I'm learning to layout PCBs and lately I came across practice that made me curious. The chip passives' pads are etched with oblong / rounded shape, instead of rectangular shape that is used in all example libraries and even the IPC-7351B standard (you can download LP Viewer for free registration and see for yourself). Here are the examples (I marked the interesting pads with yellow):
The question is: what are these rounded pads good for? Should I use them instead of rectangular ones to make my board look more "pro"?
My first thought was that it might be because it might be better for reflow soldering, but I'm bit puzzled about that reasoning. The one advantage I see with these is more routing space around such rounded pad (no "sharp" edges).
Answer
Rounded pads are better for lead-free surface mount assembly using reflow, because lead-free solder doesn't flow as well as leaded solder, and the higher temperature causes problems with the flux at the corners. They are recommended by IPC. Here is a reference I found.
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