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JULY 2025 I DESIGN007 MAGAZINE 43 D ES I G N E RS N OT E B O O K need to consider reducing conductor line and space widths or resort to sub-surface circuit rout- ing to achieve interconnect goals. Although neces- sary for the more complex applications, multilayer circuit board fabrication will add to both fabrication complexity and increased cost. PCB fabricator specialist suggests that the circuit board design engineer consider some of the major factors impacting unit cost: • Layer count (2, 4, 6, 8…) • Laminate type (material)* • Overall size of the PCB • Base copper weights in different layers • Lines and spaces on different layers • Pad sizes and PTH-to-Cu clearance • Aspect ratio and number of holes • Surface finish *Laminate materials, although having similar attributes, may be priced differently, depending on the supplier location and the number of layers. Base material specified and manufacturing tech- nology required will effectively determine overall PCB fabrication cost. As a reference, Table 1 repre- sents a typical PCB pricing scheme using a two-cir- cuit layer PCB as a base price factor. With regard to PCB size, it is common prac- tice to arrange smaller outline PCBs onto a larger outline panel arranged in an array format. This will increase process efficiency but the unit cost impact will ultimately be based on the overall panel yield (reduced by the number of individual boards on the panel that are unacceptable). As the density factor com- presses, the area surrounding each component is reduced. To resolve connectivity issues, the designer will need to consider implementing narrower widths and spacing for conductor routing. Before reduc- ing topography features, however, review the designated circuit board supplier's "stan- dard capability" and the potential cost impact when implementing higher density (HDI) fabrication tech- nologies, such as sequential buildup construction with smaller vias, blind and buried vias. The process related factors that will impact finished PCB cost are furnished in Table 2. PCB design rules can be classified into different technology levels: high-, medium-, and low-tech. Each level applies to a specific supplier's capabil- ity and each will follow standard or advanced rules. Before committing to adopting HDI or UHDI tech- nology, the designer should confirm that the PCB supplier(s) selected can furnish the preferred com- plexity level at the anticipated production quantity. • Review your PCB supplier's material offerings • Discuss any unique base material or copper foil needs • Clarify layer stacking alternatives with supplier • Define power and ground distribution objectives • Specify controlled impedance requirements When estimating circuit boards' manufactur- ing cost, the designer must consider materials, cir- cuit density, the number of circuit layers, and fab- rication process complexity. While mechanically drilled and plated via-holes are a mature technol- ogy for multilayer circuit board fabrication, the bur- ied via and laser-ablated blind microvia-hole form- ing require more sophisticated systems. Circuit Interconnect Planning Before beginning the PCB design, the designer must establish the key operating conditions of the Ta b l e 1 : P ro d u ct i o n p r i c i n g g u i d e fo r a n 1 8" x 24" p a n e l ▼ Materials represent approximately 20% of the total bare board cost Source: RUSH PCB Inc. 1