The Moisture Sensitivity Level (MSL) is the JEDEC standard.
This standard covers the phenomenon in which moisture absorption in a product and reflow during mounting cause the moisture contained in the product to vaporize and thereby resulting in volume expansion and leading to failure.
The level that expresses that risk is called the Moisture Sensitivity Level (MSL).
The higher the level number, the higher the risk. It is necessary to prevent moisture absorption at level 2 and above.
Accordingly, products at level 2 and above must be baked after a certain period of time has passed and the taped reels must be packed in an aluminum package together with a desiccant.