Hi Dave,
I have seen the "scaling" too. The ERSA rep said it was a defect,
but not being a process guy, he could not explain why. He claimed that
until the advent of the scope, the defect has gone unknown in the industry.
For those who have not seen this before, it not a cold solder joint.
Rather, it looks like an artists rendering of a cooling planet with plate
tectonics.
Actually, I believe it is quite common. I say this because I have
seen it to a lesser extent on many brand new unprocessed BGA balls when
viewed under a high powered scope. I have also seen it during cooling after
reflowing solderpaste and viewing it through a microscope. Cooling tends to
be rather uncontrolled and quite rapid.
It appears as if the surface of the solder sphere solidified before
the interior did. As the interior cooled, it shrank, pulling in the
solidified exterior surface, causing the wrinkles. When I have watched it
occur, it all happens in less than a second. There will be micro cracks,
but they run normal to the surface. Since this is a natural physical
phenomenon, I'm not sure how it is a defect. But I have not had time to
investigate further. Maybe some of our other experts can explain.
Thanks
Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]
> -----Original Message-----
> From: Dave Simmons [SMTP:[log in to unmask]]
> Sent: Monday, June 12, 2000 2:29 PM
> To: [log in to unmask]
> Subject: [TN] Scaling on PBGA Balls after reflow.
>
> Hi All,
>
> We are checking placement of some PBGA's. I have an ERSAScope on a demo,
> and when viewing the solder balls/joints of the BGA there is some
> "scaling" on the surface of the ball.
> I was wondering what this scaling is a function of (e.g. to rapid
> cooling, not hot enough, to hot during reflow?), and is it a defect I
> should be worried about. I am not seeing this "scaling" on any of the
> other parts (QFP100, 0603 chips) on the board.
> Can anyone offer any advice?
> Thanks
> David << File: Card for David Simmons >>
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