in the concentration of material

There are more coating defects, pores, cracks and other such defects, pores, cracks, which will penetrate the bath can not be removed by washing, so that the excess organic inclusions. Compared with tin-lead plating, tin plating generally crystalline pure coarse irregular crystalline particles large crystal defects is greater. So pure tin plating discoloration problem is molybdenum plating more serious than tin-lead.Tin oxide, tin oxide, the main reason for the high temperature color, so the thickness of the oxide film is directly related to temperature change color. The induction of certain factors in pure tin plating will produce a certain color of the oxide, these factors include metal impurities, organic matter, temperature, humidity, etc., showing the colors can be yellow, blue, and purple.
Porosity Porosity is also an important factor in purple. Bath and impurities will enter the pores, even straight Scientology, which leads to high purple. The increase in porosity and substrates (such as alloy segregation, the substrate heat treatment, surface crystallization point there is not conductive), the first mishandling (such as residual oil, without a net removal of the oxide layer, over-etching, etc.), performance additives, turbidity bath, plating conditions (such as current density) and so on. Can not be ignored is the grain gap, these gaps may form tiny pores.
Factors such as impurity diffusion of impurities into the copper plating severe discoloration in some frameworks such as SOT223 serious purple on with this. High Tungsten eletrode may promote organic tin oxidation discoloration, bright tin plating more than the matte color with high organic matter related to the impact.
Additives as Sn2 + electronic structure no empty d orbitals, so in electroplating, a complexing agent for tin deposition control action is very small. To form good crystallinity, the need for large surfactant molecules adsorbed by way of plating, influence on the plating process. These additive component adsorption, inclusion in the coating the coating yellowing. Therefore, from the additive is to solve the yellowing problem begin an important way.
The specific method is: use in the coating mixture and fewer additives adsorbed component. Additives to improve the ability to control the crystallization, crystalline form as perfect minimize crystal defects. The crystalline particles closely arranged at the boundary between crystal grains to reduce the gap. Avoid the use of another color, or both adsorptive after oxidation of the components of the color. Enhanced stability of the bath, the bath to prevent turbidity.
End the current lead in the electronic plating pure tin plating has been widely adopted, but the process is still widely used in the early beginning, some technical aspects is not very mature. Tin whisker problems still exist, coating discoloration problems and bath turbidity problems. These issues require in-depth study, to be addressed to promote lead-free pure tin plating technology.