Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2001-03-07
2003-02-11
Potter, Roy (Department: 2822)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S613000, C438S617000, C438S666000
Reexamination Certificate
active
06518161
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to semiconductor packaging. More specifically, the invention relates to the design and manufacturing process of a semiconductor package that allows the incorporation of more than one chip device into a single package.
2. Description of the Related Art
For a variety of reasons well known in the art, semiconductor packages that have more than one chip, otherwise known as multi-chip modules (“MCM's”), are becoming increasingly popular. One type of possible MCM is shown in
FIG. 1
, which is disclosed in U.S. patent application Ser. No. 09/461,704, entitled “Multi-Chip Package Including Memory and Logic,” filed Dec. 14, 1999, and is owned by the assignee of the present invention. The MCM shown in
FIG. 1
comprises a top die
10
stacked on top of a bottom die
12
, which is in turn mounted on a substrate
18
. The top die
10
is mounted on the bottom die
12
in flip chip fashion such that the top die
10
communicates with the bottom die
12
through a plurality of (collapsed) solder balls
20
. The bottom die
12
, in turn, communicates with the substrate
18
through a plurality of wires
14
. Thus, the bottom die
12
has two types of bond pads: flip-chip bond pads that are coupled to a plurality of solder balls
20
and wire bond pads that are coupled to the plurality of wires
14
.
Both types of bond pads are aluminum. Aluminum bond pads form effective bonds with the plurality of wires
14
. However, the aluminum bond pads may not effectively bond to the plurality of solder balls
20
, which often comprise eutectic solder (e.g., 63% Sn/37% Pb). The mismatch between the different types of bonding, solder ball and wire bond, makes it somewhat difficult to manufacture the package shown in FIG.
1
. It would be desirable to improve the efficiency of the manufacturing process for a package such as that shown in FIG.
1
.
SUMMARY OF THE INVENTION
To achieve the foregoing, the present invention provides a method for manufacturing a die comprising two different types of bond pads, one type that is compatible with wire bonding and another type that is compatible with solder bonding. In one embodiment, the bond pads that are compatible with wire bonding have a top layer of aluminum while the bond pads that are compatible with solder bonding have a top layer of copper.
All of the bond pads can initially consist of aluminum. To selectively form copper over the solder compatible bond pads, a layer of copper is disposed over all the bond pads and selectively etched away from over the wire bonding compatible bond pads. The copper can be selectively etched by disposing a layer of photoresist over the copper, removing the photoresist from over the wire bonding compatible bond pads, and then dissolving the copper in a suitable solution. The solution, dissolved copper and remaining photoresist are then removed, thereby leaving copper over the solder compatible bond pads while returning the wire bonding compatible bond pads to aluminum without an overlay of copper.
REFERENCES:
patent: 5445311 (1995-08-01), Trask et al.
Desai Kishor
Rajagopalan Sarathy
LSI Logic Corporation
Potter Roy
Westman Champlin & Kelly
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