Hi Leland,
Recommend that you proceed with micro-section analysis. X-ray often unable to see very fine interface cracks, which produce symptoms similar to those you describe.
It is possible to micro-section every ball on a BGA device, and if you have test results to narrow this down, even better. You might want to take a look at the Gerber's for the PCB and choose to orientate your micro-section to include the tracks which connect PCB pad to adjacent via. This will allow you to extend your coverage of the interconnect between device and PCB. Best to take this approach if you have specific joints to target.
Micro-section and SEM-EDS will give you feedback on all sorts of issues and allow you to examine joint between solder ball and both device and PCB. Check for intermetallic formation on the PCB pad (thickness and type), along with joint microstructure. Also check for intermetallic type and condition at BGA pad.
The micro-section will also allow you to check for cracks in the PCB laminate, and if you orientate parallel to the track connecting pad to via, this connection too.
Condition of joint metallurgy will allow you to assess whether fault/fail relates to material/processing/test conditions.
Hope that helps, and please give me a call if we can help directly.
Kind regards,
Stewart
Stewart McCracken
MCS Ltd.
Centre House
Midlothian Innovation Centre
Roslin
Midlothian
EH25 9RE
m. +44(0)7711 541735
t. +44(0)131 440 9090
f. +44(0)131 440 9085
e. [log in to unmask]
w. www.themcsgroup.co.uk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: 02 December 2010 15:36
To: [log in to unmask]
Subject: [TN] BGA Failure Analysis Recommendations
Good morning, everyone!
I'm looking for some advice on how to best analyze a BGA problem. We
had an assembly to fail in a reliability test, and have isolated the
problem to an intermittent contact on the BGA device. When downward
pressure is applied to the component it will pass. Without the
pressure, it won't.
That tells me we have either fractured a joint, had a ball to separate
from the package, or had a head in pillow (or non-wet) condition.
We don't have a BGA inspection scope in house, and I can only see two of
the four outside edges with the equipment I have. Of course, nothing is
wrong with those.
We have both 2 and 3D xray machines, but neither detect a flawed
condition.
At this point, do I go with dye and pry, or conduct a series of cross
sections?
What's the recommendations of the pros out there that have dealt with
this? Your suggestions are sincerely appreciated!
Leland Woodall
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