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34 DESIGN007 MAGAZINE I NOVEMBER 2021 increased current capacity but at 18 GHz both filled and hollow vias perform much the same. Key Points • Copper-filled vias complement thermal management. • e conventional plating process cannot close the via completely. • icker barrel plating improves the thermal transfer and current-carrying characteristics of vias at DC and low frequencies. • ermal vias are used to transfer heat from one layer to another. • FR-4 does not offer high thermal transfer. • Solid vias do not reduce the equivalent inductance of the structure. e current tends to only flow in the perimeter of the barrel due to the skin effect. • Conductive epoxy-filled is the best prac- tice for the vias to have a finished diameter between 8–18 mil. • Filling vias creates a solid core and allows for a flat surface to be plated. is keeps the solder at the assembly level from leaking through and compromising the solder joint. • e equivalent inductances for the hollow via and solid via cases are virtually identical. • At 18 GHz, skin depth effects alone will force the current to the surface of the solid via. DESIGN007 Resources 1. Beyond Design: The Proximity Effect, by Barry Olney, Design007 Magazine, March 2019. 2. "Microwave Circuit Modeling using Electromag- netic Field Simulation." D. Swanson and W. Hoefer, Guide to Copper-Filled Vias, Process & Benefits. 3. Copper & Epoxy Filled Vias, Cirexx Interna- tional. 4. "High-Power Dissipation Copper Filled Thermal Vias by Kuprion," Power Electronics News, April 23, 2021. Barry Olney is managing director of In-Circuit Design Pty Ltd (iCD), Australia, a PCB design service bureau that specializes in board- level simulation. The company developed the iCD Design Integrity software incorporating the iCD Stackup, PDN, and CPW Planner. The software can be downloaded at www.icd.com.au. To read past columns or contact Olney, click here.