Innovative Socketable and Surface-Mountable BGA Interconnections

This paper introduces a universal BGA technology that can reliably be used both in sockets and SMT applications. Socketing and SMT have been driving two different board-level interconnection technologies: LGA for socketing, to provide a stable and reworkable mechanical contact, and BGA for SMT, for low-temperature metallurgical bonding to the board. Enabling socketable BGAs has become critical to simplify microprocessor package designs and converge towards a unique product. The approach presented in this research involves the use of multi-layered coatings on solder spheres. These coatings consist of a diffusion barrier/noble metal combination designed based on diffusion models to meet the requirements of both applications. Standard surface finish Electroless Ni Immersion Au (ENIG) has been studied in detail as a first approach. This paper focuses on the challenges faced in plating ENIG on traditional SAC solder balls and a new process combining sputtering and electrodeposition is demonstrated as a promising alternative to uniformly coat solder spheres with a controlled thickness of ENIG without corrosion. A first demonstration of attaching these coated spheres to the package is also presented.