Browse Prior Art Database

Methods to Electrically Connect A1 Heat Sinks to Semiconductor Chip Packages

IP.com Disclosure Number: IPCOM000108454D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 111K

Publishing Venue

IBM

Related People

Ameen, JG: AUTHOR [+4]

Abstract

Electronic components are thermally enhanced by attaching aluminum heat sinks to the modules, flat packs, TAB's chips, and the like, through a thermally conductive, yet electrically insulating, epoxy. Insulation of the chip from the heat sink is required to prevent electrical shock to service personnel and to prevent electrical damage to the chip from electrostatic discharge. As industry quality demands increase and the need for electrical shielding also increases, it becomes desirable to ground the aluminum heat sinks and to have the ability to remove the heat sink without disturbing the component attached to it for failure analysis.

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Methods to Electrically Connect A1 Heat Sinks to Semiconductor Chip Packages

       Electronic components are thermally enhanced by attaching
aluminum heat sinks to the modules, flat packs, TAB's chips, and the
like, through a thermally conductive, yet electrically insulating,
epoxy.  Insulation of the chip from the heat sink is required to
prevent electrical shock to service personnel and to prevent
electrical damage to the chip from electrostatic discharge.  As
industry quality demands increase and the need for electrical
shielding also increases, it becomes desirable to ground the aluminum
heat sinks and to have the ability to remove the heat sink without
disturbing the component attached to it for failure analysis.

      While there are solutions for the grounding requirement (e.g.,
the use of electrically conductive epoxies, metal stakes through
holes, etc.), there are no solutions at present to allow the removal
of the heat sink without damage to the underlying component.  This is
especially true for TAB-type modules.

      Three proposals are disclosed to allow the aluminum heat sinks
to be 1) soldered in place, 2) adhesively bonded in place, or 3) used
in a combination process that allows for both soldering and adhesive
bonding.
1)  The feet of some heat sinks have holes in them to aid the
adhesion of the dispensed epoxy adhesive.  For these, tin/lead plated
copper eyelets can be "pop riveted" into these holes in the heat sink
feet (see Fig. 1).  This eyelet may then be soldered to the card
providing a reworkable interface.  At the component interface, an
aluminum solder composed of 91% tin, 9% zinc may be attached to the
aluminum heat sink in a pattern that covers an area slightly larger
than the heat sink to component interface.  If there are no holes in
the feet of the heat sink, it is also possible to use the tin/zinc
solder on the feet's bottom surface.  If the module must be replaced,
applying heat to the heat sink will cause the feet to loosen from the
card as well as the component from the heat sink.  (The thermal
adhesive will adhere to molten metal (91% tin/9% zinc solder) and as
such will let go from the heat sink.)
2)  For heat sinks that are to be totally adhesively attached, a two-
piece heat sink is pr...