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12 The PCB Magazine • April 2014 by Happy Holden, retired and Michael Carano, omg electronic cHemicals, llc. F e a t u r e This article is an update of the Holden-Carano article originally published in the February 2013 issue of The PCB Magazine. Abstract One of the most difficult printed circuit boards to adapt to Pb-free assembly processes is the high-layer count multilayer. Often, these multilayers have through-hole and hand-sol- dered components, and requirements for two or more rework cycles. The 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-4s. One solution to this problem is to rede- sign the multilayer using current design rules and newer innovative fabrication technologies. This article will review four of these new and enabling technologies: • Laser-drilled microvias • Routing BGA using channels • Contribution of new SMT connectors • Layer assignment changes (architectures) Microvias offer the most significant opportunity to reduce not only the layers and thicknesses of multilayers, but also their cost while improving their electrical performance and density. Sev- eral examples will illustrate these new oppor- tunities. Since blind vias are surface phenom- ena, to get the maximum benefit from them, layer assignment for signal, ground and power need to be reviewed and alternative construc- tions considered. These blind vias, by reducing Lead-Free Reflow for High-Layer- Count PCBs