thermal goo

[SparkyTris]

Please see attached. I had to dismantle this PCB to repair a connector. I prised the FETs off this dried goo, which I guess must be some thermally conductive glue.
is there any secret sauce to this, or could I just use any "RTV" setting silicone tube (like the tubes of goo that come with Furuno radars to seal the screws against the weather)

does instant gasket RTV work? (I did check thermal conductivity values in the data sheets but decided that couldnt be trusted bcs the units they specified were so w@nk.

 

[Jurassicspark]

)

does instant gasket RTV work? (I did check thermal conductivity values in the data sheets but decided that couldnt be trusted bcs the units they specified were so w@nk.

What units did they specify? Was it in W/MK?

Using a random RTV silicone isn't recommended it could be electrically conductive or even a good insulator sometimes (generally speaking)
Some can also be corrosive and damage the pcb.

 

[gman76]

Electrolube HTC is what I would use.

 

[mikeyd]

Don't use RTV.

Try searching for heatsink compound

I use https://uk.rs-online.com/web/p/thermal-grease/0554311 at work but you can probably get equivalent next day from other places.

 

[bernardgreen]

I also use https://uk.rs-online.com/web/p/thermal-grease/0554311?gb=s

 

[JohnW2]

Using a random RTV silicone isn't recommended it could be electrically conductive or even a good insulator sometimes (generally speaking)

I thought that all silicones were non-conductive (good insulators) once fully cured, and that RTS ones were generally even non-conductive before fully cured?

Some can also be corrosive and damage the pcb.

That is certainly true. 'Standard' silicones which give off acetic acid vapour (i.e. which smell of vinegar) should not really be used on PCBs.

 

[morqthana]

Thermal pads?

Sheet plastic for FET thermal isolation on a heatsink?

Given the traditional mica thermal pads and thermal paste for isolating FETs to heatsinks... Any reason one couldn't cut their own out of the clear plastic sheets like you sometimes get at a craft store or with notebooks? Is that a common thing? I've also recently used silicon pads without...

www.diyaudio.com

 

[SparkyTris]

Yeah this stuff isn't usual white/grey non-setting thermal compound for use on CPU's, etc. this is some sort of glue which provides the mechanical hold-down too.

 

[SparkyTris]

because there is no other bar or similar that we normally see holding TO220 packages in close squeeze with their heatsink

 

[Gasguru]

Given the lack of screws on those FETS it does look like a simple mechanical bonding rather than proper heatsinking.
Use Dowsil 744, it's an electronics grade silicon that only releases non corrosive alcohol solvents during cure.

https://uk.farnell.com/dowsil-formerly-dow-corning/744-white-310ml/rtv-silicone-744-white-310ml/dp/521838

 

[SparkyTris]

pricking around with a thermal camera, thought I may as well do an experiment.

 

[SUNRAY]

pricking around with a thermal camera, thought I may as well do an experiment.

That's pretty conclusive