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Coefficient of Thermal Expansion Reduction of Bonded Compliant Circuit Boards

IP.com Disclosure Number: IPCOM000101338D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 47K

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. With the high CTE, the 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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This is the abbreviated version, containing approximately 78% of the total text.

Coefficient of Thermal Expansion Reduction of Bonded Compliant Circuit Boards

       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.  With the high CTE, the 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 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 similar as
possible to maximize the life of the LCC solder joints.  Bonding the
PWB to an aluminum frame (24 X 10E-6 inch/inch/degree C) with an
elastomeric adhesive will result in an average PWB CTE increase to
approximately 11 x 10E-6 inch/inch/degree C.  Also, depending on the
size and geometry of the PWB and frame, localized PWB CTE may be as
high as 16 x 10E-6 inch/inch/degree C.  Such increases in the CTE
mismatch between the LCC and PWB will result in reduced solder joint
life.  Utilizing the frame design described in this disclosure will
lower the bonded PWB CTE average by about 1-2 x 10E-6
inch/inch/degree C which will improve solder joint life by
approximately 50%.

      The reduction in surface CTE of the bonded PWB is achieved with
a frame designed with relief slots.  These relief slots are
strategically mach...