Interconnect for packaging semiconductor dice and...

Details Interconnect for packaging semiconductor dice and... Interconnect for packaging semiconductor dice and...

1999-12-20

2001-12-11

Picardat, Kevin M. (Department: 2823)

Semiconductor device manufacturing: process

Packaging or treatment of packaged semiconductor

Including adhesive bonding step

C438S125000, C438S127000, C438S458000, C438S460000

Reexamination Certificate

active

06329222

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to semiconductor packaging and specifically to an interconnect for packaging semiconductor dice, and to an improved BGA package fabricated using the interconnect.
BACKGROUND OF THE INVENTION
One type of semiconductor package is referred to as a BGA package. BGA packages were developed to provide a higher lead count, and a smaller foot print, than conventional plastic or ceramic semiconductor packages. A BGA package includes an array of external ball contacts, such as solder balls, that permit the package to be surface mounted to a printed circuit board (PCB) or other electronic component. Some BGA packages have a foot print that is about the size of the die contained in the package. These BGA packages are also known as chip scale packages.
As BGA packages are made smaller, and with higher lead counts, the electrical connections between the die and the ball contacts for the package become more difficult to make. The component of the package that makes the electrical connections between the die and package is sometimes referred to as an interconnect.
One type of prior art BGA package uses an interconnect in the form of a multi layered polymer tape, such as TAB tape. The polymer tape can be provided as a “strip” or “coupon” of material for packaging several dice at a time. Typically, the polymer tape comprises a polyimide substrate having patterns of metal conductors formed thereon. In addition, portions of the conductors can comprise beam leads, formed in a configuration which allows the beam leads to be bonded to the bond pads on the die.
FIG. 1
illustrates a prior art BGA package
10
. The BGA package
10
includes: a semiconductor die
12
; a polymer tape
14
bonded to a face of the die
12
; and an encapsulant
16
bonded to the face and sides of the die
12
. The BGA package
10
also includes an adhesive layer
18
for bonding the polymer tape
14
to the die
12
. In addition, the BGA package
10
includes a dense array of ball contacts
20
formed on the polymer tape
14
. A solder mask
15
locates and electrically insulates the ball contacts
20
from one another.
The polymer tape
14
includes a pattern of metal conductors
21
that form separate electrical paths between bond pads
24
on the die
12
and the ball contacts
20
. The conductors
36
include ball bonding pads
23
that are bonded to the ball contacts
20
, and beam leads
22
that are bonded to the bond pads
24
on the die
12
. The beam leads
22
are also encapsulated in the encapsulant
16
.
A representative process for forming the BGA package
10
includes the initial step of bonding one or more dice
12
to a strip of the polymer tape
14
. The beam leads
22
can then be bonded to the device bond pads
24
. Next, the encapsulant
16
can be formed, and the ball contacts
20
bonded to the ball bonding pads
23
. The individual BGA packages
10
can then be singulated from the strip of polymer tape
14
and tested.
Typically, a thermosonic bonding process, using gold, or gold plated materials, is employed to bond the beam leads
22
to the bond pads
24
. Specialized bonding tools are required to make the bonds between the beam leads
22
and the bond pads
24
. In addition, the beam leads
22
are subjected to stresses from the bonding and encapsulation processes, and during subsequent use of the BGA package
10
. These stresses can cause the bonds to weaken and the beam leads to separate from the bond pads
24
.
Because of these and other deficiencies in conventional BGA packages, improvements in BGA packages, and in methods for fabricating BGA packages, would be welcomed in the art. The present invention is directed to an improved interconnect for constructing BGA packages. The interconnect is constructed to facilitate formation of bonded connections with the die, and to provide improved bonded connections with the die.
SUMMARY OF THE INVENTION
In accordance with the present invention, an improved interconnect for semiconductor dice, an improved BGA package, and an improved method for fabricating BGA packages, are provided.
The interconnect comprises a polymer substrate, and a pattern of conductors formed on the substrate. In the illustrative embodiment the interconnect contains multiple polymer substrates that are subsequently singulated into individual BGA packages. The conductors include end portions having bonding vias for making bonded electrical connections with bond pads on a semiconductor die. A location of the end portions and bonding vias exactly matches a location of the bond pads on the die, permitting alignment for the bonding process. In addition, the end portions and bonding vias overhang corresponding openings in the polymer substrate, permitting access for a bonding tool for performing the bonding process. The conductors also include ball bonding pads, which allow ball contacts to be bonded to the conductors, and attached to the polymer substrate.
For fabricating a BGA package, the polymer substrate can be adhesively bonded to the die with the bonding vias on the conductors, and the openings in the polymer substrate, aligned with the bond pads on the die. Metal bumps can then be formed in the bonding vias to physically and electrically attach the end portions of the conductors to the bond pads on the die. The metal bumps can be formed using a bonding tool of a wire bonding apparatus, or using a solder ball bumper apparatus. Alternately, the metal bumps can comprise solder bumps of a bumped semiconductor die that are reflowed into the bonding vias. Following forming of the metal bumps, ball contacts, such as solder balls, can be bonded to the ball bonding pads on the conductors.
The completed BGA package includes the semiconductor die, the polymer substrate adhesively bonded to the face of the die, and the metal bumps in the bonding vias bonding the conductors on the polymer substrate to the bond pads on the die. The BGA package also includes an array of ball contacts bonded to the ball bonding pads on the conductors. With this construction, the conductors establish electrical communication between the bond pads on the die, and the ball contacts on the polymer substrate. Further, the metal bumps in the bonding vias physically and electrically bond the conductors to the bond pads on the die.
The method for fabricating the BGA package includes the steps of: providing a polymer substrate comprising a pattern of conductors and a pattern of openings to the conductors; providing the conductors with bonding vias on first end portions thereof aligned with the openings in the polymer substrate; providing the conductors with ball bonding pads on second end portions thereof; adhesively bonding the polymer substrate to a semiconductor die with the bonding vias on the conductors aligned with bond pads on the die; forming metal bumps through the openings in the polymer substrate onto the bonding vias on the conductors to physically and electrically attach the conductors to the bond pads; and then bonding ball contacts to the ball bonding pads on the conductors.


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patent: 5420460 (1995-05-01), Massingill
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DiStefano, T. H., “Chip Scale Review”, May 1997, vol. 1., No. 1, pp. 20-27.

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