![]() Although electrodeposited copper has greater tensile strength and elongation before breaking, rolled copper has better elastic elongation before reaching permanent deformation. Under similar conditions, rolled copper has significantly improved resistance to cracking. Thermal Shock Resistance: Under some extreme conditions of rapid thermally cycling, electrodeposited (ED) copper may exhibit thermal stress cracks in narrow conductors.Some studies have shown that the copper profile can affect the propagation constant, with higher profile foils leading to an apparent increase in the effective dielectric constant. With modest adjustments to the input parameters, the Hall Hurray model can accurately predict conductor loss over a wide range of laminate thicknesses and frequencies. The “Hall-Huray” model, developed from a “first principles” analysis, has been recently incorporated into commercial design software. More recently, at higher frequencies and with thinner laminates, it was found that H&J significantly under predicated the increase in conductor loss with surface roughness. The H&J model became the “textbook” method for calculating the effect of surface roughness on conductor loss. Hammerstad and Jensen, incorporated Morgan’s model, along with correlated data in microstrip design method. Morgan published results of numeric simulations that indicated that a factor of two increase in conductor loss could be caused by surface roughness. It has been well-known since the earliest days of microwave engineering with wave guides that the conductor surface roughness can substantially affect the conductor loss. Of course, the rolled copper with no surface treatment is typically the smoothest. The surface roughness of different copper weights (oz) is different. Roughness data of electrodeposited (ED) and rolled (RA) copper foils with different thicknesses was obtained by using an optical surface profile. However, in our experience, the Sq (RMS) profile as measured by white light interferometry of the treated side of copper foil correlates between conductor losses. Many sources report the Rz (peak to valley) profile as measured by a mechanical profilometer. Surface roughness can be measured by mechanic and optical methods. This is surface roughness, and which has effects on the performance of high-speed PCBs. ![]() To the naked eye, coppers appear smooth, but at the microscopic level, copper foils and copper on laminates exhibit surface irregularities. What’s copper surface roughness? As a PCB design and manufacturing company, MADPCB understands it well. So if you have a really sensitive design using thin materials, it’s good to know what the average roughness is and try to understand what to expect for the variation of the roughness.In high-speed design (HSD) and fabrication, we always meet the roughness of the conductor’ surface, which is called conductor or copper surface roughness. And the roughness does impact the performance a lot.įor very high-frequency applications, the circuit geometry usually needs to be etched very accurately, and this can be done better if the Copper is thin. When the copper planes are really close together, in the case of a really thin laminate, the copper planes have a pretty significant influence. On very thin circuits, such as those for high-speed digital or millimeter wave ones, the thinner the substrate is, the more sensitive the circuit will be to the surface roughness of the Copper. But rougher Copper surface increases insertion loss, and the resistance slows down the signals. Some of that roughness is desirable because it improves adhesion with the laminate: the rougher, the Copper, the more bond area and better peel strength. The rough side of the ED Copper can vary a lot depending on how the Copper is made. ![]() The smooth side of ED copper is a little rougher than that and usually averages around point. RA Copper, on average, has a surface roughness of 0.35 microns RMS (root mean square). The grain structure of RA Copper is different from ED copper, and this impacts the etching process. The copper grain structure will parallel to the plane. The side of the Copper next to the drum will be very smooth, and the other side of the Copper will be rougher. ![]() So thicker Copper is going to take a longer time. The rotation speed of the drum determines the copper foil thickness. The RA Copper fabrication process starts by passing pure copper ingots through a series of rolling processes, resulting in the desired thickness of copper foil.ĭuring the ED Copper fabrication process, Copper is plated onto a drum. ![]()
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