Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With provision for cooling the housing or its contents
Reexamination Certificate
1999-03-17
2001-04-10
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With provision for cooling the housing or its contents
C257S675000, C438S122000
Reexamination Certificate
active
06215180
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a dual-sided heat dissipating structure and its fabrication method for integrated circuit package and particularly to Ball Grid Array package (BGA package) that has two lateral sides engageable respectively with a heat dissipating member for enhancing heat dissipating effect.
2. Description of the Prior Art
In semiconductor integrated circuit (IC) industry nowadays, how to make IC packages small size with good heat dissipating property at low cost is a goal almost universally pursued. Heat dissipating property of IC package directly affects IC performance and reliability. It is a subject attracted heavy research and development.
One of the techniques being used to address this issue is generally called “Enhanced BGA” (EBGA).
FIG. 1
illustrates an example using EBGA. The EBGA package
10
includes an IC chip
11
, a Tape Automated Bond Tape (TAB Tape)
12
which has a metallic circuitry
121
formed thereon, a plurality of solder balls
13
and a metallic heat dissipating member
16
. The solder balls
13
are attached to a bottom side of the TAB Tape
12
and are nested in a layer of non-conductive solder ball mask
14
for preventing short circuit of the circuitry
121
resulting from oversize solder balls
13
. The TAB Tape
12
has a center opening to accommodate the IC chip
11
. The IC chip
11
couples with the circuitry
121
by means of gold wires
17
. As the TAB Tape
12
is thinner than conventional wiring frame and is more desirable for multilayer circuit design, high performance and complex and multilayer metallic circuitry
121
may be produced. The whole EBGA package
10
may be made thin and small size. Furthermore the IC chip
11
and the TAB Tape
12
are adhered to the heat dissipating member
16
by means of EPOXY
18
which has good heat dissipating property. The heat dissipating member
16
also provides support for the IC chip
11
and the generally soft TAB Tape
12
.
However the structure set forth above has a non-active side of the IC chip
11
adhering to the heat dissipating member
16
. The active side i.e., the side where semiconductor circuitry located of the IC chip
11
is covered by a layer of underfilling
15
through molding process. The under filling
15
is usually a poor heat conducting resin. Most heat generated in the IC chip is taking place on the active side. The heat dissipating member
16
attached to the non-active side of the IC chip
11
thus has only limited effect on heat dissipation of the IC chip.
FIG. 2
illustrates another conventional Tape BGA package structure. The TBGA package
20
, like the EBGA package shown in
FIG. 1
, also has an IC chip
21
, a TAB Tape
22
, a plurality of solder balls
23
, a heat dissipating member
26
and a bottom underfilling
25
. However in the TBGA package
20
the metallic circuitry forms a plurality of inner leads
222
extending to a center opening of the TAB Tape
22
. The inner leads
222
are taping to bonding pads
211
located on the IC chip
21
by means of Tape Automated Bonding (TAB) process. Wire bonding process used in the EBGA package is thus omitted. Production time and cost are lower. But there is no much improvement in heat dissipating effect since the heat dissipating member
26
is still attached on the non-active side of the chip
21
.
FIG. 3
illustrates yet another example of EBGA package
30
which uses a printer-circuit-board-like substrate
32
to support an IC chip
31
. There are inner solder balls
37
to couple the active side of IC chip
31
with the metallic circuitry
321
laid on the substrate
32
. An underfilling
35
is poured between the IC chip and the substrate and surrounds the inner solder balls
37
to protect the circuitry for enhancing the package reliability. A dish-shaped heat dissipating member
36
adheres to a non-active side of the IC chip
31
and the substrate
32
by means of EPOXY adhesive
38
(or a heat conductive resin) which has relative good heat conductivity. Like the previous examples, this structure also is not able to improve heat dissipating function very much. Moreover there is a closed void space
39
formed between the heat dissipating member
36
and the IC chip
31
and the substrate
32
. The close void space
39
tends to trap moisture either from atmosphere or EPOXY adhesive
38
. In the manufacturing process, when the EBGA package
30
is soldered to a printed circuit board or under IR Reflow test, it will be heated to 230° C. in a short time. The moisture trapped in the void space
39
will be vaporized and expanded and results in the heat dissipating member
36
breaking away from the substrate
32
(commonly called “Pop Corn Effect”). In order to prevent the Pop Corn Effect from happening, an additional procedure of vacuuming or filling nitrogen gas in the void space
39
is necessary. This additional procedure will increase production complexity and cost and still cannot totally eliminate the Pop Corn Effect.
Then there is a further EBGA package scheme being introduced as shown in FIG.
4
. The EBGA package
40
has a heat dissipating member
46
adhering to an active side (i.e., where gold lines
47
are bonded) of the IC chip
41
. While the IC chip
41
generating heat may be dissipated quickly through the heat dissipating member
46
, the non-active side of the chip
41
adheres to the substrate
42
has relatively poor heat dissipating effect. Moreover to protect the gold wire
47
from unduly contact with the surroundings, the heat dissipating member
46
should be made in a T-shape and should have a greater thickness. This will make the whole package bulky.
All of this shows that there is still a lot of room for improvement regard producing low cost IC package at small size with high heat dissipating efficiency.
SUMMARY OF THE INVENTION
In view of aforesaid disadvantages, it is therefore an object of this invention to provide a dual-sided heat dissipating IC package which has two heat dissipating members adhering respectively to the active and non-active sides of the IC chip for enhancing heat dissipating effect such that the IC package may be made at a thin thickness.
It is another object of this invention to provide a dual-sided heat dissipating IC package that includes a step-surfaced heat dissipating member which may serve as a press mold for bonding the IC chip to the substrate. Hence adhering the heat dissipating member to the IC chip and the substrate may be done along with the bonding of IC chip to the substrate at the same process without additional equipment or procedure.
It is a further object of this invention to provide a dual-sided heat dissipating IC package that has a perforated dish-shaped heat dissipating member adhering to a non-active side of the IC chip so that moisture trapped in the void space formed between the heat dissipating member and the IC chip may escape without producing Pop Corn Effect.
The dual-sided heat dissipating IC package according to this invention includes a semiconductor chip which has at least one active side laid with semiconductor circuits, a substrate which has a center opening for holding the chip and a metallic circuitry that forms a plurality of inner leads extending to the center opening and coupling with the semiconductor circuits, a plurality of metallic solder balls mounted on the substrate and coupled with the metallic circuitry, a first heat dissipating member adhering to the active side of the chip and the substrate by means of a non-conductive adhesive, and a second heat dissipating member adhering to a side of the chip remote from the substrate by means of a non-conductive adhesive so that two sides of the chip may dissipate heat.
The first heat dissipating member further has a step surface which includes a thickest center portion adhering to the chip, an intermediate portion adhering to the inner leads and a thin outskirt portion adhering to the substrate. The step-surfaced first heat dissipating member may also serve as a press mold for bonding the inner leads to bo
Chen Tsung-Chieh
Hsu Cheng-Chieh
Hsu Ken-Hsiung
Peng Yi-Liang
Chaudhuri Olik
Dougherty & Troxell
First International Computer Inc.
Pizarro-Crespo Marcos D.
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