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OCTOBER 2022 I DESIGN007 MAGAZINE 45 thin Cu foil or use base materials prepared for a semi-additive Cu plating process. When con- ductor lines and spaces must be reduced fur- ther, the fabricator will utilize base materials prepared for a semi-additive or primed for a fully additive copper plating process. Exam- ples shown in Table 1 compare general process capability for subtractive, semi-additive, and fully additive copper deposition and micro-via hole-forming variations. Electrical interconnect on internal layers for the board enables significantly greater circuit routing density. e circuit path between key components can be more direct as well, pro- viding greater circuit speed and lower resis- tance. To ensure the greatest interconnect effi- ciency, the designer should alternate the over- all direction of the circuit path from one layer to another, using plated via holes to accom- modate direction change as needed. With the circuit width and space requirement already established in the CAD system, the auto router function can quickly complete the initial inter- connect process. Exhibited in Table 2 are three levels of HDI PCB conductor routing com- plexities. High-Density Circuit Fabrication Solutions For many applications, the cost of high- density printed circuit boards has remained a detractor. Although PCB complexity has increased, the prices for HDI have declined and analysts expect this trend to continue to decline further each year. is is due in part to increased competitive conditions, but we can also attribute the trend to diligence in refining fabrication process control methods and con-