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Build an SMT Reflow Oven Controller

Build an SMT Reflow Oven Controller

When designing high-speed applications, working with SMT components and soldering by hand can be tedious. Robert H8-3687-based SMT Reflow Oven Controller transforms a conventional infrared toaster oven into an effective reflow oven that ensures thermal control.
The key to good reflow is a precise multistep thermal profile, as illustrated in Figure 1. The preheating profile allows you to slowly bring the PCB to a temperature high enough to dry the solder paste (approximately 100°C) while minimizing the risk of thermal stress on the components in the reflow phase. After thermal stabilization, the board is heated as quickly as possible to the reflow temperature (approximately 250°C). The board stays above the reflow temperature for a set period of time (usually around 30 s) before it’s cooled down in a controlled fashion.

What are the key characteristics of an industrial reflow oven? Quick heating and cooling is important (the quicker the better) in order to reduce the thermal stress on the components. (The pads and solder paste have a lower thermal latency than the components themselves.) Maintaining a homogeneous temperature inside the oven is also important, especially when you’re working with large PCBs. And, last but not least, regulation is a must in order to guarantee that successive reflows follow the exact same profile. As you can imagine, I will handle the regulation with a microcontroller-based solution, so let’s focus on the low-cost oven you’ll use to replace a real reflow oven.

In order to have a quick heating time, some industrial reflow ovens use infrared heaters. Why not just buy an infrared-based toaster oven like the one shown in Photo 1? I bought mine on the ’Net for less than $150. It has two quartz heating elements on the top and a classic resistor on the bottom (a total of 1,100 W).

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