A new reduced-oxide soldering activation method

Abstract

This article describes a new reduced-oxide soldering activation (ROSATM) process that removes oxides from tin, tin-lead, and copper surfaces without the use of a flux. In this process, surface oxides are electrolessly reduced back to the metallic state by a highly reducing vanadous ion solution that is noncorrosive to most metals and is regenerated electrochemically. The electroless reduction and redox regeneration cycles form a closed loop such that oxygen gas is the only effluent. Wetting time and surface analysis data show that a ten-second exposure to the vanadous ROSA solution completely reduces all tinlead oxides that would normally be encountered on production components. The ROSA treatment has a wide operating window, provides soldering performance comparable to that attainable with a fully-activated rosin flux, and offers the promise of providing low soldering defect rates without the use ofCFC solvents. 36

Fluxless soldering

“…The preferred electrolyte is a vanadium sulphate solution with a pH of 0 . 5, which is non-corrosive to most metals (Tench et al, 1995). A distinct advantage of the ROSA process is that 14 Effect of formic acid vapour concentration (0 .…”