Reduction of Ionic Contamination: Ionix SF
Prior to final rinsing and drying, latest immersion tin systems incorporate post treatments, lowering ionic contamination levels far below IPC's specification (J-STD-001-D of 1.56µg NaCl equ./cm2) to less than 0.5 µg/ccm2. PCBs contaminated from ions such as chloride, bromide, sodium and organic acids can cause failures in electronic devices.These conductive contaminants can be responsible for corrosion, metal migration and electrical leakage. In order to quantify the degree of the potential problem the whole panel is washed in a solvent and the ionic conductivity is measured. This value relates to the ionic contamination level. The result is an average value across the whole surface. The measurement is translated into µg NaCl equivalence per square centimeter.IPC with J-STD-001-D specify a value, which shoul not exceed 1.56µg NaCl equ./cm2. Nowadays immersion tin users introduced 0.5 µg/cm2 as upper limit.
This approach is being adapted and implemented as post treatment within the immersion tin plating system.As root cause it was found out that most of the surface contaminants on PCBs are attributed to the soldermask with a clear interdependence to the type.