Why isn't my solder sticking to the joint?

Question

Accepted Answer

The most common causes are: the joint isn't hot enough (increase temperature or improve tip contact), the surfaces are oxidised or dirty (clean them, or use flux to help solder wet the surface), or the tip itself is oxidised and needs cleaning/tinning. Less commonly, it's simply not enough dwell time — but per the 3-second rule, the fix is usually more heat rather than more time. A clean, properly tinned tip touching both the pad and the lead directly is the fix for most "solder won't stick" problems.