Mechanical fatigue reliability of PBGA assemblies with lead-free solder and halogen-free PCBs

Abstract

In order to comply with the environmental legislations in Europe (WEEE) and Japan and to capture the market share in 'green' products, electronics manufacturers are beginning to introduce lead-free solder and halogen-free PCBs into their products. The change of materials impacts the entire manufacturing supply chain, from component and solders material suppliers to assembly equipment vendors. The industry has identified possible alternatives to the Sn/Pb solder alloy but the majority of US based companies, working with NEMI, are selecting SnAgCu alloys, with minor compositional variations. However, much work is still required in the area of component and assembly reliability, especially in mechanical fatigue and impact loading, where the failure drivers are independent of the coefficient of thermal expansion. In this paper, the mechanical bend fatigue reliability of Plastic Ball Grid Array (PBGA) assemblies is investigated. Reliability of traditional PBGA assemblies is compared to those built with environmentally friendly materials. Experimental data is presented for four different combinations of Tin-Lead & Lead-Free solders as well as FR4 & Halogen-Free laminate substrates - TL/FR4, LF/FR4, TL/HF and LF/HF. The fatigue life was correlated to the different failure modes. A transition in failure modes as a function of the applied load was observed. A 3-D parametric finite element model was developed to correlate the local PCB strains and solder joint plastic strains with the fatigue life of the assembly.