Critical Current Density for Inhibiting (Cu,Ni)6Sn5 Formation on the Ni Side of Cu/Solder/Ni Joints
Source: Journal of Electronic Materials, Volume 39, Number 12, December 2010 , pp. 2653-2661(9)
Abstract:The Cu/solder/Ni structure is a common joint configuration used in microelectronic packages today. In high-temperature operation of this joint structure, an appreciable amount of Cu can readily diffuse across the entire solder to the Ni side, where it might grow into a brittle bilayer structure of (Cu,Ni)6Sn5/(Ni,Cu)3Sn4. The driving force for Cu diffusion is the chemical potential gradient. To counterbalance this chemical-force-induced Cu flux (J chem Cu ), an attempt to apply a reverse electric current into a Cu/Sn(50 m)/Ni structure was made in this study. Ten current densities (j = 0 A/cm2 to 2 × 104 A/cm2) were examined at 150°C upon current stressing. The results indicated that, under current stressing of <104 A/cm2, Cu atoms were still driven to the Ni side, resulting in noticeable increase in the amount of Cu (N Cu) or (Cu,Ni)6Sn5 at the Sn/Ni interface. In contrast, N Cu decreased significantly, and the (Cu,Ni)6Sn5 was further converted into another low- Cu-content phase, (Ni,Cu)3Sn4, when j exceeded 1.25 × 104 A/cm2. Under ~104 A/cm2, the (Cu,Ni)6Sn5 thickness and N Cu remained relatively unchanged over time, suggesting that 104 A/cm2 is close to the critical current density (j crit) that can counterbalance J chem Cu . Growth of (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 under the conditions (I) j < j crit, (II) j > j crit, and (III) j ≍ j crit were also examined in this study.
Document Type: Research Article
Affiliations: 1: Department of Chemical Engineering and Materials Science, Yuan Ze University, Chungli City, Taiwan, ROC 2: Department of Chemical Engineering and Materials Science, Yuan Ze University, Chungli City, Taiwan, ROC, Email: firstname.lastname@example.org
Publication date: December 1, 2010