The AEC-Q200 thin film resistor part number from Walsin Technology (Walsin) is a 13th character: a trailing Q. We counted 1,168,998 thin film part numbers. All 461,818 that end in Q carry the AEC-Q200 label, and none of the rest do. A Q anywhere else is not a marker: it appears at position five on 114,994 parts that are not AEC-Q200.
Venatech Limited, an authorised Walsin distributor in Hong Kong, built six thin film upload files on 19 September 2026 and holds the 93,914-row parametric export beside them. This post is written from both. We parsed every part number in the six upload files and tested four plausible rules for spotting an AEC-Q200 part, then asked what happens to a part number that loses its last character. Every part number named below is real and is in the export. The AEC-Q200 parts themselves are not in the export, so we describe their numbers by pattern and name none.
Which character marks a Walsin thin film part as AEC-Q200?
The last one. We read the final character of all 1,168,998 part numbers in the six upload files and compared it with the tags column and the series label. 461,818 end in Q, and the same 461,818 carry the AEC-Q200 tag. The two agree on every row: 0 misses and 0 false positives. The other four rules we tried each fail somewhere, as the table shows.
| Rule applied to all 1,168,998 part numbers | Parts flagged | Truly AEC-Q200 | False positives | Missed | Match / mismatch |
|---|---|---|---|---|---|
| Last character is Q | 461,818 | 461,818 | 0 | 0 | Match on all rows |
| Part number is 13 characters | 637,988 | 461,818 | 176,170 | 0 | Mismatch — also catches every SF.A part |
| Part number contains a Q | 576,812 | 461,818 | 114,994 | 0 | Mismatch — Q is also a TCR code |
| Q at position five | 174,732 | 59,738 | 114,994 | 402,080 | Mismatch — wrong place, wrong meaning |
The 176,170 parts the length rule over-flags are the SF.A anti-sulfuration series, whose part numbers end in A, not Q. Its series label does not say AEC-Q200. Walsin’s own wording for the standard is compliant, not certified, and our evidence is a label in our upload files, not a document: we hold no thin film datasheet. The upload files link Walsin PDFs whose filenames end in _Q, such as ASC_WFxxT&U_Q.pdf, and we have not opened them.
Does a Q anywhere in the part number mean AEC-Q200?
No. Position five is a TCR code, and Q is a TCR code in all six series. We counted Q at position five on 174,732 part numbers. Of those, 114,994 are not AEC-Q200, and 59,738 are AEC-Q200 parts that carry a Q twice: once as TCR, once as the trailing marker. A “contains Q” search therefore returns 576,812 parts, 114,994 more than the real set.
The export has real examples. WF02Q27R4DTL is a 0201 precision thin film part with a Q at position five, rated 25 ppm/°C, and MF12Q9421FTL is a 1206 tantalum nitride part with a Q at position five, rated 50 ppm/°C. Neither is AEC-Q200. We decoded position five in our thin film part-number post on the export alone, and the upload confirms the letter set carries over.
| Export part | Size, value, tolerance, TCR, power | Q at position five | AEC-Q200 twins in the upload | Match / mismatch |
|---|---|---|---|---|
WF02Q27R4DTL |
0201, 27.4 Ω, ±0.5%, 25 ppm, 1/20 W | Yes, a TCR code | 0 | Mismatch — no AEC-Q200 series starts below 0402 |
MF12Q9421FTL |
1206, 9420 Ω, ±1%, 50 ppm, 2/5 W | Yes, a TCR code | 0 | Mismatch — MF has no AEC-Q200 series |
WF10T27R0TTL |
1210, 27 Ω, ±0.01%, 50 ppm, 1/4 W | No | 0 | Mismatch — AEC-Q200 WF stops at ±0.02% |
SF12T1R00ATL |
1206, 1 Ω, ±0.05%, 50 ppm, 1/8 W | No | 0 | Mismatch — an SF.A twin exists, not an AEC-Q200 one |
SF20T25R2BTL |
2010, 25.2 Ω, ±0.1%, 50 ppm, 1/2 W | No | 2 | Match on all five fields in the WF.Q and SF.Q files |
The twin test compares size, resistance, tolerance, TCR and rated power. Packaging is 7" reel taping and termination is Sn base (Lead free) on all 1,168,998 rows, so the other two fields cannot differ.
What happens if a BOM field keeps only 12 characters?
An AEC-Q200 part can turn into a commercial one without any error. Every part number in the export is exactly 12 characters, and a field or template sized to that drops the 13th. We cut all 461,818 AEC-Q200 part numbers to 12 characters: 314,314 land on a real non-AEC-labelled thin film part, and 304,039 land on one with identical size, value, tolerance, TCR and power.
For the WF.Q file the rule is plain: 230,884 of its 230,973 parts are a commercial WF part number with a Q appended. Cut the Q and the number is valid, in range and in the commercial file. For the SF.Q file the rule holds for 83,430 of 230,845 parts, and 10,256 of those land on a part that differs: the SF file writes code 12 for 11,472 parts at 2512 and 270 at 1206, while the SF.Q and SF.A files write it only for 1206. The remaining 147,415 SF.Q part numbers and 89 WF.Q ones, once cut, land on no part at all.
In 19 of the 230,884 WF landings the resistance column differs: the commercial WF row’s resistance field disagrees with its own part-number code, reading 98.8 Ω where the code says 100 Ω, and 8.25 Ω where it says 8.06 Ω. The AEC-Q200 twin is consistent with the code. We name no part number here because none of the 19 is in the export.
How many commercial thin film parts have an AEC-Q200 twin?
Most of the WF file, four in five of the SF file, and none of the MF file. We joined the commercial files to the AEC-Q200 files on the five specification fields. 230,960 of 373,848 WF parts (61.8%) have a WF.Q twin, and 73,174 of 91,602 SF parts (79.9%) have an SF.Q twin. MF, 65,560 parts, has no AEC-Q200 series.
| Commercial file | Parts | With an AEC-Q200 twin | Without | Match / mismatch |
|---|---|---|---|---|
| WF precision, against WF.Q | 373,848 | 230,960 | 142,888 | Mismatch on 38.2% |
| SF anti-sulfuration, against SF.Q | 91,602 | 73,174 | 18,428 | Mismatch on 20.1% |
| MF tantalum nitride | 65,560 | 0 | 65,560 | Mismatch — no series |
The 142,888 WF parts without a twin fall into four groups: 5,506 at 0201, which the WF.Q file does not offer; 52,808 at ±0.01%, where WF.Q’s tightest tolerance is ±0.02%; 16,936 more at 3 ppm/°C, where WF.Q starts at 5 ppm; and 67,638 elsewhere, of which 54,773 sit in a size, tolerance, TCR and power combination WF.Q lacks and 12,865 differ in resistance value only.
We have not seen this counted anywhere: going the other way, 62,910 of the 230,845 SF.Q parts (27.3%) are rated 10 or 15 ppm/°C, and neither the SF nor the SF.A file offers either grade as a match. An engineer who starts from a commercial anti-sulfuration part cannot reach those 62,910 by changing one letter. They have to change the TCR. For what the grades buy you, see what AEC-Q200 actually certifies.
Why is none of this visible in the parametric export?
Because all 637,988 thirteen-character part numbers sit in the three series the export lacks. We compared the two data sets on part number. The export holds 93,914 rows, every one 12 characters, and no WF.Q, SF.Q or SF.A row. The 13-character parts are WF.Q 230,973, SF.Q 230,845 and SF.A 176,170, which sum to 637,988: the same three series, and nothing else.
So a search built on the export cannot return an AEC-Q200 thin film part at all, and it cannot tell you that one exists for the commercial part you typed. The shape of that gap is in our upload-versus-export post. The chip resistor line has the same kind of letter-rule problem; the automotive suffix test is wrong on 10,209 of 234,815 rows, as we show in the chip resistor suffix post.
What should a BOM check do with a thin film part number?
Test the last character, not the whole string, and never trim to 12. We checked each rule against 1,168,998 rows, so the advice follows the counts. Test for a trailing Q to find AEC-Q200 labels. Do not search on Q alone. Keep the column wide enough for 13 characters. Then ask for the qualification report for the exact part number.
Our free cross-reference tool matches against Walsin’s published catalogue and states differences from your original; paste the part you hold and read the field-by-field result. Ready stock shows what is held in Hong Kong as at 23 September 2026. The thin film range is on the thin film page, and we hold 28 Walsin datasheets, 451 pages, none for thin film. Qualification stays with you. Confirm against both datasheets and qualify in your own circuit.
The short version
A trailing Q is the AEC-Q200 marker on 461,818 of 1,168,998 Walsin thin film part numbers, with no misses and no false positives. A Q at position five is a TCR code on 174,732 parts, 114,994 of them not AEC-Q200. Cut to 12 characters, 304,039 AEC-Q200 numbers become valid commercial ones with identical specification fields. 142,888 WF parts and 18,428 SF parts have no AEC-Q200 twin, and 62,910 SF.Q parts have no anti-sulfuration twin at all. None of the 637,988 thirteen-character parts is in the export.
Send us a thin film BOM and we will tell you which lines carry the trailing Q, which have an AEC-Q200 twin on the five fields, and which need a different TCR or tolerance. And a question back: if your BOM template truncates at 12 characters, how many of your automotive lines are already commercial parts?
Frequently asked questions
How do I tell if a Walsin thin film resistor is AEC-Q200?
Look at the last character. Across 1,168,998 thin film part numbers, the 461,818 that end in Q are exactly the ones labelled AEC-Q200. Walsin says compliant, not certified, so ask for the qualification report for the exact part number. Venatech makes no qualification claim of its own.
Does a Q in the middle of a Walsin thin film part number mean AEC-Q200?
No. Position five is a TCR code, and Q is used there on 174,732 parts. Of those, 114,994 are not AEC-Q200. A search for any Q returns 576,812 parts, which is 114,994 more than the 461,818 that are labelled.
Why is a Walsin AEC-Q200 thin film part 13 characters long?
The commercial parts are 12 characters and the AEC-Q200 parts add a trailing Q. The SF.A series adds a trailing A and is also 13 characters, so length alone over-flags by 176,170 parts. We read the Q as the marker from the tags column; Walsin has not confirmed it to us.
Can I upgrade a commercial Walsin thin film part to AEC-Q200 by adding Q?
Sometimes. For 230,884 of 230,973 WF.Q parts the number is a WF part number plus Q. For SF.Q the rule holds on 83,430 of 230,845. Match size, resistance, tolerance, TCR and power in both files first, and confirm against the datasheets.
Why does the Venatech export show no AEC-Q200 thin film resistors?
The parametric export holds 93,914 rows in 12-character form and none from WF.Q, SF.Q or SF.A. Those three series hold 637,988 part numbers in our upload files. The export is a subset of the catalogue, not the catalogue.
Which thin film parts have no AEC-Q200 twin?
All 65,560 MF parts, 142,888 of 373,848 WF parts (0201, ±0.01%, 3 ppm/°C and others) and 18,428 of 91,602 SF parts. Going the other way, 62,910 SF.Q parts at 10 or 15 ppm/°C have no SF or SF.A twin.