The Moisture Sensitivity Level (MSL) is a classification system used in the electronics industry to indicate how sensitive a particular integrated circuit (IC) or electronic component is to moisture and how quickly it must be assembled onto a circuit board after being exposed to the ambient air. MSL is especially important in the context of surface mount technology (SMT) where moisture within the package can cause ‘popcorning’ during the solder reflow process. This is where the moisture within the package greatly expands during the reflow heating which causes the package to rupture.

The MSL is typically expressed as a numerical value ranging from MSL 1 to MSL 6, with higher numbers indicating greater sensitivity to moisture. The classification is determined based on the time the component can be exposed to a specified level of humidity without undergoing a moisture-related issue. The MSL is defined by the Joint Electron Device Engineering Council (JEDEC) standards.

Here’s a brief overview of the MSL classifications:

MSL 1: Components with this classification have a very low sensitivity to moisture. They can be stored and handled without special precautions, and exposure to ambient humidity for extended periods is generally not a concern.

MSL 2-4: Components in these classes are moderately sensitive to moisture. They typically have specific handling requirements, and the time they can be exposed to ambient conditions is more limited. These components may require careful storage and handling procedures to prevent moisture-related issues.

MSL 5-6: Components in these classes are highly sensitive to moisture. They have strict handling requirements and are usually packaged in moisture barrier bags with desiccants. The exposure time to ambient conditions is very limited, and they should be assembled onto circuit boards promptly after being removed from their protective packaging.

It’s crucial for manufacturers and assemblers to adhere to the specified MSL requirements to prevent moisture absorption, which could lead to defects such as popcorning (delamination of internal layers) or solder joint issues during the soldering process. Proper storage, handling, and processing procedures are essential to maintaining the reliability of electronic components, especially in industries where high-reliability standards are critical, such as automotive, aerospace, and medical electronics.

Back to Glossary Index Page