IPC APEX 2009, Las Vegas, NV, March 31-April 2, 2009.

Copper Pad Dissolution and Microstructure Analysis of Reworked Plastic Grid
Array Assemblies

Lei Nie, Michael Osterman and Michael Pecht
Center for Advanced Life Cycle Engineering (CALCE)
University of Maryland
College Park, MD



An experimental study was conducted to examine the impact of rework processes on quality and reliability. In this study, 676 IO plastic ball grid array packages were assembled with Sn3.0Ag0.5Cu solder paste and eutectic SnPb solder paste. Selected parts on circuit boards were subjected to rework processes one time, three times and five times. X-ray inspection and environmental scanning electron microscope were used to investigate impact of part replacement on the ball grid array voids, the microstructure of intermetallic compound, and copper pads. Since the rework process includes multiple liquid solder state periods, it consumes more copper and makes the intermetallic compound growth trend an interesting topic. Copper pad dissolution was found in the samples after multiple rework processes. Lead-free assemblies consumed more copper than mixed assemblies because of higher concentration of Sn in lead-free solder. The thickness of intermetallic layer increased as the total rework time increased. Ultra thick intermetallic compound was found at the connection area between the copper pad and the copper trace after the rework processes were applied three times and five times, which may lead to reliability concerns.

Complete article is available to CALCE Consortium Members.


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