Design and Characterization of a 10 GHz Organic BGA Package

The design and electrical characterization of an organic BGA flip-chip package for >10 GHz operation is described. A comprehensive overview of the design process is given, including selection of substrate technology, layout strategy, electromagnetic modeling of critical signal paths, and thermal analysis. Test methods and hardware used to evaluate the frequency-domain and timedomain behaviors of the finished package are also covered. Laminate technology used for the interposer PCB was chosen for the excellent microwave properties of the dielectric material used, and its ability to realize small copper features. Layout of the interposer implements launches and transmission lines for 21 high-speed differential pairs, using structures designed to maintain a 100ohm differential impedance environment throughout the signal path. The use of electromagnetic field solver tools (2D and 3D, quasi-static and full-wave) was essential to the design of signal launches, layer-to-layer transitions, and coupled microstrip. The BGA package houses a flip chip that dissipates about 8W of power; therefore, the design provides a low thermal resistance path from the IC to the ambient environment. A simple modification to this interposer design produced a test structure representative of the high-speed signal path(s). This test structure was characterized in the frequency domain by utilizing broadband baluns and differential microwave probes to obtain differential s-parameters. Package performance in the time domain was investigated by timedomain reflectometry (TDR) test methods, which are invaluable for locating discontinuities in the signal path.