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Wed, 28 Jan 1998 11:52:19 -0500 |
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Johannes,
I have read the other responses you have received on this, and agree
with them. I will just give you my input from my experience. I studied
this issue when I was setting up the BGA process. Having attended a BGA
symposium, SMI, etc. and talking with experts at IBM and Motorola I choose
to go with non solder mask defined pads and to print 1:1 with the pad. We
were also placing PBGA. With PBGA the ball will melt so you do not need an
excessive amount of paste so 1:1 is fine. This may be different with
Ceramic. There are pitfalls to both solder mask defined and non-soldermask
defined, but the non-solder mask defined seem to have fewer issues. This
is the setup I used and had very good yields and the boards held up very
well under temp/humidity cycling and shock/vibration testing.
Good Luck,
Brad Kendall
Hella Electronics
Michigan SMTA President
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