Abstract: High-temperature solders having a higher melting point than solder alloys used for soldering of printed circuit boards are used for internal bonding of electronic parts, but high-temperature solders which are free from Pb have not been developed. There exist high-temperature solders which comprises Sn balls and Cu balls and which perform bonding through the formation of an intermetallic compound without melting to form a single-phase structure, but they have poor wettability to the lands of a printed circuit board or electrodes of electronic parts and have not been used. A solder paste according to the present invention is provided by mixing flux with a powder mixture of Sn powder or an Sn based lead-free solder powder with Cu or Ag powder which has Ni plating formed on its surface.

Abstract: High-temperature solders having a higher melting point than solder alloys used for soldering of printed circuit boards are used for internal bonding of electronic parts, but high-temperature solders which are free from Pb have not been developed. There exist high-temperature solders which comprises Sn balls and Cu balls and which perform bonding through the formation of an intermetallic compound without melting to form a single-phase structure, but they have poor wettability to the lands of a printed circuit board or electrodes of electronic parts and have not been used. A solder paste according to the present invention is provided by mixing flux with a powder mixture of Sn powder or an Sn based lead-free solder powder with Cu or Ag powder which has Ni plating formed on its surface.

Abstract: In reflow soldering using a solder paste formed by mixing a flux and a solder powder, the present invention suppresses the formation of voids and prevents the formation of large-diameter voids which have an adverse effect on the reliability of soldering. The flux contains a solder for which the temperature at which the decrease in mass measured by the TG method is 15 mass % is at least 5° C. higher than the peak heat absorption temperature of the solder.

Abstract: A soldering method includes exposing a solder paste including a solder powder and a flux on a member to a free radical gas and heating the solder paste to reflow the solder paste and vaporize any active components in the solder paste. Any flux residue is free of active components, so it is not necessary to perform cleaning after soldering to remove flux residue.

Abstract: A residue-free solder paste which leaves little or no flux residue after reflow soldering and which have good printability, storage stability, retainability of parts, and wettability, comprises a solder powder mixed with a rosin-free pasty flux. The flux comprises at least one solid solvent and at least one highly viscous solvent in a total amount of 30-90 mass %, in addition to at least one liquid solvent, all the solvents vaporizing at a reflow soldering temperature. The flux may further contain 0.5-12% of a thixotropic agent such as a fatty acid amide and 1-15% of an activator selected from organic acids and their amine salts, the thixotropic agent and activator vaporizing in the presence of the solvents while the solvents are vaporizing.

Abstract: A soldering method includes exposing a solder paste including a solder powder and a flux on a member to a free radical gas and heating the solder paste to reflow the solder paste and vaporize any active components in the solder paste. Any flux residue is free of active components, so it is not necessary to perform cleaning after soldering to remove flux residue.

Abstract: A residue-free solder paste which leaves little or no flux residue after reflow soldering and which have good printability, storage stability, retainability of parts, and wettability, comprises a solder powder mixed with a rosin-free pasty flux. The flux comprises at least one solid solvent and at least one highly viscous solvent in a total amount of 30-90 mass %, in addition to at least one liquid solvent, all the solvents vaporizing at a reflow soldering temperature. The flux may further contain 0.5-12% of a thixotropic agent such as a fatty acid amide and 1-15% of an activator selected from organic acids and their amine salts, the thixotropic agent and activator vaporizing in the presence of the solvents while the solvents are vaporizing.