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Chip-Heatsink Attach Using Contoured Adhesive With Glass Stand-offs

IP.com Disclosure Number: IPCOM000121260D
Original Publication Date: 1991-Aug-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 82K

Publishing Venue

IBM

Related People

Fairfull, RA: AUTHOR [+3]

Abstract

Production methods are described to mount TAB chips on flexible cables and bonding them to heatsinks with epoxy adhesive. The product requirement is for the chips to be positioned at a controlled height from the heatsink with good thermal contact, minimum adhesive voids and squeeze-outs. Two qualified methods are described: glass spheres added to the adhesive and the use of printed raised dots on the heatsink. Glass Spheres Method (Fig. 1)

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Chip-Heatsink Attach Using Contoured Adhesive With Glass Stand-offs

      Production methods are described to mount TAB chips on
flexible cables and bonding them to heatsinks with epoxy adhesive.
The product requirement is for the chips to be positioned at a
controlled height from the heatsink with good thermal contact,
minimum adhesive voids and squeeze-outs.  Two qualified methods are
described:  glass spheres added to the adhesive and the use of
printed raised dots on the heatsink.
Glass Spheres Method  (Fig. 1)

      A manufacturing process employs the glass sphere spacer method.
Graded Borosilicate glass spheres are added to the epoxy thermal
adhesive during mix preparation.  Sphere sizes range from 4 - 40
microns and represent 2% of the mixed adhesive weight.  The epoxy
containing glass spheres is then applied to the heatsink immediately
prior to chip attachment.  The shape of the printed epoxy is
controlled by a curved form printing blade, (Fig. 1a).  This produces
a domed profile to the epoxy footprint (Fig. 1b) and, during chip
attachment, minimizes voiding and gives enhanced epoxy squeeze-out
control.  Chip tilt (Fig. 1c) is corrected by applied loads of 50 g
to each chip position.  This brings the chip into direct contact with
the glass spheres, correcting any inherent tilt and displacing
adhesive to ensure a good all round bond (Fig. 1d).  Once assembled,
the adhesive is cured at an appropriate temperature and time.
Printed Dot Pedestals (Fig. 2)

      Epoxy dot pedestals of typically 25 micron height have been de
veloped using a two-pass print procedure to ensure the minimum chip
stand-off height is always met....