JPH03193467A - Manufacture of thermal head - Google Patents

Abstract

PURPOSE:To reduce the manufacturing cost by a method wherein an heat accumulation layer of a heating element and a solder dam for face down bonding of an IC chip are formed simultaneously of a same material. CONSTITUTION:After forming a conductor layer film on a substrate 1 made of ceramic and high heat resistant resin, an individual electrode 2a and a common electrode 2b are formed by patterning. Then, after applying polyimide resin having high heat resistance and high adhesion all over to an upper material of those electrodes 2a, 2b, a heat accumulation layer 4a is formed in a clearance between the individual electrode 2a and the common electrode 2b, and solder dam 4b is formed around a connection part of face down bonding of an IC chip respectively by specified dimensions simultaneously within a same process, which are cured. A heating element layer 5 is formed thereon by a vapor deposition method, a sputtering method, or a plasma CVD method, and a protective film 6 is formed to a part other than the face down bonding part of the IC chip. Since a forming process of the heat accumulation layer and a forming process of the solder dam are performed in the same processing, a fixed yield may be improved at a low cost.

Description

Detailed Description of the Invention (a) Industrial Application Field This invention relates to a thermal head for heat-sensitive recording used in facsimile machines, various printers, etc. Place it on the board,
The present invention relates to a method for manufacturing a thermal head that energizes the heating resistor element to generate heat in accordance with the information to be printed, thereby printing in color on thermal recording paper or transferring and recording onto plain paper via a thermal transfer ribbon.

(b) Conventional technology In a conventional thermal head, an IC for driving a heating resistor is used.
There are two methods for electrically connecting the chip and the individual electrodes connected to each heating resistor: a wire bonding method and a face-down bonding method using solder bumps. In this face-down bonding method, the IC
The solder bumps formed on the chip side and the lead electrodes formed on the insulating substrate are joined and electrically connected by melting the solder, but the diameter of the solder bumps is approximately 100 μm.
-, and the number of connection terminals is approximately 90 for each IC chip, so the entire thermal head has 8 dots/
In the case of R11, the number of connection points is approximately 2000 for A4 size and approximately 3000 for B4 size. This wire has small dimensions (in order to reliably connect a large number of solders, it is necessary to keep the solder connections of the connecting leads I! poles uniformly in good condition, and at the same time prevent the solder bumps on the tC chip from melting. A solder dam is required to prevent soldering onto unnecessary electrodes.The material for this solder dam must have heat resistance above the soldering temperature, fine pattern processability, and compatibility with substrate and conductor materials. High adhesion is required.

FIG. 2 is a sectional view showing an example of a conventional thin film thermal head. Here, 7 is a ceramic substrate made of alumina or the like or a metal substrate. The upper layer 8 is a glass glaze serving as a heat storage layer, and is formed by firing on the base material by a printing method or the like. On these substrates, a resistive layer 9 that becomes the heating element of the thermal head is formed by sputtering, vapor deposition, plasma CVD, etc., and then an electrode layer 10 made of aluminum, gold, etc. is formed using the same method (sputtering, vapor deposition, etc.). After removing the electrode layer corresponding to the heating element of the thermal head by etching using a photolithography technique, a protective film layer 11 is formed by vapor deposition or sputtering on the area other than the IC chip connection area to be face-down bonded. Alternatively, after forming the film on the entire surface using a plasma CVD method or the like, etching the film above the IC chip connection part, and finally applying a solder dam material such as polyimide resin to the IC chip connection part using a printing method or a spinner. , a roll coater or the like, and the solder connection portion is etched off to form the solder dam 12.

(c) Problems to be Solved by the Invention As described above, in conventional thin film thermal heads, a thin film resistor is placed on a heat storage layer of a glass glaze layer formed by a printing method etc. on an insulating substrate such as alumina. An electrode layer and a protective film layer are formed on top of the electrode layer, and the connection part of the IC chip for driving the heat generating resistor is formed using the face-down bonding method because polyimide resin is formed as a solder dam material on the electrode layer. When connecting a driving IC using a conventional method, a dedicated and complicated process for forming a solder dam was required.

This invention was made taking these circumstances into consideration, so
The present invention provides a method of manufacturing a thermal head that can improve the process yield at low cost by performing the heat storage layer forming step and the solder dam forming step in the same step.

(d) TS, Means for Solving the Problem This invention provides a heating resistor layer on a substrate, an individual electrode for supplying current to the heating resistor layer, and a common electrode, and the individual electrodes are used for driving the heating resistor. A method for manufacturing a thermal head provided with a land for connecting ICs by face-down bonding, in which first, individual electrodes and a common electrode are formed on a substrate, and then a heat storage layer is formed between the individual electrodes and the common electrode. Individual X
A solder dam is formed near the land of the pole using the same resin in the same process. Next, a heat generating resistor layer is formed on the heat storage layer from the individual electrodes to the common electrode, and a protection layer is further formed to cover the heat generating resistor layer. This is a method for manufacturing a thermal head characterized by forming a layer.

(e) Since the functional heat storage layer and the solder dam are formed using the same material and in the same process, the manufacturing work of the thermal head is reduced and the yield is improved.

(f) Examples The present invention will be described below based on examples shown in the drawings.

FIG. 1 is a sectional view of a thermal head showing an embodiment of the present invention. 1 is a substrate, and a ceramic insulating substrate such as alumina or a high heat-resistant resin substrate is used for this. After forming a conductor layer on the substrate l, it is patterned to form individual electrodes 2a and common iI electrodes 2b. Individual electrode 2
At least the terminal portion a for face-down bonding the IC chip is made of a solderable metal such as gold, nickel, copper, tin, lead, or silver.

In this embodiment, a gold plating layer 3 is formed over the entire electrodes 2a and 2b by electroless plating. After applying a polyimide resin having high reliability, high heat resistance, and high adhesion to the entire upper part of the electrodes 2a and 2b formed in this way, heat is stored in the gap between the individual electrodes 2a and the common electrode 2b using a photolithography method. In the layer 4λ, solder dams 4b are simultaneously formed in the same mold around the connecting portions (lands) where the IC chip is face-down bonded, each having a predetermined dimension, and cured. On top of that, a heating resistor layer 5 as a heating element is formed by vapor deposition, sputtering or plasma C'V as in the past.
The thermal head is completed by forming the protective film 6 by the D method and finally forming the protective film 6 on the area other than the face-down bonding portion of the IC chip.

(G) Effects of the Invention According to this invention, by simultaneously forming the heat storage layer of the heating resistor and the solder dam for face-down bonding of the IC chip from the same material, it is possible to lower manufacturing costs and improve yield. Therefore, an inexpensive thermal head can be provided.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the configuration of a thermal head showing an embodiment of the present invention, and FIG. 2 is a diagram corresponding to FIG. 1 of a conventional example. 1...Substrate, 2a...Individual electrode, 2b...Common electrode, 4a...Heat storage layer, 4b...Solder dam, 5 ...Heating resistor layer, 3...Gold plating layer, 6...Protective film.

Claims (1)

[Claims] 1. A thermal head in which a heating resistor layer, individual electrodes and a common electrode for energizing the heating resistor layer are provided on a substrate, and a land is provided on each individual electrode to connect to the IC face-down bonding method for driving the heating resistor. A method of manufacturing,
First, individual electrodes and common electrodes are formed on the substrate, then a heat storage layer is formed between the individual electrodes and the common electrode, and a solder dam is formed near the lands of the individual electrodes using the same resin in the same process. A method for manufacturing a thermal head, comprising: forming a heat generating resistor layer extending from the individual electrodes to the common electrode on the heat storage layer; and further forming a protective layer covering the heat generating resistor layer.