Electrical design and simulation of high density printed circuit boards

Abstract

High density interconnect printed circuit board technology enables significant board size and layer count reduction. Thinner innerlayer dielectric materials, reduced line widths, and closer spaced components inherent in high density board technology require a change in electrical design methodology. Most notably, the thinner dielectric thickness significantly impacts the electrical performance of the circuit board with respect to crosstalk, board capacitance, via inductance, and controlled impedance. Via inductance is significantly reduced but the possible occurrence of innerlayer capacitance and crosstalk is increased. Using either FR-4 type epoxy or higher performance materials conventional controlled impedance structures such as a stripline, microstrip, and coplanar waveguide are possible to design using current manufacturing capabilities. A 50 ohm impedance can be achieved by a microstrip or a coplanar waveguide using either dielectric material. The stripline can only achieve approximately 35 ohms with the higher performance material and 25 ohms with the FR-4 type epoxy material.