No good deed goes unpunished -- didn't really say that at all. First,
I gave you quite a bit of _very_ specific advice for a newbie or
hobbyist, which is the assumed audience for s.e.b., and could have been
assumed given your lack of specificity in your original post.
Something vague like your original post is charitably assumed to be the
result of lack of knowledge rather than lack of effort. If you'd spent
more than two minutes on your original post (from further posts, there
obviously was quite a lot more you _could_ have said without bumping up
against non-disclosure), or read the first couple of paragraphs of my
first response, you'd see that and not get offended.
Second, your problem extends a little beyond just heat sink compound (5
watts dissipated by an 0.5" X 0.5" X 4.5" heat sink in free still air
keeping t(j) below 100C and t(sink) below 60C). This seems to be a
very ambitious engineering puzzle, for which there is no easy answer.
Several engineers at s.e.d. have described things they've done with
heat sinks that approach witchcraft, and getting their advice might be
a good idea.
Also, there happened to be some good advice on the heat sink compound
to use in my first post. If you'll look at the website I suggested,
you'd see the Ultrastick phase change product, which has thermal
conductivity ratings better than the others, and looks like it might be
a good starting point (and will probably be cost competitive with the
higher-priced silver-loaded stuff). With something like this, it might
be best to start with the best, then see what kind of margin you have
to play with (unfortunately, I have the suspicion that your margin is
negative already, and getting a really good heat sink compound will
just eliminate that as a source of dither). The manufacturer also will
provide samples, especially if they're talking to someone who is a
potentially good customer.
http://www.aavidthermalloy.com/products/options/greases.shtml
Nobody told you to shut up,
.
