dewetting: one construct, many systems

In soft-matter physics, dewetting is the instability by which a thin liquid or polymer film on a surface it does not wet well spontaneously ruptures and retracts, gathering into droplets to lower its total interfacial energy, through nucleated holes or spinodal growth of surface waves. Reiter's Dewetting of thin polymer films demonstrated and modelled this break-up in thin polystyrene layers. The referent is a surface-energy-driven film retraction, measured by hole growth and droplet patterns, and it is the same physics that spoils a solder joint when molten metal recedes.[1]

Unit

The rate of hole opening and the final droplet pattern of a retracting film

Recovery means

Not applicable

Measured by

Observed by microscopy of hole nucleation and growth rate, rim and droplet spacing, and the contact angle of the retracted material

In soldering, dewetting is the defect in which molten solder first spreads over a surface and then draws back, leaving thin, irregular, raised beads of solder with bare or thinly coated metal exposed between them, a sign of a contaminated or poorly solderable surface. Humpston and Jacobson's Principles of soldering distinguishes it from non-wetting, where the solder never spread at all, and ties it to the same interfacial-energy balance that governs any retracting film. The referent is the same film-retraction instability as in soft matter, here in molten metal on a joint, judged by the fraction of surface left uncovered and the beaded appearance.[2]

Unit

The fraction of a surface left bare after solder retracts from it

Recovery means

Not applicable

Measured by

Judged by visual and microscopic inspection of beading and exposed base metal, and reproduced on wetting-balance or dip tests of contaminated coupons