Steve,
I ran across the exact same thing trying to solder
a 24" x 24" Kollmorgen Mutiwire .100 thick with lots of 2oz ground planes and
lots of PGA's.
I went out and rented (at a fairly steep price in
the mid 80's) an IR thermography system and watched those puppies go through the
process while I modified the parameters (one at a time, of course) and the most
significant effect was observed in the wave. So, being the cavalier "damned the
torpedoes" kinda guy, I tried turning on the chip wave and speeding up the
conveyor a bit. Lo an' behold... it worked, and I have the video to prove
it!
Seems "bumping" the thermal mass with the chip wave
followed by the "equillibrium time" in transit to the smooth wave was enough of
a boost to overcome the ground plane sink effect.
Using the video I finally convinced Design
Engineering to evaluate some enhancements for ground plane thermal relief
patterns. This would only work if you have design control over the PCB,
tho.
Let me know if it works!
Ed Popielarski
QTA Machine
10 Mc Laren, Ste.
D
Irvine, Ca. 92618
Ph: 949-581-6601
Fx:
949-581-2448
http://www.qta.net
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