Hi technet!

We've got a customer working with high power transistors, they want to 
use solder pre-forms to solder a heatsink on top of a row of 
transistors.  So the stackup will be PCB - transistor - preform - 
heatsink, where the heatsink will span a row of 5 transistors.

The question is how do we establish that this is working OK and isn't 
full of voids?  This is at the "ok, we think this will work but we need 
to qualify the attachment method" stage.  I've come up with a couple of 
options:

1) tear / grind it off and look for anomalies - not very sure to find 
issues.
2) x-ray it - we don't have a 3-d x-ray so I'm not confident in our 
abilities to find voiding.  We do have a nice static x-ray though and 
will try it to see how well it can see.
3) Sonoscan it to look for voids?  Would have to be outsourced.

Am I missing any obvious options?

-- 
Graham Collins
Senior Process Engineer
Sunsel Systems
(902) 444-7867