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Process for Encapsulation for Fatigue Life Enhancement

IP.com Disclosure Number: IPCOM000113552D
Original Publication Date: 1994-Sep-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Gutierrez, BL: AUTHOR [+3]

Abstract

High DNP (distance from zero-stress point) modules often require an encapsulant to meet fatigue life and/or failure rate objectives. How the encapsulant is applied controls the fillet geometry around the ball grid array module, and whether and where voids occur. The height and width of the encapsulant fillet at the module edge, and insuring that the highest DNP (the outermost four to five rows) of solder joints were encapsulated without voids, were found to be crucial to prolonging the fatigue life of the solder joints. The process contains these steps: First, the card assembly containing the module is heated to 70-100ºC. Next, a syringe is positioned <= 1.2mm from the module edge and 2-4mm above the card. Encapsulant is dispensed on three to four sides of the module.

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Process for Encapsulation for Fatigue Life Enhancement

      High DNP (distance from zero-stress point) modules often
require an encapsulant to meet fatigue life and/or failure rate
objectives.  How the encapsulant is applied controls the fillet
geometry around the ball grid array module, and whether and where
voids occur.  The height and width of the encapsulant fillet at the
module edge, and insuring that the highest DNP (the outermost four to
five rows) of solder joints were encapsulated without voids, were
found to be crucial to prolonging the fatigue life of the solder
joints.  The process contains these steps:  First, the card assembly
containing the module is heated to 70-100ºC.  Next, a syringe is
positioned <= 1.2mm from the module edge and 2-4mm above the card.
Encapsulant is dispensed on three to four sides of the module.  This
is repeated three times to build up a fillet of encapsulant extending
at least 0.025" beyond the module edge.  The encapsulant is dispensed
across the fourth side of the module to complete filling around the
highest DNP solder joints.

      This procedure produces a fillet at least 0.025" wide and
0.040" high at the edge of the module, and also encapsulates at least
the four outermost rows of the module pins.  The encapsulant is then
cured with a time/temperature profile sufficient to give the cured
material a CTE (coefficient of thermal expansion) of no more than 35
ppm/C and a glass transition temperature of at least 10...