Casting resin as potting compound?

Thread Starter

rjjenkins

Joined Apr 16, 2011
143
Is there any reason why I shouldn't use casting resin as a potting compound? The curing process is exothermic which would not be too good for some components, but I think that if you're prepared for a slow cure, it should be acceptable.

The reason for considering it is that it's cheaper, it's less viscous, and I want to encapsulate the PCB into a mould with quite fine detail.
 

GopherT

Joined Nov 23, 2012
7,983
It really depends on the components and the properties of the resin. Dielectric constant, corrosion and thermal expansion and, therefore, mechanical stresses are just a few considerations. If it is for a hobby, then try it. If it is for mission critical aerospace components, that is another story...
 

MrChips

Joined Oct 2, 2009
19,280
Resin will shrink over time. If the volume of resin is not uniform on both sides of a PCB the board will warp as the resin shrinks.
 

wayneh

Joined Sep 9, 2010
16,102
Thermal conductivity is perhaps the biggest reason to use the higher-priced potting compound. Dimensional stability is another. So if you wanted to pot a coil, for instance, that needs to fit a tight clearance and not overheat, then Bondo may not be the best choice.
 

THE_RB

Joined Feb 11, 2008
5,430
I have used ordinary body filler (fibreglass resin with filler) with success and no visible downside?
Depends on the application.
Max.
The higher the percentage of inert filler the less the shrinkage upon curing.

Polyester resin with no fillers shrinks badly, a couple of percent, which can warp and crack electronics and rip parts from PCBs.

Epoxies and Polyurethanes generally shrink as a liquid before the gel point is reached, then have little shrinkage after gelling.
 
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