We do this a lot in the oil patch with our industrial electronics. Also keeps prying eyes off our circuits when we use the black potting epoxy versus the clear stuff. The only caveat I would recommend is to insure that any heat sinked components are not completely submerged so the fins of the heatsink should protrude by at least 1/4" above the epoxy surface. So to keep the stamp cool, make sure you use darlington drivers and the like and heatsink these as required.
What to heatsink? I run my circuits for 48 hours continuously and then measure surface temperatures. Anything really high (say hotter than fresh McDonald's coffee a la Thelma) should be sinked.
Keep in mind that once you pot a circuit, that's all folks - kinda like a balloon, one pin and it's all gone (unless you have access to liquid nitrogen).
I don't know about the GC epoxy that you mentioned. I use 3M potting epoxy DP270. It has very low viscosity and very long pot life, so it flows well to fill voids. The 3M system uses an hand operated gun and a mixing nozzle to inject the epoxy free from bubbles and in perfect proportions.
In general I don't like to pot circuits. A coating of silicone resin offers protection and is repairable. But it is not enough for extremes of protection where a circuit has to be right out in the rain. I usually use a heavy coat of silcone resin on the circuit before epoxy potting, because the resin has a certain amount of flexibility that the epoxy does not, so I believe it acts as a cushion for terminations of components like surface mount capacitors that are easily damaged by flexing or expansion and contraction cycles.
It has been awhile since I have used epoxy so I cannot remember which brand we used. For the frugal amongst us, you could go to a hardware store and buy general purpose epoxy and put in some black, non-conductive paint. This works in a pinch but the only drawback is the air bubbles in the mixture. I am like Tracy in that I do not like potting circuits but sometimes you gotta do what ya gotta do.
We also took the numbers off the IC's with a dremel tool before potting. Alternatively I have been told acetone (nail polish remover) can remove the IC numbers, then you can put a reflective paint on the IC's, and then epoxy. Between all those steps and the general BS-2 characteristics, this should keep KAOS out of the PCB designs. And yes all of these steps sound like extreme paranoia but some companies have been known to resort to all of these tactics to keep the competition honest.
There are many 3M distributers, but one good source online is McMaster-Carr:
---www.mcmaster.com
--- type epoxy in the search box.
7467A18 epoxy DP-270
7467A43 applicator gun
7467A12 mixing nozzles
Another epoxy I keep around the shop is one that is available in many hardware stores, called JB Weld. It is a slow setting epoxy with better than average high temperature performance. It is pretty good for gluing heat sinks and for emergency potting out at field sites.
Eric R
Posts: 225
Comments
We do this a lot in the oil patch with our industrial electronics. Also keeps prying eyes off our circuits when we use the black potting epoxy versus the clear stuff. The only caveat I would recommend is to insure that any heat sinked components are not completely submerged so the fins of the heatsink should protrude by at least 1/4" above the epoxy surface. So to keep the stamp cool, make sure you use darlington drivers and the like and heatsink these as required.
What to heatsink? I run my circuits for 48 hours continuously and then measure surface temperatures. Anything really high (say hotter than fresh McDonald's coffee a la Thelma) should be sinked.
Keep in mind that once you pot a circuit, that's all folks - kinda like a balloon, one pin and it's all gone (unless you have access to liquid nitrogen).
Hope this helps.
Regards,
Gerry
What epoxy do you use?· I also prefer to keep prying eyes out of some of our circuits.· Right now I grind off the IC identifications with a dremel.
Chris Isaacson
I know Mouser sells about the same stuff also
In general I don't like to pot circuits. A coating of silicone resin offers protection and is repairable. But it is not enough for extremes of protection where a circuit has to be right out in the rain. I usually use a heavy coat of silcone resin on the circuit before epoxy potting, because the resin has a certain amount of flexibility that the epoxy does not, so I believe it acts as a cushion for terminations of components like surface mount capacitors that are easily damaged by flexing or expansion and contraction cycles.
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Tracy Allen
www.emesystems.com
I did a quick search using current vendors and only found GC.
Here is a 3M toll free number you can call to locate a place to purchase the 3M 2-part, black, epoxy potting compound: 1-800-245-3573 .
Regards,
Bruce Bates
It has been awhile since I have used epoxy so I cannot remember which brand we used. For the frugal amongst us, you could go to a hardware store and buy general purpose epoxy and put in some black, non-conductive paint. This works in a pinch but the only drawback is the air bubbles in the mixture. I am like Tracy in that I do not like potting circuits but sometimes you gotta do what ya gotta do.
We also took the numbers off the IC's with a dremel tool before potting. Alternatively I have been told acetone (nail polish remover) can remove the IC numbers, then you can put a reflective paint on the IC's, and then epoxy. Between all those steps and the general BS-2 characteristics, this should keep KAOS out of the PCB designs. And yes all of these steps sound like extreme paranoia but some companies have been known to resort to all of these tactics to keep the competition honest.
Just a quick comment.
Gerry Shand
---www.mcmaster.com
--- type epoxy in the search box.
7467A18 epoxy DP-270
7467A43 applicator gun
7467A12 mixing nozzles
Here is a data sheet:
www.emesystems.com/pdfs/parts/DP270.pdf
Another epoxy I keep around the shop is one that is available in many hardware stores, called JB Weld. It is a slow setting epoxy with better than average high temperature performance. It is pretty good for gluing heat sinks and for emergency potting out at field sites.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com