High-frequency inductance measurements and characterization of alloy 42 and copper packages

A network analysis based high-frequency inductance technique was used to measure the package inductance of various A42 and Cu QFP packages. A continuous frequency range of 2.6 MHz to >500 MHz corresponding to the relevant speed/bandwidth of today's ICs was employed. Results indicated that while the inductance of all the Cu packages were essentially constant across the frequency band, the inductance of A42 packages varied appreciably with the frequency. The inductance of a typical A42 package was three times that of a Cu package at 2.6 MHz but decreased to only 10%-20% higher than that of a Cu package above 250 MHz. The lead resistance of A42 also increased sharply with increasing frequency and could become an important factor in determining the electrical performance. Based upon the preliminary analyses, the frequency-dependent inductance and resistance of A42 packages were attributed to the interaction between the skin effect and the non-unity permeability of ferromagnetic materials. To verify the theory and to test possible electrical enhancement for the A42, different surface-treated packages, including an Au-plated A42, a Pd/Ni-plated A42 and a Pd/Ni-plated Cu CQFP packages were characterized for their inductance and resistance. A 3-D field solver was also used to derive the permeability of the A42 materials at different frequencies. To further study the impact on high-speed digital chips where signals are usually analyzed in the time domain, a test structure made of both A42 traces and Cu traces was characterized using a time domain reflectometer for impedance, delay, and crosstalk. Both the frequency-domain and the time-domain results for A42 and Cu packages are summarized in this paper and their implications discussed.<
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