Investigation of Factors that Influence Creep Corrosion on Printed Circuit Boards
Authors: Haley Fu, Cherie Chen, Prabjit Singh, Jing Zhang, Anil Kurella, Xu Chen, Xiaodong Jiang, Jennifer Burlingame, and Simon Lee Company: iNEMI, IST-Integrated Service Technology, Inc., IBM Corporation, Intel Corporation, Alcatel-Lucent, Alcatel Shanghai Bell, Cisco Corporation, and The Dow Chemical Company Date Published: 4/30/2012
Abstract: Test printed circuit test boards (PCBs) with various surface finishes were subjected to a mixed flowing gas environment with gaseous composition adjusted to achieve a targeted 500-600 nm/day copper corrosion rate. Board surface finishes included immersion silver (ImAg), organic solderability preservative (OSP) and lead-free hot-air-solder leveling (Pb-free HASL). The PCB test specimens were prepared by reflowing lead-free solder paste on the top side and wave soldering the bottom side with lead-free solder using no-clean organic acid flux on some specimens and no-clean rosin flux on others. The solder paste contained rosin flux with low activity and zero halides. Copper creep corrosion was observed mainly on the ImAg finished boards that were wave soldered with no-clean organic acid flux. Pb-free HASL finished boards that were wave soldered with no-clean organic acid flux experienced some severe but localized creep corrosion due to exposed copper metallization and possibly flux residues from the Pb-free HASL or assembly operations. Creep corrosion was most severe in the wave soldered boundary areas where flux residue was present. Circuit boards wave soldered with no-clean rosin flux had insignificant creep corrosion.