Reliability improvement of area array solder joints: Changing attachment pad geometry

This dissertation describes some of the fundamental issues associated with Area Array package reliability. Specifically, the robustness of the solder joint is of primary concern since the solder makes both the mechanical and electrical interconnection between the device and Printed Circuit Board (PCB). This research focuses on extending the life of the solder joint due to both mechanical and thermally induced strains. The primary driver for strain produced in a solder joint is due to the difference in thermal mechanical properties of the component and PCB. The stress/strain causes damage within the joint and eventual leads to failure. However, geometric changes in the attachment pad geometry can extend the life of the joint by reducing the stress within the device. One such proposed change is to increase the surface area of the attachment pad. Another such method to extend the fatigue life of solder joints is to change the crack propagation pathway. When a crack is propagating through a material, a change in the crack path direction can result in a reduction in the crack growth rate. This research combines the benefits of increased area and crack propagation pathway changes by making a change to the solder attachment pad geometry. Literature suggests an exposed copper pad geometry can extend the fatigue life of solder joints in area array components, however, the suggested geometry has always shown a lower mechanical adhesion of the pad to the PCB. This has been the primary obstacle to using a pad modification approach. This research has overcome the low copper adhesion strength. This work outlines critical issues in solder joint reliability, discusses the improved design, and presents work from literature. It is conclusively shown in this research that an improvement was found in the mechanical and thermal fatigue lives of area array components.