Dewetting

Dewetting is a condition that results when molten solder has coated a surface and then receded, leaving irregularly shaped mounds of solder separated by areas covered with a thin solder film and the base metal is not exposed.

Process and design-related causes:

• Solder paste flux not aggressive enough for level of oxidation present on part or PCB

• PCB pad contaminated

• Component lead contaminated

• Excessive moisture absorbed by paste

• Paste exposed beyond worklife

• Ambient humidity and temperature beyond paste work envelope

• A palladium lead finish which requires higher reflow (liquidus) temperature

Reflow-related causes:

• Peak reflow (liquidus) temperature not being attained

• Malfunctioning oven which is impeding attenuation of proper temperatures

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