer 15 as the abrasion-resistant layer are provided in two layers by a mask sputtering method. Subsequently, a photoresist is applied to the entire upper surface of the thermal head in this condition, is then exposed to light through a mask, and is developed so that the photoresist remains in the area of the pattern 20.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a thin film type thermal hesode with an improved electrode structure.

The thermal head includes, for example, as shown in FIG.
A driving electrode 3 connected to a driving circuit was formed on one side of the ceramic substrate 1, and a common electrode 4 was formed on the other side, in contact with a heating resistor 2 formed along the longitudinal direction on the surface of the ceramic substrate 1. Alternatively, as shown in FIG. 2, driving electrodes 3 and common electrodes 4 are alternately arranged on both sides of a heating resistor 2 in appropriate units. Reference numeral 5 denotes a two-layer structure of a protective film and a wear-resistant layer (hereinafter referred to as the wear-resistant layer) formed on the entire exposed portion of the heating resistor, a part of the driving electrode 3, and a part of the common electrode 4. etc.).

The driving electrode 3 and the driving circuit are connected by bonding using a method such as a tape carrier method, and a large current flows through the trench common electrode 4.

By the way, since the thin film type thermal head is manufactured by thin film forming technology, the electrodes such as the driving electrode 3 and the common electrode 4 have a thickness of 1 to 211 m at most, and cannot be formed very thick. Therefore, there is a problem that the strength of bonding to the drive electrode 3 is weak and that sufficient current cannot flow through the common electrode 4.

Therefore, in such a thermal head, the present applicant
Furthermore, we have developed a technique to solve the above problem by plating a thick layer of gold onto the exposed electrodes 2 using the wear-resistant layer 5 as a mask, and have already filed an application. As shown in FIG. 3, a cross-sectional view of an example of a thermal head manufactured by this method includes a patterned tantalum nitride (Ta2N) layer 10 serving as a heating resistor on a ceramic substrate 1; A nichrome (NiCr) layer 11 and a gold (Au
) layer 12 and gold plating layer 13 are formed in a patterned manner. The area sandwiched between the drive electrode 3 and the common electrode 4 is a heating resistor pattern 72 that contributes to heat generation. A silicon dioxide (siO2) layer 1 as a protective film is provided on the heating resistor pattern 2, including the upper part of the electrodes 3 and 4.
4, wear-resistant layer and L7 tantalum pentoxide layer ('l'a2
0s) 15 is formed. A gold layer 16 is formed on the electrodes 3 and 4 outside the wear-resistant layer 5 by plating. Since the gold layer 16 formed by plating can be formed thickly, the two problems mentioned above can be solved.However, with this method, gold adheres to a wide area other than the bonding part of the drive electrode 3, so the amount of gold consumed is reduced. There is a problem that this increases the number of times, leading to an increase in costs. Since the protective film 4 and the wear-resistant layer 15 are formed by a mask sputtering method, the ends 17 are not steep but have a gentle slope. Therefore, in the part where the wear-resistant layer 5 changes gently on the pattern of the driving electrode 3, the so-called sagging part, the edge part of the pattern 7 of the driving electrode 3 is plated with G or grows in a burr shape. However, there is also the problem that this thin gold plating layer peels off and short circuits occur between the electrodes.

An object of the present invention is to provide a method for solving the problems described in "2" in forming a gold layer by plating on the electrodes of a conventional thermal head. After forming the ltI abrasion layer, a pattern of a resist layer such as a photoresist is formed in the area including the abrasion resistant layer 5 and excluding at least the bonding part of the electrode, and using this resist pattern as a mask, the electrode is plated with gold. The aim is to achieve the above objective by applying the following.

An embodiment of the present invention will be described below.

FIG. 4(5) is a sectional view showing a state in which the wear-resistant layer is formed by 15 layers. The manufacturing process up to this state includes a tantalum nitride layer 10, a nichrome layer 11,
After forming the gold layer 12 and the gold plating layer 13 into four layers using an appropriate method, patterning is performed using photolithography to form heating resistors and electrodes. Next, a silicon dioxide layer 14 as a protective film and a tantalum pentoxide layer 15 as a wear-resistant layer may be formed in two layers by mask sputtering in the region shown in the figure.

Next, after applying photoresist to the entire upper surface of the thermal head in this state, it is exposed through a mask, developed, and
As shown in FIG. 4(B), the photoresist is left in the pattern 20 surrounded by the broken line in FIG.

That is, in this state, the bonding part 21 of the drive electrode 3 and the common electrode 4 (7) - part are not covered with the photoresist 20 and are exposed. Also, the first
No droop occurs at the pattern end 22 of the resist 20 [7].

Next, as shown in the figure, gold plating is performed using this photoresist pattern 20 as a mask. Plating proceeds only on the exposed portions of electrodes 3 and 4. Plating layer 1
The thickness of the layer 6 is preferably several μm or more, for example, about 7 layers or more. After plating is completed, the first resist layer 20 is removed using a stripping solution to form a common electrode 4 as shown in FIG.
A thermal head is obtained in which the electrode film thickness of a part of the bonding portion 21 of the driving electrode 3 is increased.

Incidentally, since the present invention has a method of increasing the film thickness of a part of the electrode, it goes without saying that the state shown in FIG. 4(A) is not limited to that of the embodiment. That is, for example, as the heating resistor layer 10, other than tantalum nitride, nichrome, Nessa film, or other known suitable materials may be used, and the electrode structure is not limited to the three-layer structure illustrated, but may also include the uppermost layer. It is also possible to use other suitable conductive materials in the lower layer, provided that only gold is used. Furthermore, the wear-resistant layer etc. 5
In addition to the illustrated structure, it is also possible to use silicon carbide (SiC), aluminum oxide (AJzO3), and the like.

As described above, according to the present invention, the resist layer is formed in a wider area than the wear-resistant layer, etc., and gold plating is applied to a part of the electrode using the resist layer as a mask, so the area where gold adheres becomes narrower. Therefore, the total amount of adhesion is reduced, and the cost can be reduced. Still, the resist layer completely covers the wear-resistant layer, etc., and there is no scum at the edges of the resist layer, so even if there is some scum at the edges of the abrasion-resistant layer, the plating will not look like whiskers. There is no such thing as growing into
Therefore, defects such as electrode short circuits due to peeling of the whisker-like plating layer do not occur. Coupled with the fact that the region to be plated thicker becomes narrower, the probability of short circuit between electrodes is also reduced, and manufacturing yield can be increased.

[Brief explanation of the drawing]

1 and 2 are plan views showing examples of patterns of a thermal head to which the present invention is applied, FIG. 3 is a sectional view showing the vicinity of the heating resistor of an improved thermal head that has already been proposed, and FIG. Figures (A) to (C) are cross-sectional views of the vicinity of the heating resistor, showing the steps of the present invention. 1...Ceramic substrate, 2...Heating resistor, 3, 4
... Electrode, 5... Wear-resistant layer etc. (protective film and wear-resistant layer), 20... Resist pattern, 21... Bonding part of electrode, 16... Gold plating layer. Patent Applicant Ricoh Co., Ltd. Agent Patent Attorney Aobai Ao and two others No. 1eA Fig. 2ζ

Claims (1)

[Claims] (1) A heating resistor is formed on the substrate, an electrode is formed on the upper surface of the connecting portion of the heating resistor, and a protective film and a wear-resistant layer are patterned on the upper surface of the exposed portion of the heating resistor and the upper surface of a part of the electrode, respectively. In the formed state, a resist pattern is further formed in the area including a protective film and an abrasion resistant layer and excludes at least the part where the electrode is bonded, and the electrode is plated using the resist pattern as a mask. The manufacturing method of the featured thermal head.