Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Configuration or pattern of bonds
Reexamination Certificate
1999-12-07
2001-06-05
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Configuration or pattern of bonds
C257S780000, C257S783000, C257S784000
Reexamination Certificate
active
06242815
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to flexible substrate based ball grid array (BGA) packages, and more particularly to flexible film substrates for use in forming flexible substrate based BGA packages and manufacturing methods thereof.
2. Description of the Related Art
FIG. 1
depicts a conventional flexible substrate based BGA package
100
typically utilizing a flexible film substrate
110
(see
FIG. 2
) for carrying a semiconductor chip
120
. The flexible film substrate
110
is provided with a plurality of chip connection pads
110
a
arranged about the periphery of the semiconductor chip
120
. The semiconductor chip
120
is securely attached onto the flexible film substrate
110
through a nonconductive adhesive (e.g., epoxy resin)
122
and electrically connected to the chip connection pads
110
a
through a plurality of bonding wires
130
. The chip connection pads
110
a
are electrically connected to a plurality of solder pads
110
b
through conductive traces
110
d.
The flexible film substrate
110
has a plurality of through-hole
110
c
disposed corresponding to solder pads
110
b.
Each solder pad
110
b
has a portion exposed within the corresponding through-hole
110
c
for mounting a solder ball
140
. The upper surface of the flexible film substrate
110
, the semiconductor chip
120
and the bonding wires
130
are encapsulated in a package body
150
. The package body
150
is formed from insulating material such as epoxy. The flexible substrate based BGA package
100
is mounted to a substrate (not shown), such as a printed circuit board, through the solder balls
140
.
Typically, the surfaces of the chip connection pads
110
a
and solder pads
110
b
are plated with a layer of metal (not shown) such as gold which bonds well with conventional bonding wire material. However, gold does not bond well with the nonconductive adhesive
122
, so the central part of the chip attaching area is not provided with solder pads in order to enhance the adhesion between the flexible film substrate
110
and the nonconductive adhesive
122
, whereby the semiconductor chip
120
is more securely attached onto the flexible film substrate
110
. However, since the solder pads
110
b
are not evenly distributed on the chip attaching area
160
of the flexible film substrate
110
, the central part thereof is prone to be deformed by the stress due to CTE (coefficient of thermal expansion) mismatch between the central part and other part of the chip attaching area
160
. This may create problems of delamination between the chip and the substrate or die cracking.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a flexible substrate based BGA package comprising a flexible film substrate having a die attaching area for carrying a semiconductor chip, wherein the flexible film substrate is provided with at least a dummy pad disposed centrally on the chip attaching area, thereby reducing problems of delamination between the chip and the substrate or die cracking.
It is another object of the present invention to provide a flexible substrate based BGA package comprising a semiconductor chip securely attached onto a die attaching area of a flexible film substrate through a nonconductive adhesive, wherein the flexible film substrate is provided with at least a dummy pad disposed centrally on the chip attaching area, and the dummy pad has a cupric oxide coating formed thereon for enhancing its adhesion with the nonconductive adhesive.
A flexible substrate based BGA package in accordance with a preferred embodiment of the present invention generally comprises a semiconductor chip securely attached onto a flexible film substrate through a nonconductive adhesive. The flexible film substrate includes a flexible film having a chip attaching area for carrying the semiconductor chip. The upper surface of the flexible film is provided with a plurality of chip connection pads, a plurality of solder pads, and at least a dummy pad which is disposed centrally on the chip attaching area. Preferably, the surface of the dummy pad has a cupric oxide coating for enhancing its adhesion with the nonconductive adhesive. The chip connection pads are arranged about the periphery of the chip attaching area. The solder pads are disposed about the dummy pad(s) and electrically connected to the corresponding chip connection pads. The flexible film has a plurality of through-holes formed corresponding to the solder pads such that each solder pad has a portion exposed within the corresponding through-hole for mounting a solder ball. A package body is formed over the semiconductor chip and the upper surface of the flexible film substrate.
According to the flexible substrate based BGA package of the present invention, since at least a dummy pad is disposed centrally on the chip attaching area of the flexible film substrate, the central part of the chip attaching area of the substrate has a better rigidity and strength to resist external forces thereby reducing the problems of die cracking or delamination. Further, the cupric oxide coating on the surface of the dummy pad has a contour of roughness, so the bonding mechanism of the interface between the cupric oxide coating and the nonconductive adhesive includes chemical bonding as well as mechanical interlock thereby greatly enhancing the adhesion between the dummy pad and the nonconductive adhesive thereby reducing the occurrence of delamination.
The present invention further provides a method for producing a flexible film substrate comprising the steps of: (A) providing a flexible film having opposing upper and lower surfaces, the upper surface of the flexible film has a chip attaching area adapted for carrying a semiconductor chip; (B) forming a plurality of through-holes in the flexible film; (C) laminating a metal layer on the upper surface of the flexible film; and (D) etching the metal layer to form a plurality of solder pads, chip connection pads, conductive traces, and at least a dummy pad, wherein the solder pads are disposed corresponding to the through-holes and electrically connected to the chip connection pads through the conductive traces, and the dummy pad is disposed centrally on the chip attaching area.
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5400950 (1995-03-01), Myers et al.
patent: 5677575 (1997-10-01), Maeta et al.
patent: 5731636 (1998-03-01), Chun
patent: 5773882 (1998-06-01), Iwasaki
patent: 5814891 (1998-09-01), Hirano
patent: 5841194 (1998-11-01), Tsukamoto
patent: 5909058 (1999-06-01), Yano et al.
patent: 6060775 (2000-05-01), Ano
patent: 6-291153 (1994-10-01), None
patent: 7-63818 (1995-03-01), None
Hsu Kao-Yu
Lee Shih-Chang
Advanced Semiconductor Engineering Inc.
Chambliss Alonzo
Chaudhuri Olik
Stevens Davis Miller & Mosher LLP
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