Materials Transactions Online

Materials Transactions, Vol.54 No.03 (2013) pp.332-336
© 2013 The Japan Institute of Metals

Microstructures Variations of Sn-9Zn-1Al and Sn-8Zn-3Bi Solder Pastes with Sn-3.8Ag-0.7Cu Solder Balls on OSP PCBs after Thermal Cycling Test

Moo-Chin Wang1, Ching-Tsung Lin2, Chi-Shiung Hsi2, Tao-Chih Chang3, Ming-Kann Liang3 and Hong-Hsin Huang4

1Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, 100 Shin-Chuan 1st Road, Kaohsiung 807, Taiwan, R. O. China
2Department of Materials Science and Engineering, National United University, 1 Lien-Da, Kung-Ching Li, Miaoli 36003, Taiwan, R. O. China
3Electronics and Optoelectronics Research Laboratories, Industrial Technology Research Institute, 195 Section 4, Chung-Hsing Road, Chutung, Hsinchu 31040, Taiwan, R. O. China
4Department of Electrical Engineering, Cheng Shiu University, 840 Cheng Ching Road, Niaosong, Kaohsiung 83347, Taiwan, R. O. China

Using an organic solderability preservative (OSP), the morphology and microstructure of Sn-9Zn-1Al (SZA) and Sn-8Zn-3Bi (SZB) lead-free solder pastes used to assemble BGA packages with Sn-3.8Ag-0.7Cu (SAC) solder balls on a printed circuit board (PCB) were investigated. The scallop-shaped (Cu,Ag)5Zn8 intermetallic compound (IMC) is formed in both SZA and SZB solder joints, and the belt-shaped (Cu,Ag)5Zn8 IMC is also formed at the interfaces of both SZA/Cu and SZB/Cu. At 125°C, the Zn atoms in the IMC layer have sufficient energy to diffuse towards the Cu pad and react with it. The IMC belt composed of island-shaped compounds formed in the SZA and SZB solder joints and the size of island-shaped compounds and amount of microvoids increased after 1,000 times thermal cycling.

(Received 2012/04/10; Accepted 2012/12/13; Published 2013/02/25)

Keywords: lead-free solder, microstructure, thermal cycling test

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