Microstructure-Evolution and Reliability Assessment Tool for Lead-Free Component Insertion in Army Electronics

This work aims to understand the reliability of Sn-Ag-Cu solder interconnects used in plastic ball grid array (PBGA) packages using microstructure evolution, laser moiré interferometry and finite-element modeling. A particle coarsening based microstructure evolution of the solder joint material during thermal excursions was studied for extended periods of time lasting for several months. The microstructure evolution and particle coarsening was quantified, and acceleration factors were determined between long-term field-use conditions and accelerated thermal cycling (ATC) conditions for PBGA packages with different form factors and for two different lead-free solder alloys. A new technique using laser moiré interferometry was developed to assess the deformation behavior of Sn-Ag-Cu based solder joints during thermal excursions. This technique can used to estimate the fatigue life of solder joints quickly in a matter of few days instead of months and can be extended to cover a wide range of temperature regimes. Finite-element analysis (FEA) in conjunction with experimental data from the ATC for different lead-free PBGA packages was used to develop a fatigue life model that can be used to predict solder joint fatigue life for any PBGA package. The proposed model will be able to predict the mean number of cycles required for crack initiation and crack growth rate in a solder joint. (a) Papers published in peer-reviewed journals (N/A for none) Krishna Tunga and Suresh K. Sitaraman, “Microstructure Evolution based Acceleration Factor Determination for SnAgCu Solder Joints During Thermal Cycling”, International Journal of Materials and Structural Integrity, Vol. 2, Issue 1, p. 173-192, 2008 Krishna Tunga and Suresh K. Sitaraman, “Using Carrier Fringes to Study the High Temperature Deformation Behavior of a BGA Package under Extended Dwell Times”, Experimental Mechanics, Vol. 48, Issue 3, p. 355-365, June 2008 Krishna Tunga and Suresh K. Sitaraman, “An Expedient Experimental Technique for the Determination of Thermal Cycling Fatigue Life for BGA Package Solder Balls”, Journal of Electronic Packaging, Vol 129, Issue 4, pp.427-433, December 2007 List of papers submitted or published that acknowledge ARO support during this reporting period. List the papers, including journal references, in the following categories: (b) Papers published in non-peer-reviewed journals or in conference proceedings (N/A for none) 3.00 Number of Papers published in peer-reviewed journals: Number of Papers published in non peer-reviewed journals: (c) Presentations 0.00 Number of Presentations: 0.00 Non Peer-Reviewed Conference Proceeding publications (other than abstracts): Number of Non Peer-Reviewed Conference Proceeding publications (other than abstracts): 0 Peer-Reviewed Conference Proceeding publications (other than abstracts): Krishna Tunga and Suresh K. Sitaraman, “Thermo-mechanical Fatigue Life Estimation of Organic BGA Packages Using Laser Moire Interferometry”, Proceedings of ASME-IMECE 2006, Chicago, IL (d) Manuscripts Number of Peer-Reviewed Conference Proceeding publications (other than abstracts): 1 Tunga, K. and Sitaraman, S. K., "Predictive Model Development for Life Prediction of PBGA Packages with SnAgCu Solder Joints." IEEE Transactions on Components and Packaging Technologies (submitted in August 2008). Tunga, K. and Sitaraman, S. K., "Fatigue Life Prediction of Lead-free Solders using Laser Moiré Interferometry," Microelectronics Reliability (submitted in August 2008). Number of Manuscripts: 2.00 Number of Inventions: