Impact properties of PBGA assemblies reflowed in nitrogen ambient and compressed air

Abstract

In this paper, the solder joint brittleness of plastic ball grid array (PBGA) assemblies has been studied by means of impact testing. The results show that the maximum impact force and the impact energy for PBGA assemblies reflowed in nitrogen ambient is higher than for those reflowed in compressed air. Reduction of the oxygen content from 1000 ppm to 50 ppm, reduces the initiation energy of impact. The impact fractured surfaces occur between the printed circuit board (PCB) pads and solder joints, i.e., in the brittle intermetallics region. The pores and impurities are mainly distributed within a ring at perimeter of the interface, with greater density at the edges than at the center. Reflow in a nitrogen ambient reduces the defect density, with reduction in oxygen content further reducing the density. Impact cracks begin from the defects of the Cu/solder interface, and propagate along the intermetallics.