I would say use another board finish - ENIG or similar - as you may have a
flatness problem with HASL. Or you can think about answers to the following
questions and see if they give you any other clues, or help us to give you
better answers:
What substrate are you using?
Are the opens occuring at first test after assembly, or in qualification
testing or are they field returns? Has any temperature cycling been carried
out?
How old are the PCB's you're using - have they become oxidised?
Have the BGA's been re-worked/replaced?
Do the opens occur with the same contacts or are they more random?
Do you have any thermally assymetrical design features near the problem
area(s) such as heavy traces running nearby, or some longer traces and some
shorter traces? These can contribute to theft of heat, which may result in
there being insufficient heat left to make a proper solder joint,
especially if they're connected to thermal, voltage or ground planes, which
will dissipate the heat even more. You may have to reduce your peak
soldering temperature and increase its duration to compensate.
How was the thermal profiling carried out? Are you certain that all the BGA
contacts are reaching proper soldering temperature?
BGA pads in general are smaller than the ball diameter. Why did
"management" pick on 0.4mm as a pad size that would improve the situation?
If you are not using via-in-pad, 0.4mm pad sizes are going to interfere
with the offset vias and probably lead to greater problems of
solderability.
What other possible causes have been considered? What causes have you
rejected?
Good Luck - you may find there is no quick answer to this problem, but I
hope for your sake it's easily solved.
Peter Duncan
Tom Colby
<tcolby@CREST To: [log in to unmask]
RON.COM> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST
Sent by: Aero/ST Group)
TechNet Subject: [TN] BGA bone of contention
<[log in to unmask]
ORG>
11/17/01
04:46 AM
Please
respond to
"TechNet
E-Mail
Forum."
Help me out with this technetters,
The problem: BGA opens on a HASL board.
The device: Motorola MCF5272, a 196 MAPBGA, 1mm pitch, ball size of
0.35/0.65. Substrate land size unknown. Footprint designed with a pad of
0.28mm.
Management's solution is to increase the pad size to 0.4mm. I say to look
elsewhere in the process for the problem.
I'd like to hear the opinions of my esteemed colleagues. What do you say
folks?
Thanks in advance,
Tom
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