Have you looked at flux as a source of the PEG surfactant contaminant?

PS.  This type of surfactant is normally water soluble, depending on PEG
content, more PEG = more soluble.  However, it is weirdly water soluble,
being more soluble in cold water than hot, so if you are rinsing with hot
water only.....bingo!

Rudy Sedlak
RD Chemical Company

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