In a message dated 5/6/99 5:36:37 AM Pacific Daylight Time,
[log in to unmask] writes:

<<
 Steve: Thanks for your explanation of IPC's activities on BGA voiding. Just
 two 'small' questions (maybe 'big' answers??):

 i./ Is that 20-30% by cross-sectional area, or volume, or what?

 ii./ Is there any comment also about WHERE the voids are located -
 solder/UBM or solder/pad?

 Ta,

 Andy>>

Hi Andy!

I'm sure it was cross-section, because you can't tell how big the void really
is using just transmission x-ray...and as to where is it is another gray area
using transmission x-ray, you just don't know. It does make a difference
where it is, I'm sure. But that points out why one should err on the side of
caution considering the size of the void.

I'm sort of guessing now, but I feel that one might assume that a void is
going to be in the solder fillet between the ball and the PCB pad unless you
can somehow determine that the BGA has voids in the balls themselves before
assembly. In which case I would send them back from where they came from.

Just another lil' update on the conference I'm attending. I went to the first
couple lectures this morning, and won't be going back until this
afternoon...all the lectures between now and then are about down at the wafer
level of these lil' puppies.

But what was interesting from the first lecture this morning, which was
titled; Key Factors in CSP BGA Reliability, by a Dr. Reza Ghaffarian from
JPL, was that all the reliability studies and tests that have been done, and
there's been a TON of them! (He had more charts and slides than I could keep
up with!) was that they were all done and performed with BGA's and CSP's that
were soldered with traditional Tin/Lead solders. I asked if there had been
any testing done with any of the alternative solders, and he had said no.

"Things that make ya' go hmmmmm...."

Sorry, I just can't drop this lead free thing...as the Georgia sheriff says;
"I think yo' inna heap of trouble boy!"

-Steve Gregory-

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