Moisture Contamination
An environmental hazard occurs when water vapor accumulates within the plastic encapsulation of a quad flat no-lead electronic device. This qfn package moisture can vaporize during the rapid heating of reflow soldering, causing internal delamination or package cracking. The mold compound behaves as a sponge, continuously drawing water from the ambient air when left unprotected.
Proper storage and tracking are necessary to prevent this accumulation.
Reflow Damage
During reflow, the internal moisture expands rapidly as it turns to steam. The high pressure can exceed the adhesion strength of the plastic to the silicon die or the lead frame. This can cause the package to bulge, crack, or separate internally.
This damage is commonly known as popcorn failure.
Protection Method
Devices are sealed in moisture barrier bags with silica gel packets and a humidity indicator card to prevent moisture absorption. If the exposure time limit is exceeded, the devices must be baked in an oven at a low temperature to dry them safely. The baking duration depends on the package thickness and the moisture sensitivity level.
Monitoring these procedures maintains the reliability of the assembly.
Material Properties
Mold compounds with lower water absorption rates and higher adhesion strength are selected to reduce the risk of cracking. Thicker packages require longer baking times to release trapped moisture. Selecting compatible materials helps prevent internal delamination during high temperature processing.
