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
• Peak reflow (liquidus) temperature not being attained
• Malfunctioning oven which is impeding attenuation of proper temperatures
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