Glue to fix a thermal fuse on a ceramic resistor

[Swake]

Hi all,

To repair a Voltex power supply in a HP 4155A I need to fix a thermal fuse (133°C) to a 10W (or more can't remember) ceramic resistor above it.

What glue should I use? Is UV solder mask glue good enough up to that temperature?

[fmashockie]

Why not use some RTV silicone? That stuff will hold well above that temp.  And its easier to remove if you need to repair something.

[Swake]

Silicone is more of a thermal insulator than conductor.
The idea here is that the thermal fuse should 'monitor' the temperature of the resistance.

[coppercone2]

get a few and experiment with it.

they don't have magic, the resistor can probobly go alot higher then the fuse that was put on it. they account for the glue

and honestly if the fuse goes, you probobly want to replace the resistor. if they expect anything different, the power supply is built stupid. Its not a feature for regulation, its a feature for gross failure

[fmashockie]

Silicone is more of a thermal insulator than conductor.
The idea here is that the thermal fuse should 'monitor' the temperature of the resistance.

Mmm true.  this stuff works really well.  It's very strong.  I use it to secure peltiers to thermal block.  But it is expensive.  https://www.digikey.com/en/products/detail/mg-chemicals/8329TFF-25ML/9608260

[inse]

Fix it with wire?

[Ian.M]

What about a dab of heatsink compound for the thermal contact then wrap it with Kapton tape?

[wraper]

Silicone is more of a thermal insulator than conductor.
The idea here is that the thermal fuse should 'monitor' the temperature of the resistance.

Nonsense, from datasheets where it's mentioned I've seen RTV silicones generally to have about half of thermal conductivity of a cheap white thermal paste, about 0.3-0.4W/m·K

[Swake]

I like that idea with the Kapton tape. Easy and reversable.

[Swake]

RTV silicones generally have about half of thermal conductivity of a cheap white thermal paste, about 0.3-0.4W/m·K

If it has 0.4W/mK it is not thermal paste, whatever the label on it says. Cheap thermal paste is an order of magnitude better. Expensive paste 2 orders of magnitude.

[wraper]

RTV silicones generally have about half of thermal conductivity of a cheap white thermal paste, about 0.3-0.4W/m·K

If it has 0.4W/mK it is not thermal paste, whatever the label on it says. Cheap thermal paste is an order of magnitude better. Expensive paste 2 orders of magnitude.

Figure for silicones, not thermal paste. Order of magnitude better is not a cheap thermal paste but quite expensive. Unless you take BS performance claims for granted. EDIT: and two orders of magnitude is non existent.

[Wallace Gasiewicz]

I used some Plumber's Epoxy. It worked well as a thermal conductor and electrical insulator.But it is VERY strong and Hard.
Epoxy Plumber's putty available ar hardware, also known as "Pig Putty" which I believe is the same stuff sold for other purposes.

[wraper]

Here you go https://mgchemicals.com/category/grease-for-electronics/thermal-paste/ Starting from 0.7 W/(m∙K)

[Swake]

That is already twice as good as you claimed. Here is the explanation on why it is like that: https://en.wikipedia.org/wiki/Thermal_paste

Tom got some other examples: https://www.tomshardware.com/best-picks/best-thermal-paste
Many are over 40 W/mK in this list.

[wraper]

That is already twice as good as you claimed. Here is the explanation on why it is like that: https://en.wikipedia.org/wiki/Thermal_paste

Tom got some other examples: https://www.tomshardware.com/best-picks/best-thermal-paste
Many are over 40 W/mK in this list.

Do you confuse thermal paste with liquid metal? 

[wraper]

That is already twice as good as you claimed.

I say it again, I wrote a figure for RTV silicone, not thermal paste which start about twice better than that. But you don't need performance even of cheap thermal paste either because you don't have much power to transfer into heatsink. And the best you could do is use inexpensive but long lasting thermal paste and a springy metal clamp to keep resistor and fuse together.

[fmashockie]

Yea what I had in mind originally was ensuring the resistor and fuse were making contact physically, (maybe using some thermal paste in between).  and then add the RTV silicone over it to keep it in place.  Just like the kapton tape suggestion.

And not all RTV silicones are made equally.  Here's an example of a thermal conductive RTV silicone.
https://docs.rs-online.com/d8cf/0900766b80f8df6e.pdf

Most thermal pastes are silicone-based as well.