Hi Kitty, Ken and you all,
Vibration sensitive joints, I have taken your words into my fishbone trouble
shooting scheme. Our BGA supplier is much engaged and I think they will
track down more in one week than what we found during months of chatting and
meetings. We have lots of young and unexperienced people and one day they
will be experts themselves, but now learning is daily life. Back to
vibration, me to suspected fragile joints, so I took one of our extremly
expensive boards and knocked on it's backside, and the BGAs fell off with a
'ping'. I have mentioned it before in this forum. But same joints could be
loaded with considerably high static force. Other components on the board,
like QFPs and DILs and others, could not be 'pinged' off despite violent
knocking the board, just the biggest BGAs. Such a 'test' may exceed the 50
G's random vibration, you have no control when knocking with a plastic
hammer, but it tells a story, namely that you deal with very fragile solder
joints. So, we are trying to understand what metallurgy this is: you can
hang a fullgrown comwboy in the package, but not give it a kick with a tiny
plastic hammer.
Your mail is taken under consideration. Very interesting!
Ingemar
-----Original Message-----
From: Kathy Kuhlow [mailto:[log in to unmask]]
Sent: den 26 januari 2001 20:51
To: [log in to unmask]
Subject: Re: [TN] Spread the knowledge...let's share...reason for BGA
crack
Ken,
I hve learned the hard way that the only reliable way to depanelize an
assembly, especially with a BGA, is to use a router. Be extremely careful
in having an operator depanel by flexing the border. You may very well
change the cause of BGA opens but still have the problem.
Kathy
>>> [log in to unmask] 01/26/01 01:06PM >>>
Nothing wrong in sharing a good info to Technet.
I have asked about the possible reason for open solder/crack at BGA to
TechNet few days ago. What we found out that the solder cracks are due to
dremer tool (?) used to remove the break away tabs. So watch out! Our mouse
bite with three hole with solid connection - no good design as it requires
lot of effort to remove break away tab. Hence our assembly house folks used
the dremer tool to remove break away tabs. Vibration of that tool generated
crack at the interface between board and the ball along the entire row
facing the break away tab.
Bottom line, do not use dremer tool and incorporate better mouse-bite design
with 4 or 5 holes with two corner holes half in the FR4 material so that
operator can initiate tab separation easily.
re,
ken patel
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