PCB Dewetting & PCB Bridging
From: Author: Publish time:2021-08-31 17:23 Clicks:47
PCB Bridging
PCB Bridging Defects
A bridge is comprised of solder that spans across two conductors that should not be electrically connected thus causing an electrical short.
Process and design-related causes:
• Excessive volume of solder due to improper pad dimension
• Excessive volume of solder due to improper stencil aperture
• Improper application of solder mask
• Excessive slump of solder paste
Reflow-related causes:
• Improper reflow profile for solder paste. Check against manufacturer’s specifications.
PCB Dewetting
PCB 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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