Solder mask composition

Claim 1

A composition useful as a solder masking coating which consists essentially of: (a) a film former comprising: (1) from 25 to about 40 weight percent of an alkyd resin of a polyester prepolymer extended with from about 25 to about 70 weight percent fatty acid; (2) from 18 to about 27 weight percent of an alkylated amino resin selected from the class consisting of methylol-melamine and methylol-urea condensates etherified with alkanols of 1 to about 6 carbons; (3) from 30 to about 45 weight percent Panamint earth having a particle size passing a screen size from 20 to 325 mesh, and weight contents of from 21 to 35 percent silicon, 15 to 28 percent aluminum, 2 to 3 percent calcium, and 1 to 2 percent iron, and a porosity of 45 percent; and (4) from 2 to about 5 weight percent of a hydrocarbon polymer having a melting point no greater than about 150° C.; and (b) sufficient organic solvent to provide a viscosity no greater than about 9,000 centipoises.