How to protect trade secrets on board with SMD components?

Question

I have a design which uses a secret technique, and I would like it to remain secret, at least for a period of time. My plan was to pot the board in epoxy. Specifically, MG Chemicals 832TC is advertised as providing "superior protection from ..., and analysis".

But then I read on PottingSolutions.com that epoxys can shear off SMD parts due to thermal expansion or contraction, especially below the glass transition temperature. It seems that the very properties that make epoxy hard to remove are those which are incompatible with fragile SMD parts.

What is the recommended way to protect trade secrets on boards with SMD parts? I was considering applying a thin coat of silicone and then filling the rest with epoxy. If it matters, this will be inside of an aluminum box.

Answer 1

I find it extremely unlikely that your product could contain 'secret' methods that can be implemented with recognizable discrete components. If anything, actual innovative design that is worth keeping a secret is at least done on the chip level, but more commonly on a process level. Things that can be implemented with discrete or at least non-custom components are most likely just obvious designs.

That being said: you're not going to have any legal force by keeping stuff secret. This is exactly what patents were made for. You don't have to increase the cost of your product and screw over the customer with unnecessary protection measures and on the other hand you get the complete right to deny any of your competitors your technology. Otherwise they'll know there's something juicy in there, reverse engineer it within .4 of a femtosecond and hide it in their products. Even if you find out, you have no way whatsoever to stop them from using the same not-so-secret.

Answer 2

I sneak my personal stock through the back door of a German producer, so I don't know any brands or numbers in an official manner, but there are low shrink and low warp epoxies as well. Although low is not zero, so if your parts are very, very fragile it may still not be safe enough.

You can add a thin layer of flexible material like silicone, but remember, this makes your epoxy much more easy to tear off of the PCB as well.

A good way to limit shrink and warp is preventing large thermal differentials over the entire area to be filled. This can be done by potting in layers, where you add a new layer when the last one is tough, but still lightly tacky.

Answer 3

Instead of building an ultimately penetrable bunker around your widget, institute a poison pill or a scorched earth policy, make it smart enough to determine whether there's any hanky-panky going on and, if so, have it destroy itself and, possibly, its environs.

Answer 4

There's a couple of methods you can use to make reverse engineering more difficult that don't require expensive methods like potting. Here's a couple:

1. Scratch off IC markings with an exacto blade. Even a sharpie is sometimes enough so someone can't read the IC marking (oh it's an LM314), see the company logo (oh it's a linear technology power supply), or read the processor family name (great they use the NXP1700 series).

2. Design the board with all traces in middle layers. Now they can't reverse engineer connections without expensive X-ray equipment. Route everything through the middle and use vias near the pins to make the connections.

Again, this will only slow someone down. If they really wanted to and had the time and money, almost anything can be reverse-engineered.