Investigation of the Effect of Temperature on the Properties of No-Clean Reflow Soldering Fluxes

With the decreasing size of microelectronics, corrosion-related reliability issues have become more abundant. The presence of no-clean soldering flux residues has been commonly identified as an accelerating factor for electrochemical corrosion. This paper discusses the investigation of five different commercially available no-clean fluxes, used in reflow solder pastes. At first, the initial composition and thermal behavior of the systems were characterized with gas chromatography (GC–MS) and thermogravimetric analysis. Based on the results, no differences were identified between the evaporation characteristics of the fluxes in nitrogen and in air up to 250°C. After initial investigation, the real-life thermal decomposition behavior, pH- and conductivity-changing capability of the fluxes were emulated in the temperature range of 50–250°C. To identify the potential specific effect of copper, the experiments were conducted with both direct bonded copper and glass substrates. No specific effect of copper was detected regarding the remaining amount of flux residue on the surface. Furthermore, after treating the samples at 250°C, no significant pH- or conductivity-changing capability was identified in the case of any of the investigated flux systems regardless of the substrate. Based on these results, the necessity of the follow-up cleaning steps must be reconsidered.