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Effect of solder bump geometry on the microstructure of Sn–3.5 wt% Ag on electroless nickel immersion gold during solder dipping

Published online by Cambridge University Press:  01 March 2005

Zhiheng Huang ,
Paul P. Conway ,
Changqing Liu  and
Rachel C. Thomson
Zhiheng Huang
Affiliation:
Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom
Paul P. Conway*
Affiliation:
Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom
Changqing Liu
Affiliation:
Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom
Rachel C. Thomson
Affiliation:
Institute of Polymer Technology and Materials Engineering, Loughborough University Loughborough, Leicestershire LE11 3TU, United Kingdom
*
a)Address all correspondence to this author. e-mail address: P.P.Conway@lboro.ac.uk
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Abstract

Continuous miniaturization of solder joints in high-density packaging makes it important to study how the joint size could affect the solder microstructure and thereby the subsequent in-service reliability. In this study, a printed circuit board with electroless nickel immersion gold (i.e., Au/Ni–P) over Cu bond pads of size approximately ∼80 μm and ∼1500 μm in diameter was dipped into a Sn–3.5Ag solder bath. The study shows that the smaller bumps, which cool more quickly, include much finer Ag3Sn particles. In addition, substantial differences in the thickness of the interfacial intermetallics and the microstructure for different dipping times are observed for different bump sizes. The results from a combined thermodynamic–kinetic model also suggest that the solder bump geometry can influence the dissolution kinetics of the pad metal into the molten solder and therefore the microstructure at the solder-pad interface and within the bulk solder.

Keywords

KineticsMicrostructureThermodynamic properties
Type
Articles
Information
Journal of Materials Research , Volume 20 , Issue 3 , March 2005 , pp. 649 - 658
Copyright
Copyright © Materials Research Society 2005

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