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Bonding Printed Wiring Board to Aluminum Heat Sink

IP.com Disclosure Number: IPCOM000102886D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 59K

Publishing Venue

IBM

Related People

Zalucha, PS: AUTHOR

Abstract

Disclosed is a method for minimizing the thermal expansion increase of a low coefficient of thermal expansion (CTE) Printed Wiring Board (PWB) caused by bonding this board to a high CTE aluminum frame. The high CTE, thermally conductive aluminum frame influences the low CTE PWB through the bond material, in turn reducing the life of the low CTE ceramic Leadless Chip Carriers (LCCs) that are soldered to the surface of the PWB.

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Bonding Printed Wiring Board to Aluminum Heat Sink

      Disclosed is a method for minimizing the thermal expansion
increase of a low coefficient of thermal expansion (CTE) Printed
Wiring Board (PWB) caused by bonding this board to a high CTE
aluminum frame.  The high CTE, thermally conductive aluminum frame
influences the low CTE PWB through the bond material, in turn
reducing the life of the low CTE ceramic Leadless Chip Carriers
(LCCs) that are soldered to the surface of the PWB.

      The mismatch in CTEs of the PWB and aluminum frame make the
selection of the proper bonding adhesive critical.  The adhesive in
the bondline must be compliant and allow the PWB to expand and
contract independent of the aluminum frame over the operating
temperature range.  Also, the adhesive must provide thermal transfer
between the PWB and frame, maintain structural integrity throughout
the life of the product in various environments, and be compatible
with later assembly processes.

      The CTE of the ceramic LCC (6 x 10E-6 inch/inch/degree C) and
the PWB (9 x 10E-6 inch/inch/degree C) should be as close as possible
to maximize the life of the LCC solder joints.  Bonding the PWB to
the aluminum frame (24 x 10E-6 inch/inch/ degree C) normally causes
the CTE of the PWB to increase to as high as 20 x 10E-6
inch/inch/degree C. Utilizing the bonding method in this disclosure
results in a bonded PWB CTE of approximately 10 x 10E-6
inch/inch/degree C.

      The adhesives ...