Optimization of PCB SI Coupon Design that Minimizes Discontinuity

Juhee Lee, Kyeongsoo Kim, Namdong Lee, Kyungsoo Lee
ISU Petasys
Daegu, Korea

The importance of signal integrity is emphasized as signal speed increases, and higher frequencies are applied. The PCB manufacturer uses SI coupons that can replace the in-product circuit to measure and calculate the signal loss. In this study, we tried to minimize the discontinuous path of Delta-L coupon by using the VIPPO (Via In Pad Plated Over) technique to improve the signal integrity. We compared the VIPPO-applied design that has minimal discontinuity with the conventional Delta-L design. In order to minimize discontinuity, circuits connected to pads and via holes were removed from the outer layer, and the pads were designed directly above the via holes. First of all, we simulated the optimized design that eliminated discontinuities using Signal Integrity Software, Simbeor. Second, we measured and verified Delta-L by using Introbotix's Accu-prober program. In the future, higher measurement frequencies will further increase signal loss due to unnecessary pathways and discrete signals, therefore minimizing the effects of discontinuity will be an important issue, and using the VIPPO technique will help to improve signal integrity.

As the speed of signals increases, the importance of signal integrity is emphasized. There are inherent components in the PCB structure that interfere with the signal quality, and how to remove them is also important.
In this study, the structure that minimized discontinuity using VIPPO method was applied to Delta-L coupon. The analysis showed that minimizing discontinuities reduced signal loss, improved accuracy in measuring SI coupons representing real products.

Small discontinuous paths also affect signal quality, and effort are needed to eliminate via and discontinuities to improve signal integrity.