PCB Design and Routing
Proper engineering practices should always be exercised. Traces should remain as short as possible. Differential signal lines should be aligned parallel even if located on separate layers. Noisy power supply lines should be kept away from sensitive digital and analog lines. Properly designed power and ground planes should be employed to reduce EMI emissions. Additionally, any unnecessary testpoints should be removed from the design, as they allow unwanted noise and interference to pass through the PCB. If testpoints are required, consider using a copper-filled pad as opposed to a through-hole pad.
Critical traces should be hidden on inner board layers and trace paths should be obfuscated to prevent easy reverse-engineering of circuitry. Use buried vias, which connect two or more inner layers but no outer layer and cannot be seen from either side of the board, to reduce potential probing points for the attacker. Be aware of electrical noise issues that these modified traces may introduce.