Abstract: A lead-free solder composition includes: 3 wt % to 5 wt % of Ag, 0.2 wt % to 0.8 wt % of Cu, 1 wt % to 7 wt % of Bi, 0.005 wt % to 0.06 wt % of Ni, 0.005 wt % to 0.02 wt % of Ge, and the balance being Sn based on 100 wt % of the lead-free solder composition.

Abstract: A silver-free and lead-free solder composition includes: 2 wt % to 8 wt % of Bi, 0.1 wt % to 1.0 wt % of Cu, 0.01 wt % to 0.2 wt % of at least one of Ni, Fe, and Co, and the balance of Sn based on 100 wt % of the silver-free and lead-free solder composition.

Abstract: A hot zone heat transfer structure of a Stirling engine is provided. One end of a cylinder includes a heated head, with its end wall connected with a hot air pipe. The cylinder accommodates a piston. The piston has an end surface corresponding to the end wall, between which a hot zone is defined. The end wall is fitted with a protruding heat conductor towards the piston, and the end surface is fitted with a concave heat-conducting portion, enabling normal overlapping of the ends of both the heat conductor and the heat-conducting portion. The overlapping may vary with the changing locations of the piston. A flanged section is set externally onto said heat conductor towards the exterior of the end wall. The heat from the head can be transferred to the central area of the hot zone via the help of the heat conductor and heat-conducting portion.