Nuts and Volts - May 2014

make sure the SM components don’t need any kind of special pretreatment and can tolerate the temperature of your toaster oven. Most people tend to start with the smaller components and then work their way up in size.

The important thing is that you take appropriate precautions against electrostatic discharge by grounding yourself. I also like to gently press each component into the solder paste so that it doesn’t pop up while the solder melts during reflow in the toaster oven. Don’t worry about any of the TH components; you’ll solder them in after the board is “baked.” Baking Your Board (Reflow)

There are many different ways that you can melt (reflow) the solder paste. I use an inexpensive toaster oven (Figure 12). Like the fridge that I store my solder paste in, the toaster oven is used only for reflowing PCBs boards and never for food. Again, be safe and only reflow in a well-ventilated area and avoid breathing in any fumes.

When I “bake” or reflow a board, I simply place it on the rack, turn the temperature up to continuous, watch for the solder paste to melt, and then turn the oven off. It’s easy to tell once the solder paste has melted because it will change from dull gray to shiny silver and shimmer (Figure 13). Just make sure that all of the solder paste has melted — especially around the larger components that take longer to heat up.

The entire process should only take a few minutes (mine typically take 1-2 minutes when the oven is hot). It’s important not to over-bake your board because — just like anything — you can burn it out.

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