Date Code: 6 Rules for Incoming Inspection and Rotation

A date code is the marking that tells you when a component was made, usually as a year and week on the reel label, the bag label and often the package itself. It is the cheapest traceability tool available at goods-in, and it is the only one that links a delivered board back to the manufacturer batch that produced it. Ignoring it is a decision that costs nothing until it costs everything.

The code does not describe condition. A part made last month and stored badly can be worse than one made three years ago and stored in a sealed bag with desiccant. Reading the date code is the beginning of the assessment, not the end of it, and the storage history is what turns the number into a judgement.

What a Date Code Does and Does Not Tell You

The manufacturing date is what the code carries. It does not say when the moisture barrier bag was opened, whether the part was re-reeled by a distributor, or whether the reel has been split and mixed. Those facts come from the label, the packaging and the supplier, not from the digits on the package.

It also does not identify the die revision. Two parts from different batches may be electrically identical, and two parts from the same batch may differ if the manufacturer changed a process mid-week. A product change notification from the manufacturer is the document that carries that information, and the date code is how you work out whether your stock is affected.

Why Date Codes Belong in Incoming Inspection

The receiving check is the last point where a problem can be caught before parts enter the store and lose their identity. Once mixed into a bin, a reel with an unusual marking can no longer be separated, and the whole stock becomes suspect if the manufacturer issues a notice.

Three questions belong in the incoming inspection step: does the date code match what was ordered, is it inside the age limit the product allows, and does it agree with the same code on every other package in the shipment. A mismatch between the label and the marking is the classic counterfeit warning sign.

Reading the Marking: Formats and Ambiguity

Formats vary between manufacturers. The four digit year and week form is the most common, but two digit year forms, three digit codes and internal lot numbers that look like dates all appear in production. Some manufacturers print only a lot code and publish a lookup table, and some put the date on the reel label only.

The practical rule is to build a small reference for the parts you buy frequently, with the format and a worked example for each manufacturer. Where a supplier re-reels or re-packages parts, the original date code should still appear on the new label so the incoming inspection step can verify it, and the absence of it should be questioned rather than accepted. Mixed batches within one reel are a traceability failure even when the parts are genuine.

Component Shelf Life and Storage Conditions

Component shelf life is not one number, because different parts age by different mechanisms. Solderability declines as the finish oxidises, which affects the whole board. Electrolytic capacitors dry out. Adhesives cure slowly in the syringe. Sensors can drift. Each of those limits should be set by the part rather than by a single company rule.

Storage conditions decide how fast the limits are reached. Sealed moisture barrier bags with desiccant and a humidity indicator card hold a part close to its as-received condition, and a controlled store with stable temperature and low humidity slows oxidation. A part on an open shelf in a humid room may reach its practical limit far sooner than its nominal component shelf life suggests.

Moisture Sensitivity Level and the Date Code

The moisture sensitivity level is a separate property from the manufacturing date, and the two are often confused on the shop floor. The level decides how long a part may stay out of its bag after opening, and the clock starts when the bag is opened, not when the part was made. A three year old part in a sealed bag can have more floor life left than a part made last month and opened a week ago.

That is why the bag carries a seal date and the store carries an opening record. Our notes on floor life and on moisture sensitivity level control set out the tracking. Where the floor life is exceeded, the part is baked and re-bagged, and the bake is recorded against the same identity that the marking provides.

<img src="https://www.gopcba.com/wp-content/uploads/2026/05/Solar-Inverter-System-PCBA.jpg" alt="Reels stacked for first in first out rotation after a date code check” />

First In First Out and the Physical Store

First in first out is a store design question before it is a discipline question. If the oldest reel is at the back of a deep shelf, it will stay there. A rack that can be loaded from one side and picked from the other, with the receipt date visible on the label, makes the rule self-enforcing.

First in first out also needs a visible marker for parts that are close to their age limit. A label colour or a separate bin for stock that must be used first turns the rule into something an operator can follow without checking every label. Our notes on moisture barrier bag handling cover the same principle for bagged stock.

Handling Parts That Are Past Their Date

A part past the age limit is not automatically scrap. It is a part whose condition has to be established before it is used. For a moisture sensitive part, that means baking to the schedule for its body size and thickness. For a part whose solderability is in question, it means a wetting check rather than an assumption.

The decision should be recorded with the reason, and the part should be marked so that the same question is not asked twice. Where a customer requires parts within a stated age at shipment, an older part cannot be consumed on that product at all, so first in first out alone will not solve it and the reel should be moved to a product that allows it. Our notes on baking records describe the paperwork that keeps this auditable.

Records, Traceability and Customer Requirements

The record that matters is the link between the date code and the finished assembly. A work order should carry the component lots consumed on it, because that is what allows a recall to be scoped in hours rather than weeks. Scanning the reel label at the point of consumption is the cheapest way to build that link.

Customer requirements vary widely, from no stated limit to a maximum age for every part on the board. Those requirements belong in the receiving standard and in the work order rather than in a verbal agreement, because a shipment can be rejected long after the parts were consumed. Where a deviation is needed, it should be agreed in writing before the build.

Writing the Receiving Rule

A workable incoming inspection rule has four parts: which parts carry an age limit, what the limit is, how the date code is verified and recorded, and what happens when the limit is exceeded. It should also name the person who can approve an exception, because otherwise every marginal reel becomes a decision at the bench.

Keep the rule short enough to be followed at the receiving desk with the carton open. A single page that names the formats, the limits and the escalation path will be used; a procedure that requires a lookup table for every part will be skipped under time pressure, and the store will fill with unverified material.

FAQ

Does an old date code mean a part is unusable? No. Age is one input, and storage condition is the other. A sealed part with desiccant inside its age limit is usually fine, while an old part that has been open in a humid room may need baking or a solderability check before it is used.

Why do some manufacturers print only a lot code? Because their internal lot numbering is more useful to them than a calendar date, and the date can be derived from it through a lookup. Ask the supplier for the mapping and keep it with the part record, rather than guessing at the digits.

Should mixed batches in one shipment be rejected? Not necessarily, but they should be recorded and kept separable. Mixed codes make traceability harder and they slow down any response to a product change notification, so the reason for the mix should be established at goods-in.