The Effect of Microstructural and Geometrical Features on the Reliability of Ultrafine Flip Chip Microsolder Joints
Authors: Huang, Zhiheng; Conway, Paul P.; Liu, Changqing; Thomson, Rachel C.
Source: Journal of Electronic Materials, Volume 33, Number 10, 1 October 2004 , pp. 1227-1235(9)
Abstract:A thermodynamic approach was used to investigate solder alloy systems containing Sn, Ag, Sb, and Pb, during both equilibrium and Scheil cooling conditions. The modeled microstructure was used to explore recent experimental results and to establish the microstructure-property relationships in microsolder joints. This approach is shown to be very useful in the transition from Pb-Sn to lead-free solders by enabling the consideration of contamination by a small amount of Pb. Molten solder interacts with the under bump metallization or print circuit board (PCB) metallization to form intermetallic compounds (IMCs). A truncated sphere structure was used to predict the solder joint geometry, and a two-dimensional finite-element (FE) method was adopted to investigate the kinetics of the dissolution of Au during the reflow process. The dissolution of Au into different volumes of solder material for three sizes of joints has been studied. In the modeling of the dissolution kinetics, the Nernst–Brunner equation is found to have poor validity for these calculations because of the dramatic change in the microscopic geometry and boundary conditions for joints at 100 m in size or smaller. A combined thermodynamic and kinetic modeling approach, with a novel interface for implementation, is also briefly discussed.
Document Type: Regular Paper
Publication date: October 1, 2004