Re: white paste


"Lostgallifreyan" <no-one@xxxxxxxxxxx> wrote in message
news:Xns97AEE1F6D50CClostgallifreyangmail@xxxxxxxxxxxxxxxx
"I.F." <dai.ode@xxxxxxxxxxxx> wrote in
news:7TR2g.3035$m4.2636@xxxxxxxxxxxxxxxxxxxx:


"Ralph Mowery" <rmowery28146@xxxxxxxxxxxxx> wrote in message
news:IER2g.8145$sq5.2397@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

"Lostgallifreyan" <no-one@xxxxxxxxxxx> wrote in message
news:Xns97AED87027969lostgallifreyangmail@xxxxxxxxxxxxxxxx
"I.F." <dai.ode@xxxxxxxxxxxx> wrote in
news:E9R2g.57197$Nh7.51688@xxxxxxxxxxxxxxxxxxxx:


<Maestro Mysterieux> wrote in message
news:jkmn42p137mgtvpvtqgdep1o6gtv2dv4o1@xxxxxxxxxx
Hi,
I disassembled a guitar amp, in order to re-solder a bad solder
joint. Now, I need to put it back together.

The PC board has a metal plate screwed onto it.
That plate also screws on to the metal chassis.I disconnected the
plate from the chassis in order to get at the bottom of the PC
board.

Between the plate and the chassis is some sort of white paste.
I want to get some more of it so that I can put on better coat;
but I have no idea what it is, what it is for, or where I can get
some.

Please advise.

Alan

The white paste is heatsink compound, which is silicon grease
loaded with magnesium oxide. In the UK I find the easiest brand to
get hold of is servisol from Maplin, any electronic component
distributor worth dealing with should stock an equivalent product.




Mmmm, goop. :)

Once you get it, remove the old with a lightly parafin-soaked rag.
(Or white spirit), taking care not to rub against plastics which
could build a
dangerous static charge of you did so.

Then apply as little of the goop as you need, Don't be tempted to
over do this, it's hard to squeeze out the surplus, and you'll get
some VERY overheated transistors in a guitar amp if you make that
film too thick. If
the heatsink surfaces are very flat, a thin semitranslucent smear is
all, if they're standard extrusions, make it slightly thicker,
definitely a milk-white smear, but no more.


I second the very thin layer. It is not a very good conductor of
heat, just
beter than air. The object is to fill in all the tiny spaces where
you do not actually have metal to metal contact. If too thick , then
it will act as a heat insulator and the transistor will actually run
hotter.



That is the biggest load of crap I've ever heard! - The manufacturers
would be prosecuted under trade description legislation if their HEAT
SINK COMPOUND was only slightly better heat conductor than air! ***
is a slightly better heat conductor than air - which would put it on a
par with your brain!

The only other possible explanation is that you are spreading
mis-information to make mischief!




Steady, it's not that bad..

It's true, if you have a thickish layer it is a poor conductor of heat.
Same would be true for metal loaded epoxy. This stuff works on the
assumption that the thickness is very small compared to its area, and if
you have too much you have too high a thermal resistance. It's designed to
take high compression, and if there's too much there, the cushioning make
that impossible.

I've seen the burned out transistors in power amps where too much was
used,
and repaired them by using a properly applied thin film after replacing
parts. Once you see that, you'll know it's true that it's a poor thermal
conductor if improperly used.

The claim that provoked my rebuttal was that bad! The suggestion that
heatsink compound has only slightly better thermal conductivity than air is
ridiculous, and persuading the OP to damage their equipment by using
insufficient heatsink compound is outrageous!

Or maybe they spread the heatsink compound that thinly themselves, and feel
that the heatsink is running cool (But the transistor isn't!) - Oh! that's
working well then.


.

Quantcast