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28 DESIGN007 MAGAZINE I FEBRUARY 2022 e allowance for etching of plated designs is shown in Table 1. Note: It is important to mention that the above guidance is for the raw copper foil weights and not any additional design features like via fill or sequential blind laminations that will add cop- per thickness to the foil. Design Compensation Because of the physics of producing printed circuits, the PCB fabricator first needs to plate the circuit pattern (pattern plate), followed by a chemical etching (subtractive) process to define the circuit line width and space. To accomplish this, the initial circuit definition will need to be compensated for line width loss due to etching to assure that the final circuit will meet the design criteria. Surface to Hole Plating Ratio Regardless of how much copper a fabricator begins with, additional copper on the surface will be plated (pattern plating) as the plated through-holes are metalized. e key here is that this is not a 1:1 ratio; more copper will always be deposited on the surface than in the holes due to a higher plating current density on the surface. A working guide would be to calculate that 1.2 to 1.4 times the average mini- mum hole thickness will be deposited on the surface. Using the industry standard require- ment of 1.0 mils in the hole, the surface would receive 1.2 to 1.4 mils of plated copper on the surface, plus any base copper thickness. Impact of Sequential Laminations and Via Fill Sequential lamination (sub- assembly processing) is used to manufacture buried/blind vias, via fill, microvias, etc. ese technologies further compound the final surface copper thickness considerations discussed above as each process requires addi- tional plating and etching pro- cesses. Designers need to fully understand the impact of additional plating processes on the final thickness of copper traces and surfaces. Understanding the cost drivers in PCB fab- rication and early engagement between the designer and the fabricator are crucial ele- ments that lead to cost-effective design suc- cess. Following your fabricator's DFM guide- lines is the first place to start. DESIGN007 Anaya Vardya is president and CEO of American Standard Circuits; co-author of The Printed Circuit Designer's Guide to… Fundamentals of RF/ Microwave PCBs and Flex and Rigid-Flex Fundamentals; and author of Thermal Management: A Fabricator's Perspective . Visit I-007eBooks.com to download these and other free, educational titles. He also co-authored Fundamentals of Printed Circuit Board Technologies and provides a discussion of flex and rigid flex PCBs at RealTime with… American Standard Circuits. Designers need to fully understand the impact of additional plating processes on the final thickness of copper traces and surfaces. Table 1.