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More info?)
A metal surface is covered in microscopic voids & lands.
o Voids contain air - which is a poor thermal conductor
o Heatsink compound is a poor thermal conductor - but better than air
Hence you only need enough heatsink compound to fill the voids.
o Excess thermal compound increases the thermal resistance
o Eventually the excess will squish out from between the heatsink & die
o However it may not do so symmetrically resulting in hot spots
Any good compound will do, but artic silver may provide a small
benefit in some marginal hot-spot applications over conventional.
A finger with clingfilm makes a good spreader, but the ideal is a piece
of flat edged plastic which can create a thin but uniform thickness film.
As a rule heatsink compound does not flow particularly well, so at the
very thin & ideal thin film layer you can get hot spots resulting. When
you remove the heatsink you can find near dry or weak contact areas.
Plain heatsink compound is cheap enough to not use improvisation
--
Dorothy Bradbury
www.dorothybradbury.co.uk for quiet NMB & Panaflo fans