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JANUARY 2025 I DESIGN007 MAGAZINE 53 Traditional multilayer board construction adds conductor layers in pairs (2-4-6 and so on). However, an excessive increase in circuit layers will affect both fabrication efficiency and manufacturing costs. Challenges facing multilayer PCB fabrica- tors include: • Tolerance control when aligning all layers in the stackup • Maintaining layer-to-layer registration during lamination • Consistent thickness control of the fin- ished board • Avoiding hole breakout when drilling or ablating vias Here are brief descriptions of three methods commonly used to fabricate multilayer circuit boards: • Sequential buildup. PCBs begin with the fabrication of a two-copper layer core as a base, followed by layering sheets of par- tially cured polymer-impregnated (pre- preg) fiberglass sheet material between copper foil layers and laminating them under high heat and pressure using a lami- nation press. • Multiple core stackup. PCBs combine two or more two-sided copper-clad lami- nate materials. Aer imaging and chemi- cal etching of the circuit pattern, workers assemble the two-layer core units with a dielectric glass-reinforced prepreg sheet between core layers, then laminate them under high heat and pressure. • Multiple core with foil cap stackup. PCBs combine two or more two-sided copper- clad laminate materials. e process fol- lows the steps noted above with an addi- tional layer of prepreg and copper foil on both outer surfaces, simultaneously lami- nated under heat and pressure. Figure 1 illustrations represent the mul- tiple-layer circuit board constructions out- lined above. e increasing quantity of signal conduc- tors, increased component density, and the number of terminals on more advanced com- ponents will probably restrict the open area on the circuit board's surface. is can impede the designer's effort to provide the most effi- cient interconnect circuit routing. As the spacing between terminal lands decreases, Figure 1: Multiple layer PCB construction variations.