High-frequency characterization of differential signals in a flip-chip organic package

As today's off-chip differential busses operate at a few Gbit/s and move to even higher speeds in the future, the chip package interconnect becomes a critical part of the entire signal transmission path. The package performance could determine the maximum frequency that the data can be transferred. The package interconnects have to be designed properly to maintain a constant characteristic impedance in order to minimize reflection and maximize transmission. To characterize the performance of packages, S-parameter measurement is widely used due to its accuracy and large dynamic range. However, a test fixture is usually required to enable the measurement. This paper describes a different method of characterizing the differential signals in a flip-chip organic package. This measurement technique probes the chip mounting pad side of the signal nets and does not require a test fixture. Both S-parameter and time domain reflectometer (TDR) measurements were compared to models extracted from electromagnetic (EM) simulations with good correlation. This technique is efficient, cost effective and provides a fast turn around time for measurements and models validation.