Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-04-05
2002-11-05
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C257S706000, C257S712000, C257S713000
Reexamination Certificate
active
06475327
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to fabrication of the electronic packages, including single-chip packages and multichip packages, and in particular, to fabrication of a plurality of cavity down chip packages having heat spreaders which also function as stiffeners attached thereto.
2. Description of the Prior Art
With continuing advances in the semiconductor industry, electronic circuitry and electronic packaging are often designed to utilize as little space as is practicable. Circuit space often is a valuable asset, which needs to be conversed, and a miniaturization of electronic circuits often improves speed, reduces noise and leads to other performance advantages. Such a miniaturization is desirable in electronics employed in various applications, such as aircraft, automobiles, cellular phones, hand carry computers, hand carry camcorders, etc. However, heat density problems often arise with increased miniaturization, since the amount of heat generated by the device increases as the number of transistors fabricated onto a single semiconductor device increases.
One type of semiconductor chip package includes one or more semiconductor chips attached to a substrate, e.g. a ceramic substrate or a plastic substrate, wherein a ceramic substrate uses ceramic material as the insulating layers while a plastic substrate uses a plastics-based material as the insulating layers. Such a semiconductor chip package, conventionally termed a chip carrier, is generally interconnected on a printed circuit card or printed circuit board. Chips can be attached to the substrate in several ways. Currently, the most popular way is wire bonding, in which electrical connections are made by attaching very small wires from the device side of the chip to the appropriate points on the substrate. Another way of attachment uses small solder balls to both physically attach the chip and make required electrical connections, which is so called flip chip bonding.
Assorted methods have been employed to mount integrated circuit chips in plastic packages for a lower cost packaging means as compared with ceramic packages. While the plastic packages are further recognized to provide several important advantages for the chip operation as compared with ceramic packages, including higher current carrying capacity, lower dielectric constant for short operational delay times, along with reduced inductance and capacitance. However, low temperature stability experienced with plastic packages still remains as a problem. This issue has gained much attention in the development of modem plastic packages. One solution to this issue is to adopt a cavity down chip package structure, in which a heat slug or a heat spreader is attached to the bottom of the package and the chip is mounted in a recess cavity!with its open side facing toward the printed circuit card or printed circuit board.
FIG. 1
illustrates a typical cavity down chip carrier
100
. It includes a plastic wiring substrate
101
with a recess cavity
102
and a heat slug or heat spreader
103
bonded to said substrate
101
with assistance of a bonding layer
104
. A side-wall electrically and/or thermally conductive layer
105
may be made to connect the heat spreader with the wiring layer in said substrate
101
for further enhanced thermal or electrical performance. A chip
106
is mounted on the heat spreader
103
inside the recess cavity
102
. The conductive wires
107
are used to interconnect the chip
106
to the substrate
101
. After the wire bonding process, the cavity
102
is filled up with an encapsulant
108
to cover and protect the bonding wires
107
and chip
106
against environmental degradation. The external connection means
109
, by which the substrate
101
is electrically connected to a printed circuit board
110
, are attached to appropriate areas on the top surface of the substrate
101
. The external connection means
108
may be conductive pins or solder balls or columns as utilized in plastic pin grid array (PPGA) or plastic ball grid array (PBGA) or plastic column grid array (PCGA). As an alternative structure, an additional heat sink may be attached to the backside of the heat spreader
103
if necessary for further enhancing heat dissipation.
In order to overcome warparge or twist in making a cavity down plastic chip carrier, a stiffener or more copper layers may sometimes be embedded. A typical example is shown in
FIG. 2. A
prior art cavity down plastic chip carrier, so called super ball grid array package, includes a circuit substrate
201
having a first surface
201
a
and a second surface
201
b
opposite the first surface and an internal copper layer
202
on the first surface
202
a
of which is attached to the second surface
201
b
of the circuit substrate
201
by means of an adhesive
203
. On the respective central portions of the circuit substrate
201
and the copper layer
202
are formed an opening so that the opening forms a recess cavity
204
through the circuit substrate
201
and the copper layer
202
. A heat spreader
205
is attached to the other surface
202
b
of the copper layer
202
with using an adhesive
206
for improving the heat dissipation characteristics. A chip
207
is mounted on the heat spreader
205
inside the recess cavity
204
with assistance of an adhesive
208
. The conductive wires
209
are used to interconnect the chip
207
to the substrate
201
. After the wire bonding process, the cavity
204
is filled up with an encapsulant
210
to cover and protect the bonding wires
209
and chip
207
against environmental degradation. The solder balls
211
, by which the substrate
201
is electrically connected to :a printed circuit board
212
, are attached to appropriate areas on the first surface
201
a
of the substrate
201
. As an alternative structure, an additional heat sink may be attached to the second surface
205
b
of the heat spreader
205
if necessary for further enhancing heat dissipation.
U.S. Pat. No. 6,034,427 (J. J. D Lan et al.) teaches the use of a stiffener for a plastic cavity down BGA, in which the stiffener is first attached to a circuit board with assistance of a prepreg and then a heat spreader is attached to the stiffener by using an adhesive film. In this method, when the heat spreader is made of copper base material, e.g. copper or copper base alloy, which is well known a relatively soft material, the cure shrinkage of the adhesive film may cause warpage during heat pressing the heat spreader together with the circuit board containing the stiffener.
U.S. Pat. No. 6,060,778 (T. S. Jeong et al.) also teaches a similar method for making a plastic cavity down BGA, which states that the BGA package has excellent heat dissipation capability, a low weight, a thinner thickness and a low manufacturing cost. The method involves the use of a first thermally conductive layer, which is attached to a circuit substrate. A second thermally conductive layer (i.e. a heat spreader) is attached to the circuit substrate containing the first thermally conductive layer. However, the method is depicted in the
FIG. 7
of the said patent but not included in the claims of the said patent. This method would encounter the same problem as described above for U.S. Pat. No. 6,034,427, i.e. warpage of the fabricated BGA is difficult to be eliminated.
It is therefore an object of the present invention to provide a method to make a plastic cavity down chip carrier having excellent heat dissipation capability, a low weight, absence of warpage and twist, and low manufacturing cost. Briefly, the present invention provides a method for first bonding two or more thermally conductive sheets to form a stiff heat spreader element and second bonding the stiff heat spreader element with a circuit board (or say integrated circuit substrate). This method is clearly different from the methods proposed by the U.S. Pat. Nos. 6,034,427 and 6,060,778, since both prior methods bond a first thermally conductive sheet with a circuit board and then bo
Chen Kuo-Bin
Hsu Shih-Ping
Tung I-Chung
Yu Jiun-Shian
Ball Michael W.
Koppikar Vivek
Phoenix Precision Technology Corporation
LandOfFree
Attachment of a stiff heat spreader for fabricating a cavity... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Attachment of a stiff heat spreader for fabricating a cavity..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Attachment of a stiff heat spreader for fabricating a cavity... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2931139