Moisture Extraction
Standards for moisture removal specify the thermal treatment required to protect moisture sensitive devices prior to high temperature reflow. Executing a dry bake cycle prevents the internal delamination and cracking commonly known as the popcorn effect. The duration and temperature are determined by the moisture sensitivity level of the component and the thickness of the package.
Oxidation Risk
Extended exposure to heat can degrade the solderability of component leads. Using a nitrogen atmosphere or lower temperatures for longer periods helps to minimize the formation of intermetallic layers. Manufacturers specify the maximum number of cycles a part can undergo before the terminal finish is compromised.
Procedure Validation
Timers and data loggers record the temperature profile to ensure compliance with IPC standards. If the power fails or the door is opened for too long, the process must be restarted or extended. Verification involves weighing samples before and after the treatment to confirm a specific mass loss.
Thermal Uniformity
Heat increases the kinetic energy of water molecules trapped within the plastic molding compound. This energy allows the vapor to diffuse through the package walls into the surrounding low humidity air. Oven air must be constantly circulated to maintain a uniform temperature distribution.
The process remains active until the internal moisture content falls below the critical threshold for safe soldering.
