Alpha radiation sources in low alpha materials and implications for low alpha materials refinement

Traditionally wafer bumps are made from Pb containing solders. Over 20 years ago IBM recognized that 210Pb has a decay chain resulting in a 5.4 MeV alpha particle that induces soft errors. A variety of efforts to produce and characterize low alpha Pb ensued. Work at Honeywell over the past several years has shown that low alpha lead activity does not follow the decay signature predicted from 210Pb secular equilibrium. Data are presented indicating that smelting has a minimal effect on 210Pb/ 210Po secular equilibrium and that other trace radionuclides are the alpha source. The implications of these data to possible alpha emitter sources in lead free solders are discussed, along with a method developed by Honeywell to remove alpha emitters from lead free solder components.