When I hand-assemble boards, I always use lots of flux, and test connections for continuity. Nevertheless, I still encounter flaky connections, particularly with through-hole header pin connectors. Over the past few days, I was debugging a seemingly random problem that would usually (but not always) go away when I connected my scope probes. The torque from the probe clamp on the header pin was improving the connection, making the problem go away.
Is there any systematic way to test for these kind of problems?