a microelectronic device is rendered resistant to reverse engineering by encapsulating it in a dual layer encapsulant . the inner layer is compatible with the operation of the device , and has a greater resistance to chemical attack then does the device . the outer layer includes a filler of barium sulfate and gadolinium oxide , to absorb x - rays and n - rays respectively , is more resistant to chemical attack than the inner layer , and includes a groove around its periphery , to preferentially allow chemical attack radially . a full chemical attack damages the device beyond usable inspection , but a partial chemical attack is insufficient to remove x - ray and n - ray concealment .