Comparison of Joint Strength and Fracture Energy of Lead-free Solder Balls in High Speed Ball Shear/Pull Tests and their Correlation with Board Level Drop Test

A comprehensive solder joint reliability study was conducted using both high-speed solder ball shear/pull and board level drop testing (BLDT). The samples were divided into groups which were subject to various periods of thermal aging (125degC, up to 500 hours) in order to accelerate the formation of intermetallic compound (IMC) in the solder joints. The ball shear tests ranged from 10 mm/s to 3,000 mm/s while the ball pull tests ranged from 5 mm/s to 500 mm/s. A total of 6 unique package constructions were evaluated, ranging from a 316 PBGA (27 mm, sq) to a 2,395 CBGA (51 mm, sq). The samples used SAC lead-free solder balls and a variety of pad surface finishes. Detailed failure analyses were performed to identify the failed solder joints and corresponding failure modes. The failure modes and loading speeds of ball shear and ball pull tests were cross-referenced with the mechanical drop tests for comparison. Correlation models were established relating drops-to-failure with both solder ball fracture force and energy.