Active solid-state devices (e.g. – transistors – solid-state diode – Encapsulated – With heat sink embedded in encapsulant
Reexamination Certificate
2000-04-07
2002-04-09
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Encapsulated
With heat sink embedded in encapsulant
C257S730000
Reexamination Certificate
active
06369455
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to integrated circuit (IC) packaging technology, and more particularly, to an externally-embedded heat-dissipating device which is designed for use with a BGA (Ball Grid Array) IC package for dissipating the IC-produced heat during operation to the atmosphere.
2. Description of Related Art
The BGA IC packaging technology allows the IC package to be made very small in height while nevertheless incorporating a large packing density of transistor elements with a large number of I/O pins. During the operation of the internal circuitry of the IC package, a large amount of heat can be generated due to the flowing of electricity through the transistor elements on the IC chip. If this heat is not dissipated, it can cause damage to the internal circuitry of the IC chip. Therefore, it is required to provide heat-dissipating means on the IC package for heat dissipation during operation.
Types of BGA IC packages include PBGA (Plastic BGA), and TBGA (Tape BGA), which are so named in terms of the material being used to form the substrate. These BGA IC packages, however, are poor in heat-dissipating efficiency since plastics, and tape are poor in heat conductivity. To allow BGA IC packages to have a high heat-dissipating efficiency, a conventional solution is to provide a heat sink or a heat slug.
FIG. 13
is a schematic sectional diagram of a BGA IC package installed with a conventional heat-dissipating device. As shown, the BGA IC package includes an encapsulant
110
, a substrate
120
, and an IC chip
130
which is attached on the substrate
120
by means of silver paste
140
and is electrically connected to the substrate
120
via a plurality of gold wires
150
. In addition, this BGA IC package is embedded with a thermally-conductive piece
100
in the encapsulant
110
. The thermally-conductive piece
100
has a support portion
101
formed in such a manner that it can support the main body of the thermally-conductive piece
100
in an overhead manner above the IC chip
130
. In the manufacture of this BGA IC package, the die-bonding process and the wire-bonding process are performed first; and after the gold wires
150
are readily bonded, the thermally-conductive piece
100
is attached onto the substrate
120
by means of an adhesive
160
. After this, a molding process is performed to form the encapsulant
110
to encapsulate the IC chip
130
, the gold wires
150
, and the thermally-conductive piece
100
, while exposing the top surface
102
of the thermally-conductive piece
100
to the outside of the encapsulant
110
so that the thermally-conductive piece
100
can come into touch with the atmosphere.
Typically, the IC chip
130
has a thickness of a=0.33 mm (millimeter); the thermally-conductive piece
100
has a thickness of c=0.3 mm; and the encapsulant
110
has a thickness of D=1.17 mm. Therefore, the bottom side of the thermally-conductive piece
100
is separated from the top side of the IC chip
130
by a distance of b=D−a−c=1.17−0.3−0.33=0.54 mm. This shows that the heat produced in the IC chip
130
during operation will be conducted through this 0.54 mm part of the encapsulant
110
to the thermally-conductive piece
100
where the heat can be more rapidly dissipated to the atmosphere since the thermally-conductive piece
100
has better thermal conductivity than the encapsulant
110
. Compared to a BGA IC package without such a heat-dissipating device, the top side of the IC chip
130
is separated from the top side of the encapsulant
110
by a distance of b+c=D−a=1.17−0.33=0.84 mm; and therefore, the IC-produced heat will be conducted entirely through a 0.84 mm part of the encapsulant
110
to the atmosphere. From experimentation, it shows that the heat-dissipating device depicted in
FIG. 13
can help increase the heat-dissipation efficiency by a factor of from 10% to 20% as compared to a BGA IC package without the heat-dissipating device.
FIG. 14
is a schematic sectional diagram of a BGA IC package installed with a modified heat-dissipating device that can help further increase heat-dissipation efficiency. As shown, the thermally-conductive piece shown in
FIG. 13
is here modified in such a manner that it is formed with a downward-protruded portion
103
′ so as to further reduce the heat path between the IC chip
130
′ and the thermally-conductive piece
100
′.
The foregoing two kinds of heat-dissipating devices shown in
FIGS. 13 and 14
, however, would cause the following drawbacks.
First, the mounting of these two conventional heat-dissipating devices on the substrate would require precise positioning so as to prevent the IC chip and gold wires from being damaged thereby. Moreover, an additional baking process is required to allow these two kinds thermally-conductive pieces to be securely fixed in position in the encapsulant, thus undesirably increasing the cycle time and complexity of the manufacture process, making the manufacture not very cost-effective.
Second, these two conventional heat-dissipating devices would be easily subjected to delamination off the encapsulant due to the fact that they are made from a thermally-conductive material with a high coefficient of thermal expansion (CTE), typically from 16 ppm/° C. to 17 ppm/° C., while the encapsulant has a CTE of only about 13 ppm/° C. This CTE difference would cause the delamination whenever the package structure undergoes a cooling process subsequent to a high-temperature treatment as solder reflow or reliability test during temperature cycle. When delamination occurs, it would make the finished package poor in quality.
Third, these two conventional heat-dissipating devices would cause undesired popcorn effect during the molding process due to the reason that the support portions thereof would cause disturbance to the flowing resin used in the molding process and thus cause the undesired forming of voids in the resultant encapsulant. During the molding process, the solder reflow would easily cause the air within these voids to explode.
Fourth, these two conventional heat-dissipating devices would take up much layout space over the substrate, making the overall package configuration less compact in size and therefore unsuitable for use with the MCM (Multi-Chip Module) type of BGA IC packages.
Fifth, these two conventional heat-dissipating devices would easily cause the flowing resin used in the molding process to flash. This is because that these two conventional heat-dissipating devices are typically formed through a stamping process, which would easily cause the corners thereof to be rounded, thus allowing the flowing resin to easily pass through the rounded corners to the exposed surface. In addition, the flashed resin would make the exposed surface of the heat-dissipating device to be unplanarized, resulting in a less effective coupling of the heat-dissipating device to external heat-dissipation means. The flashed resin can be removed through sanding or laser, but such post-treatment would degrade the outer appearance of the package configuration and make the overall manufacture process more complex, and is therefore undesired.
SUMMARY OF THE INVENTION
It is therefore an objective of this invention to provide an externally-embedded heat-dissipating device for BGA IC package, which can help reduce manufacture cycle time and cost while nevertheless providing a heat-dissipation efficiency.
It is another objective of this invention to provide an externally-embedded heat-dissipating device for BGA IC package, which can help prevent delamiantion so that the manufactured BOA IC package can be assured in quality.
It is still another objective of this invention to provide an externally-embedded heat-dissipating device for BGA IC package, which can help prevent the forming of voids in the encapsulant and thus prevent the undesired popcorn effect during the molding process.
It is yet another objective of t
Ho Tzong-Da
Huang Chien-Ping
Lai Jeng-Yuan
Corless Peter F.
Edwards & Angell LLP
Jensen Steven M.
Potter Roy
Siliconware Precision Industries Co. Ltd.
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