When a cleaning solvent kills your bond line

We chased a 3% adhesive failure spike on a catheter assembly for weeks and it turned out to be our harmless switch from 99% IPA to a premixed IPA - water blend for wipes. The water slowed evaporation just enough that operators were bonding on slightly plasticized polycarbonate. Between residual moisture and micro crazing from repeat wipes, our lap shear fell off a cliff.

What fixed it was not just reverting the solvent. We added a 30 second forced air dry, limited re-wipes to one pass, and documented a simple surface energy check with dyne pens at start of shift. We also moved the primer dwell spec from about a minute to a timed window tied to room RH. Adoption went up because the checks were fast and obvious.

For those with chemical engineering backgrounds: how do you pick cleaning and surface prep steps that are robust to humidity and operator variability? Any rules of thumb using Hansen parameters or vapor pressure that have worked for you?