Dry Packing and Component Storage
Why Storage Is a Process
Components are sensitive to moisture long before they reach the reflow oven. Plastic packages absorb water from the air, and when they are heated quickly that water turns to steam inside the body. The result is internal stress, delamination, wire bond damage and the classic popcorning crack, and none of it is visible before the damage is done. Dry packing is the method that keeps moisture out between the manufacturer’s final test and the moment the part is placed, and storage is the discipline that keeps the packing effective.
Moisture Barrier Bags
A moisture barrier bag is a laminate film with a very low moisture vapour transmission rate, sealed around the parts with a desiccant inside. The bag is not a container; it is a moisture barrier, so its performance depends on the seal. A bag that is sealed with a crease in the seam, or that is cut open and closed with tape, has lost most of its protection. The indicator card inside, which changes colour when the internal humidity exceeds a limit, is the check that tells the store whether the bag is still doing its job when it is opened.
Desiccant, Humidity Indicators and Labels
The desiccant absorbs the small amount of moisture that passes the film or is trapped at sealing, and its quantity is matched to the bag volume and the storage period. The humidity indicator card shows the condition at a glance, and a card that has reached its limit is a signal that the parts need baking rather than use. The label carries the sensitivity level, the floor life, the seal date and the maximum temperature, and it is the document that ties the part to its handling rule. Where the label is missing or unreadable, the part should be treated as though the floor life has expired.
Floor Life and the Clock
Floor life is the time a part may spend out of the bag in a controlled environment before it must be baked or resealed, and it starts when the bag is opened rather than when the parts are used. The allowed time depends on the sensitivity level and on the ambient humidity, so the same part has a longer floor life in a dry room and a shorter one in a humid workshop. The practical control is to write the opening date and time on the bag, to reseal what is not used, and to record the exposure so that the accumulated time is known rather than guessed. Parts that are counted out and left on an open bench are the ones that fail.
Dry Storage and Dry Rooms
Where parts are used in small quantities over a long period, a dry cabinet or a dry room is more practical than repeated baking, since it lets the bag be opened and resealed without the moisture returning. A dry cabinet holds a low relative humidity and gives a place where partially used reels can live between builds. A dry room extends the same idea to the whole kitting and assembly area, which removes the need to protect individual bags as carefully. Both approaches still need the humidity to be monitored and recorded, because a dry store that has drifted is worse than none, since it is trusted.
Baking and Its Limits
Baking drives the absorbed moisture out, but it has to be done within the part’s limits. The bake temperature has to stay below the point where the packaging or the terminations are damaged, which rules out high temperature bakes for many parts, and the time has to be long enough to remove the moisture from the body rather than only from the surface. Repeated baking degrades the plating and the mould compound, so it is a repair rather than a routine. Parts on reels in particular have temperature limits set by the tape and the carrier, which are lower than the part’s own limit and are often overlooked.
Record Keeping and Kitting
Storage control lives or dies on records. The seal date, the opening date, the exposure time, the bake history and the remaining floor life should follow the reel through kitting, so that the operator at the line knows whether a part is still within its allowance. Where the assembly is kitted in advance, the kitting area itself should be controlled, because a kit that sits in a humid room overnight has consumed floor life before the line ever sees it. A simple label with dates and an honest log solves most of the problem.
Humidity in the Workshop
The ambient humidity around the line decides how fast floor life is consumed, and it is the variable most often left unmeasured. In a humid climate a part that is allowed a long floor life under the standard assumption may need baking after a single shift, which is why the exposure has to be judged against the actual room rather than the nominal table. Monitoring the workshop humidity, keeping the kitting and placement areas away from doors and open windows, and shortening the time between kitting and placement all reduce the exposure without any capital cost. Where the climate makes control impossible, the dry cabinet becomes the practical answer for the parts that matter most.
FAQ
What is dry packing? Sealing moisture sensitive components in a barrier bag with desiccant so that they stay dry between the manufacturer and the build.
Why do plastic packages crack in reflow? Absorbed moisture turns to steam when the part is heated quickly, and the internal pressure damages the package.
What is floor life? The time a part may stay out of its bag in a controlled environment before it must be baked or resealed.
Can I bake any part to reset the clock? Only within its temperature limits. Tape, reels and terminations often limit the bake more than the part itself.
Is a dry cabinet worth it? Yes, where parts are used in small quantities over time; it avoids repeated baking and keeps partially used reels usable.
Conclusion
Dry packing and storage are cheap compared with a delaminated lot, so protect the bag, record the date and respect the floor life. Baking is a repair, not a habit. Storage and handling belong to quality management, the reflow that punishes damp parts sits in SMT PCB assembly, and the wider build is covered under PCB assembly. Handling rules for a new product are settled during prototype PCB assembly in 2026.
