The genuine potting compounds are expensive, I need some ideas for cheap alternatives. Poundland epoxy adhesive? Car body filler? Bathroom silicone? Something else?
I envisage the encapsulated circuit will be a 2-3cm cube with four flexible wires emerging from one face.
Any ideas for moulds and release methods will be welcome too.
I have little knowledge and interested in this thread.
All I will say is avoid anything that gives off acetic acid when curing. This is pretty good at destroying any metal surrounded by the offending compound.
You need something that flows well. Many trap air so a vacuum chamber setup should perhaps also be considered.
That looks similar to something we used 20 years ago. We called it a Brent Key, but Google just gets you an American football coach.
No, the reason I want to pot it is just for robustness. It's not my design anyway. It's an ATTiny85 LD to DTMF converter that will live inside a rotary dial telephone. Building the circuit was easy enough, but it took me weeks to discover the correct way to program the chip.
En el artículo , Graham. escribió:
Hot melt glue? Cheap and cheerful.
Melt it in a tin can on the stove, rather then use a gun - the amount you will need to use is too much to do in one go with a hand-held gun, and you can control the temperature to get the viscosity right for pouring , i.e. make it sufficiently liquid so it'll flow into voids.
use clear casting resin available from craft shops.
Or in fact I think there are resins designed for electronics
Make silicone rubber mould
Avoid anything that has acetic acid cure - ie. smells of vinegar.
Small enough that you shouldn't have too much trouble with overheating. You could get away with alumina filled epoxy.
The hot melt rigid silcone rubber would be one other choice available from craft shops (intended for making moulds) or hot melt PU glue. Why does it need to be potted?
What environmental conditions must it survive in?
Find a plastic bubble package shape about the right size and silicone oil. Proper moulds available in craft shops. Or make a one time mould in wood or plaster of Paris coated in beeswax furniture polish.
Definitely silicone not epoxy. The inside of a blob of this can get very warm indeed. assuming no dissipation issues in the circuit itself this ought to work. However I remember doing something like this with a resistor back in the 80s to set up an alarm system where both cutting and shorting the wire set the alarm off, but even in epoxy water from condensation got inside eventually and started false alarm triggering.
Cpc used to do some nice cheap little potting boxes in plastic.
Brian
Curious mind wonders why bother converting, LD still works on POTS lines. I guess modern PABX's may have dropped it though assuming, analogue not VOIP...
As it's going to be inside a phone, potting also seems a bit overkill just for robustness. Reverse engineering is another matter.
for waht to choose...
is clear polyester
Or many other places for epoxies and polyurethanes
You can use any of those & more, though I'd also avoid acetic curing silicone. Use a 380ml cart rather than pricey per ml poundland epoxy. If there's nothing high impedance in there even cheap acrylic sealant should work.
Mould release: very thin polythene sandwich bag.
Potting does seem overkill. If your construction is flaky a layer of glue on the topside of the PCB should fix it.
NT
What are you building that needs potting?
I did this as a teenager, and it worked fine. Moulds and release wax come in kits for craftwork (or did 40+ years ago).
Clear castings can look good, but you can add dyes if you want. For best results, being able to pump down with a vacuum pump can help remove bubbles, but it's not essential.
not needed at all. For the OP's use I'd want to add bubbles.
NT
Potting does seem a bit overkill to me too.
To get good water protection, some mechanical protection, and reversibility you could use paraffin wax.
For mechanical protection something from this range
Then trap the board inside the box with four cable ties retrained by hot melt glue
If you really want to pot it then
I've used the Robnor stuff in the past.
Lots of waste even with the smallest packs unless you are churning out a few dozen at a time and pot all at once.
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