Patent ID: 8847083

Claim:
A printed wiring board (PWB), comprising: a plurality of through holes into which electronic parts' leads are respectively insertable; and a plurality of metal plated lands respectively formed around the through holes, such that each of the metal plated lands is formed in an annular shape with a hole corresponding to each of the through holes, wherein a pair of each of the through holes and each of the metal plated lands are formed in a coaxial manner, an outer shape of each of the metal plated lands defines a polygon in which the number of sides is an even number, each pair of facing sides are parallel to each other, and each of the metal plated lands has circular concaves at all corners, the metal plated lands are arranged such that the sides of the polygon are parallel to corresponding sides of neighboring metal plated lands, the circular concaves are configured to draw a solder during soldering, and a pressure difference ΔP between a gas phase and a liquid phase of the solder due to a surface tension and a curvature radius R of each of the circular concaves satisfy a Laplace equation in Δ P=P (Gas phase)− P (Liquid phase)=2σ/ R where σ is the surface tension of liquid.