Jason Miller, Senior Staff Engineer, Sun Microsystems
Gustavo Blando, Principal Engineer, Sun Microsystems
Istvan Novak, Distinguished Engineer, Sun Microsystems

In this paper, we present on a new trace loss mechanism due to the glass-weave. Many PCB laminates are composed of a resin or epoxy material and glass fabric. The electrical properties of these two materials are very different. We examine the impact of the dielectric inhomogenity on differential and single-ended signal loss due to periodic loading of the glass-weave. Periodic loading results in a fundamental resonance where the distance between the discontinuities is one half of a wavelength. Periodic trace loading due to the glass weave and the effects of it have been previously ignored by the literature presumably due to the relatively high half-wave resonance it will establish. A number of key factors, which will be presented in detail, make this effect important to fully characterize and understand now. Due to these factors, glass-weave periodic loading can introduce additional losses in the insertion loss at midrange frequencies. These additional losses will be characterized in the paper using actual glass weave cross-sectional data. Parametric dependencies will be explored. The paper will also show how trace route angle and length can set up different secondary resonance patterns. Among other findings, the paper will show that although forty-five degree routes are preferred to reduce or eliminate glass weave effects, this strategy does not avoid the additional losses due to glass-weave periodic loading and in fact it results in the lowest glass-weave fundamental resonant frequency.