Effects of Bonding Conditions on Bondability Using Zn/Al/Zn Clad Solder

• Published in: Journal of electronic materials Vol. 44; no. 12; pp. 4769 - 4778
• Main Authors: Yamaguchi, T., Ikeda, O., Oda, Y., Hata, S., Kuroki, K., Kuroda, H., Hirose, A.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-12-2015; Springer Nature B.V
• Subjects: Bond strength; Boundary layer; Characterization and Evaluation of Materials; Chemistry and Materials Science; Electronics and Microelectronics; High temperature; Instrumentation; Materials Science; Optical and Electronic Materials; Soldering; Solid State Physics; Pb-free; Zn-Al solder; eutectic melting; Zn-Al-Cu solder; clad material; die attachment
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-015-4105-x

Three-layer Zn/Al/Zn clad solders have been developed for high-temperature die attachment. The clad structure is used to improve the wettability and bondability of Zn-Al eutectic solder by preventing Al oxidation. The effects of the bonding conditions on the bondability with Zn/Al/Zn clad solder were investigated. Bonding was achieved in the temperature range from 385°C to 420°C under N
2
atmosphere with oxygen concentration below 100 ppm. However, the bonding strength of the joint formed under N
2
 + 4% H
2
atmosphere was almost 0 MPa, and stripe defects and air gaps remained in the bond layer. To improve the bondability under N
2
 + 4% H
2
and expand the application range, a five-layer Cu/Zn/Al/Zn/Cu clad solder was developed in an attempt to prevent the Zn layers from being oxidized by the outer Cu layers. Cross-sectional observation of the Cu/Zn/Al/Zn/Cu clad solder revealed that the surface was covered by a Cu layer, and that Cu
5
Zn
8
layers grew between the Cu and Zn layers. This clad solder exhibited high shear strength of over 80 MPa when formed under N
2
 + 4% H
2
atmosphere, and no stripe defects or air gaps were observed in the bond layer.