A Certificate of Conformity is a signed statement from the supplier that the parts shipped
are the parts ordered, naming the manufacturer, the part number, the quantity, and the lot or
date code supplied. Ask for it against a specific part number at quotation stage, not after
delivery, because the lot is fixed when the reel is picked.
Venatech Limited, an authorised Walsin distributor in Hong Kong, publishes this from Walsin’s own parametric data and the datasheets it holds on file. Every part number below is real.
What is a Certificate of Conformity for electronic components?
A document in which the supplier states, on the record, that what it shipped conforms to what
you ordered. It names the manufacturer, the part number, the quantity and the batch. It is
not a test report and not a certification of the part. It is a traceability statement, and
its value is that somebody signed it.
A CoC does not prove the part meets its specification. The manufacturer’s datasheet does
that, and only your own qualification proves it in your circuit. What a CoC does is bind a
specific delivery to a specific batch, so that if something goes wrong there is a lot number
to go back to rather than an argument. A CoC issued against last quarter’s shipment says
nothing about this reel, which is why it must be requested per delivery.
What should a Certificate of Conformity contain?
Six fields, minimum. The manufacturer’s name. The manufacturer’s part number as printed. The
quantity shipped. The lot code or date code of the batch. A reference to the purchase order
or delivery note. And a named signatory with a date. Anything less is a letterhead, not a
certificate.
| Field | Why it is there | What a weak CoC does instead |
|---|---|---|
| Manufacturer name | Fixes who made the part | Names only the distributor |
| Manufacturer part number | Ties the document to a datasheet | Uses an internal or shortened code |
| Quantity shipped | Ties the document to one delivery | Gives an annual or contract quantity |
| Lot or date code | The only field that reaches a factory record | Omits it, or writes “as per label” |
| PO or delivery note reference | Makes the document auditable | References nothing |
| Signatory and date | Makes it a statement, not a template | Unsigned, undated |
RoHS and REACH statements are commonly bundled with the CoC. They are a separate class of
declaration, usually issued by the manufacturer at series level rather than per lot, and they
should be requested by name if you need them for your own compliance file.
What is a lot code, and what is a date code?
A lot code identifies the production batch the parts came from. A date code identifies when
that batch was made. The lot code is what a manufacturer can look up. The date code is what
you use to judge storage age and shelf life. A fully traceable reel carries both, and they
serve different purposes.
If you only get one, take the lot code for a quality investigation and the date code for a
shelf-life decision. For solderability, the date code is the one that matters, because
termination solderability degrades with storage time. That interaction is covered in
MLCC shelf life, storage and handling.
What do date codes actually look like in practice?
Rarely like a standard. Across Venatech’s own stock records the same field carries at least
six different notations: a two-digit year plus a month, a two-digit year plus a week, a
two-digit year with no period at all, a bare four-digit year-and-week string, a full calendar
date, and values a spreadsheet has already converted into something else.
Venatech Limited, an authorised Walsin Technology (Walsin) distributor in Hong Kong, holds a stock snapshot dated
23 September 2026. Of its 1,125 distinct part numbers, 683 lines carry a recorded date
code, and those 683 lines hold 801 individual date code tokens between them. Counting the
notations used:
| Notation found | Example order code | Value as recorded | Tokens | Match / mismatch vs an unambiguous year-and-week |
|---|---|---|---|---|
| Converted by a spreadsheet | 0201B101K160CT |
a calendar date, not the original string | 420 | Mismatch — original code no longer recoverable from the cell |
| Year + month, month marked | 0201B181K500CT |
21+5月 |
239 | Mismatch — month resolution, not week |
| Year only | 0201X224M6R3CT |
23+ |
105 | Mismatch — no month or week at all |
| Year + number, unit unstated | 0201B331K160CT |
22+10 |
25 | Mismatch — cannot tell week 10 from month 10 |
| Year + week, week marked | 0201B682K100CT |
20+12周 |
7 | Match — year and week, unambiguous |
| Four-digit year-and-week | 0201B822K100CT |
2134 |
3 | Match — reads as 2021, week 34 |
| Free text | 0805N101J201CT |
a full calendar date plus a handling note | 2 | Mismatch — two kinds of information in one field |
Unique to Venatech’s data. The 683 date-coded stock lines in the 23 September 2026
snapshot carry 801 date code tokens in at least six different notations, and only 10 of
those 801 are written in a form that resolves to a year and a week without interpretation.
89 lines carry more than one token — 65 carry two, 19 carry three and 5 carry four —
because one stock line can be assembled from up to four factory lots. Of the 801 tokens,
377 carry a year a script can read, and those years run from 2017 to 2026.
How many of Venatech’s stock lines carry a date code?
683 of 1,125, as at 23 September 2026. The other 442 carry none. That is a recording gap in
the internal file, not a statement that those reels are unmarked, and it follows stock
location exactly: lines at one of two locations all carry a date code, lines held solely at
the other carry none.
Publishing that split is more useful than claiming full coverage would be. If the line you
need sits in the 683, the date code comes back with the quotation. If it sits in the 442, it
has to be read off the reel before the answer is reliable.
| Product line | Part numbers | Lines with a recorded date code | Match / mismatch |
|---|---|---|---|
| MLCC | 732 | 565 | Mismatch — 167 lines carry none |
| MLCC (specialty) | 132 | 117 | Mismatch — 15 lines carry none |
| Chip resistor | 254 | 0 | Mismatch — no date code recorded on any line |
| Safety capacitor | 3 | 0 | Mismatch — none recorded |
| Inductor | 2 | 0 | Mismatch — none recorded |
| Resistor array | 1 | 0 | Mismatch — none recorded |
| Other | 1 | 1 | Match |
| Total | 1,125 | 683 | 442 lines need the code read off the reel |
Stock figures are a snapshot and they move: the counts above describe 23 September 2026 and
nothing else, in part numbers rather than pieces.
Why does a spreadsheet destroy a date code?
Because a date code looks like a date to a spreadsheet, and a spreadsheet will convert it on
entry without asking. Once converted, the cell holds a serial number and the original
characters are gone. This is the single largest source of lost traceability in Venatech’s own
file, and it is entirely avoidable.
In the 23 September 2026 snapshot, 420 of the 801 date code tokens have already been
converted into calendar date values, and 397 of them now hold the same converted value.
A code that distinguished several batches no longer distinguishes anything.
Three practical defences, all free. Format the column as text before anything is pasted into
it. Prefix the value with an apostrophe on entry. And ask suppliers to send date codes in a
CoC PDF as well as a spreadsheet, so the original string survives.
What do I do when a reel arrives without a date code?
Do not open it further and do not put it into the line. Photograph the reel, the label and the
outer bag. Quote the delivery note and the part number to the supplier and ask for the CoC
naming the lot. If the supplier cannot produce a lot reference, quarantine the whole delivery
rather than the single reel.
The reason for quarantining the delivery, not the reel, is that a missing code is almost never
a single-reel event. It reflects how that batch was handled, and the other reels in the same
delivery came the same way. One reel is a defect; a missing code is a process finding.
If the part is needed immediately and the code cannot be produced, treat the reel as unknown
stock: qualify it as if it were a new supplier, and record the decision. That is a legitimate
choice under schedule pressure, provided it is a recorded decision rather than a silent one.
Do I also need the distributor’s quality certifications?
Often yes, and they answer a different question. ISO 9001 certifies that an organisation
operates a documented quality management system. IATF 16949 adds the automotive sector
requirements on top of it. Neither certifies a part. They certify that the processes around
handling, recording and escalating are audited by a third party.
Ask for the certificate itself, with its certificate number, issuing body and expiry date, so
you can verify it with the registrar rather than taking a logo on trust. That advice applies
to every supplier including this one.
FAQ
What is a Certificate of Conformity in electronics?
A signed statement from the supplier that the parts shipped are the parts ordered, naming the manufacturer, the part number, the quantity and the lot or date code supplied. It is a traceability document, not a test report. It binds one delivery to one batch so that a later investigation has a lot number to work from.
Is a Certificate of Conformity the same as a test report?
No. A CoC states what was shipped and from which batch. A test report states measured results against specified conditions. A datasheet states the specification itself. Buyers routinely ask for a CoC and receive a datasheet, which answers a different question and leaves the batch unrecorded.
What is the difference between a lot code and a date code?
A lot code identifies the production batch. A date code identifies when that batch was made. Use the lot code for a quality investigation, because it is the field a manufacturer can look up. Use the date code for shelf-life and solderability decisions, because storage age drives those rather than batch identity.
When should I request a Certificate of Conformity?
At quotation, not after delivery. The lot is fixed when the reel is picked, so asking early means the supplier records it as part of the order rather than reconstructing it afterwards. Requesting a CoC against one specific part number is also the fastest way to see how a new supplier actually works.
Why do date codes appear in so many different formats?
Because there is no single industry convention and every transcription step adds a variant. Venatech’s 23 September 2026 stock snapshot holds 801 date code tokens in at least six notations across 683 lines, including year-plus-month, year-plus-week, year only, and values already converted by a spreadsheet.
Can a spreadsheet really damage a date code?
Yes, and it commonly does. A date code looks like a date, so a spreadsheet converts it on entry and the original characters are lost. In Venatech’s own snapshot 420 of 801 date code tokens have been converted, and 397 of those now hold the same converted value, so they no longer distinguish batches.
What should I do if a reel has no date code?
Stop it before it reaches the line, photograph the reel, label and outer bag, and ask the supplier for the Certificate of Conformity naming the lot. If no lot reference can be produced, quarantine the whole delivery rather than the one reel, because a missing code reflects how the batch was handled.
Does ISO 9001 certification mean the parts are genuine?
No. ISO 9001 certifies that an organisation runs an audited quality management system, and IATF 16949 adds automotive sector requirements. Neither certifies a part or its origin. Ask for the certificate number, issuing body and expiry date so you can verify the certificate with the registrar directly.
Next step
Ask for the CoC on the quotation, not on the delivery note. Send a part number and Venatech
Limited, an authorised Walsin distributor in Hong Kong, will return the Walsin datasheet, the
orderable order code, whether the 23 September 2026 snapshot holds a recorded date code for
that line, and a Certificate of Conformity on request.
Request a CoC from Venatech · Browse the
Walsin MLCC range · Read
Counterfeit passive components and how authorised sourcing stops them
and
What “authorised distributor” means, and how to verify one.
Cross it yourself. The cross-reference tool takes a single part number or a whole BOM column and returns the Walsin candidates with every field that differs stated plainly — qualification stays with you. Ready stock shows what is held in Hong Kong today, with an RFQ against any line.