Investigation of the Effect of PCB Base Materials and Pad Surface Finish on the Thermal Fatigue Life of Lead-free Solder Joints of PBGA and Passive Resistors

Legislation that mandates the banning of lead in electronics due to environmental and health concerns has been actively pursued in many countries during the past fifteen years. Although a large number of research studies have been performed and are currently under way in the lead-free solder area, especially on the reliability of lead-free solder joints, abundant data exists predominantly on the short-term reliability (that is, less than five years) of lead-free solder joints under single-loading conditions. Data on long-term reliability is scarce. Lead-free electronics will be deployed in many products that serve markets where long-term reliability is a critical requirement. This paper presents a design-of-experiment reliability study of lead-free solder joints. The printed circuit board (with different base materials: FR4, HT-FR4, and PI) test assemblies include two types of components (PBGA and 2512 resistors), with various terminal metallurgies, several PCB pad finishes (HASL, ImSn, ImAg, ENIG, and OSP), and two solder alloys (SnPb and Sn3.0%Ag0.5%Cu). The test vehicle design, experimental set-up, results, and failure analysis are presented here.