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36 DESIGN007 MAGAZINE I JULY 2023 Reliable bonding reduces the risk of delami- nation through thermal stresses. e tried-and- tested way of achieving a good, reliable bond is to ensure that the copper is sufficiently rough to promote adhesion to the epoxy resin in the prepreg material. As materials and bonding technology improves, the copper surfaces can be made increasingly flatter and still achieve the desired reliability. In the future, new bond- ing methods—some already here but still on the high-priced side of the equation— may allow extremely flat copper to bond reliably. Meanwhile, as the industry is heading down the road of "smoother" copper, there is still a need to model the effects of a rough surface on signal transmission. Rough Roughness Reasoning Models and Methods ere are four or five primary methods for modelling signal losses owing to roughness, depending on how you interpret them. Ham- merstad and Groisse are legacy methods, but still valid at the low GHz range. Hammerstad was developed around World War II to calculate the losses caused by machining grooves in early radar systems. Groisse extends the frequency capability a little higher. But if you are pushing into the high GHz, then these legacy models soon start to saturate, and they will both under- predict the contribution that surface roughness makes to loss. Newer methods (of the last decade or two) perform to much higher frequencies and correlate well with measurement systems. The Pulse Feature Column by Martyn Gaudion, POLAR INSTRUMENTS