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46 DESIGN007 MAGAZINE I OCTOBER 2022 trolling material utilization. e examples in Figure 1 compare circuit escape routing capa- bility for very-fine-pitch BGA. Process refinement for the ultra high-den- sity circuit includes more efficient imaging capability and greater utilization of alternative hole-forming techniques, advances in etching and plating chemistry, and refinement in base materials and lamination methods. A key con- tributor to enabling higher density circuits is in the advances made in imaging. Laser direct imaging (LDI) and diode imaging systems have become mainstream technology for a wide segment of the PCB fabrication indus- try. Where circuit pattern imaging relied on first photoplotting the circuit pattern onto film-based masters and using contact printing to transfer the image to the etch resist coating on the copper-clad panel surface, fabricators have streamlined their processes with trans- ferring the image directly from the CAD file onto the panel's resist coating. Direct imaging eliminates the effect of contact film stability and improves layer-to-layer registration capa- bility. Before committing to adopting any level of UHDI technology, however, the designer should take the time to consult with the des- ignated PCB supplier(s) selected to validate their capability to furnish the required com- plexity level at the expected production quan- tity. Many users have already established a business relationship with key pre-qualified suppliers that have demonstrated their level of expertise and proficiency. ese suppliers can be the designer's best source for evaluating the design before manufacturing, oen suggesting refinements that will affect both cost and reli- ability of the finished product. Note: e feature size dimensions furnished in the above tables may be beyond the process capability of many printed circuit board fabrica- tors. To minimize production delays, review the selected fabricators' design rules before initiating the HDI or UHDI project. DESIGN007 Vern Solberg is an independent technical consultant, specializing in SMT and microelectronics design and manufacturing tech- nology. To read past columns, click here. Figure 1: Planning escape routing for very fine-pitch array components.