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34 PCB007 MAGAZINE I APRIL 2023 A thick, high layer-count multilayer is one of the hardest printed circuit boards to adapt to lead-free assembly processes. e rea- son: Multilayers oen have through-hole and hand-soldered components and require two or more reflow cycles. e higher reflow tem- peratures and slower wetting of lead-free sol- ders place an enormous strain on the laminate and copper-plated hole barrel. In many cases, the boards cannot be assembled reliably, even with newer, higher thermal performance FR-4 materials. One solution to this problem is to redesign the multilayer using current design rules and newer innovative fabrication technologies. Microvias offer a significant opportunity to reduce the layers and thicknesses of multilay- ers at a reasonable cost—all while improving electrical performance and density. Consider blind vias, which are surface phe- nomena. To get maximum benefit from them, layer assignment for signal, ground, and power must be reviewed, and alternative con- structions should be considered. Reducing the number of through-holes helps increase routing density and lower layer usage. You can achieve higher connector density and improve electrical performance by replacing through-hole connectors with surface-mount connectors. ese new multilayers are not only thin- ner, cheaper, and easier to design, but are less Lead-free and the Fabrication Challenge, Part 1 Trouble in Your Tank by Michael Carano, IPC CONSULTANT

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