Ball bonding method on a chip

Details Ball bonding method on a chip Ball bonding method on a chip

1999-10-15

2001-01-23

Ryan, Patrick (Department: 1725)

Metal fusion bonding

Process

Plural joints

C228S180220, C438S613000, C438S051000, C438S055000, C438S064000, C438S108000, C438S123000, C029S829000

Reexamination Certificate

active

06176417

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a ball bonding method on a chip and more particularly to the configuration of the ball or bump on the second bonding pad such that all of the balls or bumps have a uniform shape and size of vertical tips.
2. Description of the Related Art
For many years wire bonding prevented damage to the bonding pad from the capillary hitting the bonding pad directly by forming a ball on the bonding pad prior to wire bonding so that the capillary would hit the ball during wire bonding. The ball-forming process comprises the following steps: ball formation on a capillary; thermocompression bonding on a bonding pad; capillary horizontal movement for stitch bonding; and capillary vertical movement for wire cutting.
U.S. Pat. No. 5,641,079, issued on Jul. 12, 1994 to Mathew et al., discloses method for bond wire connection and a conductive bump thereof prior to stitch bonding. As shown in
FIG. 1
, U.S. Pat. No. 5,641,079, a substrate
100
is attached to a chip
110
which has a second bond point as well as a bonding pad
111
. A capillary
120
of the thermosonic or thermocompression ball bonding tool forms a bump on each bonding pad
111
and connections are made to the bonding pads
111
of the chip
110
by means of stitching bonding in a way which does not damage the chip
110
. A bump
121
is formed at the free end of the wire in the capillary
120
. Then, the clamp
130
is closed to hold the wire.
As shown in
FIG. 2
, the capillary
120
is moved down in a vertical direction to the second bonding point so as to let the bottom of the bump
121
weld to the bonding pad
111
. Then, the capillary
120
does not hit the bonding pad
111
and the clamp
130
of the capillary
120
is opened to release the wire.
As shown in
FIG. 3
, the capillary
120
is moved in a horizontal direction thereby moving the tip as well as connection part
122
to the side. Then the capillary
120
is moved down again in a vertical direction so as to press the tip
122
of the bump
121
to form a thin neck. Then, the capillary
120
is opened to hold the wire.
As shown in
FIGS. 4 and 5
, the capillary
120
is moved up in a vertical direction and then the clamp
130
is closed thereby cutting the thin neck portion which connects to the tip
122
of the bump
121
such that the bump
121
is left on the bonding pad
111
. Because the bump
121
on the bonding pad
111
is pressed by the capillary
120
, the tip
122
of the bump
121
is formed in a particular direction and collapse shape. The direction and collapse shape of the tip
122
determines the parameter (e.g., the movement) of the wire bonding tool for the second bonding so as to increase quality and reliability of products. However, the direction and collapse shape of the tip
122
of each bump
121
are various and parameter adjustment of each wire bonding is impossible in this circumstance. Thus only one set of parameters can be used in each wire bond, and we are unable to control the quality and reliability of wire bonding of products under these parameter controls.
The present invention intends to provide a ball with a uniform shape and height for wire bonding at a second bonding point to decrease the variability of the ball and increase work window range in such a way as to mitigate and overcome the above problem.
SUMMARY OF THE INVENTION
The primary objective of this invention is to provide a ball bonding method on the chip where a ball is bonded at a second bonding point and then pulled to form a uniform body and tip which provide for uniform wire bonding thereby decreasing the variability of wire bonding and increasing the reliability of products.
The present invention is a ball bonding method in accordance with an embodiment comprising steps of: a wire is burned to form a ball on a capillary; the capillary is moved down to a second bonding point for ball bonding; and the capillary is moved up in a vertical direction thereby pulling the tip of the ball to be cut such that the ball has an uniformly shape body and tip. Therefore, the ball provides uniform body shape and tip height for wire bonding at a second bonding point under lower variability conditions.
When wire bonding on a ball at a second bonding point, the present invention allows a larger wire bonding area and products thereof have the same quality and reliability.
Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description and the accompanying drawings.


REFERENCES:
patent: 5328079 (1994-07-01), Mathew et al.
patent: 5616520 (1997-04-01), Nishiuma et al.
patent: 5633204 (1997-05-01), Tago et al.
patent: 5821494 (1998-10-01), Albrecht et al.
patent: 5871141 (1999-02-01), Hadar et al.
patent: 5957371 (1999-09-01), Miyano et al.
patent: 6020220 (2000-02-01), Gilleo et al.

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