Nonaqueous Halide-Free Flux Reactions with Tin-Based Solders

• Published in: Journal of electronic materials Vol. 44; no. 4; pp. 1144 - 1150
• Main Authors: Qu, Guoying, Weinman, Craig J., Ghosh, Tanushree, Flake, John C.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.04.2015; Springer Nature B.V
• Subjects: Aqueous solutions; Characterization and Evaluation of Materials; Chemical reactions; Chemistry and Materials Science; Electronics and Microelectronics; Equilibrium; Instrumentation; Materials Science; Optical and Electronic Materials; Soldering; Solid State Physics; Tin; pH; flux; equilibrium; carboxylic
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-015-3635-6

New halide-free fluxes are becoming more prevalent in electronic packaging; however, their efficacy and reactive behavior with conventional solders has not been well characterized. In this work, we examine nonaqueous halide-free flux reactions of tin (Sn)-based solder surfaces using electrochemical methods. Cyclic voltammetry was used to study reactions of Sn(II) and Sn(IV) species, x-ray photoelectron spectroscopy (XPS) was used to study surface chemistry, and chronopotentiometry was used to quantify equilibrium constants of Sn–carboxylic complexes. Reactions were investigated using carboxylic acid solutions such as adipic acid or maleic acid in polyethylene glycol. Carboxylic acid-based fluxes are practically inactive toward SnO 2 removal at room temperature (25°C); however, some species are capable of removing the oxides at temperatures as high as 180°C and at pH as low as 0.1. XPS results suggest the H + activity of the carboxylic acid is the key to removing SnO 2 on Sn-based solder surfaces. Equilibrium coefficients and potential-pH diagrams are given to elucidate the influence of pH on Sn surfaces.