Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package
Reexamination Certificate
2002-02-21
2003-05-20
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
C257S675000, C257S625000, C257S584000, C438S024000
Reexamination Certificate
active
06566743
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for removing heat from electronic equipment, and in particular, a heat pipe system for removing heat from semiconductor chips and packages.
DESCRIPTION OF THE RELATED ART
FIG. 1
shows a cross sectional view of a conventional semiconductor package
10
. The package
10
includes a substrate
15
, a lid
20
, and a semiconductor chip
25
. The semiconductor chip
25
is bonded to the substrate
15
utilizing solder and/or epoxy. Such a package
10
is often referred to as a ‘flip chip’ package, as the package is manufactured by ‘flipping’ the semiconductor chip
25
so that its terminals face terminals formed on a side of the substrate
15
. Typically, ball-shaped solder terminals
30
are formed on either the terminals of the semiconductor chip
25
or the terminals of the substrate
15
, or both. Thus, when the package
10
is heated, the solder balls
30
melt and create a reliable connection between the chip
25
and the substrate
15
. Epoxy
35
may also be used in addition to the solder balls
30
to create a more reliable connection and provide stress relief.
When the package
10
is operated in its usual fashion, heat generated by the junctions of the semiconductor chip
25
is conducted through the chip and the lid
20
, before exiting the package
10
. Typically, heat is generated at the terminals of the semiconductor chip
25
and the terminals of the substrate
15
, and therefore must pass through the solder
30
and epoxy
35
, through the chip
25
body, and through the lid
20
before exiting the package
10
.
In most cases the lid
20
is coupled to a heat sink or similar heat dissipation apparatus (not shown), to assist in moving heat away from the chip
25
. The lid
20
is usually made of a low coefficient of thermal expansion (CTE) material such as Copper Tungsten (CuW) or Aluminum Silicon Carbonate (AlSiC). Such materials minimize the thermal stress caused by the mismatching of the CTE's of the chip and the lid materials.
It has been shown that either AlSiC or CuW has a thermal conductivity large enough to effectively spread local, high heat fluxes. Previous attempts have been made to embed more conductive materials such as chemical vapor deposited (CVD) diamond and thermal pyrolytic graphite materials into AlSiC materials to achieve thermal conductivity values up to 1,000 Watts/m-K (meter-Kelvin). However, these approaches are generally quite expensive and cannot provide sufficient heat spreading performance at some very high heat flux conditions.
Heat pipes, and in particular flat heat pipes, have been shown to be able to spread very high heat fluxes (e.g., above 100 Watts/centimeter
2
(W/cm
2
)) with minimal thermal resistances. In a typical application, a flat heat pipe has an equivalent thermal conductivity of at least 50,000 W/m-K, which is an improvement of approximately 50 times over the AlSiC-CVD diamond material. One example of a flat heat pipe currently being produced and used for this purpose is the Therma-Base™ heat pipe produced by Thermacore, International, Inc. of Lancaster, Pa. (the assignee of the present application).
A basic heat pipe comprises a closed or sealed envelope or a chamber containing an isotropic liquid-transporting wick and a working fluid capable of having both a liquid phase and a vapor phase within a desired range of operating temperatures. When one portion of the chamber is exposed to relatively high temperature it functions as an evaporator section. The working fluid is vaporized in the evaporator section causing a slight pressure increase forcing the vapor to a relatively lower temperature section of the chamber defined as a condenser section. The vapor is condensed in the condenser section and returned through the liquid-transporting wick to the evaporator section by capillary pumping action.
Because it operates on the principle of phase changes rather than on the principles of conduction, a heat pipe is theoretically capable of transferring heat at a much higher rate than conventional heat conduction systems. Consequently, heat pipes have been utilized to cool various types of high heat-producing apparatus, such as electronic equipment (See, e.g., U.S. Pat Nos. 5,884,693, 5,890,371, and 6,076,595).
However, conventional heat pipes cannot be bonded directly to most semiconductor chips due to the mismatching that occurs between the material from which the heat pipe is formed (e.g., Copper (Cu)), and the material from which the semiconductor chip is formed (e.g., Silicon (Si)).
Some have suggested that the solution may lie in conversion of the package lid itself into a heat pipe, thus avoiding the bonding problem. However, there are several shortcomings with this approach. First, AlSiC (i.e., the material from which the lid is formed) is chemically incompatible with water (one of the best working fluids for heat pipe cooling of electronics), and other possible fluids (e.g., refrigerants) cannot provide the necessary thermal performance without advanced and sometimes expensive wick designs. Second, Silicon (Si) and AlSiC are difficult to machine, thus increasing the manufacturing costs of such heat pipes. Finally, Tungsten (W) and Copper Tungsten (CuW) are heavy and expensive, and their compatibility with water is also questionable at best.
Therefore, there is currently a need for a system for effectively transferring maximum heat from a semiconductor chip package and having a CTE that is compatible with the chip package.
I.
SUMMARY OF THE INVENTION
The present invention is a semiconductor package including at least one semiconductor chip within a housing, the housing including a lid which overlies at least one semiconductor chip and a heat-dissipating device coupled to the housing, the heat-dissipating device including at least one area formed of a material with a low coefficient of thermal expansion.
The above and other advantages and features of the present invention will be better understood from the following detailed description of the exemplary embodiments of the invention which is provided in connection with the accompanying drawings.
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patent: 5223747 (1993-06-01), Tschulena
patent: 5843807 (1998-12-01), Burns
patent: 5884693 (1999-03-01), Austin et al.
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patent: 6075287 (2000-06-01), Ingraham et al.
patent: 6076595 (2000-06-01), Austin et al.
patent: 6150195 (2000-11-01), Chiu et al.
patent: 6191478 (2001-02-01), Chen
patent: 6238954 (2001-05-01), Ma et al.
patent: 2001/0052652 (2001-12-01), Smith et al.
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