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Design News, March 2013

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Mechatronics Using Heavy Copper & EXTREME Copper in PCB Design & Fabrication for Maximum Reliability Power electronics products using heavy copper circuitry have been in use for many years in the military and aerospace industry and are gaining momentum as a technology of choice in industrial applications. By Dave Basista, epec engineereD technologies V arious power electronics products are being designed every day for a range of applications. Increasingly, these projects are taking advantage of a growing trend in the printed circuit board industry: Heavy Copper and EXTREME Copper Printed Circuit Boards. What defines a heavy copper circuit? Most commercially available PCBs are manufactured for low-voltage/low power applications, with copper traces/planes made up of copper weights ranging from 1/2 oz/ft2 to 3 oz/ft2. A heavy copper circuit is manufactured with copper weights anywhere between 4 oz/ft2 to 20 oz/ft2. Copper weights above 20 oz/ ft2 and up to 200 oz/ft2 are also possible and are referred to as EXTREME Copper. For our discussion here we will focus primarily on Heavy Copper. The increased copper weight combined with a suitable substrate and thicker plating in the through holes transforms the once unreliable, weak circuit board into a durable and reliable wiring platform. The construction of a heavy copper circuit endows a board with benefits such as: • Increased endurance to thermal strains. • Increased current carrying capacity. • Increased mechanical strength at connector sites and in PTH holes. • Use of exotic materials to their full potential (i.e., high temperature) without circuit failure. •Reduced product size by incorporating multiple copper weights on the same layer of circuitry (see Figure 1). • Heavy copper-plated vias carry higher current through the board and help to transfer heat to an external heatsink. • Onboard heatsinks directly plated onto the board surface using up to 120-oz copper planes. • Onboard high-power-density planar transformers. Although the disadvantages are few, it's important to understand the heavy copper circuit's basic construction to fully appreciate its capabilities and potential applications. Heavy Copper Circuit Construction Figure 1: sample featuring 2 oz, 10 oz, 20 oz, and 30 oz copper features on the same layer. Standard printed circuit boards, whether double-sided or multilayer, are manufactured using a combination of copper etching and plating processes. Circuit layers start as thin sheets of copper foil (generally 0.5 oz/ft2 to 2 oz/ft2) that are etched to remove unwanted copper, and plated to add copper thickness to planes, traces, pads, and plated-through-holes. Design News | march 2013 | www.d esign n ews.com –M4–

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