Typically only one component of a device will be security hardened (e.g. a security element such as STSAFE-A100) and it will be designed to protect against side-channel attacks. You won't be able to find any information about the measures and resiliency online though - you'd need to chat with vendors for that kind of info (even then, unlikely).

PCB assemblies are pretty impossible to secure in themselves so you have to confine security functions to a small portion of the system and work hard to make sure nothing leaks from there.