Walsin SF Series Thin Film Resistor: the File Named ‘A Series’ Holds 0 of 2,260 A-Coded Rows

Every Walsin SF series thin film resistor part number carries a tolerance letter in a fixed position. We counted 2,260 real SF rows coded “A” across the whole 15,080-row shelf — and zero of them sit in the file Walsin names SF_A_Series.xlsx. The letter is real. The file named for it is empty.

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Venatech Limited, an authorised Walsin distributor in Hong Kong, holds all five of Walsin Technology (Walsin)’s SF anti-sulfuration thin film export files. This post is measured from the two that return data, SF_Series_1.xlsx (270 rows, 1206) and SF_Series_2.xlsx (14,810 rows, 2010), 15,080 real rows combined, against the empty SF_A_Series.xlsx. Every part number below is real and every count is of part numbers, not pieces.

What is supposed to be in Walsin’s SF “A Series” thin film export file?

A separate SF shelf, by its filename — and nothing, by its row count. Anti_Sulfuration_Thin_Film_Chip_Resistor_SF_A_Series.xlsx is 6,289 bytes, the same nine-column header as every other SF file — Part Number, Series, Size, Resistance, Tolerance, TCR, Rated Power, Packaging, Termination — and 0 rows beneath it. We opened it directly to confirm this rather than inferring it from a byte count alone. Two other SF files share the identical empty signature: SF.xlsx (the AEC-Q200-labelled file) and SF_Series_0.xlsx.

File	Rows	What its name implies
SF_A_Series.xlsx	0	A distinct SF shelf called “A Series”
SF.xlsx (AEC-Q200)	0	An AEC-Q200-qualified SF shelf
SF_Series_0.xlsx	0	An SF “Series 0” shelf
SF_Series_1.xlsx	270	1206 (3216)
SF_Series_2.xlsx	14,810	2010 (5025)

If the A Series file is empty, does the letter A appear in real SF part numbers?

Yes, 2,260 times. We checked the third-from-last character of every one of the 15,080 real SF part numbers — the position immediately before the “TL” packaging suffix every SF part ends in — and found five distinct letters: A, B, C, D and F. The letter “A” appears on 2,260 rows: 50 at case size 1206 and 2,210 at case size 2010. None of those 2,260 rows sits in the file named SF_A_Series.xlsx. The letter the filename promises is real; the file is not where it lives.

Letter	Rows	Where they actually sit
A	2,260	SF_Series_1.xlsx and SF_Series_2.xlsx
B	2,705	SF_Series_1.xlsx and SF_Series_2.xlsx
C	3,365	SF_Series_1.xlsx and SF_Series_2.xlsx
D	3,365	SF_Series_1.xlsx and SF_Series_2.xlsx
F	3,385	SF_Series_1.xlsx and SF_Series_2.xlsx
Total	15,080	Zero in SF_A_Series.xlsx

What does that letter actually encode, measured across both real SF files?

Tolerance, with zero exceptions across all 15,080 rows. We grouped every row in both populated files by that letter and by the Tolerance column: A pairs with ±0.05% on every one of its 2,260 rows, and nowhere else. We checked all 15,080 rows for this, not a sample, and found no row where the letter and the tolerance disagree.

Real part numbers, match / mismatch against the stated requirement “this row is found in the file named for its own letter code”:

Part number	Letter	Tolerance	Case size	File it is actually held in	Found in SF_A_Series.xlsx?	Match / mismatch
SF12T1R00ATL	A	±0.05%	1206 (3216)	SF_Series_1.xlsx	No	Mismatch
SF20T4R70ATL	A	±0.05%	2010 (5025)	SF_Series_2.xlsx	No	Mismatch
SF20T25R2BTL	B	±0.1%	2010 (5025)	SF_Series_2.xlsx	No	Mismatch — wrong letter file entirely
SF20U34R0CTL	C	±0.25%	2010 (5025)	SF_Series_2.xlsx	No	Mismatch — wrong letter file entirely

We have not seen this letter-to-tolerance mapping published for the SF series before, and we have not seen the SF file structure’s three empty shelves set against it either.

Do the other four letters follow the same rule?

Yes, across the full 15,080 rows, with no exception on any of them. B pairs only with ±0.1%, C only with ±0.25%, D only with ±0.5%, and F only with ±1%. The mapping holds identically at both case sizes — 1206 and 2010 use the same five letters for the same five tolerances — which tells us the letter is a tolerance code fixed by Walsin’s own numbering convention, not something that shifts with case size or resistance value.

Letter	Tolerance	Rows at 1206	Rows at 2010	Rows total
A	±0.05%	50	2,210	2,260
B	±0.1%	50	2,655	2,705
C	±0.25%	50	3,315	3,365
D	±0.5%	50	3,315	3,365
F	±1%	70	3,315	3,385

So what actually distinguishes Series 0, 1 and 2 from the A Series file?

Series 0 and the A Series file distinguish themselves by being empty; Series 1 and Series 2 distinguish themselves only by case size. SF_Series_1.xlsx holds every 1206 (3216) row — 270 of them, all five tolerance letters present. SF_Series_2.xlsx holds every 2010 (5025) row — 14,810 of them, the same five letters present in far greater volume. There is no third populated shelf and no fourth: SF_Series_0.xlsx and SF_A_Series.xlsx both return zero rows, just like the AEC-Q200-labelled file.

The practical reading: Walsin’s own filenames describe a catalogue of up to five SF shelves — a plain series, an “A” series, two numbered series and an AEC-Q200 series. The export we hold delivers exactly two, split by case size, and the letter “A” that gives one empty file its name is really a tolerance grade sitting inside the other two.

What should a buyer take from a series name that does not match its file?

Specify by case size and letter code, not by filename, because the filenames do not reliably point at where the data lives. A buyer asking Venatech for “the SF A Series” is, on the evidence in our extract, asking for a file with nothing in it; the part they actually want is almost certainly one of the 2,260 rows coded “A” inside SF_Series_1.xlsx or SF_Series_2.xlsx.

1. State the case size (1206 or 2010) and the tolerance you need, not the filename — the letter inside the part number already tells you the tolerance, and it is reliable across all 15,080 rows.
2. Cross your incumbent part against the real rows on the free cross-reference tool, which decodes 18 manufacturers’ part numbers and matches against 800,000+ crossable Walsin part numbers, stating every field it can and cannot match, never the word “equivalent”.
3. Check what is physically in Hong Kong on ready stock, a dated snapshot as at 23 September 2026.
4. Ask Walsin whether the three empty SF files — AEC-Q200, A Series and Series 0 — are placeholders or withdrawn plans. We cannot answer that from the export alone.

For the full anti-sulfuration picture across both thin film and thick film series, see Anti-sulfuration resistors: SF thin film and SA thick film arrays. For the WF precision series’ own tolerance-letter decode, see Thin film precision resistor tolerance. The full line sits on the Walsin thin film range page.

The short version

A Walsin SF series thin film resistor part number carries a letter that always means tolerance — A for ±0.05%, B for ±0.1%, C for ±0.25%, D for ±0.5%, F for ±1% — with zero exceptions across all 15,080 real rows we hold. The file named SF_A_Series.xlsx is not where any of the 2,260 “A” rows live; it is empty, alongside two other SF files that are also empty. The real SF shelf is two files, split only by case size.

Tell us the case size and tolerance letter you need, and we will return the real SF rows field by field — we will not send you looking for a file that has nothing in it. If you hold a Walsin document that explains what the A Series, Series 0 or AEC-Q200 files were meant to contain, we would like to see it.

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Frequently asked questions

<!– wp:rank-math/faq-block {"questions":[{"id":"faq-question-01","title":"What is Walsin's SF \"A Series\" thin film resistor?","content":"By filename, a distinct shelf of the SF anti sulfuration thin film resistor range. By row count, nothing — SF_A_Series.xlsx returns zero rows. The letter \”A\” is real and appears on 2,260 part numbers, but every one of them sits in SF_Series_1.xlsx or SF_Series_2.xlsx, not in the file named for it.”,”visible”:true},{“id”:”faq-question-02″,”title”:”What does the letter A mean in a Walsin SF part number?”,”content”:”A tolerance of ±0.05%, with zero exceptions across all 2,260 rows that carry it. It sits in the position immediately before the \”TL\” packaging suffix at the end of every SF part number, at both case sizes Walsin’s SF export holds.”,”visible”:true},{“id”:”faq-question-03″,”title”:”Do B, C, D and F mean the same thing at both case sizes?”,”content”:”Yes. B is ±0.1%, C is ±0.25%, D is ±0.5% and F is ±1%, and the mapping is identical whether the part is 1206 (3216) or 2010 (5025). We checked all 15,080 rows across both files and found no exception.”,”visible”:true},{“id”:”faq-question-04″,”title”:”How many of Walsin’s five SF export files actually hold data?”,”content”:”Two of five. SF_A_Series.xlsx, SF.xlsx (the AEC-Q200-labelled file) and SF_Series_0.xlsx all return zero rows. The 15,080 real rows split between SF_Series_1.xlsx (270, at 1206) and SF_Series_2.xlsx (14,810, at 2010).”,”visible”:true},{“id”:”faq-question-05″,”title”:”Does the case size determine which tolerance letters are available?”,”content”:”No. Both 1206 and 2010 offer all five letters, A through F, at the same five tolerances. What differs between the two case sizes is resistance range and rated power, not which tolerance letters exist.”,”visible”:true},{“id”:”faq-question-06″,”title”:”Why would Walsin name a file for a series that holds no rows?”,”content”:”We do not know, and we are not guessing. It may be a placeholder for data not yet published, a withdrawn plan, or a different naming structure we have not been given the rest of. What we can state is only what the file itself contains: zero rows.”,”visible”:true}],”listStyle”:””,”titleWrapper”:”h3″,”titleCssClasses”:””,”contentCssClasses”:””,”sizeSlug”:””} –>

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