Void Formation by Kirkendall Effect in Solder Joints



From experiments by Smigelskas and Kirkendall [1], it was demonstrated that in a binary solution the rates at which the two types of atoms diffuse are not the same. Due to this phenomenon, it has frequently been observed that voids, or pores, form in the region of the diffusion zone from which there is a flow of mass. The formation of these voids strongly influences the mechanical properties. The Kirkendall experiment studied the diffusion of zinc and copper. Similar results have been found for a large range of binary alloys. In soldered joints, due to diffusion at the interfaces solder/substrate, void formation has been observed. For the new lead free solder alloys, the details of void formation by the Kirkendall effect have not been studied in great detail. Although a large amount of data are published, a comprehensive and detailed overview is lacking. Different researchers employ different process condition (reflow temperature and time, number of reflows, annealing temperature and time), which makes the comparison difficult. In general, only a reference is made to the occurrence of Kirkendall voids. In the first part of this paper, the principles of diffusion and the Kirkendall effect will be briefly described. This is followed by the mechanism of void formation. Finally, the effects in soldered joints will be discussed for a number of solder systems, which experience void formation by the Kirkendall effect.


Solder Joint Diffusion Couple Void Formation Interdiffusion Coefficient Kirkendall Void 


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© Springer-Verlag London Limited 2011

Authors and Affiliations

  1. 1.Delft University of Technology, Materials Science and Engineering Joining and Mechanical BehaviourDelftThe Netherlands
  2. 2.Mat-Tech BVEindhovenThe Netherlands

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