VK Logger Ham Radio Forum Archive

Hi all

What is the best way to mechanically AND thermally mount a loose thermistor to an aluminium chassis?
The thermistor will be under the PCB (with clearance), close to where the PA active device's stud passes through the chassis.



This is inside a 1980's era Philips FM828/25A Power Amplifier.
The thermistor leads will run out, so that ultimately, software monitors the temperature.

At the moment, one side of the thermistor connects to +5V.
It would be easier if it connected to ground instead, but it doesn't.

My initial thought was to araldite the leads in place (leads insulated, of course), and use normal heatsink compound with the thermistor's head.
Unless there is thermal compound that is also a "glue"?

Or a glue that has uniform thermal properties from cold > hot and is reasonable at conducting heat?

Any suggestions please?

How about a solder lug with heatshrink over the tab holding the thermistor body in place then heatsink compound over the top?

In the past I have used ARCTIC SILVER ADHESIVE - it's a 2-part epoxy suchly:-

http://www.ebay.com.au/itm/Arctic-Silve ... 27c8e9294e

It is thermally conductive but electrically non-conductive, and is excellent stuff for 'gluing' high-power LEDs, transistors, non-inductive power resistors and etc.

It is fairly expensive but actually 'goes a long way'. I keep mine in my refrigerator along with my AARON ALPHA cyanoacrylate (the best super glue !), but let it warm up
to room temperature before use. Clean your surfaces with methylated spirits or isopropyl alcohol etc., and spend a bit of time to thoroughly mix the two components. My tubes
are still useable after 2 years in my refrigerator. The thinner the glue is applied the better it conducts heat. For your use you will only need a match-head sized blob of each component.

You will find other uses for this good stuff...but note :- there is a thermal paste vs a thermal glue.

EDIT:- the link I posted to eekbay is not necessarily the cheapest or best for you - there's an Australian seller which will likely be faster with delivery.

Bill VK5ACY
PF95sb

Thanks Lou & Bill.

A solder lug is a good idea, but does add some mechanical "hassle".
I never knew the thermal adhesive existed... never needed it before, I guess.

After a bit of research today, I was interested in thermal conductivity of plain old Araldite glue.
I used the heatsink compound on hand as a starting benchmark, which was 0.9W/mk.
Maybe the Araldite would be ok?
Nope!
It's 8.4 x better than air though.

I could not find any data on the Artic Silver product (except MSDS), but before I pressed the "Buy It Now" anyhow, I discovered "Heatsink Plaster".
This stuff is primarily made for the PC market, to glue heatsinks onto CPUs etc that do not have proper mounting tabs - hmmm... that sounds familiar.
Gets plenty of positive reviews (albeit from cap on backwards wearing PC gamers!).

As a bonus, good old Jaycar stocks Heatsink Plaster, cat # NM-2014 $7.95.
Will duck out tomorrow and get some from the local store.

@0.671W/mk, its thermal conductivity isn't as good as the $30 kit from RS, but it's 1/4 of the price.

If you're in no hurry, then it can be purchased off eBay for under $3.50 delivered, ex Hong Kong. I'm not sure about his 1.2W/mk claim though.
But then again, if the 1.2W/mk figure is correct, then even better!

Will give this gunk a try.

arctic silver thermal adhesive/epoxy would be the most suitable. it should be designed for high temperature applications.

the problem with araldite is the bond softens above 60 degrees. while your design temperature might be well under that it's important to consider the failure modes of having the thermistor come loose if the glue weakens.

I have used superglue on computer heatsinks with good effect, gluing metal to ceramic (cpu surface, that should suggest the age!!). a blob of thermal paste in the middle and a small dot of superglue in each corner then press it on and hold it in place until the glue takes. that heatsink was never coming off again!!!

I got a tube of the heatsink plaster - brilliant.
Has a consistency similar to normal heatsink compound.
Gets tacky after 10-15 minutes.
Came back to it an hour or so later, and set nicely.
Very use to use, just squeeze it out of the tube.


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