Evaluation Technique for Complex Permittivity of Mid-Loss Underfill Materials by a Cut-Off Circular Waveguide Method in Millimeter Wave Bands

Abstract

Underfill materials are used in a packaging of millimeter wave IC. However, there are few reports for dielectric properties of underfill materials in millimeter wave region. A cut-off circular waveguide method is one of a powerful technique to evaluate precisely complex permittivity in millimeter wave region. This method may be useful not only for low-loss materials, but also for mid-loss ones with loss tangent of 10^-2 order. In this paper, an evaluation technique based on the cut-off circular waveguide method is presented to measure mid-loss underfill materials. As a result, the relative permittivity ε_r and the loss tangent tanδ are in the range of 2.8∼3.4 and (1.0∼1.6)×10^-2, respectively. Also, the measurement precision is 2.3% for ε_r ≅ 3 and 40% for tanδ ≅ 10^-2.