Moisture Barrier Bag Sealing and Desiccant Control

A moisture barrier bag protects a component from the humidity in the air until it is opened. Everything about the pack, the seal, the desiccant and the indicators, exists to make the storage life predictable rather than hoped for.

What the Bag Has to Do

The bag has to keep moisture out, which means a metallised layer that is continuous across the whole surface including the folds. A crease that breaks the layer is a leak even though the bag looks intact.

The bag should be handled so that the barrier layer is not creased. Our storage notes describe the handling discipline that applies.

Making the Seal

The seal is made with a heat sealer at a set temperature, pressure and dwell, and all three matter. A seal that is too cold has an incomplete bond and one that is too hot thins the material at the seam.

The sealer settings belong in the work instruction. Our fabrication notes list the points to confirm.

Seal Width and Its Verification

The seal width is specified by the packaging standard and it is checked by visual inspection and by a peel test on a sample. A narrow seal or one with a channel through it fails the same check.

The peel test is destructive and it is done on a trial seal. Our quality notes describe the record.

How Much Desiccant

The desiccant quantity depends on the bag volume, the barrier performance and the storage duration required. The calculation is defined by the packaging standard rather than chosen by eye.

Adding more desiccant than required is a cost and not a margin. Our component selection notes describe the specification.

Indicators and Their Meaning

A humidity indicator card shows the condition inside the bag at the moment it is opened, and it is the only evidence of how the pack behaved during storage. A card that has changed colour means the components need a bake.

The card should be read before the components are touched. Our bake schedule notes describe the schedule that follows.

Opening and Resealing

Once the bag is opened the floor life starts, and the remaining components need a new bag, new desiccant and a new card. Reusing the old bag is acceptable only where the seal can be remade above the original line.

The remaining floor life should be recorded for the parts that are used. Our floor control notes describe the records.

Verification

The verification is a sealer with recorded settings, a seal width measured and a peel test on a sample, a desiccant quantity calculated rather than estimated, and a humidity indicator read before the components are handled.

Our first pass yield notes describe how the results are recorded.

Process Control and Verification

Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design. The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel.

Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage. Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch.

Reviewing the design before the data is released is cheaper than correcting it after the panel is in the tank, because every step downstream inherits the decision made at the front end. Documenting the assumption is part of the design work, and a short note on the drawing prevents a question that would otherwise arrive a day later and cost a day of schedule.

The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed.

Checks Before Release

The checks that matter are the ones performed on the product rather than on a sample kept for the purpose, because a coupon that travels with the panel is the only evidence about that panel. Where a requirement can be measured, it should be measured at the point of manufacture and recorded against the board or the lot it applies to.

A parameter that is set once and never re verified drifts, and the drift is usually discovered by a defect rather than by the record. The tooling, the material and the profile form one system, and a change to any of them should be assessed against the other two before it is released.

Where the process window is narrow, the measurement resolution has to be better than the window, or the data cannot distinguish a good part from a marginal one. A record that identifies the operator, the date and the settings is worth more than a record that identifies only the result.

FAQ

Can a bag be resealed? Usually yes, provided the new seal is above the old one and the bag still has enough material. A bag with creases through the barrier should be replaced.

Does a clear bag work? Only if it has the same barrier layer. A plain polyethylene bag controls dust and not moisture.

What does gopcb provide in packaging? We provide a sealer with recorded temperature, pressure and dwell, a seal width measured against the standard with a peel test on a sample, a desiccant quantity calculated from the bag and the storage duration, and a humidity indicator read before the components are handled.