Provided are a Ni ball, a Ni core ball, a solder joint, solder paste and foamed solder which are superior in the impact resistance to dropping and can inhibit any occurrence of a poor joints. An electronic component 60 is constructed by joining a solder bump 30 of a semiconductor chip 10 to an electrode 41 of a printed circuit board 40 with solder paste 12, 42. The solder bump 30 is formed by joining an electrode 11 of the semiconductor chip 10 to the Ni ball 20. The Ni ball 20 according to the present invention contains purity which is equal to or higher than 99.9% and equal to or lower than 99.995%, sphericity which is equal to or higher than 0.90, and Vickers hardness which is equal to or higher than 20HV and equal to or less than 90HV.

In a stainless steel flux cored wire comprising a stainless steel shell and a flux filling the shell, the amount of Si contained in the entire wire is 2.5% by mass or higher, preferably 3.0% by mass or higher in terms of SiO.sub.2, and the amount of at least one compound selected from the group consisting of polytetrafluoroethylene, graphite fluoride and perfluoropolyether contained in the flux is 0.005 to 0.10% by mass of the total mass of the wire in terms of F, preferably 0.020% by mass or higher. By employing such a constitution, in welding of CrNi-based and Cr-based stainless steels and other materials, fume generation and hexavalent chromium leaching can be significantly reduced, and excellent welding workability can be provided.

A method of preventing variation of the viscosity of a solder paste, and flux for producing solder paste, viscosity of which is prevented from varying. In the flux, which is suitable to be mixed with solder powder to produce the solder paste, an amount of methacrylate polymer which reduces a thixotropic index of the solder paste and enhances viscosity thereof is contained. As the methacrylate polymer, polyalkyl methacrylate having an alkyl group is preferable, and it is preferable that an addition amount of polyalkyl methacrylate is 05.-5.0 mass % of the flux. Further, as a thixotropic agent, hardened castor oil is preferably added.

Provided are a Ni ball, a Ni core ball, a solder joint, solder paste and foamed solder which are superior in the impact resistance to dropping and can inhibit any occurrence of a poor joints. An electronic component 60 is constructed by joining a solder bump 30 of a semiconductor chip 10 to an electrode 41 of a printed circuit board 40 with solder paste 12, 42. The solder bump 30 is formed by joining an electrode 11 of the semiconductor chip 10 to the Ni ball 20. The Ni ball 20 according to the present invention contains purity which is equal to or higher than 99.9% and equal to or lower than 99.995%, sphericity which is equal to or higher than 0.90, and Vickers hardness which is equal to or higher than 20 HV and equal to or less than 90 HV.

A flux containing rosin, a solvent, a thixotropic agent, an amine hydroiodide, and an activator (provided that the amine hydroiodide is excluded), in which the amine hydroiodide includes a heteroalicyclic amine hydroiodide, is provided in the present invention. As the heteroalicyclic amine hydroiodide, at least one selected from the group consisting of piperidine hydroiodide and pipecholine hydroiodide is preferable. According to such flux, the generation of voids during soldering can be further suppressed.

A flux containing rosin, a solvent, a thixotropic agent, an amine hydroiodide, and an activator (provided that the amine hydroiodide is excluded), in which the amine hydroiodide includes a heteroalicyclic amine hydroiodide, is provided in the present invention. As the heteroalicyclic amine hydroiodide, at least one selected from the group consisting of piperidine hydroiodide and pipecholine hydroiodide is preferable. According to such flux, the generation of voids during soldering can be further suppressed.