A STUDY OF HALOGEN-FREE PRINTED CIRCUIT BOARD ASSEMBLY FOR LEAD-FREE SOLDER JOINTS UNDER DROP IMPACT TEST

摘要

After the adoption of lead-free electronic products, the halogen-free electronic products have become an inevitable trend in recent years for environmental protection. Portable electronic products are the growth areas for electronics manufacturing industry. These portable products are prone to accidental drops which can cause internal circuit board damage e.g., solder joint failures. Therefore, drop impact performance of solder joint of Halogen-free printed circuit board is a critical concern to electronic product manufacturers. Our study in this paper depended on JESD22-B110 condition B and JESD22-B111 standards, which used an impact pulse profile with a peak acceleration of 1500G and a pulse duration of 0.5 ms. Five PBGA components with Sn-4Ag-0.5Cu solder balls were mounted on the test board by the Sn-lAg-0.5Cu solder paste, and the ANSYS software was employed to analyze the stress distribution in the joint structures. The results of drop test showed that most of the fractures occurred around the pad on the test board first and then cracks propagated across the outer build-up material. Finally, the inner copper trace was fractured due to the propagated cracks, resulting in the failure of the PCB side. The simulation results indicated that the maximum interfacial peeling stress was located at the outmost solder joint on the PCB side. Instead of crack of intermetallic compound upon copper pad, the failure was crack propagation from copper pad to PCB copper traces and resin layer. As the introduction of halogen-free PCB was gradually increased in electronic products, the new material might result in additional reliability issue during the usage of electronic equipment. The PCB failure would become the major cause of failure in reliability test. Therefore, the properties of halogen-free build-up material chosen in halogen-free assemblies should be carefully considered for drop reliability test.