solderfillet
Solder fillet refers to the concave, triangular-shaped connection formed between a component lead or pad and a plated through-hole (PTH) or a surface mount pad on a printed circuit board (PCB) after soldering. It is a critical visual indicator of a good solder joint. The fillet develops as molten solder is drawn by capillary action into the annular ring around the PTH or onto the pad and then wets both the component lead/pad and the PCB pad.
A properly formed solder fillet should exhibit a smooth, shiny surface and be free of voids, excessive
The size and shape of a solder fillet are influenced by several factors, including the surface tension