Summary: what are MSL levels?
MSL is the moisture sensitivity rating for plastic-packaged ICs, classified under IPC/JEDEC J-STD-020 and handled per J-STD-033. The level sets the "floor life": how long parts can sit at 30 °C / 60% RH or below after the bag is opened before reflow. MSL 3, for example, is 168 hours. MSL 2 through 5a must be dry packed for shipment: parts, desiccant, and a humidity indicator card sealed together in a moisture barrier bag (MBB) and heat-sealed. If the humidity indicator card has changed color when the bag is opened, or the floor life has been exceeded, parts must be baked before reflow; otherwise moisture in the package vaporizes during reflow and can cause delamination or cracking (the so-called popcorn effect).
Why ICs fear moisture
Plastic packaging materials absorb moisture from the air. During reflow, ICs reach 245–260 °C; moisture in the package vaporizes instantly and pressure rises, which can delaminate the package internally or even crack it, known in the industry as the "popcorn effect" (TI, AN-2029).
MSL grades "how easily a part absorbs moisture and how much is too much." Two standards divide the work: J-STD-020 defines how to test and which level a part belongs to; J-STD-033 defines how each level is packed, stored, shipped, and baked (TI, MSL Ratings and Reflow Profiles).
MSL table: floor life by level
| MSL level | Floor life | Conditions | Dry pack? |
|---|---|---|---|
| 1 | Unlimited | ≤30°C / 85% RH | Not required |
| 2 | 1 year | ≤30°C / 60% RH | Required |
| 2a | 4 weeks | ≤30°C / 60% RH | Required |
| 3 | 168 hours | ≤30°C / 60% RH | Required |
| 4 | 72 hours | ≤30°C / 60% RH | Required |
| 5 | 48 hours | ≤30°C / 60% RH | Required |
| 5a | 24 hours | ≤30°C / 60% RH | Required |
| 6 | Bake before use, then reflow per label | ≤30°C / 60% RH | — |
Sources: TI, AN-2029, TI, SPRABY1A. TI notes that most semiconductor products are MSL 3 or higher; MSL 1 isn't moisture-sensitive even at 85% RH and needs no dry packing.
"Floor life" is cumulative time, counted from opening the moisture barrier bag until reflow is complete. In conditions cooler and drier than 30 °C / 60% RH, the allowable time is longer; in hotter, more humid conditions, it's shorter.
How is dry packing done?
Parts rated MSL 2 to 5a must be dry packed per J-STD-033 before shipment. The process (eesemi, Dry Packing, TI, AN-2029):
Make sure parts are dry
Parts must be dry before bagging; bake first if needed to drive moisture out of the package.
Into a barrier bag (MBB)
MBBs are mostly aluminum foil laminates that must heat-seal, block moisture, and be static-protective.
Add desiccant and a humidity card
Desiccant absorbs residual moisture in the bag; the humidity indicator card (HIC) records the highest humidity the bag has reached, so the receiver can tell as soon as it's opened.
Vacuum and seal
In practice, the bag is vacuumed to conform to the contents and then heat-sealed. Sealing with tape or by folding provides no moisture protection.
Labeling
Mark the outside of the bag with the MSL level, bag seal date, and caution notes, so downstream users know the time limit after opening.
Per J-STD-033, an intact dry pack can be stored for at least 12 months from the bag seal date; some manufacturers set longer limits based on their own qualification, such as TI's 3 years (at or below 40 °C / 90% RH) (TI, AN-2029).
At high-volume OSATs, this is often the most labor-intensive part of the packing station: checking part numbers, bagging, sealing, folding, and labeling are all done by hand. To see which steps can be automated, see "Automatic semiconductor inner-box packing machine."
Reading the humidity card
A humidity indicator card has three spots, 5%, 10%, and 60%, which are blue when dry and turn pink when humidity exceeds that value. Check it immediately after opening the bag; the reading rules are printed on the card. Using a J-STD-033 card as the example (TI, AN-2029):
| Part level | When to bake |
|---|---|
| MSL 2 | 60% spot is not blue |
| MSL 2a–5a | 10% spot is not blue and 5% spot has turned pink |
| Before use | Don't use cards with a pink 60% spot |
The color change is reversible, and cards turn blue again once dry; but cards that have been exposed to humidity above 60% read inaccurately at low humidity and shouldn't be reused (Desco, TB-9086). Card text may vary slightly by standard version; go by what's printed on the card you have.
Past floor life? Baking
When floor life runs out, or the humidity indicator card shows moisture, parts must be baked before reflow. J-STD-033 sets bake times at three temperatures, 125 °C, 90 °C, and 40 °C, based on package thickness, MSL level, and how long the limit was exceeded. Below is an excerpt for packages 1.4 mm thick or less (TI, AN-2029, excerpted from J-STD-033B.1):
| MSL | 125 °C Exceeded >72 h | 125 °C Exceeded ≤72 h | 90 °C ≤5% RH Exceeded >72 h | 40 °C ≤5% RH Exceeded >72 h |
|---|---|---|---|---|
| 2 | 5 hours | 3 hours | 17 hours | 8 days |
| 2a | 7 hours | 5 hours | 23 hours | 9 days |
| 3 | 9 hours | 7 hours | 33 hours | 13 days |
| 4 | 11 hours | 7 hours | 37 hours | 15 days |
The carrier determines the bake temperature. Carrier tape, reels, and tubes are low-temperature carriers and can't be baked above 40 °C with the parts in them; only high-temperature trays can withstand 125 °C (TI, AN-2029). So once reeled parts absorb moisture, they often need a week or two of baking. That's the value of doing dry packing properly at the shipping end: it saves downstream bake time and lead time.
The table is an excerpt; thicker packages, BGAs, and stacked packages take longer. For actual conditions, refer to J-STD-033 and the component manufacturer's documentation.
J-STD-033 key points
| Item | Key point |
|---|---|
| Full name | Handling, Packing, Shipping and Use of Moisture/Reflow Sensitive Surface Mount Devices |
| Issued by | Jointly developed by IPC and JEDEC (JEDEC) |
| Current version | J-STD-033D, April 2018 |
| vs. J-STD-020 | 020 sets the level; 033 sets packing, storage and baking |
| Scope | Floor life, dry pack materials, labels, storage, baking |
This article summarizes key points and is not a translation of the standard; the original must be purchased from IPC or JEDEC.
FAQ
What does MSL level mean?
MSL stands for moisture sensitivity level and indicates how easily a plastic-packaged IC absorbs moisture. There are eight levels: 1, 2, 2a, 3, 4, 5, 5a, and 6. The higher the number, the shorter the time parts can sit at 30 °C / 60% RH after the bag is opened. Levels are determined by J-STD-020 testing and handled per J-STD-033.
How long is MSL 3?
MSL 3 floor life is 168 hours: after opening the moisture barrier bag, parts must be reflowed within a cumulative 7 days at or below 30 °C / 60% RH. Beyond that, they must be baked first. Most semiconductor products are MSL 3 or higher.
Which MSL levels need dry packing?
MSL 1 doesn't need dry packing. MSL 2 through 5a must be dry packed for shipment: parts sealed in a moisture barrier bag (MBB) with desiccant and a humidity indicator card. MSL 6 must be baked before use regardless of packing and reflowed within the time on the label.
How do you read a humidity indicator card?
Check the card immediately after opening the bag. Per the text on J-STD-033 cards: for MSL 2 parts, bake if the 60% spot isn't blue; for MSL 2a to 5a parts, bake if the 10% spot isn't blue and the 5% spot has turned pink. Go by the text printed on the card.
Can reeled ICs be baked at 125 °C as is?
No. Carrier tape, reels, and tubes are low-temperature carriers, and manufacturer documentation says they can't be baked with the parts above 40 °C; only high-temperature trays can withstand 125 °C. Reeled parts can only be baked at 40 °C, which takes days.
What's the current version of J-STD-033? Is there a Chinese version?
The current version is J-STD-033D, published in April 2018 and jointly developed by IPC and JEDEC; it must be purchased from IPC or JEDEC. This article summarizes key points; for formal decisions, refer to the original standard.