Manufacturing method of electron device

In the case of soldering electronic components to circuit board, only consider the past temperature profile soldering electronic components to thermal shock, such as wetting soldering, without considering the influence of the interface to reflux welding strength after welding. Thus the problem of interface fracture often occurs reducing the thermal load on the welding portion weld strength. The present invention solves this problem as follows: melt temperature using the temperature profile on the fixed electrode portions to weld the circuit board, respectively, in accordance with an appropriate reflux welding face strength evaluation test range obtained without reducing the strength of the weld face, whichever is in accordance with compound thickness of the solder surface of the thermal load is determined uniquely obtained based on the appropriate range to reflux at any temperature profile having a peak temperature. By welding appropriate reflux in this range, the strength of the welding surface of the welding mass production is not reduced.