Investigation of high frequency characteristics of Ag-based wirebonds

In this paper, high frequency characteristics of Ag alloys, for example, Ag-Au-Pd and Ag-Pd, were studied. At 20°C, the electrical resistivity of pure Ag, Au, and Pd is 1.587 μΩ·cm, 2.214 μΩ·cm, and 10.54 μΩ·cm, respectively. Depending on the metallurgical distribution of Pd in the Ag-Au alloy or Ag alloy wire bonds, the high frequency behaviors of the wire bond could vary drastically. For example, if Pd is distributed mainly on the surface, the surface impedance of the Ag-alloy wire bond could be drastically increased as the frequency is increased. Agilent´s Vector Network Analyzer (VNA) was used to obtain the S-parameters up to 67 GHz, well beyond the first resonance frequency. R, L, and C were extracted by converting the measured S-parameters. To our knowledge, this paper could well be the first one to report the effects of Pd distribution on the RF characteristics (due to the skin effect) of the Pd coated/doped Ag alloy wire bonds. Analyzing the high frequency characteristics along with reliability assessment of Pd coated/doped Ag-alloys (such as cross-sectional micrographs), an optimized Ag-based wirebond can be picked.