General > General Technical Chat
Encapsulating electronics in candle wax?!
Ian.M:
It may be worth experimenting with adding a small proportion of medical grade liquid paraffin to the wax to soften it to reduce stress due to shrinkage and to make small cracks more or less self-healing.
Back to the aluminum idea - its reasonably simple (albeit tedious) to drill a bunch of holes in an aluminum block to isothermally couple TO-92 devices. As package stress must be minimized for this application, they should be slip-fit in the holes with heatsink compound to improve thermal coupling, and should be soldered to the PCB after seating them in the block.
tautech:
--- Quote from: james_s on November 21, 2020, 11:55:42 pm ---I've seen some kind of wax used in a lot of radios from the 70s-90s to cover things like coils and such to keep them from being disturbed. I don't know if it's paraffin though, and I haven't seen it used to pot an entire circuit.
--- End quote ---
And earlier.
I've seen PCB's almost covered in wax and if the stress from cooling paraffin was sufficient to damage a modern SMD design I'd eat my hat ! :P
Siwastaja:
Do not try to pot. It's more complex than you think. You'll spend a year getting it right. Before you get it right, it significantly reduces the reliability of your PCB assembly, cracking capacitors and so on.
And when you are prototyping and building small batches, 99% likely you want to open the product up to measure something, even if you were completely sure that won't be needed.
Just buy a waterproof case with proper silicone gaskets / o-rings and you're done.
magic:
--- Quote from: The Soulman on November 21, 2020, 07:53:59 pm ---Good question, I should have mentioned its for voltage reference build from a bunch of LM329 in to-92 housing for lack of availability
(discontinued) of the hermetically shielded metal can version.
It is believed the voltage over time is more stable for a hermetically shielded device because of the lack of moisture ingress/change
with seasonal changes.
--- End quote ---
I wonder if wax is really less permeable to moisture than epoxy resin.
You could try to seal the epoxy package in a TO35/TO3 metal can (2N2219/2N3055).
Still, I think long term changes in temperature may slowly affect the distribution of trapped moisture between the epoxy and the air, unless everything is dehumidified before assembly.
David Hess:
A mixture of various things is commonly used with paraffin wax to improve its performance as potting compound. Paraffin wax by itself is not very good but adding 20% beeswax considerably improves it.
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