Electronic – the purpose of irregularly shaped SMD pads

layoutpcb-assemblypcb-designsurface-mount

Looking at a this buttons recommended footprint, I found these irregularly shaped pads:

TL3315 button footprint

The protrusions from the pads are way to small to act as solder thieves, and the button itself has gull wing pins that don't mimic the form of those pads in any way:

TL3315 product picture

What is the purpose of the odd shape of those pads? Is there any reason why I shouldn't just draw those pads as rectangles on my PCB layout?

Best Answer

I saw many datasheets and created many custom devices in EAGLE, this one is not much complex and does not involve many calculations although I tend to agree with commenters to your question that there might be better ways to describe the part's footprint.

Please notice the caption under the drawing: it says mounting rather than board footprint or whatever. This shows shape of soldering area, not shape of the pad itself. Big areas are intended for close contact with button's pins, while small perpendicular areas seem to be designed for extra solder "pour out" space.

You can make pad of any shape given the areas drawn on the mounting schematic is not covered by the solder mask.