Analysis of SMT component land pad discontinuity effect on the overall transmission line impedance in high-speed applications

Abstract High-speed and high-frequency PCB interconnect solutions with the slightest discontinuities in physical geometry along microstrip transmission line can significantly degrade integrity of signal being transferred. This paper presents an analysis SMT component pads their impact on successive impedance. During 0805, 1206 2512 package size pad discontinuity evaluations it was spotted, that increasing deviation from target impedance affects segment following discontinuity. A 25 Ω offset at reduces afterwards by up to 7 Ω. 37 results a reduction 15 , whereas 45 change leads 30 effect is also present multiple evenly-spaced discontinuities. But single reference plane cut-out, which twice as wide discontinuity, substantially improves overall line, including drop.