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September 2015 • SMT Magazine 115 mon 'center hot spotting' sometimes present in traditional reflow ovens; individual zone tem- peratures are extremely close to product board temperatures, making it easier to profile; lower overall equipment cost, since a plenum is not required methods of board transportation There are two common techniques used for conveying boards through a multi-zone oven: 1. Belt conveyor 2. Edge or pin conveyor A conveyorized mesh belt, typically stainless steel or other non-corrosive alloy, is the most common method. Air is able to flow through the belt for even heating on the top and bottom of the board. The pin or edge-type conveyor carries the board by the edges in a continuous line, allow- ing unobstructed airflow around the board. This method can be integrated within a modular in- line system with other assembly machines. Either method works equally well for single- or double-sided boards. Edge conveyors can add some cost that may not be necessary. For inte- gration with other in-line systems, consult the Surface Mount Equipment Manufacturers As- sociation (SMEMA), which writes connection standards for modular circuit board assembly integration. Inerting systems If an inerting system is advised for a specific product application, nitrogen is the most com- mon gas used for reducing or eliminating oxi- dation during reflow. However, in most low- to medium-volume assembly environments, in- erting is typically not needed. When specified, an inerting system can add approximately 10% more to the cost of a basic reflow oven, and most manufacturers offer it. In the next column, Reflow Ovens, Part 3, I will address the following: 1. Software and controls 2. Onboard PLC profiling 3. PC-driven profiling 4. Third-party profiling and validation 5. Power management smt robert voigt is vp of global sales at DDM novastar inc. To reach voigt, click here. Smt quiCK tipS seLeCtING A reFLOW OveN, pArt 2 continues figure 2: airflow pattern in a horizontal convection conveyorized oven.

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