During the application of sulfate electroplating tin additives, after the workpiece is treated for a certain period of time under reflow conditions (temperature at 260°C) after tin plating, purple or blue will appear on the surface of the coating.
Author: Marisa
During the application of sulfate electroplating tin additives, after the workpiece is treated for a certain period of time under reflow conditions (temperature at 260°C) after tin plating, purple or blue will appear on the surface of the coating.The plating turning purple will affect the solderability of the plating or cause mounting failures, which many customers do not accept. Why does the plating turn purple?
According to the on-site experience and product characteristics, there are mainly four reasons:
1. Oxidation of tin. The tin plating layer is oxidized at high temperature, and the different thickness of the oxide film is directly related to the high temperature discoloration. Generally, the oxide film is blue when the thickness is 20~30nm at high temperature, and purple when it is 30~50nm.
2. Porosity. The plating solution or impurities enter the pores of the plating layer, and some directly reach the substrate, causing high temperature purple. The increase in porosity is related to poor substrate, improper pretreatment, additive performance, turbidity of the plating solution or improper operation during electroplating.
3. The influence of impurities. Impurities at high temperature will cause tin oxidation and discoloration, and the diffusion of impurities such as copper into the plating layer will cause serious discoloration.
Paying attention to the above 3 points can prevent the tin plating layer from being oxidized and turning purple, which affects the quality of the workpiece, and can also better use sulfate electroplating tin additives.