A network analysis based high-frequency inductance technique wasused to measure the package inductance of various A42 and Cu QFPpackages. A continuous frequency range of 2.6 MHz to >500 MHzcorresponding to the relevant speed/bandwidth of today's ICs wasemployed. Results indicated that while the inductance of all the Cupackages were essentially constant across the frequency band, theinductance of A42 packages varied appreciably with the frequency. Theinductance of a typical A42 package was three times that of a Cu packageat 2.6 MHz but decreased to only 10%-20% higher than that of a Cupackage above 250 MHz. The lead resistance of A42 also increased sharplywith increasing frequency and could become an important factor indetermining the electrical performance. Based upon the preliminaryanalyses, the frequency-dependent inductance and resistance of A42packages were attributed to the interaction between the skin effect andthe non-unity permeability of ferromagnetic materials. To verify thetheory and to test possible electrical enhancement for the A42,different surface-treated packages, including an Au-plated A42, aPd/Ni-plated A42 and a Pd/Ni-plated Cu CQFP packages were characterizedfor their inductance and resistance. A 3-D field solver was also used toderive the permeability of the A42 materials at different frequencies.To further study the impact on high-speed digital chips where signalsare usually analyzed in the time domain, a test structure made of bothA42 traces and Cu traces was characterized using a time domainreflectometer for impedance, delay, and crosstalk. Both thefrequency-domain and the time-domain results for A42 and Cu packages aresummarized in this paper and their implications discussed
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