Tray and Moisture Sensitive Component Handling

Why Trays and Dry Packs Exist

Surface mount components are shipped in trays, tubes, or tape and reel for one reason: the placement machine has to pick them up in a known orientation at speed. The packaging is also a storage environment. Trays and tubes keep parts separated and protect leads from damage, while moisture barrier bags with desiccant keep hygroscopic plastic bodies dry until the line is ready to use them.

The dry pack is not a convenience. Plastic packages absorb water from the air, and when the package is heated to reflow temperature, that water turns to steam inside the body. The pressure can crack the package, delaminate the die attach, or push the internal structure apart, a failure known as popcorning. Once it happens the part may still pass electrical test and fail later, which makes it one of the more expensive defects to discover.

Handling combines two disciplines: mechanical protection of the parts and control of the moisture they have absorbed. Both are managed by the packaging and by the rules the shop floor follows after the package is opened.

Moisture Sensitivity Levels

Components are classified by moisture sensitivity level, or MSL, which describes how long a part can be exposed to ambient air after the dry pack is opened before it must be baked. A lower MSL number means a more sensitive part with a shorter allowed exposure. The exposure limit is expressed as floor life, and the clock starts when the bag is opened.

Floor life is cumulative, not per build. A part that sits out for two days, goes back into a bag, and comes out again the following week continues from where its clock stopped unless it has been properly re-dried and re-packed. Many shop floor problems come from treating the exposure as a single event rather than as an accumulating total.

The level is determined by the package thickness, the body material, and the die attach, and it is printed on the bag label along with the date code and the required bake conditions. That label is the authoritative instruction, not the part number or a general rule.

Floor Life and Bag Opening

Managing floor life means logging when each bag is opened and where the parts are stored. Parts that will not be consumed within their floor life should go back into a dry environment, either a resealed bag with fresh desiccant or a dry cabinet held at the specified humidity. A humidity indicator card in the bag shows whether the desiccant has been exhausted, and a card that has changed colour is a signal that the bag was compromised.

Once a part exceeds its floor life, the options are to bake it or to discard it. Using it without either is a risk that may not show up until the assembly is in the field. Where a build schedule is uncertain, keeping parts in a dry cabinet rather than on an open bench is the simplest control.

Carriers themselves should be treated as part of the storage system. Trays that are stacked, dropped, or stored uncovered collect dust and can transfer it to components, and trays that are reused across products should be cleaned and inspected so that a damaged pocket does not misalign a part during placement.

Baking Rules

Baking drives absorbed moisture out, but it is not a universal cure. The temperature and time depend on the package type and the carrier. Parts supplied in tape and reel cannot be baked at the higher temperatures used for trays, because the tape and the reel will not survive; those parts need a lower-temperature bake for a much longer time, and the reel material has its own temperature limit that must be respected.

Baking also has limits. Repeated high-temperature bakes oxidize the leads, which degrades solderability, and some packages have a maximum number of bakes specified by the manufacturer. Baking is a corrective action, not a routine step, and a line that bakes every incoming part has a storage or scheduling problem to solve first.

The bake should be logged for each lot, including temperature, duration, and the quantity, and the parts should be returned to a dry environment immediately afterwards. A part that is baked and then left on an open bench has simply restarted the problem.

Tray Handling and ESD

Component trays are as much an electrostatic discharge control as a mechanical one. Conductive and dissipative trays drain static charge, while ordinary plastic trays can hold a charge that damages a sensitive die when the part is picked up. The tray type must match the sensitivity of the components, and trays should never be substituted across products without checking that the material is appropriate.

Placement machines add their own stresses. Nozzles and feeders can damage parts if the pick force is too high or the pocket is not holding the part squarely, and mis-picks that fling a part across the machine are both a yield loss and a source of contamination. Feeder setup and nozzle selection are part of tray handling, not separate from it.

Manual handling is where most damage happens. Parts should be removed from trays with tools designed for the package, not fingers, and operators should be grounded and trained on the specific component families they handle.

Shop Floor Control

Effective control comes down to a few simple disciplines: a log for every bag that is opened, a dry storage location that is actually monitored, a defined rule for how long parts may sit on a line, and a bake procedure with documented temperatures and times for each package type. Signage at the line, showing the floor life of the parts in use, keeps the rule visible.

The controls should extend to the end of the line as well. Parts left over after a build should be returned to dry storage with their floor life recorded, and any lot that has exceeded its limit should be clearly marked so it is not used without being baked.

Auditing these practices periodically, rather than only after a failure, is what keeps the process honest. Moisture damage is invisible at assembly, so the discipline has to be maintained before the evidence appears.

FAQ

What is floor life? The time a moisture sensitive component may be exposed to ambient air after the dry pack is opened before it must be baked or re-dried. The allowance is printed on the bag label and depends on the moisture sensitivity level.

Can all parts be baked at the same temperature? No. Trays and tape and reel have different temperature limits, and packages have a maximum number of bakes. The label and the manufacturer’s data give the permitted conditions.

What is popcorning? A package crack or internal delamination caused by moisture turning to steam during reflow. It can pass electrical test and fail later, which is why moisture control matters.

Does the floor life clock reset if parts go back in a bag? Only if they are properly re-dried and re-packed. Simply putting parts back in a bag without baking does not reset the accumulated exposure.

How should leftover components be stored? Return them to a dry cabinet or a resealed bag with fresh desiccant, record the exposure already used, and mark any lot that has exceeded its limit so it is not used without baking.

Conclusion

Tray and moisture sensitive handling is mostly discipline: know the floor life of every bag, keep parts dry when they are not being used, bake correctly and only when required, and treat carriers as part of the electrical and mechanical protection of the parts. Doing this consistently prevents popcorning and the slow failures that follow it, and it costs far less than the field returns it avoids. Readers can compare our material on SMT assembly, PCB assembly, quality management, and PCB manufacturing for how component controls fit the wider process in 2026.