EVALUATION OF Pb-FREE BGA SOLDER JOINT RELIABILITY ON Ni-BASED SURFACE FINISHES USING ALTERNATIVE SHEAR AND PULL METROLOGIES

摘要

This technical paper summarizes the findings and conclusions from a comprehensive examination of Pb-free solder ball bonding, comparing ball shear and cold ball pull testing results. The paper compares results obtained from conventional speed (slow) ball shear and cold ball pull testing with the results from newer high-speed test parameters. Relationships between ball shear and cold ball pull results are examined. Findings are also compared for two different substrate surface finishes: a process-of-record electroless nickel / immersion gold finish (ENIG), and an electroless nickel / electroless palladium / immersion gold finish (Ni/Pd/Au). Testing variables include surface finish deposit thickness, solder ball diameter and solder resist opening diameter, ball shear speed and cold ball pull speed. Test results are presented as graphical analyses of ball shear and cold ball pull forces and fracture modes, as well as microscopic examinations. Interpretation of the results includes determinations of the fracture modes for the various test methods and deposit conditions. Conclusions are offered regarding the two test methods and parameters, the performance of the two surface finishes and their interaction within Pb-free applications.