Study of Electromigration-Induced Failures on Cu Pillar Bumps Joined to OSP and ENEPIG Substrates

• Published in: Journal of electronic materials 2012-12, Vol.41 (12), p.3368-3374
• Main Authors: Hsiao, Yu-Hsiang, Lin, Kwang-Lung, Lee, Chiu-Wen, Shao, Yu-Hsiu, Lai, Yi-Shao
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Electrical engineering; Electronics and Microelectronics; Instrumentation; Materials Science; Optical and Electronic Materials; Physics; Solid State Physics; Substrates
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-012-2293-1

This work studies electromigration (EM)-induced failures on Cu pillar bumps joined to organic solderability preservative (OSP) on Cu substrates (OSP–bumps) and electroless Ni(P)/electroless Pd/immersion Au (ENEPIG) under bump metallurgy (UBM) on Cu substrates (ENEPIG–bumps). Two failure modes (Cu pad consumption and gap formation) were found with OSP–bumps, but only one failure mode (gap formation) was found with ENEPIG–bumps. The main interfacial compound layer was the Cu 6 Sn 5 compound, which suffered significant EM-induced dissolution, eventually resulting in severe Cu pad consumption at the cathode side for OSP–bumps. A (Cu,Ni) 6 Sn 5 layer with strong resistance to EM-induced dissolution exists at the joint interface when a nickel barrier layer is incorporated at the cathode side (Ni or ENEPIG), and these imbalanced atomic fluxes result in the voids and gap formation. OSP–bumps showed better lifetime results than ENEPIG–bumps for several current stressing conditions. The inverse Cu atomic flux ( J Cu,chem ) which diffuses from the Cu pad to cathode side retards the formation of voids. The driving force for J Cu,chem comes from the difference in chemical potential between the (Cu,Ni) 6 Sn 5 and Cu 6 Sn 5 phases.