Effect of long and short Pb-free soldering profiles of IPC/JEDEC J-STD-020 on plastic SMD packages

摘要

The Pb-free soldering temperature-time profile T(t) in the IPC/JEDEC J-STD-020 specification, which is used in the moisture sensitivity level (MSL) classification of plastic SMD packages, has a wide time range. We found that in a thick package, MQFP-80 the long soldering profile is worse than the short one whereas in a thin package, TSSOP-38 the result is surprisingly the reverse. Because moisture diffusion inside the package is much slower than thermal diffusion, the wide time range in T(t) profile is found to have an effect on the MSL of packages with different geometries. The results suggest a strong need to reduce the width of soldering range in the J-STD-020 specification. Further studies done on A2-coated leadframe packages, namely DSO-20 and MQFP-80, found quite similar MSL performance for both long and short soldering profiles.