Moisture Sensitive Device Management for Meter Boards

A smart meter communication board carries a main controller, a wireless module, memory, isolation devices and power conversion, and a proportion of the soldering problems that appear on such a board do not originate in the reflow oven at all. When an integrated circuit has been out of its packaging for too long, or when the remainder of a reel has not been resealed, the risk of package damage and of unstable soldering rises when the part reaches the oven.

Why the Packaging State Belongs in the Record

The symptom is not usually visible in an ordinary visual inspection, which is what makes it dangerous. A line that adjusts the reflow profile without checking when the material was opened and how it was stored will see the same fault return on the next order. Material state is therefore managed from the moment the project is quoted rather than explained after the assembly has been completed.

The reason is that a plastic package absorbs moisture from the air. When the part is heated rapidly, that moisture turns to steam inside the package, and the pressure it produces can crack the body or separate the moulding compound from the die pad. Loss of a moisture sensitive device is not always catastrophic, which is why the failures appear as intermittent joints and unstable readings rather than as a board that will not start.

What the Quotation Stage Should Establish

When the bill of materials is supplied, it helps to include the manufacturer part number, the package, the reference designators, the quantity and the range of parts that may be substituted. For the wireless module, the memory and the controller in particular, the customer should say whether the material is supplied by the customer or purchased by the factory.

Where the customer provides stock material, its packaging condition, the date it was purchased, whether the seal has been broken and how it has been stored since then all matter. An intact outer box does not mean that the parts inside are in a state that suits the process, and the assessment is made from the packaging label, the incoming condition and the requirement of the project.

During import the Gerber data, the bill of materials, the coordinates and the assembly drawing are checked against each other. Where a part number is incomplete, where one reference designator has several possible types or where a substitution is not clearly permitted, the question is raised before the order is scheduled. Material that has not been confirmed is not put on the line on the basis that the package looks the same.

Incoming Inspection and Quantity

When the material arrives, the outer packaging, the reel, the label, the quantity and the physical condition are checked. A broken sealed bag, an abnormal desiccant, an incomplete label or a mechanically damaged reel is recorded separately, because each of them changes what is done next.

Quantity deserves attention when the customer supplies the material. If the delivered quantity is close to the theoretical requirement, there is no allowance for loading, for changing a reel, or for the small losses that occur at the machine, and the run can stop halfway through for want of a handful of parts. The quantity is compared with the requirement plus a working allowance before the material is accepted.

A meter communication board is often built in several communication versions, so mixing the versions is a specific risk. Two modules of the same size can carry different communication methods, different firmware or a different suffix, and size is not a way to tell them apart. Before loading, the physical label, the bill of materials part number, the reference designator and the feeder position are connected to one another.

Baking Is a Decision, Not a Default

Whether a part needs baking follows from its packaging information, its exposure history, the temperature the packaging material can survive and the customer requirement. Applying one temperature and one duration to every device in the building, for the sake of being safe, is not a controlled process and can damage parts that did not need it. Some tape, tray and packaging materials cannot enter a baking oven at all, so the handling method is confirmed first.

Once a seal is broken, the exposure time is recorded and the material is handled under the conditions the process requires. A reel that will not be used immediately is resealed and returned to a dry environment. A dry pack with a humidity indicator card that has changed colour is treated as a signal to look more closely rather than as decoration.

When production is interrupted, the exposure of the material already loaded on the machine is part of the same calculation, not only the material still in the store. Before the line restarts, the reels on the machine, the boards waiting to be placed and the paste are all confirmed to be in a state that can continue.

Loading and the First Article

Once the material is ready, the loading information is built from the current, effective bill of materials. The first article confirms not only the orientation of the parts, the reference designators and the joints but also the actual type of the key devices and the wireless module. If the customer approves a substitute at short notice, the approval is kept with that order and states which reference designators it affects.

Printing, placement and reflow are still set from the structure of the board. Material management does not replace paste inspection, the first article check, optical inspection or the joint inspection, but it removes a source of variation that would otherwise be attributed to the machine.

If one device type shows a cluster of package or soldering defects after reflow, the material lot, the opening record, the print condition and the temperature profile are analysed together. Calling it a machine accuracy problem without those records is a conclusion that the data do not support.

Returning the Remainder

At the end of a small order, the remaining reels are counted and their state is recorded. Material that can be kept is repackaged against moisture or returned to the appropriate storage environment, and material whose exposure cannot be established is kept apart from the qualified remainder so that the next order does not draw on it by accident.

The delivery documentation states the revision of the key materials used, the remaining quantity of customer supplied material and any substitution that was confirmed during the build. When the next order uses the remainder, the customer can judge from the record whether it needs to be assessed again. Our component procurement group manages the incoming material and the storage, the SMT assembly line applies the exposure control, and the records are held under quality management.

FAQ

Does every sealed part need to be baked? No. The requirement follows the packaging information, the exposure history and the material of the packaging, and it is decided per part rather than applied to everything.

Why record the opening time? Because the exposure allowed depends on it, and because the record is the only way to know the state of a reel that has been partly used.

What happens to leftover material? It is counted, recorded and either repacked for dry storage or separated from the qualified stock, depending on what can be established about its condition.