Evaluation of NiPdAu as an alternative metal finish on PCB

• Published in: Circuit world Vol. 25; no. 2; pp. 18 - 26
• Main Authors: Mei, Zequn, Eslambolchi, Ali
• Format: Journal Article
• Language: English
• Published: MCB UP Ltd 01.06.1999
• Subjects: Metals; Printed circuit boards; Surface finishing
• ISSN: 0305-6120
• DOI: 10.1108/03056129910258252

Multilayer surface finish, from the bottom to top, of electroless Ni, electroless Pd, and immersion Au NiPdAu have been introduced in the printed circuit board PCB industry recently. This paper reports an evaluation of this surface finish from the perspective of solder joint attachment reliability, especially to see if the NiPdAu could be immune from the brittle interfacial fracture of PBGA on electroless Niimmersion Au, recently observed and reported by us. PCBs with NiPdAu finishes, made from two vendors with varied Pd layer thickness were attached with PBGA packages, and tested in fourpoint bending. When joint strength is strong, bending tests resulted in peeling off the PCB pads otherwise, brittle fractures occurred at the interface between solder balls and PCB pads. After aging, solder joints on all NiPdAu and reference metal finishes failed by the same brittle fracture at the interface between NiSn and AuSn intermetallic compounds. It is concluded that the interfacial fracture was controlled by something other than the Pd, and the existence of the Pd did not prevent the interfacial fracture. Also, the presence of Pd could not prevent the Au migration and subsequent fracture.