Reel Storage: 6 Rules for Moisture Sensitive Parts

Reel storage is a set of rules for keeping moisture sensitive components dry between the supplier and the placement machine. Plastic packages absorb water from the air, and that water turns to steam at reflow temperature. The result is internal stress that can crack the package or delaminate the interface between the moulding compound and the die pad.

The rules are not complicated, but they depend on records that are easy to skip when the line is busy. A bag that is opened without a date, a reel that sits on a shelf for a week or a humidity indicator that nobody reads all undermine a storage system that looks well organised on paper.

<img src="https://www.gopcba.com/wp-content/uploads/2026/09/5-2.jpg" alt="Component reel storage shelves with dry pack bags in a store” />

Why Reel Storage Rules Exist at All

Every plastic package carries a moisture sensitivity level that states how long it may be exposed to ambient air before it must be baked. That period is the floor life, and it starts the moment the sealed bag is opened. Reel storage is the discipline that keeps the exposure inside the limit.

Absorbed moisture does not cause an immediate defect. It creates damage during reflow that may pass inspection and fail later, which is why the control has to be preventive. There is no test that finds a package which was exposed too long but has not yet cracked.

Dry Pack, Desiccant and the Sealed Bag

Moisture sensitive parts arrive in a dry pack: a foil bag, a desiccant sachet and a humidity indicator card, with a label stating the level, the bag seal date and the floor life. The bag is the storage system, and the desiccant is what holds the internal humidity down once the bag is closed.

A bag that is punctured, torn at a corner or left unsealed has lost its protection. Reels that come in cardboard boxes with no bag should be treated as already exposed, and the MSL handling rule then applies from the delivery date rather than from an opening date.

Reading Humidity Indicator Cards and Labels

The humidity indicator card shows how much moisture the air inside the bag contains, and the reading should be taken before the parts are used. A card that has changed colour beyond the limit stated on the label means the bag was not sealed properly or has been open longer than assumed.

The label matters as much as the card. The bag seal date, the moisture sensitivity level and the floor life are printed there, and the storage system depends on those values being transcribed onto the reel or the traveler when the bag is opened.

Floor Life Tracking Once a Bag Is Open

Floor life is consumed by exposure to ambient air, and it is paused only by returning the parts to a dry environment within the time the standard allows. A simple log with the opening date and the accumulated exposure is enough for a store that handles a limited number of levels.

Where several levels are in use, labels and colour codes reduce mistakes. The point is that the person loading the feeder has to know, at a glance, whether the reel in hand still has floor life left, and the general rules are collected in moisture control in SMT storage.

Racks, Humidity and Temperature in the Store

A dry cabinet or a nitrogen cabinet holds parts at a controlled humidity and allows floor life to be reset within limits. Ordinary shelves do not, so they must be used only for parts whose exposure is being counted, with the temperature and humidity of the room recorded rather than assumed.

Air conditioning that runs cold at night and warm during the day creates condensation cycles on reels, which is worse than a stable warm room. The store should be monitored, and the log should be reviewed when parts fail a subsequent process step, not only when an audit is due.

Partial Reels, Splices and Return to Store

A partial reel that comes off the machine has consumed floor life and should be returned to a dry cabinet with a label showing the accumulated exposure. Where a reel has been spliced, both the original and the added length carry the earlier exposure figure, because the conservative value is the safe one.

Reels should also be checked for physical condition before they go back into the store. Tape that has been crushed, cover tape that has lifted and reels that have been dropped all cause feeder problems later, and the handling notes in reel handling cover the checks worth making.

Baking Before Assembly: When and How

When floor life is exhausted, the part is baked before use at a temperature and time taken from the standard and from the label. High temperature baking suits parts that can take it, while low temperature baking takes much longer and is used for reels and trays that would not survive the heat.

Baking is a controlled operation with its own record, because an oven that overshoots can damage tape, reels and solderability. The practice of logging bake temperature, time and operator is the same one used in component baking records for every other heat exposure.

Popcorning, Delamination and Failure Evidence

The failure mode that all this prevents is popcorning, where the package swells and cracks as trapped moisture expands during reflow, and delamination, where layers inside the package separate without an external crack. Both are found by scanning acoustic microscopy or cross section rather than by eye.

When a failure is confirmed, the first records to check are the storage log and the bake history, because the cause is usually an exposure that was not counted. Boards that were stored before assembly under the rules in bare board storage have the same need for a dated record.

Records, Audits and Stock Rotation

Rotate stock so that older reels are used first, and make sure the rotation respects floor life rather than the date of arrival alone. A reel that arrived early and sat sealed has full life left, while a reel that arrived late but was opened on receipt may have none.

Audit the store against the standard the customer requires, and keep the results with the IPC reference for moisture sensitive handling. An audit that only checks whether the cabinet is tidy misses the point; what matters is whether every open reel has a date and a remaining figure.

FAQ

How long can a reel stay out once the bag is opened? That depends on the moisture sensitivity level printed on the label, and it ranges from unlimited for the lowest levels to a few hours for the most sensitive parts. The floor life figure on the bag is the one that applies.

Can a humidity indicator card be reused after the bag is closed? The card in the bag describes the air that was sealed with it, so it should be read before opening and replaced if the bag is resealed with new desiccant. Reusing a card that has already changed colour gives no information.

Is baking always the answer when floor life runs out? Baking restores the parts to a dry state, but it counts as another thermal exposure and has to be recorded. Where a part is time and temperature sensitive, the alternative is to plan the build so that reels are opened close to the point of use.