How do you read and verify IC date codes to spot remarked chips?

Date code formats you will meet

Worked examples on parts we handle

A Texas Instruments TPS54302DDCR carries the device code on one line and a seven-character trace string on the next. The string is not decodable from a published key: it is checked by entering the package marking into TI's own part-marking lookup, which returns the device and its date/lot information. Read it the other way round — a trace string that the manufacturer's lookup will not resolve is the finding, not the formatting.

An STMicroelectronics STM32F407VGT6 uses the plain YYWW form, so week 45 of 2023 is written 2345. The check that matters is not the arithmetic but the agreement: the same code must appear on the reel label and in the shipping documents, and the week has to be possible — a 2023 date code on a line whose final buy was in 2019 is proof of a re-mark, however clean the laser etching looks.

A Microchip ATMEGA328P-AU is the classic case for the mold-dimple check instead: these parts are re-marked in volume, and the giveaway is often the pin-1 index dimple and the mold gate texture rather than the digits. Look at the dimple first when the date code itself reads plausibly.

Why a re-marked or salvaged lot fails the check

• Package marking against reel label: the sealed reel barcode reads one lot, and the parts inside carry a different date code — or several different date codes across the same carrier tape. Mixed codes on one tape are not a normal factory output.
• A date the line could not have produced: where an IC was discontinued by a published product discontinuation notice, a spot lot carrying a date years after that notice is a re-mark or a clone.
• Marking that dissolves: original factory markings are cut into the package by laser. Re-markers sand the surface, spray a black polymer layer to hide the sanding, and laser over it. That layer is shallow and hazy at the character edges, and pure acetone takes it off.
• Typography and tooling that do not match: legitimate markings come from the manufacturer's own laser optics and typeface. Re-marked parts often show uneven character spacing, tilted characters, an incorrect logo bevel, or mold dimples that have been filled with resin.

The incoming protocol we run on a lot

1. 01 Acetone wipe on the marking surface. A swab of pure acetone is rubbed across the date code and marking. Factory laser marking is cut into the package and does not move; a re-marked blacktop layer smears onto the swab and starts to expose what was underneath.
2. 02 Stereomicroscope pass at 45x. The pin-1 index dimple and the mold gate cavities are compared against the package. Authentic parts carry the virgin mold texture in those recesses; a blacktopped part has resin pooled in them, glossier or partially filled.
3. 03 Decode the reel label, not just the part. An industrial 2D imager reads the DataMatrix on the manufacturer label. Lot, date code and country of origin encoded there are then compared with what is marked on the package — the mismatch is the finding.
4. 04 Lead finish and coplanarity. Salvaged pulls are often re-tinned, which shows as uneven solder over tarnished base metal, solder bridging at the package edge, or lead thinning. Lead coplanarity and finish are checked before the lot is accepted.

What an overseas buyer receives before dispatch

A buyer several thousand kilometres away cannot look at the part, so the check has to travel. Before an order is packed, the lot is photographed under the stereomicroscope — package markings, pin-1 dimple, lead finish — together with the sealed reel label, and the uncompressed images go to the buyer on WhatsApp or Telegram.

The buyer or their engineer confirms the date codes and lot numbers against those photographs. Only after that does the material go into a moisture-barrier bag and out on the booked freight. The point is not that we say the lot is genuine; it is that the buyer can see the same evidence we are looking at.