In the last decades, the supply chain of printed circuit boards (PCBs) becomes distributed with growing complexity of PCB designs and the economic trend of outsourcing the PCB manufacturing. This makes the PCBs more vulnerable to security attacks, such as tampering, snooping, and electromagnetic (EM) attacks. Because of the large feature size of PCBs (compared to integrated circuits), it is challenging to protect the PCBs from those attacks or proof the suspected attacks. For the same reason, PCBs are vulnerable to non-invasive reverse engineering by X-ray tomography as well. In this paper, we propose a novel silicon carbide (SiC) coating technique to provide passive protection for PCBs from in-field tampering, snooping and EM attacks. In addition, capacitive sensors are designed based on the SiC coating, offering active defense against those attacks. The coating and sensors can be implemented on PCBs in cost-efficient ways and the area overheads are minimized. The insulating coating also allows an extra tungsten-based painting to be applied to prevent the X-ray reverse engineering.