1) coating weight: thicker, the better. But thicker more Tin consumption, higher costs.
2) Tin-iron alloy layers: more micro-keys the better, characterized by ATC and its thickness;
3) dissolution of iron: the ISV, the less value the smaller the Tin layer microporous;
4) steel matrix surface impurities: the PLA, this value is the smaller, the better;
5) Tin grain size: observed by treatment, grain is, the larger the better.