|
Methylsulfonic acid (MSA)-based tin-lead plating solution produces suspended solids that may cause rough plating and excess solder on plated parts. In this paper, the composition of these particles was identified and, based on the experiments done and historical data, a mechanism for the formation of the rough surface morphology was proposed. Monitoring the turbidity of the plating solution is important in ensuring the quality of plated parts. Turbidity is caused by suspended particles and published literatures confirm that the presence of suspended particles is one cause of rough plating. This study confirmed that plating solution turbidity was brought about by suspended stannic oxide particles in the solution. Furthermore, the protrusions caused by localized deposition of tin in the electrode induced the rough surface morphology of the plated parts. The availability of oxygen in air is a significant factor in the formation of stannic oxide in the solution and should be minimized. Since different plating chemistries have different absorbance curves, the level of turbidity at which rough plating will be exhibited must be determined on a case-to-case basis. Critically turbid plating solutions can be immediately clarified by flocculation. If the plating bath is monitored and controlled properly, flocculation may even be unnecessary.
|
