Steve
We do a similar beast, thick board with a bonded on heatsink, there are a couple of dozen DIPs going through it.  And like you, we have to use RMA flux on the beast.  Couldn't prebake as the foam fluxer would not work and I'm not into hand spraying.

After much pulling out of hair (which explains my current look), we did find a solution.  Our 'ol wave solder, the venerable C2000 machine, has been modified by putting a convection preheater on the top in the first zone.  For these particular boards the heater has to be cranked up higher than with the usual 6 layer stuff.  Works like a charm, our defect rate is near zero now and nobody beats me up (on this issue anyway!).

To justify it I had to get a scrap board, thermocouple it (top and bottom) and show that while the temperature on the bottom was great, there was no way the flux was getting activated on the topside.  Now I have a great temp profile and life is good.

regards

Graham Collins
Process Engineer, Litton Systems Canada, Atlantic Facility
(902) 873-2000 ext 6215

>>> [log in to unmask] 08/15/00 10:58PM >>>
You may have read about my problems with the way pins connect to inner planes
and all that, but now the last few days I've been trying to wave assemblies
that have metal heat-sinks bonded to the top of the PCB with the PTH
components installed on top of the heat-sink and then into the PCB...

Again, I've tried everything that my feeble mind (at this point) can possibly
do to wave these bloody things...

I'm thinking that designs such as these cannot be wave soldered with any good
results. Am I wrong in thinking that? Do these designs have to be hand built?
Am I just spinning my wheels trying to wave solder them?

Gawd, I'm getting beat-up by so many people because I can't figure out how to
wave these pieces of...of...of..."work"...

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