A situation that the volume expansion difference in circumferential side and the outer nuclear material is flicked occurs to provide a bonding material which does not occur.
In nuclear material 10 a solder alloy plated film on the surface of the core 12 consisting of A Sn and Bi, Bi in the solder plating layer 16 is distributed in the solder plating layer 16 at a concentration ratio in a predetermined range is nuclear material, nuclear material distributed in the solder plating layer within a predetermined range the concentration ratio of 91.7 to 106.7% of Bi. Bi in the solder plating layer is a homogeneous, Bi concentration ratio over its entire area, including the inner circumferential side 14 of the solder plating layer, the outer peripheral side is within a predetermined range. Therefore, the inner circumferential side to melt earlier than the outer peripheral side, a situation such as volume expansion difference between the inner and outer peripheral sides are flicked nuclear material occurred does not occur. Since the entire solder plating layer substantially uniformly melted, since no positional deviation of the nuclear material that might be generated by the displacement of the molten timing, there is no risk of short circuit between electrodes.
.FIELD 4