Reliability Impact of Defects in Lead-Free BGA Solder Joints – A Systematic Study

In high volume manufacturing environments, design rules and process variables must be tightly controlled to prevent latent defects in solder joints. These types of defects can arise due to deviations in PCB quality, assembly process, and handling. Poorly formed solder joints can escape in electrical tests and in-line non-destructive testing, only to cause early field reliability problems.

In this study, a systematic DOE approach has been adopted to study the long term reliability impact of lead free solder joint defects. A novel test vehicle was developed wherein daisy chain lead-free 0.8 mm pitch 60-ball BGA components were assembled on single and double-sided MiniDIMM cards. In addition to a normal production process, a variety of latent solder joint defects were intentionally introduced under controlled conditions. The types of defects introduced may stem from PCB design, PCB fabrication, solder paste printing, component placement, reflow, cleaning, and handling operations. Several defects were manufactured at two levels of severity. The cards were subjected to board level thermal cycling test from 0 to 100 ºC, and the daisy chain resistances were continuously monitored during the test. The results showed that several types of latent defects had a very detrimental impact on long term reliability, while some of the other defects did not have a measurable impact on fatigue reliability.