Immersion tin as a high performance solderable finish for fine pitch PWBs

A new high performance immersion tin incorporating a co‐deposited organic provides a highly solderable PWB surface finish. The process is described and includes solderability data after accelerated aging and extended processing. Studies of SIR, metallic dendritic growth and ionic contamination are included. A final section shows the benefits for fine pitch assembly, including the yield improvements seen at reflow, ICT and final inspection. The reliability questions are answered and conclude that the flat solderable tin process provides a cost‐effective and yield‐enhancing planar alternative to Nickel‐Gold, HASL and OSPs.