Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Die bond
Reexamination Certificate
2000-11-21
2003-01-07
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Die bond
C257S786000, C257S666000
Reexamination Certificate
active
06504257
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an apparatus and method for providing mechanically pre-formed conductive leads for use with, for example, micro-ball grid array packages.
BACKGROUND OF THE INVENTION
As the trend toward decreasing the size of microelectronic packages continues, manufacturing challenges are continuously encountered. One manufacturing challenge is the need for reliable lead bonding.
FIG. 1
is a partial cross-sectional elevational view of a typical micro-ball grid array (micro-BGA) package
10
. The micro-BGA package
10
includes a die
12
having a plurality of bond pads
14
formed thereon. A spacing layer
16
(typically composed of an elastomer material) is formed on the die
12
, and an interposer
18
(typically composed of a dielectric material, such as a polyimide tape) is formed on the spacing layer
16
. An adhesive layer
20
is formed on the interposer
18
.
The micro-BGA package
10
also includes a plurality of conductive leads
22
. One end of each lead
22
is coupled to one of the bond pads
14
, and the opposite end of the lead
22
terminates in a ball pad
24
that is coupled to the interposer
18
by the adhesive layer
20
. An encapsulating material
26
is disposed over the conductive leads
22
and the exposed areas of the die
12
to seal and protect the leads
22
and die
12
from environmental elements. A conductive bump
28
(typically composed of solder) is formed on each ball pad
24
. Finally, a coverlay
30
is formed at least partially over the micro-BGA package
10
.
The micro-BGA package
10
may be coupled to an electrical circuit (not shown), such as a printed circuit board, by engaging the bumps
26
with corresponding contact pads on the circuit. Micro-BGA packages of the type shown in
FIG. 1
are shown and described, for example, in U.S. Pat. Nos. 5,663,106 and 5,777,379 to Karavakis et al, and in U.S. Pat. No. 5,821,608 to DiStefano et al, which patents are incorporated herein by reference.
FIG. 2
is an isometric view of a partially-constructed micro-BGA package
10
A of
FIG. 1
prior to the addition of the encapsulating material
26
, the coverlay
30
, or the conductive bumps
28
. Typically, the leads
22
are formed from a sheet of conductive material using standard cutting and etching processes to form a lead array
40
. The lead array
40
includes a base
42
, the plurality of conductive leads
22
, which project from the base
42
, and the ball pads
24
, which are formed at the ends of the leads
22
. Each lead
22
may include a frangible section
44
. Processes for forming the lead array
40
are shown and described, for example, in International Pat. Publication WO94/03036 published Feb. 3, 1994, or U.S. Pat. No. 5,629,239 to DiStefano et al, both of which are incorporated herein by reference.
The ball pads
24
and leads
22
are engaged with the adhesive layer
20
to couple the ball pads
24
and leads
22
to the interposer
18
. Then the leads
22
are bonded to the bond pads
14
of the die
12
. A bonding tool
50
is typically used to bond the leads
22
to the bond pads
14
. As described in U.S. Pat. No. 5,629,239, the bonding tool
50
moves downwardly toward the die
12
until it engages the lead
22
. The bonding tool
50
continues moving downwardly, snapping or breaking the frangible section
44
of the lead
22
, and downwardly bending the lead
22
until the lead
22
engages the bond pad
14
. The bonding tool
50
then bonds the leads
22
to the bond pads
14
in the conventional manner (e.g. thermally, ultrasonically, etc.).
Alternately, one or more of the leads
22
may be broken by depressing a cutting blade (not shown) against the leads
22
, bending the leads
22
downwardly until the frangible sections
44
are snapped or broken, as described in U.S. Pat. No. 5,629,239. The bonding tool
50
is then applied to the lead
22
to continue bending the lead
22
downwardly until the lead
22
engages the bond pad
14
and is bonded into position.
One significant problem attributable to these manufacturing methods, however, is that the downward bending and snapping of the leads
22
during the bonding process can adversely effect the physical and electrical connections throughout the micro-BGA package
10
. For example, the physical attachment of the ball pads
24
and the leads
22
with the adhesive layer
20
and the interposer
18
may be weakened or detached during the bending of the leads
22
, and during the snapping of the frangible sections
44
. Also, after one of the leads
22
is bent and bonded to the corresponding bond pad
14
, the physical and electrical connection between the lead
22
and the bond pad
14
may be weakened or detached due to flexure of the micro-BGA package
10
(especially the elastomer spacing layer
16
) as one or more adjacent leads
22
are being bent, snapped, and bonded to the associated bond pads
14
.
Thus, the bending moments exerted on the leads
22
, and the compressive forces of the bonding tool
50
on the leads
22
, may be communicated throughout the micro-BGA package
10
as the leads
22
are snapped and bent into engagement with the bond pads
14
. These forces and moments may adversely impact the physical and electrical connections between the components of the micro-BGA package
10
, resulting in a significant rate of failure.
SUMMARY OF THE INVENTION
The present invention relates to an apparatus and method for providing mechanically pre-formed conductive leads for use with, for example, micro-ball grid array (micro-BGA) packages. In one aspect of the invention, an apparatus includes a forming chuck engageable with a first surface of a conductive sheet, and a receiving chuck engageable with a second surface of the conductive sheet opposite from the forming chuck. The forming chuck has a raised forming portion alignable with one or more lead members formed in the conductive sheet, and the receiving chuck has a receiving portion alignable with the forming portion and shaped to closely conform to at least part of the forming portion.
In operation, the conductive sheet may be compressed between the forming chuck and the receiving chuck to mechanically pre-form the one or more lead members into one or more pre-formed conductive leads. Alternately, the operation may further include forming the lead members in the conductive sheet. Because the conductive leads are mechanically preformed prior to attachment to the micro-BGA package, the bending moments and compression forces associated with forming and bending the conductive leads are not transmitted to the components of the micro-BGA package.
In one aspect of the invention, the raised forming portion includes a ridge having a polygonal cross-sectional shape and the receiving portion comprises a channel. Alternately, the raised forming portion includes a partially-pyramidal block and the receiving portion comprises a pocket. In yet another aspect, the raised forming portion includes a plurality of blocks and the receiving portion comprises a plurality of pockets.
In still another aspect of the invention, an apparatus includes a press coupled to the forming chuck that controllably engages the forming chuck against the conductive sheet. Alternately, the press may be coupled to the receiving chuck. In yet another aspect, an apparatus includes a handler for controllably positioning the conductive sheet before and after engagement with the forming and receiving chucks.
REFERENCES:
patent: 3347442 (1967-10-01), Reber
patent: 3597839 (1971-08-01), Jaccodine
patent: 3689991 (1972-09-01), Aird
patent: 3934783 (1976-01-01), Larrison
patent: 5024367 (1991-06-01), Terakado et al.
patent: 5153981 (1992-10-01), Soto
patent: 5184068 (1993-02-01), Twigg et al.
patent: 5233221 (1993-08-01), Bregman et al.
patent: 5277356 (1994-01-01), Kawauchi
patent: 5322207 (1994-06-01), Fogal et al.
patent: 5536909 (1996-07-01), DiStefano et al.
patent: 5586389 (1996-12-01), Hirao et al.
patent: 5629239 (1997-05-01), DiStefano et al.
patent: 5663106 (1997-09-01), Karavakis et al.
patent: 5674785 (1997-
Bettinger Michael
Ellis Ronald W.
Reynolds Tracy
Dorsey & Whitney LLP
Micro)n Technology, Inc.
Potter Roy
LandOfFree
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