Boy! Have you ever got a good one! I used to be in a production team that
assembled boards that were bonded, as you describe, to an aluminium cold
wall. Flexi connectors at top and bottom joined the boards together as a
single "cassette". We didn't use BGA's though.
I can't help you with low temp solder ball info, but if I may share my
initial reaction/thoughts with you - I am wondering how you will change the
BGA, even with low temp solder balls. The adhesive we used to bond the
boards to the cold walls was Abelstik Film adhesive, and the bonding was
carried out at 100 deg C (+/-). Removal of the boards was carried out at a
similar temperature, to soften the bond enough to pull the boards off.
During the assembly process, the temperature had to be monitored frequently
to ensure it didn't get too hot. Overheating the adhesive damaged the bond.
For your BGA, the board will have to be heated from the bottom as well as
from the top to effect removal. If the board is still attached to the
heatsink, the temperature soak will be very long, and this plus the final
reflow temperature may not do the bond any good. Removing the board from
the heatsink, cleaning it of adhesive, replacing the BGA, and bonding the
board back onto the heatsink is, however, a very big task. Unless the
module is a high value item, or no longer in production, I would consider
writing it off and replacing it with a new one. I don't think there are
many shortcuts round the problem.
I really wish you the very best of luck - it looks like maintainability
wasn't a factor in the design of this unit.
Peter
"Jindra, Larry" <[log in to unmask]> 07/05/2002 07:24 AM
Sent by: TechNet <[log in to unmask]>
Please respond to "TechNet E-Mail Forum."; Please respond to "Jindra,
Larry"
To: [log in to unmask]
cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: [TN] Low Temp BGA Balls
I've got a module with PCAs bonded to both sides of an .100" aluminum
heatsink. A 35mm BGA needs replacement. Does someone out there have
experience with using low-temp solder balls on BGAs, or should I file this
away under R for Rube Goldberg?
Larry Jindra
Mfg Engr Group Lead
TRW Radio Systems
[log in to unmask]
w) 858-592-3424
f) 858-592-3940
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