Title :
Modeling and simulation-the effects of grain coarsening on local stresses and strains in solder microstructure
Author :
Chanchani, Rajen
Author_Institution :
Sandia Nat. Labs., Albuquerque, NM, USA
Abstract :
A critical issue in the long-term reliability of solder connections used in electronic packages is joint failure during thermal cycling. At present, solder is assumed to be a homogeneous single-phase metal in most finite element analyses to predict solder joint fatigue failures. However, in the last decade, several metallurgical studies have shown that solder microstructure may have a role in early solder joint failures. Investigators have observed that solder microstructure coarsens in local bands during aging and during thermal cycle fatigue. In a failed solder joint, the fatigue cracks are found in these bands of coarse grains. It is speculated that the grain coarsening increases local strains within the microstructure, thereby increasing the likelihood for a crack to initiate. The objective of this study is to model and simulate the effect of grain coarsening on local stresses and strains. During solidification of eutectic Pb/Sn solder, two types of microstructures form: lamellar and equiaxed. In this study, the author has developed a computer code to generate both types of microstructures of varying grain coarseness. This code is incorporated into the finite element code that analyzes the local stresses and strains within the computer-generated microstructure. The FE code, specifically developed for this study, uses an algorithm involving the sparse matrix and iterative solver. This code on a typical single-processor machine will allow the analyst to use over 1 million degrees of freedom
Keywords :
ageing; assembling; circuit reliability; crystal microstructure; eutectic alloys; failure analysis; fatigue cracks; finite element analysis; grain refinement; internal stresses; lead alloys; packaging; soldering; solidification; stress analysis; tin alloys; FE code; SnPb; aging; coarse grains; computer code; computer-generated microstructure; crack initiation; early solder joint failure; electronic packages; equiaxed microstructure; eutectic Pb/Sn solder; failed solder joint; fatigue cracks; finite element analysis; finite element code; grain coarseness; grain coarsening; grain coarsening effects; homogeneous single-phase metal; iterative solver; lamellar microstructure; local strains; local stresses; long-term reliability; modeling; simulation; solder connections; solder joint failure; solder joint fatigue failures; solder microstructure; solder microstructure coarsening; solidification; sparse matrix; thermal cycle fatigue; thermal cycling; Aging; Capacitive sensors; Computational modeling; Electronic packaging thermal management; Failure analysis; Fatigue; Finite element methods; Microstructure; Soldering; Stress;
Conference_Titel :
Advanced Packaging Materials: Processes, Properties and Interfaces, 1999. Proceedings. International Symposium on
Conference_Location :
Braselton, GA
Print_ISBN :
0-930815-56-4
DOI :
10.1109/ISAPM.1999.757301