Steve,
If the copper has been rolled there will have been some work hardening. It
could well be worthwhile annealing it BEFORE doing the final milling. Same as
one does for BMS (Bright Mild Steel)
Annealing copper is easy - get it red hot and then let it cool - or dump in a
bucket of water. Although for tubing, that can lead to water boiling in the
tube and shooting out of the open end.
73
Peter G3RZP
========================================
Message Received: Dec 12 2013, 08:35 AM
From: "Steve Thompson" <g8gsq72@gmail.com>
To: amps@contesting.com
Cc:
Subject: Re: [Amps] Arctic Silver
I'll echo other's comments about Arctic Silver, which I've used on
numerous high power transistor amps.
Taking for granted that the copper heatspreader and main heatsink
are milled truly flat, the crucial thing is to get the transistor
flange flat as well. The majority I've handled are not anywhere
near flat, and always bowed upwards in the centre (something that
hasn't improved since the package style first appeared ~30 years
ago). I use the method mentioned by others - fine emery face up on
glass. Mirror glass is good, as it tends to be made better and any
imperfections in the surface show up.
If the copper spreader is thick enough, the heat is spread over a
large enough area whereby the heat sink compound is less
significant and the regular white stuff can be used - but even
that varies in quality. I stick to Dow Corning or Emerson.
Don't assume your copper spreader is flat just because it was
machined so in the workshop. Most of it is rolled and it's quite
normal for it to change a bit after the hard outer layer is
skimmed off (just like timber).
Steve
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