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How to Read a Date Code

The standard electronics date code format is YYWW — a four-digit code where the first two digits are the year and the last two are the work week. A part marked 2318 was manufactured in week 18 of 2023. Some manufacturers use a three-digit code (YWW) for years within a decade, or a longer format that includes facility or shift codes.

Date codes appear on component packages (usually the case marking), reels, tape, and manufacturer documentation. They are a manufacturing date — not a shelf-life expiration date — though shelf life limits are calculated from the manufacturing date.

Why Date Codes Matter for Purchasing

Customer Acceptance Windows

Many customers — particularly in defense, aerospace, and high-reliability industries — specify maximum acceptable date code age in their purchase orders. A common specification is two years from date of manufacture for commercial components; some customers accept older date codes with re-screening or bake processing. If you're sourcing components for a customer with date code requirements, the date code on the lot must be verified before the purchase is committed.

Moisture Sensitivity

Surface-mount devices rated at moisture sensitivity levels (MSL) 2 and above have a floor life limit once removed from dry-pack packaging. The J-STD-020 standard defines floor life by MSL level — from 4 weeks at MSL 2 to 6 hours at MSL 6. Components stored improperly can absorb moisture that causes popcorning during reflow — catastrophic package failure from steam pressure inside the package.

Older date codes increase the probability that original packaging has been opened, humidity barriers compromised, or floor life consumed. For high-MSL components sourced from the open market, baking per J-STD-033 is standard practice before use.

Obsolescence and Last-Time Buys

In the independent market, old date codes often represent the last remaining inventory of a discontinued component. A lot with a 2008 date code on a part discontinued in 2010 may be the only supply left in the world. In this context, the date code isn't a quality problem — it's evidence of provenance, and verifying it against the manufacturer's production records is part of authentication.

Date Codes and Counterfeit Detection

Date code inconsistency is one of the primary indicators of counterfeit or remarked components:

• Date codes that post-date the last known production run — a part stamped with a manufacturing date after the device was discontinued is almost certainly remarked
• Inconsistent date codes within a claimed single lot — if a lot supposed to be uniform shows multiple date code years, parts from different lots (or different manufacturers) have been mixed
• Date codes that don't match supplier documentation — the lot number and date code on the component should match the manufacturer's certification documents

At RH Electronics, date code verification is a standard part of incoming inspection. We check component markings against supplier documentation and cross-reference against known production records for discontinued parts. For high-value lots, we use XRF and microscopy through accredited independent labs to confirm package construction and marking authenticity.

What to Ask When Sourcing from the Open Market

• What is the date code of the available lot?
• Does the date code fall within your customer's acceptance window?
• Is the packaging original? Has the humidity barrier been opened?
• For high-MSL components: has baking been performed or is it available?
• Does the date code match the manufacturer's documentation for this part number?

RH Electronics provides date code information with every quote. If a lot's date code is outside a standard acceptance window, we tell you — and advise on re-screening or baking options. Submit a quote request with your date code requirements specified.