PBGA solder ball coplanarity impact evaluation

A study was conducted to examine the sensitivity of solder joint integrity for PBGA assembly and post rework process yields to the change of the solder ball coplanarity specification from 0.15mm to 0.20mm as well as to increase the level of confidence with respect to the specification change. The study considered the following experimental variables: solder ball coplanarity; stencil thickness and aperture design; whether the assembly also experiences a wave soldering process; the rework method, i.e. whether there is dispensing of solder paste or just a flux. Electrical continuity tests were performed after PBGA assembly and rework. Accelerated thermal cycling and thermal shock tests were then used to evaluate the solder joint reliability. Additionally, standoff heights of PBGA solder joints were measured through cross sectioning samples. Statistical comparisons of the mean standoff height between different PBGA coplanarity groups, where different experiment variables were applied, allowed for determination of the variation of BGA solder joint integrity.