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44 DESIGN007 MAGAZINE I JULY 2024 cess. In this process, the circuit assembly is gradually heated to the temperature where the solder composition becomes liquidus, com- pleting the joining of component terminals to the circuit land patterns. e four primary methods used for solder termination of surface mount components in medium- and high-volume production opera- tions are: • Convection dominant reflow • Infrared (IR) reflow • Conduction transfer • Wave solder e convection-dominant solder-reflow pro- cess is favored by many high-volume manu- facturers. ese systems have been developed for in-line solder processing, transporting the circuit board (with placed SMT components) through a series of heat zones and progres- sively converting the deposited solder paste to a liquidus state. e temperature of the assem- bly will gradually rise upward to a peak tem- perature between 240°C and 260°C, promoting wetting between the components' terminals and the circuit board's land patterns. Preparing for Conveyor Board Transfer Placement systems commonly have belt conveyors to transfer the board through each stage of the assembly process. e belt system supports the board or panel on two edges. Key factors that will influence assembly sys- tem compatibility: • Board thickness (thin boards may require a smaller panel) • Weight of components (may require support) • Maximum board outline limit (machine dependent) Panel development: From a process effi- ciency standpoint, multi-unit panels can increase line throughput, sometimes signifi- cantly, by allowing simultaneous parallel pro- cessing of multiple circuit boards, especially during stencil solder paste printing, reflow- solder processing, and, when required, post- process cleaning operations. During the planning stage of the board design, the designer will be responsible for recognizing the conveyor edge keep-out zones and, when developing the two-sided SMT cir- cuit board, observing the maximum height profile for components mounted on the bot- tom surface of the circuit board. When developing the panel for conveyor han- dling, the designer must extend the width of the panel to prevent physical contact between component elements and the conveyor trans- port mechanism. e panel detailed in Figure 2 represents a typical circuit board outline for con- veyor transfer between the systems. Figure 2: Panel layout with tooling holes and global fiducial features for solder deposition.