Thanks, Steve. We build a VME board that has one Ceramic BGA and two
Plastic BGA's. Originally, the ceramic was a CIC (Column Interposed
Ceramic) until it became unavailable. Don't know which Power PC chip you're
using, but ours is going obsolete, to be replaced by a plastic one, which
makes things more consistent, at least.
Although the ceramics have high MP solder balls, I have never attempted to
reflow them. To do so meant cooking other components on the board, so we
just used eutectic solder, made sure the profile was right for that and
soldered. The plastic BGA balls reflowed but the ceramics' balls remained
solid while the solder paste alloyed itself as it would to any other leaded
component (ish). Built this way, the boards have now passed every test
we've thrown at them, and have just passed their Safety of Flight tests, so
we're quite pleased.
Hope this helps.
Peter
Steve Gregory <[log in to unmask]> 12/11/2002 08:35 AM
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cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: Re: [TN] profiling BGAs
Good comment Peter!
I am about to embark on assembling a VME card (there's been a few emails
from me about this assembly), that has 19-BGA's. Some of the BGA's have
eutectic solder balls, some have hi-temp solder balls...those are the
ceramic devices...Power PC microprocessors. I thought I would concentrate
on those...
Want to "tweek" the profile so they solder good...the rest of the BGA's
will need to follow. If they don't, then the design isn't manufacturable...
-Steve Gregory-
Hi, Werner,
I'm a little puzzled. I believed the reason why so many folks drill up
into
the central ball of a BGA to place a T/C, is because it's these central
contacts that generally suffer from insufficient heating owing to the
shading effect of the overlying body of the component. If the BGA's outer
body temperature only is measured, isn't this going to be much hotter than
the balls underneath, and especially those in the centre of the array?
Which, then, is the best way to thermally profile a BGA, in your
experience, or does it depend on BGA size versus T/C size?
Peter
Werner Engelmaier <[log in to unmask]> 12/11/2002 07:54 AM
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cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: Re: [TN] profiling BGAs
Hi Toby,
Your question is a good one.
What I have done--and it works--was to grind a depression in the ceramic
component body deep enough for the T/C beat to fit flush into it. Than I
epoxy the beat into this depression; the surface is still flush so not to
affect the heat transfer. I also epoxy the length of T/C wires which ends
with the T/C onto the the surface of the commponent; thus, the impact of
the
wires being heated faster than the component body and thus a giving me a
higher t-reading at the T/C is minimized. This works for both IR and
Convection reflow ovens.
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com
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