Hi technetters

In Lyn Lynch's reply to Jim Marsico, I beg to differ on the comment of coating 
remaining under the device and causing stess thru TCE mis-match. Providing the 
Acrylic coating has a low Youngs Modulus, there should be no unacceptable 
additional stress.

We have had one or two customers who chose to "thin dip" followed by spraying 
to leave a gap under the devices but the majority apply a standard dip viz: 
Maximum solids at typically 200 to 300 cps - In at less than 12 inches per 
minute - Out at less than 6 inches per minute. This should give you MIL Spec 
thickness at around 0.0015 inches.

The high capillarity of these materials should ensure good underfilling which 
we would particularly recommended for BGAs. How will you know? Helluva good 
question - X-ray?! Or why not try tesing with dummy BGA's on coupons processed 
the same way as your main assemblies, resist, paste, etc., and pull off the 
BGA and take a look. If you tracked the process, you should get good 
repeatability.

Graham Naisbitt
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