Moisture Concentration
The maximum amount of water vapor that air or a solid material can hold at a specific temperature determines the rate of moisture absorption. In manufacturing environments, relative humidity saturation in the air drives the rate of moisture ingress into plastic encapsulated microcircuits and fiberglass substrates. When the moisture concentration in the air is high, components absorb water until they reach equilibrium with their surroundings.
Plastic Bake
Moisture-sensitive devices must be stored in dry cabinets or moisture barrier bags to prevent them from absorbing moisture. If components are exposed to high relative humidity saturation levels for periods exceeding their floor life, they must undergo a baking cycle to remove the trapped moisture before assembly. This baking process typically involves heating the components at 125 degrees Celsius for 24 hours to drive out moisture without damaging the packaging.
Failure to bake exposed parts can lead to internal vaporization during reflow, which results in internal delamination and package cracking.
Delamination Risk
Laminates exposed to high moisture levels run the risk of copper separation and internal blistering when heated to high reflow temperatures. Controlling the relative humidity saturation in storage areas is therefore critical to preventing moisture-induced defects during soldering operations. Assembly plants monitor and log the environmental conditions in assembly areas to ensure compliance with humidity standards.
