Nuts and Volts - May 2014

hold your PCB using a stencil frame. You could buy a more professional style model, or use duct tape and a few old pieces of plastic as I do. Sometimes I use a few old blank PCBs from previous projects. The important thing is that the scraps are the same thickness as your current PCB.

A friend of mine mentioned that he would tape his stencil frames to 14” x 14” polished flooring tiles that he had left over after remodeling. They ended up working very well for him because they provided a heavy flat surface that he could also easily store with the stencil still attached.

I followed his advice and purchased a couple of light colored polished floor tiles from a home improvement store for a few dollars. The light color lets me know where any solder paste is, and the smooth surface makes it easy to clean.

Once you have a sturdy work surface, tape your frame around the PCB. Then, line up the stencil with the solder pads on the PCB, and tape it down on one side (Figure 9).

You’re now ready to apply the solder paste. Applying the Solder Paste

To apply solder paste, begin by cleaning the PCB and preparing the paste. I personally use 90% isopropanol and a coarse plastic brush. To prepare the solder paste, I let it warm up to room temperature and then mix it in its container until it reaches a smooth texture with a slight shine (while wearing rubber gloves).