Electronic – Stencil apertures


When ordering a desktop stencil for laying down solder paste, there is an option to specify the stencil's aperture. Rectangular, home plate, trapezoidal…what's the difference between them? Is there one that is preferred for hand-populating surface mount parts?

Best Answer

If you choose rectangular, the stencil will come back with exactly the geometry you've specified in your Gerber files. If you specify "home plate" the manufacturer will shrink the pads by 10% or thereabouts, but make the pads 5 sided, which improves soldering success rates in automated board stuffing. I've not heard of trapezoidal pads before, but I assume it's a similar tweak to improve solderability.

For hand soldering surface-mount parts, you can safely stick with rectangular. The biggest improvement you can make is to get access to a stereo microscope for soldering. It makes a huge difference. You'll probably find that the limiting factor on your soldering ability is not your hand-eye coordination, but your vision. Obviously, a microscope improves your vision substantially.

Update: I just ran into this today-- "trapezoidal" does not refer to the the footprint of the stencil hole. It refers to adding a slope to the cut, so if you were to look at the stencil from the side, you would see a trapezoid. "Laser cutting apertures with trapezoidal walls and also rounding corners will offer better paste release," according to a Texas Instruments datasheet.