Development of resource-saving and environmentally safe beryllium bronze soldering technology

The composition of the solder, which provides the necessary technological properties of the product, namely, electrical conductivity and mechanical strength of the junction was selected. The possibility of brazing beryllium bronze with a silver contact plate by furnace brazing using fluxes based on NaCl: CaCl2: CaF2 salts, respectively (24: 61: 15% mass) in the atmosphere was established. The possibility of brazing BrB2 beryllium bronze in the atmosphere using a research flux based on the eutectic of the NaCl – CaCl2 system (28…72% wt.) adding 15% CaF2 over a copper layer is shown. The technology for brazing beryllium bronze BrB2 with silver contact plates with silver solder PSr68 has been developed. The brazing process is combined with the hardening operation, which allows avoiding additional thermal operations; flux residues are removed during hardening and do not actually need additional cleaning operations; applied solder, flux components and technologies for applying a layer of copper are not scarce and relatively cheap, which can significantly reduce the cost of the product, subject to the requirements of the technical specifications. A technological process that makes it possible to refuse of using vacuum systems and toxic fluxes has been developed.

OPTIMIZATION OF CHEMISTRY FOR A VAPOUR PHASE PROCESS TO DEFLUX NO CLEAN LEAD FREE MATERIALS ON PCBS

The cleaning action to remove baked-on solder flux residues after reflow, also known as defluxing, from printed circuit boards has become more and more challenged because of the higher densities in today's electronics, miniaturization, lower stand off components, and complex geometries where the packaging has evolved from 2D to 3D. This situation becomes even more difficult in No Clean lead free assembly where higher process temperatures are applied causing charring to flux residues. In addition, traditional chemicals like CFC's, HCFC's, brominated solvents, detergents and glycols cannot longer do a good cleaning job anymore because most flux formulations have changed. An hydrocarbon solvent used as co-solvent in vapour phase application has been re-formulated under three main criterias: environmental legislations, toxicity, and defluxing performance The results from the laboratory stage have been applied to clean the fluxes of three No Clean lead free solder pastes used in mass production of printed circuit boards assemblies with high densities interconnections and exposed to harsh environmental conditions.

Thermal decomposition of solder flux activators under simulated wave soldering conditions

Purpose The aim of this work is to investigate the decomposition behaviour of the activator species commonly used in the wave solder no-clean flux systems and to estimate the residue amount left after subjecting the samples to simulated wave soldering conditions. Design/methodology/approach Changes in the chemical structure of the activators were studied using Fourier transform infrared spectroscopy technique and were correlated to the exposure temperatures within the range of wave soldering process. The amount of residue left on the surface was estimated using standardized acid-base titration method as a function of temperature, time of exposure and the substrate material used. Findings The study shows that there is a possibility of anhydride-like species formation during the thermal treatment of fluxes containing weak organic acids (WOAs) as activators (succinic and DL-malic). The decomposition patterns of solder flux activators depend on their chemical nature, time of heat exposure and substrate materials. Evaporation of the residue from the surface of different materials (laminate with solder mask, copper surface or glass surface) was found to be more pronounced for succinic-based solutions at highest test temperatures than for adipic acid. Less left residue was found on the laminate surface with solder mask (∼5-20 per cent of initial amount at 350°C) and poorest acid evaporation was noted for glass substrates (∼15-90 per cent). Practical implications The findings are attributed to the chemistry of WOAs typically used as solder flux activators. The results show the importance WOA type in relation to its melting/boiling points and the impact on the residual amount of contamination left after soldering process. Originality/value The results show that the evaporation of the flux residues takes place only at significantly high temperatures and longer exposure times are needed compared to the temperature range used for the wave soldering process. The extended time of thermal treatment and careful choice of fluxing technology would ensure obtaining more climatically reliable product.

Relative effect of solder flux chemistry on the humidity related failures in electronics

Purpose – This paper aims to investigate the effect of no-clean flux chemistry with various weak organic acids (WOAs) as activators on the corrosion reliability of electronics with emphasis on the hygroscopic nature of the residue. Design/methodology/approach – The hygroscopicity of flux residue was studied by quartz crystal microbalance, while corrosive effects were studied by leakage current and impedance measurements on standard test boards. The measurements were performed as a function of relative humidity (RH) in the range from 60 to ∼99 per cent at 25°C. The corrosiveness of solder flux systems was visualized by the ex situ analysis using a gel with tin ion indicator. Findings – The results showed that the solder flux residues are characterized by different threshold RH, above which a sudden increase in direct current leakage by 2–4 orders of magnitude and a significant reduction in surface resistance in the impedance measurements were observed. Practical implications – The findings are attributed to the deliquescence RH of the WOA(s) in the flux and chemistry of water-layer formation. The results show the importance of WOA type in relation to its solubility and deliquescence RH on the corrosion reliability of printed circuit boards under humid conditions. Originality/value – The classification of solder flux systems according to IPC J-STD-004 standard does not specify the WOAs in the flux; however, ranking of the flux systems based on the hygroscopic property of activators would be useful information when selecting no-clean flux systems for electronics with applications in humid conditions.