IEEE Trans. on Device and Materials Reliability, Vol. 10, No. 2, pp. 276-286, June 2010

Microstructural Analysis of Reworked Ball Grid Array Assemblies Under Thermomechanical Loading Conditions

Lei Nie, Member, IEEE and Michael Osterman, Member, IEEE
Center for Advanced Life Cycle Engineering (CALCE)
University of Maryland
College Park, MD20742 USA.

Michael Pecht, Fellow, IEEE
Center for Advanced Life Cycle Engineering (CALCE),
University of Maryland
College Park, MD 20742 USA
and
Department of Electronics Engineering,
City University of Hong Kong,
Kowloon, Hong Kong

Abstract:

Plastic ball grid array packages (Sn3.0Ag0.5Cu) were assembled with Sn3.0Ag0.5Cu and Sn37Pb solder paste to form Pb-free and mixed BGA assemblies. The Pb-free and mixed assemblies were subjected to one (1X) rework cycle and three (3X) rework cycles. All the reworked Pb-free and mixed assemblies were then subjected to a temperature cycling test with a temperature range of −55 ◦C–125 ◦C. The cycles to 0.1% failure of 1X reworked Pb-free assemblies was 18% smaller than that of non-reworked Pb-free assemblies, and the cycles to 0.1% failure of 3X reworked Pb-free assemblies was approximately 100% smaller. However, the cycles to 0.1% failure 1X reworked mixed BGA assemblies was approximately 200% larger than that of the non-reworked mixed BGA assemblies, and the cycles to 0.1% failure 3X reworked mixed assemblies was 35% larger. Detailed microstructural analysis and geometry analysis were provided to explain the temperature cycling reliability differences between the non-reworked and reworked assemblies, as well as the differences between the Pb-free assemblies and the mixed assemblies. The increase in the temperature cycling reliability of reworked mixed assemblies was found to be related to more homogenous Pb-rich phase distribution in the bulk solder.

Index Terms—Ball grid array (BGA), failure analysis, rework, temperature cycling reliability.

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