JPH0362525A - Bump structure and its formation - Google Patents

Abstract

PURPOSE:To suppress the expansion of a ball bump to the outside and to reduce a shearing stress, which is applied to an electrode pad, by a method wherein an insulating film is provided on a chip in such a way as to come into contact to the side surfaces of the bump. CONSTITUTION:An Au ball bump 4 is adhered on an electrode pad on an Si chip 1. A polyimide film 5 is applied, a resist mask 6 is provided to etch away the film 5 and the resist mask is removed. Thus, the side surfaces of the bump are surrounded with the film 5. When a load is applied to the bump 4 from over the bump, the expansion of the bump to its lateral direction is suppressed by the film 5. Accordingly, a shearing stress, which is applied to the pad, is reduced and a crack stops generating under the pad.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to countermeasures against under-pad cracks that occur during inner lead bonding onto pads, and particularly relates to a bump structure that reduces the force applied to the pad and a method for forming the same. .

[Conventional technology]

Conventionally, as shown in FIG. 3, bumps 4 were formed by connecting only the ball formed at the tip of the wire to the electrode pad 3 on the silicon chip l using a ball bonding method. Here, the surface protective film 2 is located above the peripheral portion of the electrode bump 3, but does not contact the ball bump 4. Then, perform inner lead bonding (ILB) between the inner leads of the film carrier and the bumps on the IC chip.
They were joined using technology.

[Problem to be solved by the invention]

In the conventional ball bump described above, the pounding load necessary for ILB is applied to the lead surface aligned with the bump using a pounding tool, but this load deforms the bump and causes stress at the electrode pad and bump bonding position. There was a problem in that the insulating layer under the surface of the metal film of the pad was destroyed by concentrating. The relationship between the distance from the center of the ball and the stress there is shown in FIGS. 4 and 5 based on simulation experiments. The mechanism of crank occurrence is that the resultant force of the shear stress due to expansion of the ball periphery due to deformation and the compressive stress due to the pounding load is maximum at the ball's outermost diameter, resulting in cracks under the pad from the ball's outermost diameter. It was found that this occurs.

[Differences between the invention and the prior art]

In the conventional ball bump forming method described above, the bump is deformed by the load and heat during ILB, and under-pad cracks occur due to stress concentration around the bump that occurs at that time. The polyimide film on the side surface suppresses outward deformation of the ball bump, thereby reducing concentrated stress and preventing the occurrence of under-pad cracks.

[Means to solve the problem]

The ball bump forming method of the present invention disperses the shear stress that causes the ball bump to spread outward due to load.
It has an insulating film that reduces stress applied to the electrode pad.

〔Example〕

Next, the present invention will be explained using the drawings.

FIG. 1 is a longitudinal sectional view of a chip according to a first embodiment of the present invention. The ball bump shown in FIG. 1 and a polyimide film as an insulating film material are formed by the following procedure. A gold ball bump is attached to an electrode pad on a silicon chip (FIG. 1(A)) using a ball bump technique using a ball wire bonding technique (FIG. 1(B)). Next, a polyimide film is applied as an insulating film (Fig. 1 (C)), a resist is applied, and a mask is used to remove only the resist at the bump portion (Fig. 1 (D)), the polyimide film is etched, and the resist is further removed. After removing the ball bump, the side surface of the ball bump is surrounded by a polyimide film as shown in FIG. 1(E). FIG. 1(E) is a diagram showing a completed bump structure. In this structure, by attaching a polyimide film, the ball bump tends to expand in the lateral direction due to the load applied to the ball bump from above during ILB, but by suppressing it with polyimide polishing, it is possible to prevent this expansion. Since the stress component applied to the pad is shear stress, which is lower than before, the resultant stress is only compressive stress or total stress, which ultimately reduces the stress value during ILB and prevents the occurrence of cracks under the pad. I can do it.

In the second drawing of this specification, a "silicon chip" refers to a silicon wafer during the manufacturing process, and a silicon chip substrate after being divided into chips.

FIG. 2 shows a second embodiment that differs from the first embodiment described above in the procedure for forming the PO/1 bump and the polyimide film.

The procedure is shown below. First, a polyimide film 5 is coated on the silicon chip 1 (Fig. 2(A)), and then the polyimide on the pad portion is removed using etching technology (see Fig. 2(A))). C)). Then, a ball bump is formed on the pad. (Figure 2 (D)).

As a result, during ILB, the ball bump tries to expand in the lateral direction, but the polyimide film hits the bump and prevents the bump from deforming in the lateral direction, reducing the shear stress component on the pad, resulting in the same result as in the first embodiment. get. This second embodiment differs from the previous embodiments in that it is not necessary to return from the assembly process to the diffusion process, thereby simplifying the process.

〔Effect of the invention〕

As explained above, in the present invention, on the side surface of the ball bump,
By forming a polyimide film to suppress the outward expansion of the ball bump during ILB,
It is possible to reduce the shear stress on the electrode pad, and only compressive stress is applied to the pad, resulting in a reduction in stress, which was previously caused by stress during ILB. This was effective in preventing cracks under the pad.

4,

[Brief Description of the Drawings] Figures 1(A) to 1(E) are cross-sectional views showing the first production method of the present invention in the order of steps, of which Figure 1(E) is a longitudinal cross-sectional view after the ball bump and polyimide film are formed. FIG. 2(A) to FIG. 2(D) are cross-sectional views showing the manufacturing method of the second embodiment of the present invention in the order of steps. FIG. FIG. 3 is a vertical cross-sectional view of a chip during conventional ball bump formation. FIGS. 4 and 5 are diagrams showing the relationship between the distance from the ball bump center and the stress during ILB. l...Silicon chip, 2...Surface protective film, 3...Electrode pad, 4...Ball bump, 5...Polyimide film , 6...
・Resist, 7... Lead, 8... Load direction, 10... Stress curve without insulating film, 11... With insulating film stress curve, 12
...Compressive stress when there is an insulating film, 13...
... Shear stress due to ball expansion when there is an insulating film,
14...Combined stress when there is an insulating film, 15.
...Compressive stress without insulating film, 16...
...Shear stress due to ball expansion without insulating film, 1
7...Composite stress when there is no insulating film.

Claims (2)

[Claims] (1) In a ball bump in which a bump is formed by connecting a ball to an IC chip electrode using ball wire bonding technology, an insulating film is provided on the chip so as to be in contact with the side surface of the bump. bump structure. (2) A step of forming a ball bump on the electrode pad surrounded by a surface protective film, a step of forming an insulating film on the entire surface including the top of the ball bump, and selectively removing the insulating film on the ball bump. A method for forming a bump in which the side surface of the ball bump is surrounded and in contact with the side surface.