Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2001-01-30
2002-10-22
Thompson, Gregory (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C029S890100, C257S707000, C257S713000, C257S780000, C257S786000, C257S693000, C257S738000, C174S051000, C174S264000, C361S718000, C361S722000, C438S122000
Reexamination Certificate
active
06469897
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to integrated circuit packaging technology, and more particularly, to a TBGA (Tape Ball Grid Array) package assembly with grounded heat sink and method of fabricating the same.
2. Description of Related Art
BGA (Ball Grid Array) is an advanced type of integrated circuit packaging technology which is characterized by the use of a substrate having a front surface for mounting a semiconductor chip and a back surface provided with a ball grid array (i.e., an array of solder balls) to serve as external connecting points for the packaged semiconductor chip to be electrically coupled to external circuitry such as a printed circuit board (PCB).
TBGA (Tape Ball Grid Array) is an improved type of BGA technology which is characterized by the use a of thin tape, typically made of polyimide, as the substrate for mounting the semiconductor chip and the ball grid array. The TBGA technology allows the overall package size to be made very compact in size.
FIG. 1A
is a schematic sectional diagram showing an example of a conventional TBGA package assembly. As shown, this TBGA package assembly includes: (a) a tape
110
; (b) a heat sink
120
having a downward-facing chip-mounting cavity
121
and adhered to the tape
110
by means of an adhesive layer
113
; (c) a semiconductor chip
130
mounted in the chip-mounting cavity
121
of the heat sink
120
; (d) an array of solder-ball pads
140
provided on the back surface of the tape
110
, including a subgroup of grounding solder-ball pads
141
and a subgroup of I/O solder-ball pads
142
; (e) a solder mask
150
formed on the back surface of the tape
110
while exposing the solder-ball pads
140
; (f) a plurality of grounding plugs
160
formed in the tape
110
, which connect the heat sink
120
to the grounding solder-ball pads
141
; (g) a set of bonding wires
170
bonded to the semiconductor chip
130
, including a subset of grounding wires
171
and a subset of I/O wires
172
; (h) a ball grid array
180
(i.e., an array of solder balls) attached to the array of solder-ball pads
140
, including a subgroup of grounding solder balls
181
and a subgroup of I/O solder balls
182
; (i) an encapsulation body
190
for encapsulating the semiconductor chip
130
.
The foregoing package assembly is characterized by that the semiconductor chip
130
can be connected to external grounding points (not shown) via a grounding path composed of the grounding wire
171
, the heat sink
120
, the grounding plugs
160
, the grounding solder-ball pads
141
, and the grounding solder balls
181
, as indicated by the dotted arrows in FIG.
1
A. During SMT (Surface Mount Technology) process for mounting the finished TBGA package on a PCB (not shown), it allows the packaged semiconductor chip
130
to be connected to the PCB's grounding lines (not shown) via the grounding solder balls
181
.
Further, as shown in FIG.
1
B and
FIG. 1C
, by conventional TBGA technology, each grounding plug
160
is formed by first punching a hole
161
through each grounding solder-ball pad
141
into the tape
110
, and then filling each punched hole
161
with an electrically-conductive material, such as solder or silver epoxy.
The forgoing process step for forming the grounding plugs
160
, however, has the following drawbacks.
First, as illustrated in
FIG. 1C
, since the polyimide-made tape
110
is non-wettable to solder, a tiny gap
162
would be undesirably left between each resulted grounding plug
160
and the inner wall of the punched hole
161
, making the grounding plug
160
only bonded to the heat sink
120
but unbonded to the inner wall of the punched hole
161
and thus loosely secured in position. In addition, since the punched hole
161
is formed by punching through each grounding solder-ball pad
141
, it will reduce the effective solder wetting area of the grounding solder-ball pad
141
, making the substantially attached grounding solder ball
181
to be reduced in overall bonding strength, resulting in a weak ball shear strength to the grounding solder ball
181
. This would undesirably cause potential reliability problem to the finished TBGA package.
Second, since the opening of the punched hole
161
for the grounding plug
160
is on the back surface of the tape
110
, it requires the solder used to form the grounding plug
160
to be filled from the bottom side of the package assembly into the punched hole
161
, which is considered a difficult process step.
Third, it would undesirably cause some moisture or air to be trapped in the punched hole
161
, undesirably making the resulted grounding plug
160
to be poorly bonded to the heat sink
120
and bulged out in position that would cause the subsequently attached grounding solder balls
181
to be also bulged out in position with respect to the I/O solder balls
182
, thus making the overall ball grid array
180
uncoplanarized that would degrade the quality of SMT (Surface Mount Technology) process for mounting the finished TBGA package on a printed circuit board (not shown).
Patents related to TBGA fabrication, include, for example, the U.S. Pat. No. 6,020,637 entitled “BALL GRID ARRAY SEMICONDUCTOR PACKAGE”. By this patented technology, however, since it also involves the fabrication of grounding plugs by punching through the grounding solder-ball pad and the tape, the above-mentioned drawbacks still exist.
SUMMARY OF THE INVENTION
It is therefore an objective of this invention to provide a new TBGA technology which can allow grounding solder balls to have greater ball shear strength so as to make them more firmly secured in position.
It is another objective of this invention to provide a new TBGA technology which allows the electrically-conductive material used to form the grounding plug to be filled from the top side of the package assembly instead of from the bottom side, so as to make the filling step easier to carried out.
In accordance with the foregoing and other objectives, the invention proposes a new TBGA package and method of fabricating the same.
The TBGA technology according to the invention is characterized by that the grounding plug is formed by first forming a via hole in the heat sink and a via hole in the tape without penetrating through the grounding solder-ball pad, and then filling an electrically-conductive material, such as solder or silver paste, into the heat-sink via hole from the top of the package assembly until filling up the tape via hole and the heat-sink via hole. As the semiconductor chip is mounted in position, its grounding pads are electrically bonded to the heat sink, thereby allowing the semiconductor chip to be externally grounded through the grounding plug, the grounding solder-ball pad, and the grounding solder ball.
The TBGA technology of the invention allows the resulted grounding plug to be firmly secured in position due to the filled solder being wettable to the heat sink, thereby providing a greater ball shear strength to the grounding solder ball that is subsequently bonded to the grounding plug. The finished TBGA package is therefore more assured in the reliability of its grounding structure.
REFERENCES:
patent: 5409865 (1995-04-01), Karnezos
patent: 5739581 (1998-04-01), Chillara et al.
patent: 5796170 (1998-08-01), Marcantonio
patent: 5844168 (1998-12-01), Schueller et al.
patent: 6020637 (2000-02-01), Karnezos
patent: 6288900 (2001-09-01), Johnson et al.
patent: 6326244 (2001-12-01), Brooks et al.
Ho Tzong-Da
Huang Chien-Ping
Pu Han-Ping
Corless Peter F.
Edwards & Angell LLP
Jensen Steven M.
Siliconware Precision Industries Co. Ltd.
Thompson Gregory
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