An Ultra-Wideband BGA-Via Transition for High-Speed Digital and Millimeter-Wave Packaging Applications

This paper presents a high-performance BGA-via transition structure suitable for multilayer system-in-package (SiP) applications over a wide frequency range from DC up to the F-band. The main issues involved in designing and optimizing the entire vertical transition path, starting from a motherboard and ending at the top surface of a BGA module package are outlined. The module substrates were manufactured in a standard, multilayer low-temperature co-fired ceramic (LTCC) process. The ceramic modules with plastic-core solder balls were mounted on a motherboard using standard surface-mount assembly processes. The RF performance of the developed transition structure was validated with on-wafer scattering parameter measurements. The measured results correlated very well with full-wave electromagnetic (EM) simulations, exhibiting return and insertion loss values better than 22 dB and 0.6 dB, respectively, up to 50 GHz. Moreover, the EM simulations demonstrated that the 1-dB cut-off frequency of the complete BGA-via transition structure can be extended from 55 GHz up to nearly 70 GHz at the expense of poorer return loss.