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42 DESIGN007 MAGAZINE I JULY 2025 D ES I G N E RS N OT E B O O K developed and documented by industry mem- bers of the U.S.-based Joint Electron Device Engi- neering Council (JEDEC) and the Japan Elec- tronics and Information Technology Industries Association (JEITA). In regard to product qual- ity, workmanship assessment, and reliability test- ing standards, manufacturers (both domestic and international) rely on standards developed by industry members of the International Electro- technical Commission (IEC) and the Global Elec- tronics Association (formerly IPC). These stan- dards have been developed to help manufactur- ers achieve quality, reliability, and consistency of their end products. Although the interconnect of less complex cir- cuit boards can be accommodated on the outer layers of the circuit board, the transfer of most of the interconnects between components on the higher component density applications will require subsurface circuit layers; a minimum clearance area around each device must consider access for inspection, and when necessary, rework or replacement of defective components: • Maintain uniform spacing between passive components • Establish minimum clearance for semicon- ductor packages • Avoid close spacing to and between higher profile devices • Determine clearances for rework tool access • Consider specialized equipment for removal and reattachment of large ICs When planning component placement and esti- mating the area requirement, consider both compo- nent outline dimensions, overall component thick- ness or height, and, to enable automated assembly and post-process inspection, the minimum clearance recommended (Figure 1) between components. Establishing PCB Assembly Process and Design Complexity The circuit board complexity can range from the very basic one- or two-layer substrate to the more com- plex multilayer construction. As component density increases, several key issues must be addressed: • Ratio of surface mount passive to active component area • Physical variations of pin-through-hole (PTH) components • Power and ground distribution and thermal management • Allowable number of circuit layers • One side or two side, mixed (SMT and PTH) technology To avoid potential delay in the overall manufac- turing process, the PCB design engineer will need to have a clear understanding of the designated PCB supplier's process capability and design rule criteria. If possible, establish a communication channel with the PCB supplier to review and eval- uate the circuit board design file before prototype fabrication and again before releasing the design for production quantity. To assure a successful outcome of circuit board fabrication, it is important that the designer recog- nize the manufacturing process complexities and associated cost impact, especially when implement- ing the more sophisticated fabrication procedures. Conductor routing protocols must be estab- lished in advance—the space separating via-hole lands, microvia lands, and/or component attach- ment lands (referred to as "channel width"). When these channels are restricted, the designer will ▼ F i g u re 1 : P rov i d i n g S M T c o m p o n e nt c l e a ra n c e to fa c i l i t ate a s s e m b l y, i n s p e ct i o n , a n d rewo r k a c c e s s . 3.0 mm 3.0 mm 3.0 mm