The common reasons for yellowing are:
1, furnace temperature is too high, high mobility, pinhole coating caused excessive copper tin penetration
2. The tin layer is too thin and the copper tin is permeated quickly.
3. Excessive halogen residue of flux and insufficient acid washing on the surface of copper
4, the packing time is too fast, the heat is not scattered, too much impurity tin
5. copper material quality is not passed, too many heterozygous
Because of the temperature effect of atomic movement speed, so the hot cold fast yellow
This problem is dealt with as follows:
1. die diameter > line through +0.02mm (the purpose is very simple can not be too thin);
2. after 2 hours after production, it can be repackaged. (purpose: internal heat dissipation)
3. the good welding flux and the concentration of the flux are mainly influenced by the flux of the soldering flux.
4. choose better oxygen free copper wire.