I have added a page explaining what water-soluble flux is, including its residues and analysis methods.

ゼストロンジャパン
Water-soluble flux is a flux based on water, using water-soluble polymers such as polyoxyethylene alkyl ether. Currently, in Japan, rosin-based flux is the mainstream for soldering in electronics assembly, but due to the growing environmental awareness such as the SDGs, there is a movement to explore the transition to water-soluble flux, which is expected to have a VOC reduction effect. This document explains the role and applications of water-soluble flux, as well as residues, analysis methods, and cleaning methods.
