Flipchip on board (FCOB): solderability, reliability and the role of surface finish

Five surface finishes were evaluated for their effects on the solderability and reliability of FCOB assembly. Several test vehicles were employed in this evaluation for different purposes. Test vehicle boards were pre-conditioned and processed to simulate the storage and actual production environment. The surface finishes were found to have profound impact on the solderability and reliability of flip chip on board. The interactions between surface finish, flip chip bump metallurgy and configuration, underfill material, flux and pad geometry must be taken into consideration and optimized to achieve both solderability and reliability.