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Im trying to find a coating for my PCB in order to protect it from reverse engineering. I want it opaque, non-conductive and with a low thermal resistance. Basically I do not want that someone replicates my circuit easily. I´ve beens searching a lot on coatings but did't find anything that suits to all my requirement. Anyone with an idea?

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    \$\begingroup\$ It is approximately impossible to stop reverse engineering. Security systems of any sort usually only keep honest people out. Two pot epoxy is a good start to keeping honest people out. \$\endgroup\$ – Russell McMahon Mar 9 '15 at 13:00
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    \$\begingroup\$ If anyone "worth their salt" can observe WHAT your circuit does then they are liable to be able to design something from scratch that does about the same. | Suggestion: Tell me the special functionality (not circuitry) that your design achieves and I'll tell you how to achieve it with no reference to your actual circuit. And, if I can't for some reason. Olin or Dave or ... will be able to. \$\endgroup\$ – Russell McMahon Mar 9 '15 at 13:02
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    \$\begingroup\$ Actually from your description is sounds like it would be much faster to replicate the circuit from functional spec than to clone it. Cloning is way overrated, and so is secrecy unless this is for military use of the like. \$\endgroup\$ – Olin Lathrop Mar 9 '15 at 13:29
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    \$\begingroup\$ Even without any efforts to make reverse engineering more difficult, a circuit like you describe is going to be simpler to reimplement than reverse engineer. You're trying to prevent people from doing something they'll never want to do anyway, and costing yourself money in the process. \$\endgroup\$ – Nick Johnson Mar 9 '15 at 13:57
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    \$\begingroup\$ So you want to make throwaway crap to fill the landfill? The only thing hiding your design does is make it harder to fix when it breaks. I seldom bother to reverse engineer something I want to copy, it is cheaper to grab a reference design. The only time I bother reverse engineering is to fix something broken. \$\endgroup\$ – hildred Mar 9 '15 at 18:31
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There is no such thing. If someone really wants to reverse engineer your circuit board, they will be able to do it. The only question is how much trouble, and therefore expense and time, it will take.

At best, you can make it too difficult for the casual copier, although that's probably not who you are worried about. The closest thing that matches your spec is to "pot" the circuit board. There is stuff called potting compound specifically for this purpose. There are many different types, from 2-part epoxy mixes, to goop that cures over time or with heat. Each has their own set of hassles and expense at your end.

If you do still end up doing this, make sure to use material specifically intended for this. Some of the potting compounds are silicone based, but there is a wide range of silicones. Some emit acetic acid as a byproduct of curing, for example. Those won't be sold as potting compound for electronic circuits. But someone seeing silocone potting compound, and then the acid-cure stuff cheaper may have a bright idea how to save money.

Silicone is usually transparent. Butalene rubber is sometimes used for potting, especially for high voltage circuits. It's really sticky and gooey stuff until cured, yucc.

Before you go potting your circuit board, think carefully about whether the advantages are really worth the significant cost on your end. Potting won't slow down much a determined cloner that already has the equipment in place. It that's who is going to copy your circuit, you are actually doing the cloner a favor by making your product more expensive than it needs to be and allowing him a nice margin to undercut you. Potting also has other drawbacks beyond just the expense. It makes the product heavier, allows for less power dissipation of components, can trap unwanted dirt and moisture, and makes diagnosing of field failures difficult.

In summary, don't pot to prevent cloning, since it won't. Pot if you need a high voltage barrier, want to withstand a harsh environment, or want to add mechanical ruggedness.

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  • \$\begingroup\$ I must agreee Olin, for the true professionals there are no barriers! But anyway my purpose was to prevent the "casual" replicators as you said...I will only scracth or cover my ICs references with pot. TY \$\endgroup\$ – eduardo Mar 9 '15 at 15:38
  • \$\begingroup\$ @eduardo there ain't such thing as "casual" replicator AFAIK. If somebody RE things for a living, he's hardly a casual. OTOH, if he doesn't, you obviously don't have to protect your design from him. Protecting from DIY hackers? duh. \$\endgroup\$ – user20088 Mar 9 '15 at 20:53
  • \$\begingroup\$ What is more likely: people buying your product, even though it is not serviceable and more expensive due to the cost of epoxy, or people buying a similar competitor's product that is serviceable and that they can modify to conform to the spec of your product since it is not covered in epoxy? \$\endgroup\$ – Sanchises Mar 10 '15 at 12:21
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    \$\begingroup\$ @sanch: Why are you telling me this? The OP is who wants to pot his circuit. I'm arguing against that. \$\endgroup\$ – Olin Lathrop Mar 10 '15 at 13:10
  • \$\begingroup\$ @OlinLathrop It was meant as a comment to the OP but I figured it was more related to this answer than to the question. I'm still sort of getting the hang of SE, sorry. \$\endgroup\$ – Sanchises Mar 10 '15 at 13:12
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I think the goal is silly, but the obvious answer is to make a multi-layer board and hide all the traces on the inner layers.

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  • \$\begingroup\$ It is a good solution but fails in therms of cost maybe more than the epoxy solution. Anyway I think now Im more confident in leaving components/traces without cover. I will only scratch my ICs references. \$\endgroup\$ – eduardo Mar 9 '15 at 15:29
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    \$\begingroup\$ @eduardo: A 4 layer board will be a lot cheaper than any "epoxy solution". \$\endgroup\$ – Olin Lathrop Mar 9 '15 at 17:23
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    \$\begingroup\$ This works well at confusing honest people. Long ago I met people who made a living keeping legacy IBM multilayer boards going long after they failure rate was usually too high to keep the systems alive. They had become expert at tracing multi layer boards with buried tracks. \$\endgroup\$ – Russell McMahon Mar 9 '15 at 22:24
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    \$\begingroup\$ I'd make a 4-layer circuit as suggested by George, and put random crap tracks on the top and bottom layers to make the thing a bit more difficult to reverse. But as many people noted, somebody wanting to reverse engineer your circuit will do it, no matter what you do. Don't forget that one can X-ray the circuit and see the buried traces... \$\endgroup\$ – Ale Mar 10 '15 at 15:06
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You can dip your PCB in silicone rubber. Once hardened this stuff is hard to get off. Makes your assembly waterproof as well :-)

But keep in mind that such measures won't even stop an enthusiastic amateur from reverse-engineering. It makes it more messy and time consuming, but that's it.

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