A unique and specific application for coatings involves tamper-proofing of electronic circuit boards and assemblies. Secure systems for military and space electronics must prevent access to stored information and prevent reverse engineering. Even some commercial and consumer products such as toys and smart cards may require such protection, e.g., preventing competitors from determining a circuit design or the nature of an IC chip.
To be effective, tamper-proof coatings must first be opaque to prevent visual examination and hard enough to prevent microprobing. Furthermore, they must be difficult to remove by the normal thermal, chemical, or mechanical means without destroying the underlying circuitry and secure devices. Hence, highly cross-linked thermosetting polymer structures that are resistant to high temperatures are better than linear thermoplastic polymers that melt at low temperatures. Polymers that have a high Tg are better than those having a low Tg. Adhesion to all surfaces should be so strong that the coating cannot be separated from the surfaces without the surfaces themselves being destroyed in the process. The coating should also be formulated to prevent non-invasive detection methods such as x-ray and neutron-ray examination. In addition to all these requirements, any coating or process used must still be compatible with the operation and reliability of the electronic circuits. Often multilayers of several different coating materials including ceramics are used in order to achieve all the desired requirements.