Have you ever unsealed a reel of small ICs and wondered why the label carries a code like "MSL 1" or "MSL 3"? That code is a moisture sensitivity level, and it tells you exactly how long those components can safely sit on your factory floor before they are soldered onto a board. Of all the levels, moisture sensitivity level 1 is the friendliest for any assembly line, because it demands no dry packing at all. This article explains what MSL 1 means, why moisture matters, and how it affects real PCB and PCBA manufacturing.
What is a moisture sensitivity level?
Plastic-packaged electronic components such as ICs, connectors, and sensors can soak up moisture from the air. The moisture sensitivity level (MSL) is a rating that describes how much moisture a package can tolerate and how long it can stay exposed to factory conditions before reflow soldering. The rating is defined by the industry standards IPC/JEDEC J-STD-020 and J-STD-033, which also set the corresponding floor life for each level.
When a moist package is heated rapidly during reflow, the trapped water turns to steam and expands. If the package absorbed too much moisture, the sudden pressure can crack the plastic body, lift the die, or cause delamination between the moulding compound and the lead frame. This failure is often called the "popcorn effect." The resulting micro-cracks may not be visible to the naked eye, yet they can break bond wires or let contamination reach the chip, causing latent field failures weeks or months later.
What does level 1 actually mean?
MSL 1 is the highest (most forgiving) rating. A component classified as MSL 1 is considered essentially not moisture sensitive, even when stored at up to 30°C and 85% relative humidity. In practical terms, it has unlimited floor life: once you open the dry pack, there is no time limit before it must go through reflow. Components rated MSL 1 do not need to be dry packed, and they do not need to be baked before assembly.
To appreciate how special this is, here is how the other levels compare at the industry-standard referencing temperature:
MSL level
Floor life after the dry pack is opened
Condition
1
Unlimited
30°C / 85% RH
3
168 hours (7 days)
30°C / 60% RH
5a
24 hours
30°C / 60% RH
6
Must be baked before use
30°C / 60% RH
The lower the number, the more robust the package. By the time you reach level 3 and below, a strict floor-life clock starts ticking the moment the moisture barrier bag is opened, and the components usually need to be baked before reflow if that window is exceeded.
How is an MSL 1 rating determined?
The rating is assigned after the component passes a qualification test defined in JEDEC J-STD-020. In the test, devices are exposed to a controlled temperature and humidity soak, then sent through reflow three times to simulate mounting, rework removal, and re-mounting. Afterward, the package is inspected for delamination with scanning acoustic tomography (SAT) and the devices are functionally tested. A package that survives all of this without moisture-related damage earns its MSL classification.
The final rating depends largely on the moulding compound and the internal construction of the package. Epoxies with low moisture absorption and a tight bond to the lead frame are what allow a part to reach MSL 1, which is why you tend to see level 1 on mature, well-optimised package designs.
Why MSL matters for your PCB assembly project
If your design relies mainly on MSL 1 parts, handling is straightforward and your
SMT pcb assembly line can run without the extra drying and dry-pack logistics that lower-rated parts demand. However, most real boards mix components of different levels, so a reliable assembly partner must manage the most sensitive part on the board, not just the average. Baking, dry storage, and strict floor-life tracking are the difference between clean joints and hidden internal cracks.
Farway Electronic treats moisture sensitivity as part of its standard handling discipline. Component management includes incoming quality inspection, controlled and anti-static warehousing, and storage that keeps materials within their allowed conditions. When you choose
PCBA OEM manufacturing with Farway, the same care carries through the entire build, and finished boards move on to
PCBA testing so that any assembly-related defect is caught before boards reach your production line or your customer.
Practical tips for buyers and engineers
Whether you buy components yourself or hand your BOM to an EMS partner, a few habits keep moisture risk low:
Check the MSL code on the label before storing any loose components.
Keep moisture barrier bags sealed until the parts are actually needed on the line.
For levels 2 and below, record the time the bag was opened and track the floor life.
If a sensitive part exceeds its floor life, bake it per the manufacturer's profile before reflow.
Ask your assembly supplier how they handle moisture-sensitive parts in their process.
The takeaway
Moisture sensitivity level 1 is the easiest rating to work with: no dry packing, no floor-life clock, and no baking, even at up to 30°C and 85% relative humidity. But a reliable product depends on managing every level that appears on your board. Understanding MSL helps you choose the right components and the right manufacturing partner, so your prototypes and production runs stay free of invisible moisture-related failures.
