# Moisture Sensitivity Level (MSL)

> Source: https://netray.co/glossary/moisture-sensitivity-level
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Glossary

## Short answer

Moisture Sensitivity Level (MSL) is a rating, defined in the J-STD-020 and J-STD-033 standards, that states how long a surface-mount component can be exposed to factory air before it must be baked, to avoid cracking during reflow.

## Aliases

- MSL
- MSD
- moisture sensitive device
- floor life

## Category

manufacturing

## Full Definition

Plastic packaged parts absorb moisture from the air. In reflow, that moisture can turn to steam and cause popcorning, delamination or internal cracks. The MSL rating, from level 1 (unlimited floor life) through levels 2, 2a, 3, 4, 5, 5a and 6, sets the allowed floor life after the dry bag is opened. For example, level 3 allows 168 hours at factory conditions, and level 6 parts must be reflowed within the time stated on the label after bake.

Parts arrive in moisture barrier bags with a desiccant and humidity indicator card. Once opened, the clock starts. If the floor life is exceeded, the parts are baked at a specified temperature and time before use, or returned to dry storage in a dry cabinet that can pause or reset the clock under J-STD-033 rules.

Tracking this is a material control problem. Many factories record the bag open time on the reel label or in MES, with dry cabinet location. ERP inventory can carry MSL level as an item attribute, and lot or location records can flag material that needs baking before it is issued to a work order. Without this, floor life is tracked on paper.

For SMT planning, MSL also shapes kitting: a level 3 part kitted a week ahead of a build may expire on the shelf.

## Why It Matters

- Moisture damage can be latent, passing test and failing later in the field.
- Floor life expiry leads to bake cycles that delay builds and can degrade solderability if repeated.
- Customers in aerospace, medical and automotive may require records of moisture control.
- MSL as an item attribute in the ERP lets kitting and issue logic warn about restricted parts.

## In Practice

A level 3 BGA reel is opened Monday at 8:00. The floor life is 168 hours, but the line only uses part of the reel before the weekend. The operator returns it to a dry cabinet at 4 pm on Monday, and the MES logs 8 hours used. If it had been left out past 168 hours cumulative, the reel would need a bake before the next work order could use it.

## Faq

### What does MSL 3 mean?

**Answer:** A part with MSL 3 has a floor life of 168 hours at factory conditions after the dry bag is opened, before it must be baked or re-stored.

### What happens if floor life is exceeded?

**Answer:** The part must be baked per the standard before reflow, or scrapped if it cannot be recovered, because moisture can damage it during soldering.

### Can an ERP track MSL?

**Answer:** It can hold the MSL level as an item attribute and flag restricted lots, while open-time clocks are usually tracked by MES or dry cabinet systems.

## Search terms

what is MSL, moisture sensitivity level, MSL floor life, J-STD-033, moisture sensitive devices, component baking

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