Moisture Sensitive Devices (MSDs) are electronic devices encapsulated with plastic compounds and other organic materials. These include PCBs. Moisture from atmospheric humidity will enter these permeable materials by diffusion and preferentially collect at the dissimilar material interfaces.
During solder reflow, the combination of rapid moisture expansion and materials mismatch can result in package cracking and/or delamination of critical interfaces within the package.
These defects are nearly impossible to detect during the PCB assembly and test process. They lead to a number of failure modes that have a negative impact on manufacturing yields and cause early life field failure of the finished electronic products.