RF flip-module BGA package

We recently described a flip-chip package with integrated thin-film inductors and capacitors in a VCO tank circuit of a single-chip GSM transceiver IC. By embedding the passive components in a Si-on-Si substrate, we eliminated spurious resonances that were caused by the parasitics of the original 64-TQFP IC package. However, compared with the bare die, the resultant Si-on-Si structure is larger in all dimensions due to the inclusion of a flip-chip mounted transceiver IC and a surface-mount varactor. We have developed a novel BGA package structure with a hole milled in the center to accommodate the silicon-on-silicon assembly. The interconnections rely exclusively on flip-chip solder technology and no wire-bonds are needed. To verify that the package does not degrade the performance of the RF circuits, we have performed electromagnetic field simulations to extract critical inductance and capacitance parameters. Parasitic inductances of the original TQFP and the new packages are comparable due to their similar dimensions. Nonetheless, a major advantage of the new package structure is that it permits the integration of key passive components inside the package where they are unaffected by package parasitic impedances.