JPS63124432A - Method of forming wiring of film carrier - Google Patents

Abstract

PURPOSE:To improve junction strength between an IC chip and the lead of a film carrier by a method wherein, after bumps are formed on a bump forming substrate whose surface has a fine unevenness, the IC chip is bonded to the lead wires with the bump between. CONSTITUTION:A fine unevenness is formed on the surface of a bump forming substrate. A Ti.Ag conductive film 12 is formed on the surface 11 of the substrate 10 and a predetermined pattern is formed on the film 12 with photoresist 13 or the like and bumps 20 are formed in the pattern. Therefore, fine unevennesses are formed on the rear surfaces of the bumps 29 too corresponding to the unevenness of the surface 11. The leads 31 of a polyimide film 30 are made to correspond to the bumps 20 and the bumps 20 are fixed to the leads 30 by pressure. The bumps 20 on the substrate 10 are transcripted onto the leads 31 by the fixing by pressure. Then the leads 31 onto which the bumps 20 are transcripted are fixed to Al pads 41 of an IC chip 40 by pressure. At that time, oxide films formed on the surfaces of the pads 41 are removed by the unevenesses formed on the rear surfaces 21 of the bumps 20. With this constitution, the junction strength can be improved.

Description

[Detailed description of the invention]! BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming wiring on a film carrier.

In response to the recent demand for thinner electronic devices, various methods have been proposed. One of them is a method of mounting integrated circuit elements (hereinafter referred to as IC chips) using the TAB method.

This TAB method is particularly effective in reducing the thickness of a film carrier when an IC chip is attached to the film carrier. As an example of the process of the TAB method, the surface of a bump forming substrate is coated with a conductive film, a patterning technique is used to form bump openings on this conductive film, and a plating technique is applied to the bump openings. A bump consisting of AU etc. is grown. Thereafter, the bumps are pressed and heated to be transferred to Cu foil leads formed on the polyimide film, and then the IC chip is attached to the adhesive.

By the way, the surface of the bump forming substrate is usually polished to a mirror surface with a surface roughness of 150 Å or less, so the back surface of the bumps formed on that surface will also be smooth. ing.

On the other hand, the pads of IC chips to which bumps are bonded are usually made of aluminum, and therefore a thin (several tens of nanometers) oxide film is formed on the surface of the aluminum.

Therefore, when an IC chip is bonded to a lead wire of a film carrier through the bump, the aluminum oxide film tends to be unable to be removed effectively because the back surface of the bump is smooth.

Especially Aj! The oxide film near the center of the pad is difficult to remove, and therefore All and aluminum tend not to form an alloy. As a result, the strength of the bond between the Aff pad and the bump varies, and the performance of the product may deteriorate. There is a problem that the wires do not become the same and there is a risk of wire breakage.

The present invention was devised in view of the above circumstances, and is a film carrier that can effectively remove the natural oxide film on the surface of the AJ band, thereby improving the aforementioned bonding strength and, in turn, improving the performance of the product. The purpose of this invention is to provide a wiring formation method.

In the present invention by Ruta Kuchi, after bumps are formed on a bump-forming substrate having fine irregularities on the surface by a patterning means, an IC chip is attached to the lead wire of a film carrier via the bumps.

1. Since the bump-forming substrate has fine irregularities formed thereon, the back side of the bumps formed based on this has the same shape, that is, has an irregular shape.

When a bump is bonded to an An pad of an IC chip, the fine irregularities formed on the back surface of the bump serve to push away a thin oxide film formed on the surface of the bump.

Practical JIL Example - Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows bumps 20 on a bump-forming substrate 10 according to the present invention.
FIG. 2 is a schematic cross-sectional view showing a state in which .

The bump forming substrate 10 has a surface 11 of 0.5 to 1.0
This is a glass substrate on which microscopic irregularities on the order of μm are formed.

The surface 11 of this bump-forming substrate 10 has a thickness of approximately 0°1 μm.
A conductive film 12 of titanium and platinum is formed by vapor deposition or the like, and a predetermined pattern 131 is formed on the conductive film 12 using a photoresist 13 or the like as a plating mask, and bumps 20 are further formed on the pattern 131 by a technique such as plating. It is formed with

Therefore, the back surface 21 (see FIG. 2) of the bump 20 formed using such a bump forming substrate 10 also has fine irregularities corresponding to the unevenness of the front surface 11 of the bump forming substrate 10.

Figure 3 shows Cu foil leads 3 of polyimide film 30.
1 is a schematic process diagram for attaching bumps 20 to IC chip 1 and wiring the leads 31 to IC chip 40.

The bumps 20 formed on the pattern 131 and the leads 31 of the polyimide film 30 are made to correspond to each other at approximately 300°C.
The bump 20 and the lead 31 are crimped together (see Fig. 3 (al.
and FIG. 3 (see bl).

By this pressure bonding, the bumps 20 of the bump-forming substrate 10 are transferred to the lead 31 side (see FIG. 3 (C1)).

The bump 20 is transferred to the AIV and pad 41 of the IC chip 40, and the pad 31 is pressed (see FIG. 3 fdl).
.

At this time, since minute irregularities are formed on the back surface 21 of the bump 20, the oxide film several tens of nm thick formed on the surface of the Aj2 pad 41 flows outward due to the irregularities on the back surface 21 and is removed. Ru. That is, A7! The natural oxide film on the surface of the pad 41 is pushed away by the unevenness on the back surface 21 of the bump 20.

-Example 1■ B1 Results According to the method for forming wiring on a film carrier according to the present invention, fine irregularities are formed on the back surface of the bumps.
When bonding a lead with a bump to the AA band of an IC chip, the oxide film on the surface of the Aj2 pad is removed due to the unevenness on the back surface of the bump, increasing the actual bonding area and increasing the I.
The bonding strength between the C chip and the leads is increased, product variations are eliminated, and there is no risk of wire breakage. In addition, since the level difference in the unevenness on the bottom surface of the bump is about 0.5 to 1.0 μm,
Coverage of the conductive film or photoresist is not deteriorated, and the shape of the bump is not affected.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a bump-formed substrate according to the present invention;
FIG. 2 is a schematic enlarged cross-sectional view taken along line 1--A in FIG. 1, and FIG. 3 is a schematic process diagram for attaching bumps to leads of a polyimide film and wiring an IC chip to the leads. DESCRIPTION OF SYMBOLS 10... Bump formation board|substrate, 11... Surface of hump formation board|substrate, 12... Conductive film, 131... Pattern, 20... Bump, 31... Lead, 40...
・・IC chip. Patent Applicant ROHM Co., Ltd. Agent Patent Attorney Takaharu Ohnishi Figure 1 Figure 2 Figure 3 (a)

Claims (1)

[Claims] (1) Wiring of a film carrier characterized in that after bumps are formed by patterning on a bump-forming substrate having minute irregularities on the surface, an IC chip is attached to the lead wire of the film carrier via the bumps. Formation method.