Comprehensive Study on Thermal Aging and Ball Shear Characterization of SAC-X Solders

Abstract

Ball Grid Array (BGA) is a surface mount chip package commonly used in many microelectronics products. It has solder balls array underneath the package provide electrical connection and mechanical support to the PCB. BGA is well-known for its low inductance, high lead count` and compact size. BGA chips are simpler to align to the printed circuit board. It is due to leads, which known as “solder balls” or “solder bumps,” are further apart compare to the leaded packages. Tin-silver-copper (Sn-Ag-Cu) is a popular solder ball is also well-known as SAC, is a lead-free alloy [1, 2]. SAC is currently a dominant alloy system used to substitute tin-lead because of it adequate thermal fatigue properties and is close to eutectic with wettability and strength meeting require specification. However for more stringent reliability requirements such as in automotive applications, SAC solder will have difficulties to meet the reliability at board level when the footprint surpasses a certain dimension. This lead to the research and study for alternative solder alloys, such as SACQ and QSAC. The properties of the SAC305, SACQ and QSAC such as Tensile Strength, Elongation, and Hardness will be compared. Studies of the solder joint of various type of solder balls with BGA in terms of failure mode upon balls shear and measurement of the ball shear strength. These solder alloys need to subject to High Temperature storage (HTS) for extended duration up to 3000hrs under high temperature conditions. Details of the experimental results including the failure mode and the intermetallic characterization and correlations will be shared and discussed.