It looks like "foot-in-the-mud" to me. How thick is your
Ioan,
It looks like "foot-in-the-mud" to me. How thick is your stencil and is
the aperture 1:1 with the pad?
Regards,
George
George M. Wenger
Senior Principle FMA / Reliability Engineer
Wireless network Solutions
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908) 546-4531
[log in to unmask]
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Wednesday, November 15, 2006 9:57 AM
To: [log in to unmask]
Subject: [LF] Separation in BGA joints
Hi TNLF-ers,
please have a look at http://stevezeva.homestead.com/files/Ioan_Ball.jpg
, many thanks to Steve again.
What can I tell you: no-clean SAC305 at the bottom, the balls read a
sort of SAC with 3%Ag and 1.75%Cu The reflow profile seems to be OK, I
measure 246C under the periphery of the BGA, with a thermocouple that is
squeezed there. I know it is not rigorous, I did not drill, I am not
measuring inside the joint. But even if I am 20C off, the materials
should be molten and coalesce, isn't it?
The intermetallics solder paste - PCB pad are OK, the wetting is good,
the BGA balls seem to have changed shape, they are almost collapsed,
there is physical contact between the balls and the paste, but no joint.
The question is: why do I see the separation line? What can cause that?
Should I bother investigating the process, or do I have a sort of
contamination? Or the BGA ball alloy has a higher melting point?
Thanks,
Ioan
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