Tin-lead deposits provide excellent performance for bumping applications. However, this coating is being phased out because of environmental concerns. The two main commercial alternatives to tin-lead processes are pure tin and tin-silver. Recently similar formulations were released by a number of chemical suppliers. Compared to the Tin-lead process, there are additional components as well as new challenges for metrology. This presentation describes some of the analytical methods required for this project.
Analysis of Acid and Tin remained mainly the same as for the Tin-Lead process. Standard acid-base and red-ox titration provide good accuracy and reproducibility of analysis.
Silver can be determined by AA, but this method cannot be easily automated. Traditional titration or spectrophotometric methods for silver does not work in presence of complexer. We were able to overcome this obstacle by use of masking reagent.
Proper operation of the bath requires an excess of complexer, so that 100% of silver ions are complexed. We developed a unique titration method in which the position of knee-point on titration indicates the concentration of free complexer.
In order to control grain size, suppressive agents (grain refiner, surfactant, or both) are used. CVS method is at it best for such analysis. All of these analysis are available in QualiLab Elite. Analysis time 5-10 min. Accuracy 5-10%. Reproducibility within 5%.