Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – Insulating material
Reexamination Certificate
2001-01-30
2002-12-31
Clark, Jasmine J B (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
Insulating material
C257S717000, C257S712000, C257S783000
Reexamination Certificate
active
06501171
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to organic laminate chip carrier packages which mount encapsulated semiconductor chips, such as plastic ball grid array (PBGA) packages providing for the mounting of so-called flip-chips, and wherein the chips are usually overlaid with a heat spreading cap designed to balance the coefficients of thermal expansion (CTE) and the stiffness of a substrate which is exposed on sides opposite of the chips, in order to compensate for mismatches in the coefficients of thermal expansion, and resulting in contractions which cause the entire package arrangement to warp, leading to delamination between an encapsulant and cap and resulting in failure of connect joints and the ball grid arrays.
The concept of compensating for any mismatches in coefficients of thermal expansion (CTE) and resultant contraction which are encountered between the various components of a wire bond or flip chip package or module including encapsulated semiconductor chips mounted on substrates, and with heat sinks supported on the chips in the form of caps in order to reduce heat-induced warpage tending to separate the components and leading to failures of the electrical connects and ball grid arrays adversely affecting the functioning and reliability of the packages has been widely addressed in the technology and industry. Nevertheless, notwithstanding the considerable efforts expended in order to solve the problems which are encountered, the utilization of the heat-spreading caps or heat sinks has only been partially successful in maintaining the relative flatness of the components and avoiding warping, inasmuch as the heat-spreading cap only balances the thermal dissipation above the substrate directly above the chip. The foregoing difficulties are encountered due to package warping as a result of thermal stresses generated, in that the normally utilized epoxy adhesives which cement the chip and cap to the substrate may not match the coefficients of thermal expansion of the substrate. One of the possible failure mechanisms is delamination of the epoxy interface between the chip and the cap as a result of thermally induced thermal stresses. Also, the tendency of the epoxy adhesive to absorb or desorb moisture may readily cause additional expansion and contraction and result in further warpage of the entire module structure, leading to an operative failure of the arrangement.
2. Discussion of the Prior Art
At this time, various types of structures have been employed in the technology which concern themselves with the provision of means for dissipating heat which is generated during the operation of the module, and to avoid thermal expansions and contractions which would conceivably cause the module to warp, leading to operative failure and/or reduction in the service life thereof.
In particular, the semiconductor chips have been equipped with superimposed heat sinks in the form of so-called caps or covering structures which are adhesively fastened thereto; for example, such as through the interposition of an epoxy adhesives or the like, and wherein the caps extend generally above the areas defined by the surface extent of the chips. Such caps are normally constituted of a heat-conductive material, such as steel or copper. Other types of caps may incorporate multiple layers of different materials or have fins formed thereon providing enlarged surface areas for dispersing and dissipating heat, whereas other structures may have the caps extending beyond the confines of the chip and be suitably shaped to theoretically optimize the rate of heat dissipation from the module arrangements.
Alcoe et al U.S. Pat. No. 5,877,043, which is commonly assigned to the assignee of the present application, discloses an electronic package incorporating a flexible substrate, stiffener and semiconductor chip. In that instance, there are provided a plurality of strain relief structures at various locations about the package so as to prevent surface wrinkling associated with large differences in coefficients of thermal expansion (CTE) between the various package elements. Although this provides for a heat dissipation structure, there is no disclosure of a unique cap design analogous to that contemplated by the present invention.
Tokuno et al U.S. Pat. No. 5,777,847 discloses a multichip module including a metallic cover plate fastened by means of a support pillar to a substrate, and wherein the plate is constituted of a heat conductive material, preferably such as copper or other suitable metal, such as aluminum or aluminum alloy.
Marrs U.S. Pat. No. 5,485,037 discloses a heat sink in the form of a cap or cover structure arranged above semiconductor chip which is mounted on a substrate, and which includes a plurality of holes adapted to be filled with a suitable filler material facilitating the dissipation of heat in a generally uniformly dispersed manner across the surface of the chip while maintaining the essential rigidity or stiffness of the heat sink or cap.
Baska et al U.S. Pat. No. 5,745,344 discloses a heat-dissipating apparatus including spaced fins for absorbing heat generated by an electronic device.
Liberty et al U.S. Pat. No. 5,213,868 is directed to a thermally conductive interface material of a polymeric binder and one or more thermal filters so as to form a heat sink for an electronic component.
Caletka et al U.S. Pat. No. 6,104,093 discloses a thermally enhanced and mechanically balanced flip chip package and method of forming the package. However, unlike the present invention, the description of recesses in this patent resides in the context of peripheral steps, and further non-flat; i.e. varying thickness cross-section. This patent does not teach nor suggest the use of small-sized apertures to promote adhesion, but rather promotes adhesion by enrichment of surface chromium and use of silane coupling agents rather than small-sized apertures.
Other types of structures which have been employed as heat sinks and which are arranged above encapsulated semiconductor chips and fastened thereto with the intermediary of epoxy adhesives, which may include heat conductive greases, including cap configurations incorporating pluralities of holes in varying specified sizes and arrays, and also scallops formed along the edges of the caps extending over the edge portions of the chips located therebeneath so as to allow for improved degrees of heat dissipation therefrom.
Although the foregoing types of cap or cover construction forming heat sinks are adapt in dissipating heat from the semiconductor chips and ball grid arrays, so as to reduce or possibly eliminate warpage encountered between the various electronic package components; in effect, the substrate mounting the semiconductor chips and the caps or cover structures forming the heat sink mounted above the chips to reduce warpage and potential failure of the ball grid arrays and the entire package modules, pursuant to the invention further improvements in design and construction would still further enhance the degree of heat dissipation through the caps so as to assist in eliminating warpage between the components and improve upon operational reliability, while increasing the service life of the package module or arrangement.
SUMMARY OF THE INVENTION
In order to improve upon the current state-of-the-art in the design and construction of cap structures which will extensively reduce or obviate delamination thereof from an adhesive or dielectric material bonding the cap structure to a chip; in effect, improving the interfacial adhesion therebetween, the cap structure is provided with a multiplicity of small-sized perforations forming increased surface areas for the bonding and creating of mechanical interlocking means between the components. The perforations which are provided in the cap structure, the latter of which is preferably of a flat or planar configuration, and wherein the perforations extend therethrough or at least partially thereinto, may be formed through a photolithography pro
Farquhar Donald S.
Houser David E.
Papathomas Konstantinos I.
Clark Jasmine J B
Fraley, Esq. Lawerence
International Business Machines - Corporation
Scully Scott Murphy & Presser
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