Parametric Study of Solder Flux Hygroscopicity: Impact of Weak Organic Acids on Water Layer Formation and Corrosion of Electronics

Kamila Piotrowska*, Rameez Ud Din, Flemming Bjerg Grumsen, Morten Stendahl Jellesen, Rajan Ambat

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The presence of solder flux residues on the printed circuit board assembly surface is an important factor contributing to humidity-related reliability issues that affect device lifetime. This investigation focuses on understanding the hygroscopic nature of typical wave solder flux activators—weak organic acids—under varied temperature conditions. In situ x-ray diffraction measurements assessed the effect of high temperature on the crystal structure of organic activators. The hygroscopicity studies were carried out under relative humidity (RH) levels varying from 30% to ∼ 99% and at temperatures 25°C, 40°C, and 60°C. Water absorption levels were determined using the gravimetric method, and the influence on reliability was assessed using electrochemical impedance and leak current measurements performed on the surface insulation resistance comb patterns. The corrosion studies were correlated with the hygroscopicity results and solubility data. Corrosion morphology was analysed using the optical microscopy and scanning electron microscopy. The results show that the hygroscopic nature of typical solder flux residue depends on its chemical structure and temperature. An increase of temperature shifts the critical RH level for water vapour absorption towards lower RH range, accelerating the formation of a conductive electrolyte and the occurrence of ion transport-induced electrochemical migration. The overall ranking of flux activators with the increasing order of aggressivity is: palmitic < suberic < adipic < succinic < glutaric < dl-malic acid.

Original languageEnglish
JournalJournal of Electronic Materials
Volume47
Issue number7
Pages (from-to)4190-4207
ISSN0361-5235
DOIs
Publication statusPublished - 2018

Keywords

  • Climatic reliability of electronics
  • Corrosion
  • Humidity
  • Hygroscopicity
  • Solder flux

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