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~misfit~[_3_]

Once upon a time on usenet wrote:
"What's the grain diameter? If it's larger than the depth of the
cracks and crevasses in the aluminum extruded heat sink, then you're
taking a step backwards."

Now you're getting into the RMS finish left by the machines. In mass
production I doubt it is very good. It is likely the grain is fine
enough, in fact I have seen the results of machining on the surface
and it looks like manufacturers are derating enough or just don't
care.

"The bulk of the heat is passed by metal to
metal contact. "

Which is why I apply as much pressure as possible before tightening
any screws. The strip, some devices are mounted by clips and the
pressure depends on its modulus of elasticity. One advantage is that
over time it presses continually and closes the gap, if any.

There is this pink **** out there that has such a high viscosity that
I consider it unacceptable. It is hard to squeeze out of the damn
tube, as such it would take so much force to actually get the high
spots down to metal to metal contact that it would probably damage
the device.

I have used tools to compress these, and I know when to stop. When
you tighten the vise grips or whatever a little bit more and get no
more goop then it is pretty much done. In the case of a large STK IC
for example, I will take the old part and put it on top of the new
part so it spreads the force and isn't likely to break the case.
Squeeze the whole shebang until no more comes out.

In my opinion you should never 'squeeze' it tighter than the clip / fastener
is going to hold it. Otherwise you squeeze too much out and are left with
voids.

As far as the compound and its additives, diamond dust is probably
the best. Copper beats aluminum or zinc oxide, but diamond blows
their doors off. It also has a very good dielectric strength except
for blue diamond. Apparently whatever "impurity" is in there causes
it. I don' t feel like looking up what that is, feldspar or some ****
? Doesn't matter. Diamond does have a cost though, just how much is
that semiconductor worth ?

"The lack of flatness also causes problems when one tries to using
such a heat sink as a lapping plate. "

I wouldn't do that with a computer CPU. I have done it a few times
with other devices and that was only so mush, I did not really remove
any significant material. Truth is I was low on the "bird****" so I
thinned it out a bit. Beats nothing and the guy didn't want to wait.

Actually I have cleaned a bunch of them with coffee filters. They do
remove some metal. In fact the did it to VCR heads as well, seeing
that black on it was not dirt, it was aluminum. It is time to stop,
but the heads were about as clean as they'll ever get, and it may
have enhanced head to tape contact a bit. Just don't take off too
much or there will be a bunch of wear and there goes your gap and
azimuth offset sooner.

"If you want to see how bad it can get, take a black felt tip pen
and "paint" the top of the CPU or the heatsink black. Find a flat
surface (glass is good). Drop a sheet of fine emery cloth (2000
grit) on the flat plate. "

Actually the coffee filter should work.

That sounds like scraping. you know you have machines, and the ways
are straight. Well those are cut on machine with straight ways so
they are straight. And the ways for that machine are cut on a... this
could go on forever. What is the FIRST reference ?

Scraped on plates. People actually scrape them by hand. they have a
special surface on which the high spots are perfectly flat to withing
a millionth of an inch, but there are valleys for oil. A roller will
roll perfectly straight, or any guide that does not damage the plate.
How to achieve this ?

They take two plates that are somewhat flat and blue them and put
them together, where the bluing is not is a high spot so they take
that down with the scraping tool. The two plates eventually seem
flat, but they might not be. One could be perfectly concave and the
other convex to the exact same degree so they mate, but are not
straight. So they have to use a third plate. you can't have a concave
and a convex plate math another plate, it is simply impossible. And
with hand tools they get them within millionths of an inch. I have
watched them, and watched them sell them. Most companies do not need
that accuracy but some do. they cannot tolerate a copy of a copy of a
copy of a copy of flatness, they want the original. My friend makes
the originals.

This is more accurate than polishing granite plates or even
countertops. usually those are done with optical flats and/or light
at an oblique angle, along with a good eye. I got a few sample from
my late friend who did those granite and marble tops at his day job,
other times he was a sculptor. I commissioned him to do one but he
died so it is not done. i use those samples to process food, meat
usually because we buy in bulk. not easy lugging a piece into the
kitchen but it is worth the trouble, and I like to use on the
occasions when I make a real pizza. All the pizza places around here
just get worse and worse. They mostly suck or charge an arm and a
leg.

"thermal cycling tends to pump the grease away from hot spots
leaving rather voids"

Hopefully those voids are where metal to metal contact was actually
achieved. They are usually under spring pressure.

No such luck. They're usually where there was little contact. Metal-to-metal
tends to stay that way duriung thermal cycling as long as pressure is
constant.

I've done a lot of work on laptops, a lot of them nasty to get into so it's
best to do it right first time. I've also lapped more than my share of CPU
'spreaders' (IHSs) and (desktop machine) heatsink bases.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

"Thermal expansion in an extrusion isn't uniform and
you will see bending in the heatsink. "

Mass production. I am surprised things work as well as they do. but
all the mid fi audio amps are junk. Of course they want things to
last two days past the warranty. One day is pushing it a bit too
much.