Manfred wrote:
I do agree on the interfaces being extremely important, and the
most important one is that between the FET and the spreader.
Soldering the FET to the spreader is essential when the
application has high power dissipation, like 600 watts from
each device, which is usual in class AB linear service. Thermal
paste, even the best one, just isn't good enough.
I'll add a caveat - soldering has the potential to be the best
option, provided that the joint is complete. I worked with power
rf where die carriers were soldered to flanges in a fancy oven
with nitrogen atmosphere etc. and voids still happened. With a
large contact area, in open air with flux around I see
opportunities for it to go wrong.
Soldering becomes the second best option if you blow a device.
If you work on getting the flange properly flat, clamping does
give good results but it takes work. Transistors out of the packet
are nowhere near good enough.
With water cooling, why not sit the transistor over a pocket and
run the coolant directly against the flange? That's a method I saw
in production test at the Philips (as it was) factory.
NEC had an ill fated TV broadcast tx which cooled the transistors
with compressed air blown directly onto the flange. In terms of
cooling I was told it worked just fine, the problem came when the
nozzles blocked with dust.
Steve
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|