Heat-dissipating structure for integrated circuit package

Details Heat-dissipating structure for integrated circuit package Heat-dissipating structure for integrated circuit package

2001-03-02

2001-11-27

Picardat, Kevin M. (Department: 2822)

Semiconductor device manufacturing: process

Packaging or treatment of packaged semiconductor

Metallic housing or support

C438S124000, C438S127000

Reexamination Certificate

active

06323066

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to integrated circuit (IC) packages, and more particularly, to a heat-dissipating structure for use in an integrated circuit package, such as a BGA (Ball Grid Array) integrated circuit package, for heat dissipation from the integrated circuit package during operation.
2. Description of Related Art
BGA integrated circuit packages allow the integrated circuit package to have a low profile while nevertheless incorporating a large packing density of electronic components with a high package pin count. During the operation of the integrated circuit chip, a large amount of heat can be generated due to the flowing of electricity through the electronic components on the integrated circuit chip. If this heat is not dissipated, it can cause damage to the internal circuitry of the integrated circuit chip. Therefore, it is required to provide heat-dissipating means on the integrated circuit package for heat dissipation during operation.
Types of BGA integrated circuit packages include PBGA (Plastic BGA), CBGA (Ceramic BGA), and TBGA (Tape BGA), which are so named in terms of the material being used to form the substrate. Among them PBGA integrated circuit packages, however, are poor in heat-dissipating efficiency since plastics are poor in heat conductivity. To allow PBGA integrated circuit packages to have a high heat-dissipating efficiency, a conventional solution is to provide a heat sink or a heat slug.
The U.S. Pat. No. 5,736,785 to Chiang et al. discloses a BGA integrated circuit package that is provided with a heat sink.
FIG. 5
shows the structure of this BGA integrated circuit package. As shown, the patent utilizes a heat sink
116
which is mounted on a substrate
104
on which an integrated circuit chip
102
is mounted. The heat sink
116
is formed with a circular downwardly-protruded portion
116
a
in the center thereof, which is abutted on the top side of the integrated circuit chip
102
, allowing the heat produced from the integrated circuit chip
102
to be dissipated by the heat sink
116
to the atmosphere. Further, the heat sink
116
is formed with another four downwardly-protruded portions
116
c
which are dimensioned with a larger depth than the protruded portion
116
a
so that the entire body of the heat sink
116
can be supported on the substrate
104
. The heat sink
116
is further formed with an upwardly-protruded portion
116
d
which is exposed to the outside of the integrated circuit package so that the heat can be dissipated to the atmosphere.
The use of the foregoing heat sink
116
for heat dissipation, however, has the following drawbacks. First, since the integrated circuit chip
102
is very fragile and small in size, the abutting of the heat sink
116
on the integrated circuit chip
102
would easily cause the integrated circuit chip
102
to crack during the cooling process of the encapsulate
112
, or during the cooling process of the integrated circuit package after solder reflow, or during the temperature-cycle reliability test. This is because that the copper-made heat sink
116
has a significantly greater coefficient of thermal expansion (CTE) than the integrated circuit chip
102
(copper has a CTE of 18 ppm/°C., while integrated circuit chip has a CTE of 3 ppm/°C.); and therefore, during a cooling process, the heat sink
116
would cause a thermal compressive stress to the integrated circuit chip
102
, thus causing the integrated circuit chip
102
to be cracked.
Second, since the resin-made encapsulant
112
has a large CTE of about 20 ppm/°C. and encloses a large part of the active surface of the integrated circuit package (the term “active surface” refers to the surface part of the integrated circuit chip where electronic components are formed), it would also easily cause the integrated circuit chip
102
to be cracked or delaminated from the encapsulant
112
during the cooling process of the integrated circuit package.
Third, during molding process, the existence of the downwardly-protruded portion
116
a,
116
c
would cause disturbance to the resin flow, thus causing undesired forming of voids in the resulted encapsulant
112
. The forming of these voids would easily cause a popcorn effect during the solder-reflow process, which might result in damage to the integrated circuit package.
Fourth, the heat sink
116
is still considered unsatisfactorily low in heat-dissipating efficiency due to the fact that the upwardly-protruded portion
116
d
is relatively small in extent compared to the overall size of the heat sink
116
; and therefore, the majority of the heat would dissipate through the following path: chip→encapsulant→heat sink→encapsulant→atmosphere. Since the resin-made encapsulant
112
has a heat conductivity of just 0.8 w/m° K., the heat dissipation through this path would be undoubtedly low in efficiency.
One solution to the foregoing problems is shown in FIG.
6
. This solution is characterized in the provision of an improved heat sink
116
′ which is unabutted on the integrated circuit chip
102
′. This feature can prevent the resin flow during the molding process to be subjected to disturbance as well as prevent the heat sink
116
′ from causing a thermal compressive stress on the integrated circuit chip
102
′ during the cooling process. In addition, the heat sink
116
′ is formed with a large exposed area to the atmosphere, which can help increase the heat-dissipating efficiency.
One drawback to the forgoing solution, however, is that, since the integrated circuit chip
102
′ is entirely encapsulated in the encapsulant
112
′, the cooling process would nevertheless cause the encapsulant
112
′ to bring a thermal compressive stress to the integrated circuit chip
102
′ during the cooling process. Moreover, the heat sink
116
′ is still considered unsatisfactorily low in heat-dissipating efficiency, since most of the heat from the integrated circuit chip
102
′ is transferred to the heat sink
116
′ via the encapsulant
112
′ and the encapsulant
112
′ is quite low in heat conductivity. Still moreover, the integrated circuit package shown in
FIG. 6
is incapable of providing a strong mechanical strength to the integrated circuit chip
102
′, making the integrated circuit chip
102
′ vulnerable against the thermal compressive stress from the resin-made encapsulant
112
and the tensile stress from the silver-paste layer.
Furthermore, the above-mentioned two BGA integrated circuit packages respectively shown in
FIGS. 5 and 6
would provide a penetrating passage to allow atmospheric moisture to penetrate through the encapsulant to the integrated circuit chips enclosed therein, which may cause the integrated circuit chips to function improperly during operation.
SUMMARY OF THE INVENTION
It is therefore an objective of this invention to provide a heat-dissipating structure for integrated circuit package, which can help prevent the encapsulant to cause a large thermal compressive stress on the integrated circuit chip during the cooling process.
It is another objective of this invention to provide a heat-dissipating structure for integrated circuit package, which can offer a larger heat-dissipating efficiency than the prior art.
It is still another objective of this invention to provide a heat-dissipating structure for integrated circuit package, which can help increase the mechanical strength of the integrated circuit chip, so that the integrated circuit chip can be prevented from being subjected to thermal compressive stress and tensile stress resulted from the encapsulant during packaging process.
It is yet another objective of this invention to provide a heat-dissipating structure for integrated circuit package, which has a larger exposed area to the atmosphere than the prior art so that the heat-dissipating efficiency can be increased as compared to the prior art.
It is still yet another objective of this invention to provi

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