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76 DESIGN007 MAGAZINE I JUNE 2022 Copper foils used in the PCB industry are deceptively complex. Copper is an excellent electrical conductor and thermal conductor, which makes copper foil ideal for the conduc- tive layers of most PCB applications. ere are many other copper foil properties which are important for an engineer to understand. e copper foils used in the PCB industry are typically made as rolled wrought copper (rolled annealed copper or RA) or as electro- deposited (ED) copper. Rolled copper is made by starting off with a copper billet and then going through successive rolling processes to reduce the copper billet to a copper foil at the desired thickness. ED copper is made with an electrolytic plating process, where copper is plated on a large drum and peeled off as copper foil while the drum rotates. e speed of the drum rotation will dictate the thickness of the copper foil. Aer the copper foils are made, both RA and ED copper go through several processes to apply treatments to the copper. ere are many varieties of treatments applied to the copper and for many different reasons. Some treatments are a passivation treatment to ensure the copper does not oxi- dize until the consumer uses it. Other treat- ments are applied to the copper to help with good chemical bonding with certain resin sys- tems (e.g., PPE vs. PTFE). Due to differences in the resin system, the materials react differ- ently to the various treatments. Since each resin system has different bonding character- istics, some treatment/resin combinations An Overview of Copper Foils Lightning Speed Laminates by John Coonrod, ROGERS CORPORATION

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