Board-level solder joint reliability of high performance computers under mechanical loading

Several changes in high performance computer system design, construction and materials have resulted in potentially greater risk of solder joint failures under mechanical loading. In addition to mechanical/thermal challenges created by the increased volumetric density and power dissipation of components in the system assemblies, computer products increasingly include Pb-free solder and circuit board materials that are often more brittle than their Sn37Pb containing predecessors. Although servers and computer sub-assemblies are unlikely to witness severe impact loading under end-use conditions, high strain-rate events nonetheless occur during board assembly, test, handling and shipment. This paper provides a brief overview of characterization test methods, modeling approaches, and acceptance criteria used to establish component fracture strength, circuit board strain and solder joint reliability of electronic assemblies under various mechanical stress conditions. In addition, key parameters associated with optimization of solder joint brittle fracture strength are identified.