Moisture Sensitivity Level Testing (MSL)
Moisture Sensitivity Level testing (MSL testing) is performed to initially identify the classification level of nonhermetic solid state surface mount devices (SMDs) that are sensitive to moisture-induced stress. The purpose of moisture sensitivity level testing 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 moisture sensitivity level 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 moisture sensitivity level. The test sequence for MSL is listed below. The reflow temperatures are dependent upon package thickness and volume and whether Pb-free or SnPb solder.
- Initial Visual Inspection
- 1st Acoustical Microscope
- Bake 24 hours at 125 C
- Moisture Soak
- Reflow 3X
- Final Visual Inspection
- 2nd Acoustical Microscope
Moisture Soak Requrements for MSL 1, MSL 2, MSL 2A, MSL 3, MSL 4, MSL 5, MSL 5A, and MSL 6.