Kit guide

How to ship moisture-sensitive chips

CopperPCB · October 1, 2026

Many chips quietly absorb moisture from the air. In the reflow oven that moisture turns to steam and can crack the package from the inside. A few minutes of care when you pack your kit prevents it.

What MSL means

Every plastic-packaged chip has a Moisture Sensitivity Level, or MSL, set by the IPC/JEDEC J-STD-020 standard. It tells you how long the part can sit in normal factory air after its sealed bag is opened before it must be soldered or baked dry. That window is called floor life.

Levels 2a through 6 assume conditions of 30°C and 60% relative humidity or less. Many common microcontrollers, power chips and BGAs are MSL 3. A week sounds generous until a bag is opened to count parts, left on a bench, and shipped across the country.

Why it matters

Reflow heats a board to well over 200°C in a few minutes. Moisture trapped in the plastic expands as steam and can delaminate the package or crack it, sometimes with an audible pop, which is why it's called popcorning. Damage can be invisible from outside and show up later as an intermittent fault.

How to find your part's MSL

• The bag label. Moisture-sensitive parts ship in a sealed bag with a caution label showing the level and floor life.
• The datasheet, usually in the ordering or packaging section.
• Your distributor's product page, which normally lists it next to the package type.

What a proper dry pack looks like

Moisture-sensitive parts arrive in a moisture barrier bag, a foil-like sealed bag, with a desiccant pack and a humidity indicator card inside. The card has printed spots that change color when humidity inside the bag has risen too far.

How to ship them to us

1. Ship it exactly as it arrived. If the distributor's sealed bag is intact, don't open it. Forward it with your kit.
2. Don't open bags to count parts. Your cart already includes extras, and the label tells you the quantity.
3. If a bag has been opened, put the parts back in with fresh desiccant and the indicator card, reseal it as tightly as you can, and write on it roughly how long it was open. A note in your build request works too.
4. Put your build number on the outer package, as with everything else in your kit.

What happens if parts have absorbed moisture

If the indicator card or the open time says a part is past its floor life, it has to be baked dry before reflow, following J-STD-033. Parts on tape and reel can't take high oven temperatures, so baking them takes much longer at low heat. If your parts need it, we'll tell you the same day we check in your kit, so you can decide whether to wait or send fresh ones.

More from the bench

• What's in the jellybean jar

  The brands behind every free passive on your board, from Murata capacitors to Vishay resistors, and why we chose them.

• Brands we like to see in your kit

  Chips, connectors and LEDs make your board yours. If you're choosing them, these are the makers we'd pick.

• The true cost of buying your own jellybeans

  Passives cost pennies. Buying them for a prototype run costs a lot more than that. Here is where the money and time really go.

• Designing for 0402: a practical guide

  Footprints, tombstoning, vias, fiducials and capacitor derating. How to lay out a board that builds cleanly with 0402 and larger parts.