Ed-

Ceramic package BGAs (CBGA) typically use a combination of eutectic
solder attach with high temperature solder  (90Pb/10Sn) columns
(non-reflowing) because...


"This hierarchical structure creates a consistent and reproducable gap
or standoff between the ceramic package and the card. This standoff
accomodates the mechanical strains geenerated during normal machine
power cycling, caused by the thermal mismatch between the ceramic
carrieer and the card...":


This is taken from text "Ball Grid Array Technology,"  McGraw-Hill
(1995), John Lau, Ed., pg.133 of Chapter 5, "An Overview of Ceramic Ball
and Column Grid Array Packaging", by T. Caulfield, M. Cole, F. Cappo, J.
Zitz and J. Benenati.



High Tg FR-4 and BT epoxy laminate based PBGAs are a near perfect CTE
match to typical PWBs they are attached to, and thus get away with
eutectic solder spheres.

-Michael Alderete
------------------------------

Date:    Tue, 15 Sep 1998 10:10:23 -0400
From:    Ed Holton <[log in to unmask]>
Subject: Re: X-ray for open joints on BGA's ?

I am curious, why are the ceramic BGA solder balls not eutectic and made
with the 90/10 Pb/Sn solder?

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