Effects Of Materials, Design And Process On Intermetallic Formation And Evolution In Solder MicrobumpsAuthors: K. Schnabl, L. Wentlent, K. Mootoo, E. Perfecto, M. Lu, and P. Borgesen
Company: Binghamton University, IBM Microelectronics, and IBM Research
Date Published: 10/13/2013 Conference: SMTA International
We report results of an ongoing systematic study of the evolution of the intermetallic bond layer and the solder microstructure and resulting properties in microbump based assemblies during reflow or thermocompression bonding and subsequent aging. Pure Sn as well as alloys with two different initial concentrations of Ag were considered. Thicknesses down to 5.5µm were deposited and reflowed for different lengths of time on Cu and Ni pads of different thicknesses and diameters ranging from 153?m to 11?m. Systematic trends are emerging: Initial thicknesses and the subsequent growth of individual IMC layers in aging vary in non-trivial manners with the combination of pad finish, reflow parameters, solder thickness, and solder composition. Different thicknesses and structures were achieved than in SMT assembly. The coupled growth of Cu3Sn and Cu6Sn5 on Cu pads is more complex than the growth of Ni3Sn4 on Ni, but thinner solder generally leads to faster IMC growth.
Pb-free, microbump solder, Intermetallic (IMC) growth, Effect of Ag, Kirkendall voiding
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