Hi Larry!

Hoo-boy! I know what you're dealing with! We've built an assembly here that
we occasionally get back to replace a 352-pin CQFP on one of the two
assemblies that are bonded to an aluminum heatsink...I think it's thicker
than .100" too. The other kicker is that the CQFP also has a loctite adhesive
applied to cover at least 70% of the surface area beneath the part. When we
build it, we print paste, dispense adhesive to cover 70% of the surface area
beneath the part, place it, and reflow/cure at the same time. Then we get the
whole conformally coated assembly back to rework the part when it dies...fun
stuff huh?

We just got a new rework machine here that I think is the neatest thing since
sliced bread. It's called a PDR Lightmaster Pro. Uses focused infrared light.
No need for different sized nozzles for different sized components, you just
focus the light-beam to the size of the part.

The thing about this machine that I love, is that thermal mass is not a
concern. One of the things that I did when deciding to buy this machine was
to get that ceramic QFP monster, with the aluminum heatsink bonded to it,
along with the part being epoxied to the PCB, and try to remove it....piece
O' cake! You won't cook the fab either! There's non-contact thermocouples
that monitor PCB temp along with part temp, that feeds-back to the software
that controls the profile in a closed-loop fashion.

Maybe, you might want to send it my way and see what I can do? Don't think
you wanna try using low temp balls if the assembly is bonded to a
heat-sink...don't think they would last, as obviously the assembly is putting
out some heat...

We had some people from your company visit us a few weeks ago...looking at us
to build some Commanche stuff for ya'll...

-Steve Gregory-


> 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 BGA's, 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
>