IC Date Codes and Shelf Life: How to Read Them and When Older Stock Is Still Fine

A date code on an integrated circuit is usually four digits in YYWW form: the year and week the part was assembled and sealed. It is not the date the silicon was made, and it is not an expiry date. Semiconductors don't expire. What ages in storage is solderability, as lead finishes slowly oxidize, and, in plastic surface-mount packages, absorbed moisture, which IPC/JEDEC J-STD-033 manages through moisture sensitivity levels (MSL).

Older stock is fine when it stayed in a sealed dry pack or was stored correctly, and when the humidity indicator card or a bake confirms it is dry. The familiar "date code within two years" rule is a buyer's contract term, not a standard: the industry association ECIA recommends dropping blanket date-code restrictions, and manufacturers such as Analog Devices and Renesas ship date codes up to five years old.

We check date codes on every shipment we handle. This guide covers how to read the codes, what the standards actually say, and a checklist for accepting older parts.

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How to read a date code

The four-digit format: YYWW

Most ICs follow the EIA-476 convention used in ECIA's weekly date-code calendar: two digits for the year, two for the week. Weeks run Sunday to Saturday, so week 01 can start in the previous December. In ECIA's 2026 calendar, week 01 runs from 28 December 2025 to 3 January 2026 and is coded 2601 (ECIA).

So 2347 means week 47 of 2023, late November 2023.

Manufacturer variations

Small packages have no room for four digits, and every manufacturer has its own marking scheme. Always check the marking section of the datasheet or the manufacturer's marking guide.

Watch out for single-digit year codes: they repeat every ten years, so a "3" can mean 2013 or 2023. The lot code and the marking style for that package tell them apart.

Passive components: IEC 60062 letter codes

Capacitors and resistors often use the two-character code from IEC 60062: a letter for the year and a character for the month. The year letters run in a 20-year cycle that skips letters easily confused with digits:

Months are 1 to 9, then O, N and D for October, November and December. So J5 is May 2017 (TDK marking guide). Manufacturers differ in details: Vishay prints October as the digit 0 and also uses four-digit YYWW codes (Vishay).

Date code, lot code and wafer date

• The date code is the assembly or seal date, not the wafer date (TI, Analog Devices and Renesas all define it this way). Wafers can wait before assembly: Infineon allows unsawn wafers to be stored for up to 36 months (Infineon).
• The lot or trace code identifies the wafer or assembly lot. The date code only gives the time. Together they identify a production batch.
• Several date codes in one pack are normal. Analog Devices allows up to three date codes per reel, two per tube and three per tray stack (ADI date code policy).

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What actually ages in storage

Three things matter, and the silicon itself is rarely one of them.

1. Moisture. Plastic packages absorb moisture from the air. During reflow it turns to steam and can crack the package or delaminate the die ("popcorning"). This is what MSL ratings control.
2. Solderability. Lead and terminal finishes oxidize slowly, and intermetallic layers grow. Heat accelerates both, which is why baking has limits.
3. Handling. Damaged packaging, ESD exposure and bent leads, all of which depend on how the stock was kept rather than how old it is.

Long-term studies support this. Texas Instruments found that 20 device types stored for 2 to 17 years could still be reflowed, with an expected solderable life beyond 15 years (TI SLVA304). Rochester Electronics reports that parts from 57 reel date codes aged 3 to 16 years were assembled by an independent contract manufacturer with zero defects (Rochester study; a vendor's own test).

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Moisture sensitivity and floor life (J-STD-033)

The MSL is printed on the moisture-sensitive label and in the datasheet. It sets the floor life: how long a part may sit outside its dry bag before it must be reflowed or baked. The current revision of the handling standard is IPC/JEDEC J-STD-033D (2018); the classification standard is J-STD-020F (2022) (JEDEC).

Sources: TI AN-2029, onsemi AND8003.

Dry pack and the humidity indicator card

A dry pack is a moisture barrier bag with desiccant, a humidity indicator card (HIC) and a label showing the MSL and the bag seal date.

• Sealed-bag shelf life. J-STD-033D gives a minimum shelf life of 12 months from the seal date, at less than 40 °C and 90% RH. Twelve months is a minimum, not an expiry: when the bag is older, the humidity indicator card decides. Manufacturers state longer periods. TI rates its standard dry packs for 3 years from manufacture and extended packs, marked "+5", for 6 years (TI AN-2029); Infineon allows 36 months from the date code for dry-packed parts, 60 months for some product groups (Infineon).
• Reading the card when you open the bag. For MSL 2a to 5a parts, bake if the 10% spot is not blue. For MSL 2 parts, bake if the 60% spot is not blue. A card whose 60% spot has turned pink must not be reused (TI AN-2029).

Baking

J-STD-033 allows three bake temperatures: 125 °C, 90 °C at ≤5% RH, and 40 °C at ≤5% RH. The time depends on the MSL, the package body thickness and how far the floor life was exceeded. Two examples for MSL 3 parts whose floor life was exceeded by more than 72 hours:

Source: TI AN-2029, Table 5. BGAs larger than 17 × 17 mm and stacked-die packages need 96 hours at 125 °C.

Three cautions:

• Tape, reels and tubes can't go above 40 °C. Only high-temperature trays can be baked at 125 °C. Parts on reels are either baked slowly at 40 °C or moved to high-temperature carriers.
• Baking costs solderability. It accelerates oxidation and intermetallic growth. The standard limits cumulative baking above 90 °C, so don't bake "just in case".
• Only a bake resets floor life fully. Short exposures can be reset by putting parts back into dry storage for a multiple of the exposure time, and storage at ≤5% RH counts the same as a sealed bag. Reflow and rework never reset it (onsemi AND8003).

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Storing parts for longer than a year

For storage beyond 12 months, the reference is the IEC 62435 series on long-term storage of electronic semiconductor devices: general requirements, deterioration mechanisms, data, storage conditions, and separate parts for dies and wafers, packaged devices, MEMS, passive components and special cases such as memories (IEC webstore). JEDEC JEP160A (2022) gives guidelines for the same task.

In practice, good long-term storage means:

• sealed manufacturer packaging, or dry cabinets at ≤5% RH (or nitrogen) for opened parts;
• stable temperature, with no condensation cycles;
• ESD-safe packaging and handling;
• original labels kept with the parts, and the dates of every bag opening recorded.

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The "two-year date code" rule

Many purchase orders say "date code not older than 24 months". That is a buyer requirement written into contracts, not a JEDEC, IPC or IEC rule.

• Buyers set it. Celestica, for example, requires date codes no older than 24 months at receipt (Celestica). Some aerospace suppliers accept older parts with solderability test evidence (PacSci EMC).
• The industry association recommends dropping it. ECIA's 2023 guidance recommends removing general date-code restrictions, notes that the old military retest-after-three-years rule was removed around 1995, and says component warranties don't depend on age (ECIA GIPC).
• Manufacturers ship older codes. Analog Devices ships date codes up to five years old and states that this "does not mean older product is in any way substandard" (ADI). Renesas ships assembly date codes up to five years old (Renesas).
• Distributors can't promise a specific code. DigiKey accepts a date-code range in order notes but cannot guarantee a particular code (DigiKey forum).

If your quality system has the rule, keep it, but write it so you can approve exceptions with a solderability test. For an end-of-life part, a strict two-year limit can mean there is no compliant stock left anywhere.

Solderability testing

When parts are older than your limit, or their storage history is unknown, a solderability test per J-STD-002 settles the question. Samples are usually conditioned first with steam aging, which simulates long storage, and then tested by dip-and-look or wetting balance (TI SBOA152A). It costs far less than a failed production run.

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Date codes as a counterfeit signal

Falsifying the date or lot code is a classic counterfeiting technique, and a mismatch should always trigger a closer look. But a mismatch alone is not proof:

• several date codes in one reel are allowed (up to three at Analog Devices);
• the label shows the assembly date while the top marking may show a marking date (Infineon labels work this way);
• single-digit year codes repeat every decade.

What deserves real suspicion: a date code that doesn't follow the manufacturer's format for that package and plant; identical date and lot codes on parts that should come from different lots; a label date code that matches no part in the reel; or a date code later than the manufacturer's last production of that part, unless the parts come from an authorized aftermarket manufacturer. Our guide to avoiding counterfeit components covers the full inspection process.

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Checklist: accepting older date-code stock

1. Is the packaging factory-sealed? Check the bag seal date and, once opened, the humidity indicator card.
2. What is the MSL, and was floor life exceeded? If a bag was opened, find out when and under what conditions.
3. Bake if the card or the floor-life count says so, at a temperature the carrier can take.
4. Order a solderability test if the parts are older than your limit or their storage history is unknown.
5. Verify the marking against the manufacturer's format: label against top marking, date code against lot code.
6. Record the date codes, test results and bake history with the lot.

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How SZCHIPS handles date codes

We verify date codes on every shipment as part of our IDEA-STD-1010-B incoming inspection, together with markings, package condition and documentation. Suspect parts go to third-party labs for further testing, and test reports ship with the order. If your project has a date-code requirement, put it in your RFQ and we will quote only stock that meets it, or tell you plainly when none exists. Send an RFQ.

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FAQ

What does the date code on a chip mean?

It is the year and week the part was assembled and sealed, usually written YYWW: 2347 means week 47 of 2023. It is not the wafer date and not an expiry date. Small packages use shortened codes defined in each manufacturer's marking guide.

Do electronic components expire?

No. Semiconductors have no expiry date. What ages is solderability and, for plastic surface-mount parts, moisture content. Parts kept in sealed dry packs or proper dry storage remain usable for many years: TI's storage study found parts stored for up to 17 years could still be reflowed.

Is a five-year-old date code acceptable?

Often, yes. Analog Devices and Renesas ship date codes up to five years old. Check the packaging, the humidity indicator card and the floor life, and run a solderability test if your quality system requires one for older parts.

What does "23+" mean in a component quote?

It is open-market shorthand for "date code 2023 or newer". "DC 2+ years" means the stock is more than two years old. Ask for the exact date codes before ordering if your build has a date-code requirement.

How long can parts stay out of the dry bag?

It depends on the MSL: unlimited for MSL 1, one year for MSL 2, four weeks for MSL 2a, 168 hours for MSL 3, 72 hours for MSL 4, 48 hours for MSL 5 and 24 hours for MSL 5a, at no more than 30 °C and 60% RH. MSL 6 parts must be baked before every use.

Can parts on tape and reel be baked at 125 °C?

No. Tape, reels and tubes are low-temperature carriers rated to 40 °C. Bake them at 40 °C and ≤5% RH, which takes days, or move the parts to high-temperature trays for a 125 °C bake.