When electronic components are mounted on a surface of a circuit board, a cream solder is conventionally used in which Sn-37 mass % Pb eutectic solder in the form of the metal particles is kneaded with flux. Sn-37Pb eutectic solder has a eutectic temperature of 183° C. The temperature profile is designed so that the maximum temperature within the reflow oven is 220° C. to 240° C. in order to make the minimum temperature on the board to be the eutectic temperature of the Sn-37Pb eutectic solder or greater in cases in which the board has large dimensions, and components having considerable heat capacity are mounted on the board.
A conventional Sn—Ag eutectic-based solder alloy material such as that described in Japanese Patent No. 3027441 has a melting temperature is 220° C. or higher, which is about 40° C. higher than 183° C. The latter temperature is the melting point of ordinary Sn-37Pb eutectic solder. The solder alloy material is used as a substitute material for Sn-37Pb eutectic solder in connections between printed circuit boards and electronics components.
In Japanese Patent No. 1664488 (Japanese Laid-open Patent Application No. 59-189096), Bi is added to the Sn—Zn-based solder to ensure higher strength. In Japanese Laid-open Patent Application No. 9-94687, adhesion strength is increased by adding 0.1 to 3.5 mass % of Ag to an Sn—Zn-based solder. Also, in Japanese Laid-open Patent Application No. 2001-347394, Al, In, Ni, Cu, Ag, and other elements are added to an Sn—Zn-based solder to increase strength (hardness), improve wettability, and lower the melting point. In Japanese Laid-open Patent Application No. 2002-195433, Ag and Bi are added to an Sn—Zn-based solder to increase strength (hardness), improve wettability, and lower the melting point. In Japanese Patent No. 3357045 as well, Al is added to an Sn—Zn-based solder to improve wettability.
[Patent Document 1] Japanese Patent No. 3027441
[Patent Document 2] Japanese Patent No. 1664488
[Patent Document 3] Japanese Laid-open Patent Application No. 9-94687
[Patent Document 4] Japanese Laid-open Patent Application No. 2001-347394
[Patent Document 5] Japanese Laid-open Patent Application No. 2002-195433
[Patent Document 6] Japanese Patent No. 3357045