Mechanical bend fatigue reliability of lead-free and halogen-free PBGA assemblies

In order to comply with impending legislative regulations in Europe (WEEE) and Japan and meet market demand for environmentally friendly 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 solder-material suppliers to assembly equipment vendors. The manufacturability and reliability of several alternative lead-free alloys have examined in the literature. A 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 and lead-free solders as well as FR4 and 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 three-dimensional parametric finite element model was developed to correlate the local PCB strains and solder joint plastic strains with the fatigue life of the assembly.