I've designed a circuit that I plan to market very soon, but I'd like to embed it in a rock-solid resin so as to prevent malicious inspection, or reverse engineering. The circuit barely draws any power, and so heat dissipation is not an issue.

Any hints as to where I could find an appropriate resin for this application?

 

Hello there. I would recommend Master Bond EP21FL once you encapsulate then try to remove it would destroy the circuitry itself and any components attached to the PCB,it is a toughened, two component epoxy system for bonding, sealing and potting. Excellent resistance to impact . Superior electrical insulation properties. Low exotherm upon cure. Long working life. Serviceable from -100°F to +250°F. Withstands 1,000 hours 85°C/85% RH.
T-peel strength 10-15 pli
generally there's four types.Epoxy, Polyester, Polyurethane and Silicone,
they are generally hard and tough and exhibit low shrinkage on cure.
They are characterised by an excellent level of mechanical properties, good high temperature performance and good adhesion to a wide variety of substrates, and show excellent chemical resistance across a wide range of chemicals.
Fast cure hardeners can be used but these generate a lot of heat during cure, giving rise to a high exotherm which can damage electronic components and cause high mechanical stresses on both components and the circuit.
Polyurethane resins are elastomeric or rubbery in their cured state and are preferred where circuits to be potted contain delicate components such as ferrites or those with fragile legs.
Polybutadiene based urethanes are available, however, and these are very resistant to water, both during the curing process and in the final cured state.
Silicone resins tend to be more expensive than epoxies or urethanes, but find a use where high and or low continuous operating temperatures (-50 to 200°C) are involved. When potting RF circuitry the potting resin can introduce capacitance effects between conductors on the printed circuit board and alter unacceptably the characteristics of the circuit.
EDIT: the the above information was provided by a mix of personal experience with the product & specifications were copied & pasted by me, from the manufacturer's website.

 

Check out Bondo Fibreglass resin, used in high performance water craft, hence it sets up Pretty HARD!

 

Black pourable polyurethane resin and make a real black box!

 

Fibre glass resin can also be coloured. !,
Resin Dye at craft stores and Amazon etc.

 

Talk to a company called Tactotek. They build circuits on polycarbonate film (silver ink printed traces, conductive epoxy instead of solder). They die-cut the film to fit into the mold and then injection-mold polycarbonate resin over the part. Resistors, LEDs cap touch can all be encapsulated. They are working on encapsulating more ICs and sensors. PC is pretty hot but new components are getting higher snd higher temp compatible.

https://tactotek.com/

a company, Shepard Lock, won an award at CES 2020 and it was made by their process. A smart door lock that links to your cell phone and NFC.

The final products are pretty cool looking (thin, illuminated cap-touch, ...).

 

Epoxy encapsulation can be a false feeling of security. I did this a long time ago. The stuff was as hard as a rock. Someone reverse engineered my circuit and a 3rd party emailed me my schematic. One of the hobby magazines did an article on how to compromise encapsulated circuits. They mentioned different chemicals to soak it in and to scrape it very gently in a process that can take many days depending on the material.

 

Someone reverse engineered my circuit and a 3rd party emailed me my schematic

When I worked at Delphi Packard Electric, we had a machine to do that. When one of the automobile competitors came out with something the EE's thought was interesting, they sent it to the RD lab. Most of the time this thing of interest was some sort of computer type module, in an aluminum finned case and filled with epoxy. Bolt it down and there was a multi tooth carbide flycutter that kept making machining passes over the item. Heavy passes at first to get into the circuit area, then very small, 0.001" passes, after each pass a digital camera took a picture of the surface of the cut. Doing it this way allowed it to capture the circuit and many times even component numbers with out an operator standing there for as long as it took. Kind of "reverse engineering on steroids".

 

Back on the topic, Loctite/Henkel sells a lot of different formulas for different situations of doing this encapsulation. https://www.henkel-adhesives.com/us/en/products/encapsulants.html

 

Kind of "reverse engineering on steroids".

Rather kind of "Pirates of machined circuitry" ...

 

To make the package much harder to analyze, use discrete wires for many of the connections, and leave them a bit above the PCB for the encapsulation. Then stripping it away will tend to break connections and make analysis more challenging. Also add extra wires that go nowhere, to add to the confusion.

 

I don't think we should be helping @cmartinez until he shares his schematic and describes the application.

Working on a schematic to show you even as I type ... but here's the application:

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I don't think we should be helping @cmartinez until he shares his schematic and describes the application.

Given that the TS did not ask for any help at all with the design of the circuit, I disagree. The question was very clear along with the explanation of why it was presented. I did not add any information about adding a detonation layer or some of the other things, only perfectly reasonable assistance. BUT when CM makes their second million on the creation I will expect them to buy the donuts for those who helped.

 

BUT when CM makes their second million on the creation I will expect them to buy the donuts for those who helped.

I'm feeling generous today ... so yes, you can expect donuts AND coffee as a token of my appreciation ... make that a cappuccino, if you like ...