Moisture Sensitivity Level (MSL) is the test performed to initially identify the classification level of nonhermetic solid state surface mount devices (SMDs) that are sensitive to moisture-induced stress. Its purpose is to determine how SMD’s are to be properly packaged, stored and handled to avoid damage during assembly solder reflow attachment.

A package’s MSL should be established prior to subjecting the part to the preconditioning sequence. This level will dictate storage times for unsealed devices awaiting assembly. MSL testing is usually performed at two levels chosen to bracket the expected level of capability and should be performed at the highest temperature that the SMD is expected to see during its’ actual assembly.
IPC/JEDEC J-STD-020 is the standard that is followed to determine a package’s MSL. The test sequence is listed below. The reflow temperatures are dependent upon package thickness and volume and whether Pb-free or SnPb solder.

Test sequence:

Initial Visual Inspection
1st Acoustical Microscope
Bake – 24 hr. – 125 C
Moisture Soak
Reflow 3X
Final Visual Inspection
2nd Acoustical Microscope

Moisture Soak Requirements:

Note: An accelerated equivalent moisture soak may be used but with CAUTION as noted in the IPC/JEDEC J-STD-020 standard.