Heat Sink Paste

Several different substances are used.  The simplest is zinc oxide which is a white paste.  It is also what is used in the thick suntan block products.  From zinc oxide the choices increase in price up to a range of themally conductive metal powdered paste products.   These products are usually grey in color and act similar to peanut butter.  Once they get hot, the pressure of the heat sink mounting apparatus causes the excess heat sink thermal compound to flow out to the edge of the electrical component.  

Anything that can help transfer the heat from the electrical component to the heat sink material is helpful.  Polishing the two metal surfaces to a FLAT smooth surface before applying the paste is also helpful.  

Usually if the manufacturer mounted the component to a heat sink, then there was a good reason, including life expectancy of the component.

In military applications, two highly polished surfaces are used with no heat conductive compound, if the surfaces are truly flat and highly polished, you get really good heat transfer.

gunrunnerjohn posted:

In military applications, two highly polished surfaces are used with no heat conductive compound, if the surfaces are truly flat and highly polished, you get really good heat transfer.

Yeah, but then just a simple 7805 regulator mounted to a heat sink would cost $50.   Too much for trains!

I forget the name of it, but didn't some components used to come with a small sheet of material meant to mount between the component and the heat sink?  I'm thinking a TO-220 style case such as was common for simple regulators in the past.

-Dave

Dave45681 posted:

I forget the name of it, but didn't some components used to come with a small sheet of material meant to mount between the component and the heat sink?  I'm thinking a TO-220 style case such as was common for simple regulators in the past.

-Dave

Mica.

Mica is insulator.  G

  I think the gasket sheet was to make sure no cracking occurred when the screw tightened, should the outer case not sit flush with the metal sink. 

That or electrical isolation. I've never seen an explanation, and never had good reason to check a sink for isolation from any legs before.

I guess that as thin as the gaskets are, filling air gaps between two uneven surfaces would promote heat transfer.

There is also a rubberized material that is for heat conduction that was used for some as well.

AmeenTrainGuy posted:

It is called thermal paste. They use it between the heat sink and CPU on computers. Thermal paste is a heat conductive paste that is used to get better heat conduction. It fills in all those microscopic imperfections on the objects that can trap air in them and cause a loss in the heat sink's performance.  

I use NT H1.  Nothing better.  https://noctua.at/en/nt-h1.html

Back in the early days of electronic ignitions in automobiles heat sink paste was applied between ignition modules and the polished surface in or on the distributor. Most technicians kept a tube in their tool box.  In fact I still have one sitting around. Distributors (and carburetors) are a thing of the past and I don't miss them, not even a little bit. If you are looking for just a bit of heat sink paste ask your local garage of they have some to spare.

Earl

ASE Master Tech

No there not gone. Real cars still have them!

I used to buy the 'heat sink' grease from Radio Shack.  But don't forget the 'clear' backside with the insulator; don't leave home without it.

  I gave up working on cars because of efi "chases" of all kinds; too much work. I always kept a carb. car for winter too. The carb. motor was the only thing that always started at under 10°f...besides VWs Bosch syst.. Cars of this century, the efi is way better with computers that learn "whats best" as they work. I must have replaced 50 of my own distributor modules when they were on cars though. Heat sinked with paste or not, they were a pita I don't miss. 

In a pinch, a heavy grease will work for a while; it beats nothing.

Thanks to all who responded

Adriatic posted:

 

In a pinch, a heavy grease will work for a while; it beats nothing.

Every drug store sells tubes of pure zinc oxide it works as well as anything not specifically sold as thermal paste certainly better than a heavy grease ( which runs when hot) and it's hard not to pass a drug store per mile in any metro area. Or why not order a 2 oz tube of real thermal paste today and have it ready next time you need it. 2 oz will be a life time supply for most of us. Here is a link to about 2000 ads for thermal heat sink paste on eBay. I like the stuff with no oils or silicone in it. It does not run.  TECHSPRAY makes a good one.

https://www.ebay.com/sch/i.htm...c+paste&_sacat=0

"In a pinch" "for a while"   

A good automotive grease; 350° industrials up to 1200° and remain stable. Auto grease is a common staple. .... and what about Saturday night or deep snow... or those in the rurals? 

The component would likely cook before it hit 350° 

  Wipe it after the squish and there isn't enough to worry about in the gap to drip anyhow...."till monday". 

Thermal paste never ever dripped or migrated? No oily yellow ooze ?    

    But, in more rural areas, the sun blocker might likely already be in the medicine chest..   just maybe 

Used to see paste on early electronic train boards. I don’t see it anymore. Improvements have probably eliminated the need. It was messy.

The product I use is Dow Corning 340 silicone heat sink compound. I have a tube I've been using for several years. Stuff gets on you if you just look at it. Not sure if it's still available.

Regards,

Mike

Rod,  heat sink compound is as important today as it ever was.  I am not as fond of compounds that use silicone as the silicone tends to migrate out of the joint and get on surrounding components.   J

Agree with Mike, Dow Corning 340 was the white thermal compound I used for years in aviation electronics. It is still available, but pricey. The other product I used for personal automotive repairs (e.g. distributor HEI modules) and electronic kit building was silicone grease.