Design and characterization of a high-performance wire-bond ball-grid-array package

Abstract

The wire-bond ball-grid-array (BGA) package is of interest because of its low cost and high pin counts. For better electrical performance, the coupling in the wire-bond regions needs to be contained. This paper shows a double-swizzle design that reduces coupling by ∼40% from a reference single-swizzle design. The smaller coupling was achieved through the proper assignment of ground wires. Test packages with shorted load were built, and the measurements were done by connecting either a vector network analyzer (VNA) or a time-domain reflectometer (TDR) to the balls of the package. The coupled models of bond wires, fanouts, traces, and plating stubs were then extracted from the measured data by a customized extractor. The extracted models gave some insights into the package. The attenuation was larger than expected. Some spikes in the measured S11 plots were attributed to the coupling. A package model without coupling would not be able to capture these spikes. Yet there were other spikes that were unexplained. They were finally tracked down to be caused by the Vdd plane and routing. Connecting decoupling capacitors between Vdd and ground balls moved the resonance spikes to higher frequencies. Shorting the Vdd and ground balls eliminated these mysterious spikes altogether.