The tip end of the bonding tip is defined between first and second edges. A first inclined surface gets remoter from a first terminal at a position remoter from the first edge. The second inclined surface likewise gets remoter from the first terminal at a position remoter from the second edge. The solder is contoured by first and second contours on the first terminal. The second terminal is located on the solder between the first and second contours. The tip end of the bonding tip is urged against the second terminal. Heat is transferred from the bonding tip to the solder. The melted solder spreads into gaps between the second terminal and the first and second inclined surfaces. The solder is thus prevented from spreading outside the contour of the first terminal. This results in a reliable avoidance of a short circuit between the adjacent first terminals.