Metal working – Method of mechanical manufacture – Electrical device making
Patent
1998-02-05
2000-10-24
Young, Lee
Metal working
Method of mechanical manufacture
Electrical device making
29832, 29830, 29837, 29842, 438119, 257700, 257706, 156 94, H05K 334
Patent
active
061347760
ABSTRACT:
A direct chip attach to heatsink structure is shown and described which implements rework when the chip must be removed and replaced. A laminated heatsink includes a metal heatsink with a foil layer adhered to the chip attachment surface with the assembly secured to a carrier at a cutout opening therein that defines the chip attach site. The adhesive, either a dry film adhesive or a pressure sensitive adhesive, secures foil layer to heatsink and provides the interface of separation when a chip must be removed and replaced. By peeling the foil away from the heatsink, the foil, chip and non-reworkable die attach adhesive are removed as a unit, leaving no chip attach adhesive residue at the attachment site to be scraped or abraded away. The replacement chip can be installed either by directly installing with new die attach adhesive or by first restoring the foil layer prior to chip installation. The foil may be applied over the entire surface of the heatsink or may be patterned to provide the laminated foil coating only beneath the chip attach site. Further, the foil and heatsink may be of dissimilar metals to impart varying characteristics, such as a solderable surface to an aluminum heatsink.
Also, the technique would be applicable to direct chip attachment directly to a rigid or flexible electronic circuit carrier assembly. In another form, the invention may be implemented using a foil layer with adhesive on both sides to secure the chip to a heatsink at the carrier assembly chip attach location. A further form of the invention uses a tape cavity packaging structure wherein the carrier assembly includes a laminated carrier/heatsink with aligned openings that create a chip attach cavity in the package and foil bonded to the heatsink across the base of the chip cavity by a layer of adhesive that also presents a chip attach adhesive across the base of the chip attach cavity. The structure affords a low profile assembly, enables rework/replacement, shortens wire lengths and reduces wirebond loop heights.
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U.S. Patent application Ser. No. 08/349,854, filed Dec. 6, 1994, entitled Reworkable Electronic Apparatus Having a Fusible Layer for Adhesively Attached Components, and Method Therefor.
U.S. Patent application Ser. No. 08/530,452, filed Sep. 19, 1995, entitled Method and System for Reworkable Direct Chip Attach (DCA) Structure with Thermal Enhancement.
International Business Machines - Corporation
Lahtinen Robert W.
Smith Sean
Young Lee
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