Potting compound

Thread Starter

rjjenkins

Joined Apr 16, 2011
160
Hello
I'm looking for some kind of reversible potting compound, i.e something that sets solid but can be melted if necessary to access the parts. i.e. something with a melting point of maybe ~100C but hard when set. (The reason for wanting to encapsulate is to protect the parts from shock/movement.) Is there such a thing?
 

Thread Starter

rjjenkins

Joined Apr 16, 2011
160
Yes it's not quite liquid enough as it comes out of the glue gun - you can't really pour it. Maybe if it was heated further.
 

jpanhalt

Joined Jan 18, 2008
10,109
Waxes are made with a variety of melting points from quite hot to room temperature. Some are used to measure temperature as when heat treating metals. Just pick one that sits you.
 

Tonyr1084

Joined Sep 24, 2015
4,925
100% total encapsulation may not be needed. If they need that much support then they should be mounted in a holder of some sort. Care to share a picture of what you're working on? Simple silicone may be sufficient to hold parts up to some fairly robust shock and vibration. Which leads to another question - - - what kind of shock and vibration are you anticipating? 2G? 5G? 50G? That's also important information as some materials may not be able to withstand higher shocks and vibrations.
 

Thread Starter

rjjenkins

Joined Apr 16, 2011
160
Yes I've got something similar - polymorph. It melts at a low temperature but is still very viscous.
Some of these conformal coatings appear to be acrylic based, and although they are non-viscous and set fairly fast when brushed on, I'm not sure they would set acceptably fast if poured into an enclosure. I believe acrylic is quite difficult to work with (for amateurs)
 

jpanhalt

Joined Jan 18, 2008
10,109
Why not wax, as mentioned earlier? Beeswax melts at 65-70°C (the melting points seem to vary depending on the bee species). Carnauba and paraffin are also considerations. Beeswax and paraffin are free flowing when melted. I suspect the same for carnauba , but have no experience with it. Beeswax and paraffin are certainly cheap and do not interfere with rework, Rosin melts at 120°C, which may be too high.
 
I second the suggestion for the wax approach.

Before the advent of modern potting compounds, it was extensively used in electronics.

The major gotcha with wax is that it is an effective thermal insulator.
If your circuit requires natural convection heatsinking, it will prevent proper cooling.
 

Thread Starter

rjjenkins

Joined Apr 16, 2011
160
Why not wax, as mentioned earlier? Beeswax melts at 65-70°C (the melting points seem to vary depending on the bee species). Carnauba and paraffin are also considerations. Beeswax and paraffin are free flowing when melted. I suspect the same for carnauba , but have no experience with it. Beeswax and paraffin are certainly cheap and do not interfere with rework, Rosin melts at 120°C, which may be too high.
I’m not against wax but the melting points seem low - eg paraffin wax candles will go very soft if not melt in direct sunlight. There is micro crystalline wax but I’m not sure how free flowing it becomes when molten.
Rosin is worth investigating.
 

jpanhalt

Joined Jan 18, 2008
10,109
I’m not against wax but the melting points seem low - eg paraffin wax candles will go very soft if not melt in direct sunlight. There is micro crystalline wax but I’m not sure how free flowing it becomes when molten.
Rosin is worth investigating.
As I mentioned, wax melting points are easily adjusted and commercial products are used for measuring temperatures to at least 800°F. What temperature do you want?
 

Thread Starter

rjjenkins

Joined Apr 16, 2011
160
As I mentioned, wax melting points are easily adjusted and commercial products are used for measuring temperatures to at least 800°F. What temperature do you want?
About 100 degrees c I think. The main requirement is for it to set solid, flow freely as a liquid, and melt at a temperature that components can withstand but won’t occur in ambient conditions.

I took your interesting point about wax but couldn’t find much information on line about wax melting points and how to adjust them. I kept finding candle making sites.
 

jpanhalt

Joined Jan 18, 2008
10,109
Get beeswax and some ordinary rosin (yes, the type used to make flux and violins work). Mix the two to get the proper temperature. Source: Scientific American, Amateur Scientist, circa 1953. It was used as a sealant for a high-vacuum system.

EDIT: When some people think of wax, they think of candles and Crayons. It is really a sub-specialty of chemistry. Long before WWII, encasing stuff in Cosmoline (https://en.wikipedia.org/wiki/Cosmoline) was common for protection from rust. Even today when you buy cutting tools for machines, they will come encased in a wax.

A quick search for 100°C melting wax yielded this:
https://www.globalsources.com/si/AS/Henan-Dongyang/6008828143035/pdtl/Sasol-Wax/1049625524.htm
https://www.sasol.com/sites/default/files/content/files/0260.SAS-BR-IW_chemistry_WEB_0.pdf
http://www.sasolwax.com/products-applications/paraffin-waxes/adhesives/

Maybe you can get a free sample of 100# or so? Better yet, get some beeswax and rosin and experiment. Flake shellac can sometimes be substituted for rosin, but I believe it melts at a much higher temperature.
 
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