Moisture Sensitivity Level — Floor Life and Baking for BGA and QFN

Why moisture sensitivity decides whether a BGA actually survives reflow #

A sealed moisture-sensitive package looks identical to a dry one on the reel. The difference only shows up on the SMT line, when the board passes through the reflow oven. If water has been absorbed into the plastic body, the vapour pressure inside the package rises fast as the temperature climbs past 200 °C. The expansion can crack the package or delaminate the die attach — the classic "popcorn" failure — and the damage is often hidden under the lid or inside a BGA that cannot be visually inspected after mounting.

For buyers and EMS teams, this is not just a factory problem. A moisture-sensitive lot that sat too long in open storage, or arrived in a torn dry-pack, may be unsellable or unusable even though the date code and markings look perfect. Knowing the part's Moisture Sensitivity Level (MSL) and its remaining floor life is part of accepting a consignment responsibly.

What MSL actually measures #

MSL is a classification of how long a packaged device can sit exposed to ambient humidity before it must be mounted or re-baked. It is defined by IPC/JEDEC standard J-STD-020, which assigns a level based on the time a part survives at a controlled condition of 30 °C and 60 % relative humidity before reflow without damage. A lower number means the part tolerates more exposure; a higher number means it must go onto the board almost immediately after the moisture barrier bag is opened.

The classification reflects the package construction: thin, large-body, and cavity-type packages absorb and trap more moisture, so they rate worse. A fine-pitch BGA, a QFN with an exposed pad, or a stacked-die package almost always carries an MSL of 3 or tighter, while many leaded or coarse-pitch parts are MSL 1 or 2.

The MSL floor-life reference #

Floor life is the permitted exposure time at ≤30 °C / 60 % RH after the dry-pack is opened (or after a bake resets the clock). The values below follow J-STD-020:

The key point for procurement is that MSL 3 and above turn the bag-open date into a deadline. A part bought "as stock" may already be past its floor life if it was opened and re-bagged by a broker without baking.

Reading the dry-pack label before you accept a lot #

A genuine moisture-sensitive part ships in a moisture barrier bag with desiccant and a humidity indicator card (HIC). Before accepting the shipment, check:

• MSL marked on the label — confirm it matches the datasheet; some vendors ship the same device in different MSL grades by package option.
• Bag-seal date and HIC colour — the humidity card should read dry (typically below 5–10 % RH). A pink or saturated card means the barrier failed.
• Remaining floor life — if the bag was opened by the supplier, ask for the open date and the bake record.
• Intact desiccant pouch and no puncture — a torn bag resets the floor-life clock to zero.

For a part like the XC7Z020-2CLG484I Zynq-7000 BGA, this discipline matters: it is a thin, fine-pitch BGA and is normally rated MSL 3, so a broker "opened-and-rebagged" unit with no bake certificate should be treated as expired until proven otherwise.

What happens if floor life expires #

When a part exceeds its floor life, it is not automatically destroyed — but it is no longer safe to reflow. The standard remedy is a controlled bake that drives the absorbed moisture back out, after which the floor-life clock restarts. Reflowing without baking risks internal cracking, intermittent failures, and field returns that surface weeks after the board ships.

The safe rule is simple: never reflow a moisture-sensitive part past its floor life unless it has been baked and the new floor life is documented.

Baking: when and how #

Baking is governed by IPC/JEDEC J-STD-033, which also covers packing, handling and the bake schedule. The short version buyers should understand:

• Temperature: the standard bake is 125 °C (±5 °C). Lower-temperature bakes exist for parts that cannot take 125 °C, but they take far longer and must follow the standard's alternative tables.
• Duration scales with package thickness: thin packages need a shorter bake than thick ones. A common 24-hour bake applies to typical thin packages; thicker bodies require longer exposure per the J-STD-033 thickness table.
• Re-baking resets the clock: each completed bake restarts the floor life from zero, which is useful but also means the part must be re-sealed promptly.
• Not every part may be baked: some devices are marked "do not bake," and baking can shift date codes or affect parts with internal moisture sensors or certain finishes. Confirm with the manufacturer before baking a part that is not clearly bake-eligible.

Baking is a recovery step, not a substitute for good storage. A lot that needs baking on arrival is a signal that the handling chain — not the silicon — failed.

Buyer checks before RFQ and acceptance #

When requesting a quote on moisture-sensitive parts, include the MSL requirement and ask the supplier to ship in original sealed dry-pack with the humidity card. For long-lead or allocated parts that may sit in inventory, specify the maximum acceptable floor-life consumption at delivery so the lot is mountable when you need it.

Conclusion #

Moisture Sensitivity Level is the hidden shelf-life stamp on every BGA and QFN. MSL 1 and 2 are essentially worry-free, but MSL 3 and above make the dry-pack open date a real deadline: exceed it and the part must be baked per J-STD-033 before reflow, or it risks popcorning and latent field failure. Buyers protect themselves by confirming the MSL on the label, requiring an intact dry-pack with a dry humidity card, tracking the floor-life clock, and refusing opened lots that lack a bake record. Treat moisture sensitivity as a handling qualification, not a cosmetic detail — a part that passes every marking check can still be unusable if it absorbed humidity on the way to your line.

For package identification and sourcing checks, see our guides to common IC package types and IC package types for buyers. If you need a moisture-sensitive part verified in sealed dry-pack, start from the XC7Z020-2CLG484I part page or open an RFQ.