The Nature of Insoluble Residues Formed on Printed Circuits Soldered with Rosin Fluxes

Insoluble residues may be formed for a number of reasons as a result of flux‐solder‐conductor reactions occurring during the crucial operation of soldering, in which both metals and fluxes are molten and at elevated temperatures. The consequences can be serious, since corrosion of joints may be aggravated, coatings may not adhere or bridging between conductors may occur. One such residue, which was formed during defluxing of printed circuits with a commercial methanol‐fluorocarbon solvent, has been characterised in some detail. It appears to be a tin abiate complex which remains insoluble in most solvents except organic amides.