What is Fillet
A fillet refers to the concave formation of solidified solder that is found between the land or pad and the component lead during the soldering process. It is a part of the soldering technique used to mount components on a PCB. The quality and shape of the solder fillet play a crucial role in evaluating the overall soldering quality.
Using fillets improves the etched yield and material strength of the PCB. They are particularly beneficial when the pad diameter is larger than the connecting strand width. By applying fillets, acute angles at the interface between conductors and pads can be avoided, which helps minimize the concentration of stress at the interface.