Investigation of the Effect of Temperature on the Properties of No-Clean Reflow Soldering Fluxes
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https://doi.org/10.1007/s11664-020-08407-0 Ó 2020 The Minerals, Metals & Materials Society
Investigation of the Effect of Temperature on the Properties of No-Clean Reflow Soldering Fluxes } GACS ,1,4 LA ´ SZLO ´ KOCSIS,1 CSABA NE ´ METH,1 JENO 2,3 2 ´ ´ ´ JUDIT MATYASI, and DENES SZIEBERTH 1.—Robert Bosch Hungary Kft., Gyo¨mr}oi u´t 104, Budapest 1103, Hungary. 2.—Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, M} uegyetem rkp. 1, Budapest 1111, Hungary. 3.—B & B Analitika Kft., Szent Gelle´rt te´r 4, Budapest 1111, Hungary. 4.—e-mail: [email protected]
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. Key words: Soldering flux, temperature, pH, conductivity, electronics reliability
INTRODUCTION The increasing amount of printed circuit board (PCB)-based products and the continuous effort for miniaturization has skyrocketed the demand for various soldering technologies, especially for reflow and wave soldering. For a reliable solder joint, pure metallic surfaces are required; however, other than gold and platinum, all metals have a certain thickness of a non-metallic surface layer (e.g.: oxide, sulfide) which prevents the interaction between the solder material and the copper substrate.1 In order
(Received April 6, 2020; accepted August 11, 2020)
to remove this hindering layer, various fluxes are used in the soldering process. The role of the flux is to react with the metal oxides and to remove them from the surface as well as to protect the cleaned metal from further re-oxidation.2 A typical flux usually consists of a solvent, a carrier and an activator. As a solvent, commonly a mixture of alcohols is used with the role of solubilizing the other
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