of the present invention therefore is capable of forming a low melting point solder paste such as a paste including in sn alloy solder fig3 also teaches that if both solder pastes are compared to each other at the same temperature the solder paste including azobis has higher wettability compared with that of ordinary solder paste which does not include azobis because the wetting time of solder paste including azobis is smaller than that of the solder paste which does not include azobis as described before the viscosity of prior art solder paste varies from time to time especially when low melting point solder paste is used this decreases uniformity and reproducibility of thickness of solder paste coating the soldering area wettability of solder and decreases the reliability of soldering but it has been found that when radical generator of azobis is added into the flux the solder paste is not hardened even after it is stored for six months this means that the shelf life of the solder paste of the present invention has been elongated to a greater extent therefore the solder paste of the present invention is suitable for screen printing assuring high reliability of the soldered part in fig4 the change of viscosity of the soldering paste with time is shown in the figure a curve connecting solid circles shows the variation of viscosity of a prior art solder paste which.