Abstract: A fully-fluorinated and fully saturated fluorocarbon, containing at least two condensed or non-condensed six-membered rings, seventeen carbon atoms and from 28 to 32 (inclusive) fluorine atoms in its molecule, and having a boiling point from 250.degree. to 265.degree. C.; provided that where the rings are non-condensed they are separated by not more than 4 carbon atoms. Such multi-ring C.sub.17 saturated-perfluorocarbons are produced by the saturation fluorination of the corresponding multi-ring hydrocarbons and are suitable for use as high-temperature vapour-soldering fluids, especially for use with solders melting above 200.degree. C.