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4.1.7 Pop corning
Pop corning is when the housing of a component delaminates as a result of heated fluid that if steam is blown out
of the housing.
The moisture can reside in: Housing material, between different materials in the housing of the component.
The popcorn effect can occur when moisture-sensitive electronic components are stored for a longer period
without moisture protective packaging they slowly absorb moisture from the ambient air.
The storage of moisture sensitive components is regulated in IPC/JEDEC J-STD-020D (MSL classes, English
moisture sensitive level).
Through In the reflow oven evaporates the moisture due to the rapid rise in temperature, resulting in a volume
expansion.
Consequences are: cracks in the casing and the delamination of the substrate.
The dangerous of the popcorn effect is that it is not immediately detected as it occurs under the device, for
example are BGAs.
Vapor phase soldering significantly reduces this error probability.
4.1.8 Poor Wetting
The primary root cause of poor wetting is excessive oxidation of solder powder, component leads, and the PCB
pads prior to the reflow. If the overall heat input is too high, and the solder paste has a limited oxidation tolerance,
the flux activity of the solder paste will be weakened and lead to poor wetting. In this case the reflow profile
should be adjusted more toward a standard type to reduce the overall heat input.
4.1.9 Voiding
The root cause of the solder voiding is primarily due to the entrapment of flux during the reflow stage. Formation
of solder voids increases with the oxidation level of both solder paste and the PCB pads. Un-wetted spots on the
pads, or un-digested solder oxide particles from solder paste in the bulk of molten solder will entrap small amounts
of flux. This in turn will expand/explode into a void at the solidification stage. A lower overall heat input and higher
activity of flux will help in this situation.