Patent ID: 6416863
Filing Date: 2002-07-09
Classification: B23K,H05K,Y10T

Abstract:
A method of encapsulating solder metal powder in which the powder is provided with a thin polymer protective layer by a polymerization reaction running on the surface of the solder powder, with the following steps:a) producing a suspension of powder and a hydrophobic liquid, b) generating a hydrophobic surface layer on each metal particle by adding a cationic tenside with a chain length of C1 through C20 with continuous stirring to form a brush structure on the hydrophobic layer of step (a), c) stirring the mixture of steps a) and b) until formation of a viscous homogeneous mass, d) adding a radically polymerizable monomer to the mass of step c) and which forms a thermoplastic polymer with a glass temperature Tg of at least 60Â° C. below the solidus temperature of the solder powder, e) adding an organic initiator to start an interfacial polymerization reaction with incorporation of the hydrophobic layer of step b) and formation of a protective layer of thermoplastic polymer which has fluxing agent characteristics, f) introducing the mass of step e) into an aqueous preparation with continuous stirring, whereby the preparation contains an emulsifier for suspension stabilization and controlling the polymerization reaction by tempering to 50Â° to 90Â° C. and maintaining this temperature for at least 120 min, and g) cooling, washing and recovering the encapsulated solder powder of steps e) and f).