Heat sink compound

[Jemison Richard]

I can't really do better than those that have already described differences
between heat sink compounds and dielectric grease.  You can get dielectric
grease at NAPA for about $5 USD.  

Rick

> -----Original Message-----
> From:	Frederic Breitwieser [SMTP:frederic.breitwieser at xephic.dynip.com]
> Sent:	Saturday, January 09, 1999 3:49 PM
> To:	diy_efi at efi332.eng.ohio-state.edu
> Subject:	Heat sink compound
> 
> >A salesperson at AutoZone tried to sell me some heat sink
> >compound stating that it was a dialectic.  Of course I challenged
> >the statement and he told me that he had used heat sink compound to
> >insure good connections.
> >Is heat sink compound a dialectic?  Curious minds want to know!
> 
> Most heat sink compounds are diaelectrics, which is an
> electronic insulator, but a thermally conductive substance. 
> Most components mounted on a heat sink either use the heat
> sink as a thermal dissapation device, or, if the heat sink
> is part of the circuit (in the case of much larger
> electronic devices sometimes), the part is bolted to the
> heat sink to ensure a reliable electronic connection as well
> as thermal conductivity.
> 
> While in college, I worked for a small manufacturing company
> in NJ, where I had the opportunity to assemble electronic
> motor brakes.  The devices varying in size from a 120V 5A
> capacity up to a 660V 120A capacity often relied on the heat
> sinks (which were 1/4" aluminum "C" channel about 2' long,
> 8" wide, and 2" high on the larger models) as a primary
> conductor.  What I found "interesting" is they were using 0
> guage cable, yet holding the parts to the heat sinks with
> severely undersized screws, which are severely narrower than
> the wires they crimped and bolted to the heat sinks.  The
> point of the story is they apparently had the same
> impression as your autozone friend, that the heat sink
> compound conducts electricity - the larger devices this
> company just attempted to introduce into the market kept
> failing due to the limited current capacity of the small
> mounting screws between the part and the heat sink - since
> the compound doesn't conduct electricity very well.
> 
> Aside from the "goo" type of heat sink compounds, there are
> a few other choices.  THere are these little mica washers
> typically used over the years underneath TO-3 transister
> cases, acting as an insulator for electricity, but a
> reasonable conductor of heat.  Not as good as the compounds,
> but they are easier to work with.  Some manufacturers have
> had problems with human-assembled products because some
> products receive more heat-sink compound than others, and
> depending on how far to the limits the unit was designed,
> "Pop" goes the unit.  Radio Shack experienced this with
> their home receivers back in the late 70's for a brief
> period.