Soldering wires to PCB tabs/holes
I'm doing a lot of soldering recently, and I noticed something peculiar - most of the time, it's a non-issue to solder a wire onto a PCD tab or into a through-hole (non-english speaker, not sure what the exact terms are). But with a few modules, it seemed almost impossible to make the solder "connect" to a tab. I tried flux as well, but it took many tries, and I even ruined one module by my continued attempts.
I cannot remember anymore what those components were (I think it was some buck-boost thingy where it was really bad) - so more generally asking, are there some differences in tabs I should be aware of? Can I spot them somehow? Any different techniques I should use?
And I'm sure it's not the iron. I can move on from a "problematic" components one to another and solder just fine.