If it can be x-rayed, it's not that hard to figure out the wiring.
(I've done it with help from my very curious and helpful dentist <G>)
Are the component values important?  If so, consider adding dummy
components and circuitry that does nothing (using the no connection
  pins on the DC-DC convertor).

You want a compound that is hard but not rigid.
Rigid is easy to chip off or grind away. If it is flexible, it is
a bugger to grind, but can be pried, peeled or cut away.

Make sure to have largish holes through the board so that the
compound passes through and binds together top and bottom.
Makes it harder to chip or peel off.

The thermoset plastic that is used for ICs is ideal, but not
readily found. I would suggest 2 part fiberglass resin or
auto body putty, but your circuit will probably need a conformal
coat for protection against leakage and possible corrosive
effects. "Bondo" is cheap and very hard once set up,
and available anywhere. It is viscous initially, and then
sets up very solidly, but it does release a fair bit of heat
if you have a thick blob. Just use less catalyst then recommended
to slow the reaction down.

Have fun keeping the thieves out. If they want it badly enough,
they will get it.

Consider making the IP into a 'module' that you can entirely
encapsulate. Something like the AC-DC power bricks one can buy.
If it looks like a 'vanilla' brick, the chances of attack are slim.

Robert

Jesse Lackey wrote:

> Hello all,
> 
> I've just finished a product that uses a specialized dc/dc controller 
> (designed for a wholly unrelated field) with some further tweaks to 
> solve a particular thorny problem.
> 
> It took three major redesigns to get here, 100s of hours, etc.
> 
> But... it could be easily copied.  And can't be patented.
> 
> So... at the very least I'm going to (carefully) sand off the markings 
> on the IC.
> 
> But it would be great to seal everything up as well.  Only the dc/dc 
> section need be protected, there is no need to encapsulate everything. 
> Ideally just a tablespoon of viscous goo poured over it.
> 
> Now I realize there are limits to what can be protected, the goal is to 
> make it hard enough that casual poking around won't yield any clues. The 
> product is a specialized enough thing that there aren't many companies 
> in the business field that would be interested in it, so it doesn't need 
> to withstand some concerted, well-equipped "attack".
> 
> Has anyone been in this situation before?
> 
> Any advice appreciated!
> Thanks
> Jesse
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