Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With provision for cooling the housing or its contents
Reexamination Certificate
2000-04-07
2003-01-07
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
C257S706000, C257S707000, C257S719000
Reexamination Certificate
active
06504243
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electronic systems, and more particularly to heat transfer systems and devices used to transfer heat energy produced by a semiconductor device during operation to an ambient.
2. Description of the Related Art
Semiconductor devices (e.g., integrated circuits) dissipate electrical power during operation, transforming electrical energy into heat energy. At the same time, several key operating parameters of a semiconductor device typically vary with temperature, and reliable device operation within specifications occurs only within a defined operating temperature range. For high performance devices, such as microprocessors, specified performance is only achieved when the temperature of the device is below a specified maximum operating temperature. Operation of the device at a temperature above an upper limit of the operating temperature range (i.e., a maximum operating temperature) may result in irreversible damage to the device. In addition, it has been established that the reliability of a semiconductor device decreases with increasing operating temperature. The heat energy produced by a semiconductor device during operation must thus be removed to an ambient environment at a rate which ensures reliable operation.
Several different types of removable heat sinks are available for conveying heat energy generated within an integrated circuit housed within a pin grid array (PGA) package to a surrounding ambient.
FIG. 1
is an exploded view of a known electronic apparatus
10
including a heat transfer apparatus
12
for coupling to a PGA device
14
positioned within a zero insertion force (ZIF) socket
16
. PGA device
14
includes a PGA device package housing an integrated circuit (IC), and includes multiple pin terminals arranged across an underside surface providing input/output capability for the IC. Heat transfer apparatus
12
includes a heat sink
18
and a spring clip
20
. An upper surface of heat sink
18
includes multiple pins projecting upwardly and arranged in rows. ZIF socket
16
includes multiple holes in an upper surface for receiving the pins of PGA device
14
, a handle
22
along one side for operating an internal pin coupling mechanism, and multiple pin terminals arranged across an underside surface for coupling the pin terminals of PGA device
14
to electrically conductive traces of a printed circuit board.
As is common, ZIF socket
16
also includes two latching projections
24
A and
24
B extending outwardly from opposite side surfaces. Spring clip
20
has two apertures
26
A and
26
B dimensioned to allow respective latching projections
24
A and
24
B to pass therethrough. In an assembly operation, PGA device
14
is mounted upon the upper surface of ZIF socket
16
. With handle
22
in a raised position, the pin terminals of PGA device
14
are inserted into corresponding holes in the upper surface of ZIF socket
16
. Handle
22
is then lowered to actuate the internal pin coupling mechanism of ZIF socket
16
.
With PGA device
14
positioned within ZIF socket
16
, the underside surface of heat sink
18
is brought into thermal contact with the upper surface of PGA device
14
. Spring clip
20
is then installed to hold heat sink
18
in place relative to PGA device
14
and to urge the underside surface of heat sink
18
toward the upper surface of PGA device
14
. Spring clip
20
is installed by passing resilient bowed arms
28
of spring clip
20
between adjacent rows of pins on the upper surface of heat sink
18
such that apertures
26
A and
26
B are located directly above respective latching projections
24
A and
24
B. Sufficient downward pressure is then applied to portions of spring clip
20
above apertures
26
A and
26
B such that bowed arms
28
are deformed and latching projections
24
A and
24
B pass through respective apertures
26
A and
26
B. Following installation of spring clip
20
, deformed bowed arms
28
exert a force between heat sink
18
and ZIF socket
16
which urges the underside surface of heat sink
18
toward the upper surface of PGA device
14
.
It is now common to mount integrated circuits to substrates using the well known controlled collapse chip connection (C
4
) or “flip chip” techniques. Device packages including integrated circuits mounted to substrates using the flip chip method are commonly known as flip chip packages.
FIG. 2
will now be used to describe a problem which arises when PGA device
14
of
FIG. 1
is a flip chip PGA device.
FIG. 2
is a cross-sectional view of a known flip chip embodiment of PGA device
14
of FIG.
1
. In the embodiment of
FIG. 2
, PGA device
14
includes an IC
32
mounted upon an upper surface of a substrate
34
using a flip chip technique, and a cover or lid
36
secured over IC
32
. A layer
38
of a thermal interface material thermally couples an upward facing backside surface of IC
32
to an underside surface of lid
36
. Lid
36
is attached (e.g., adhesively) to the upper surface of substrate
34
about outer edges of the upper surface of substrate
34
, and at locations
40
A and
40
B in FIG.
2
. Multiple solder bumps connect a set of I/O pads on a frontside surface of IC
32
to corresponding bonding pads on the upper surface of substrate
34
. Substrate
34
includes multiple electrical conductors connecting pins
42
to bonding pads on the upper surface of substrate
12
.
The area of the upper surface of lid
36
may be, for example, about 4 square inches. In contrast, the area of the backside surface of IC
32
, thermally coupled to lid
36
, may be about 0.3 square inches. Thus when the underside surface of heat sink
18
(
FIG. 1
) is thermally coupled to the upper surface of lid
36
, the effectiveness of the transfer of heat energy from IC
32
to heat sink
18
is heavily dependent upon the thermal resistance, and the heat spreading ability, of lid
36
. Further, a substantial amount of the heat energy generated within IC
32
is conducted into substrate
34
. For heat energy within substrate
34
to reach heat sink
18
(FIG.
1
), the heat energy must travel through the attachment points between substrate
34
and lid
36
about the outer edges of the upper surface of substrate
34
, and at locations
40
A and
40
B in FIG.
2
. Heat transfer paths between a portion of substrate
34
adjacent to IC
32
and the heat sink are thus relatively long, and include substantial distances within substrate
34
. As a result, the effectiveness of the transfer of heat energy from substrate
34
to heat sink
18
is heavily dependent upon the thermal resistance of substrate
34
, as well as the rather uncertain thermal resistances at the attachment points between substrate
34
and lid
36
.
It would thus be desirable to have a heat removal apparatus for a flip chip PGA device including a heat sink in more effective thermal communication with both the IC and the substrate of the flip chip PGA device. The desired heat removal apparatus would more effectively remove heat energy both from the IC and the substrate, thereby increasing the reliability of the PGA device.
SUMMARY OF THE INVENTION
A heat transfer apparatus is described for coupling to a pin grid array (PGA) device including an integrated circuit and mounted within a socket (e.g., a zero insertion force or ZIF socket). The socket is mounted upon a surface of a printed circuit board (PCB) and includes two latching projections extending from opposite side surfaces. The heat transfer apparatus includes a thermally conductive heat sink and a spring clip for holding the heat sink in position relative to the PGA device. The heat sink may be made from a metal (e.g., aluminum), and may have multiple structures (e.g., fins or pins) extending from an upper surface.
The heat sink has an opening in an underside surface for housing the PGA device and the socket. The heat sink also has a lip surrounding the opening for thermally coupling to the PCB about the socket. The heat sink also has a pair of holes extending through the heat sink
Andric Anthony
Eyman Lewis M.
Advanced Micro Devices , Inc.
Chaudhuri Olik
Ha Nathan W.
Kivlin B. Noäl
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