Pan Pacific Symposium Conference Proceedings


MICROSTRUCTURE AND SOLDERING PROPERTIES OF CSP SOLDER JOINTS USING Sn-Zn-Bi SOLDER

Author: Atsushi Yamaguchi et al.
Company: Matsushita Electric Industrial
Date Published: 2/18/2003   Conference: Pan Pacific Symposium


Abstract: BGA and CSP packages have appeared to realize higher density Printed Circuit Boards (PCBs) than QFP packages with products becoming more miniature and lightweight. Lead-free solder with a lower melting point is desired to apply products which can not use Sn-Ag-Cu lead-free solder due to the limits of heat-tolerance of electric components.

Then, we studied the soldering properties of CSP solder joints using Sn-8Zn-3Bi solder with a melting point of 197 °C. We determined how the soldering conditions affected the solder joint properties by analyzing microstructure and mechanical properties. We found that void formation was suppressed by a temperature profile that provided incompletely melting of solder-balls of CSPs.

And we also found that the joint strength reflowed at 230°C failured at a significantly short life in a bending fatigue test, on the other hand, the joints reflowed at 210°C had a longer fatigue life both in as-reflowed condition and high temperature exposure test. A Au-Zn layer formed between the Cu-Zn layer and the Ni pad in joints is considered to improve the joint strength.

Key words: lead-free solder, CSP, Sn-Zn-Bi solder, Sn-Ag-Cu solder-ball, microstructurer.



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