Pan Pacific Symposium Conference Proceedings


IMPEDANCE AND PROPAGATION DELAY CHARACTERIZATION FOR FR-4 PRINTED CIRCUIT BOARDS

Author: S. Pochareddy
Company: State Univ. of NY - Binghamton
Date Published: 2/13/2001   Conference: Pan Pacific Symposium


Abstract: Printed Circuit Boards (PCBs) are increasingly being considered as critical components of electrical and electronic subsystems. Signal integrity is a critical factor on electrical and electronic subsystems operating at higher logic speeds. Transmission lines on PCBs directly affect the signal integrity. Impedance and propagation delay are the two most important characteristics of transmission lines. A good understanding and control of these two characteristics is a must. An accurate prediction model is imperative to calculate the impedance of a transmission line prior to design. This practice, which could shorten design cycle time, is essential particularly to original equipment manufacturers (OEMs). It is also essential for the OEMs to characterize the supply base to manufacture controlled impedance PCBs.

In this research, three 2-dimensional impedance prediction tools were compared. A 14-layer FR-4 PCB was designed as a test vehicle with different transmission line configurations and structures. A stack-up was designed with dielectric materials of varying thickness and glass to resin ratio. The test vehicle design addressed issues relating to single-ended, edge-coupled differential and coplanar impedance. Propagation delay was measured to determine the effective dielectric constant of FR4 on finished boards. Statistical analysis was performed to understand the impact of design and process parameters on impedance and propagation delay.

Keywords: PCB, TDR, OEM, FR-4, Impedance, Propagation delay.



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