Growth of a Au-Ni-Sn intermetallic compound on the solder-substrate interface after aging
Ni/Au metallization layers are used with increasing frequency to protect Cu substrates in ball grid array microelectronic packaging. The external Au layer provides oxidation and corrosion resistance during storage prior to assembly, while the intermediate Ni layer acts as a diffusion barrier that inhibits the formation of a thick Cu-Sn intermetallic layer during aging. During soldering with eutectic Pb-Sn, the Au dissolves into the molten solder and forms fine, needle-shaped AuSn{sub 4} intermetallic precipitates that are retained in a dense distribution in the bulk of the solder joint after it has solidified. However, recent research by Mei et al. has revealed a new and potentially problematic phenomenon that seems to be peculiar to the Ni/au metallization. They found that after extensive aging (150 C for 2 weeks in their case), the Au-Sn intermetallic redeposited onto the solder-substrate interface. The reconstituted interface was significantly weakened and failed by brittle fracture along the surface between the redeposited Au-Sn and the Ni{sub 3}Sn{sub 4} layer that formed during reflow. While the interfacial redeposition of Au-Sn intermetallics has been observed previously, the mechanism remains unknown. The present work was undertaken to identify the mechanism of this phenomenon and explore methods for controlling it.
- Research Organization:
- Univ. of California, Berkeley, CA (US); Lawrence Berkeley National Lab., CA (US)
- OSTI ID:
- 20023154
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 3 Vol. 31; ISSN MMTAEB; ISSN 1073-5623
- Country of Publication:
- United States
- Language:
- English
Similar Records
Effects of metallic nanoparticle doped flux on the interfacial intermetallic compounds between lead-free solder ball and copper substrate
Laser versus IR reflow soldering of eutectic tin-silver solder