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Mike S[_4_] Mike S[_4_] is offline
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Default Heat sink grease

On 4/21/2018 10:31 AM, wrote:
On Sat, 21 Apr 2018 15:13:02 +1200, "~misfit~"
wrote:

Once upon a time on usenet
wrote:
"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. "

Disagree. What seem like voids are either the points of actual metal
to metal contact or so close that you can't see the compound.
Remember I said a bead or daub, if it is spread it is almost for sure
not even and that will cause actual voids where it traps the air at
the low spots of the compound. Some of those clips are too weak to
overcome the viscosity of the compound, and some of that aluminum
stuff they make the heatsinks out of is very soft and the screws
might strip. The main thing is not to let it come up or move. If it
is done right they are usually stuck pretty good though.


I've pressed very hard on some components, watched the compound come out all
around then, on relasing the pressure to 'fastener pressure' have seen some
of the ooze suck back in and sometmes air suck back in. Granted these
weren't on ideal surfaces but since then, on those types of interfaces I let
the fastener do the squeezing.

"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."

Agreed, with anything. It's been said "How come there is never enough
time to do it right but always enough time to to it again". I have
even told people now and then "Hell no I don't want to do it right, I
just don't want to do it again". I also don't want the liability, if
the part fails guess what ?

"I've also lapped more than my share of CPU
'spreaders' (IHSs) and (desktop machine) heatsink bases. "

I haven't done that many processors in PCs, I just follow
instructions. I did much work in power supplies and amps,
unfortunately lapping is simply impossible on most. I also agree with
Jeff Leiberman's caveat about making the surface concave. If you do
that it could be worse than not lapping at all.


I have variously sized bits of glass that I use as backing for the wet'n'dry
sandpaper that I use to ensure relative flatness. The glass isn't as flat as
gauge blocks but it's sufficient.

I only lapped in some
output ICs once actually. I was extremely low on compound so I
thinned out what was leftover and lapped with it. The ICs required no
insulator being a totally plastic package. At the end of the lapping
I had them in position and moved no more so that if there were any
larger particles in there they would stay put, embedded and not keep
the surfaces away. The only reason I was even able was because I was
retrofitting a pair of LM3886 in place of a big STK and made a clip
that went from one mounting screw to the other. I had plenty of room.
(I would have put i pre outs and had the guy use an external power
amp but the damn tone controls were in the global feedback loop)

Luckily I don't have to do much of that anymore or I would have a
caulking gun full of compound like this one place I worked. Makes it
easier to apply and I would never run out. They did but it took years
even with a bunch of techs working.


For laptops, desktops and critcal ICs I use Arctic Silver. I bought a 'PC
builders' size syringe of it. For less critical stuff I use either
Electrolube HTC or, for 'cheap jobs' that need a lot of it and have large
contact areas / raditaors (mostly aluminium LED PCBs to heatsinks), stuff I
get from AliExpress.

The reason the glass is so flat is because it is floated on molten tin
in order to flatten it. So it should match the curvature of the earth.
Though not flat enough to use as a surface plate for much of the
inspection work I do it is still very flat and plenty good enough to
use with wetordry paper to flatten stuff like the sealing surfaces for
air compressor reed valves.
Eric


Interesting. I remember reading that ocean water is higher near
underwater mountain tops due to increased gravitational attraction and
measurable from satellites, I wonder if tanks could be designed with
non-flat bottoms to counteract what you mentioned.