Is this the only BGA on you board?
Is this artifact found on other products?
Are the PWB finishes the same on all products?
Has this BGA been REWORKED/RESTENCILED/REBALLED?
Is this an outer ROW solder bump or INNER?
It is not a good practice to use LF sphere with SnPb solder paste.
Victor,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Wednesday, November 15, 2006 9:58 AM
To: [log in to unmask]
Subject: Re: [TN] Separation in BGA joints
George, Victor,
foot-in-the-mud, head-on-pillow. It seems that you two are talking about
the same thing, but what is it and why is this happening?
The stencil is 6 mils thick with square apertures, the dimension equal
to the diameter of the pad. ENIG finish.
Time above liquidous is 65s.
Due to pressures from our customers we run many lead-free BGAs on leaded
paste at 220C. If this forms joints, why LF on LF would not form joints
at 246C, or let's say 230C if I am really off in my temp measurements?
Thanks,
Ioan
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Tempea, Ioan
Sent: Wednesday, November 15, 2006 9:57 AM
To: [log in to unmask]
Subject: [TN] 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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