Microstructures and Shear Strength of Sn-Zn Lead-free Solder Joints

Kim, Kyung-Seob; Yang, Jun-Mo; Yu, Chong-Hee

Journal of KWJS 2003;21(7):59-64.
Published online December 25, 2003.

Microstructures and Shear Strength of Sn-Zn Lead-free Solder Joints

Kyung-Seob Kim, Jun-Mo Yang, Chong-Hee Yu

Abstract

Microstructure and shear strength or Sn-Zn lead-free solders and Au/Ni/Cu UBM joint under thermal aging conditions was investigated. The samples were aged isothermaIly at 100 'C and 150"C for 300, 600, and 900 hours. The IMCs(lntermetaIlic Compound) at the interface between solder and UBM were examined by FESEM and TEM. The results showed that the shear strength was decreased with aging time and temperature. The solder baIl with high activated RA flux had about 8.2% higher shear strength than that of RMA !lux. Poor wetting and many voids were observed in the fractured solder joint with of RMA !lux. The decreased shear strengths were caused by [MC growth and Zn grain coarsening. Zn reacted with Au and then was transformed to the β -AuZn compound. Although AuZn grew first, y -NisZn21 compounds were formed with aging time. The layers indicated by Ni5Zn21(]), (2), and (3) were formed with the thickness of -0.7 um, -4 um, and -2 um, respectively.