Chip Resistor Part Number Suffix: An Automotive Letter Rule That Gets 10,209 of 234,815 Walsin Parts Wrong

The chip resistor part number suffix is two things written as one: a packaging letter and a termination letter, then an optional variant flag. We parsed all 234,815 Walsin chip resistor part numbers. A rule that reads a trailing J, V, W or Z as automotive labels 10,209 parts the series name does not.

Every cross-reference tool and every BOM script that decodes a chip resistor ends up reading the last few characters of the part number, and most of them read those characters with a rule someone wrote once and never counted. Venatech Limited, an authorised Walsin distributor in Hong Kong, holds the 137 chip resistor export files published by Walsin Technology (Walsin), 64 of which hold parts, and the two chip resistor datasheets that Walsin has sent us. This post is written from both: the suffix of every part number, set against the Packaging and Series columns of the same row, and against the code legends printed in the datasheets. Every part number below is real. We will not tell you a suffix means a grade. We will show you where it does and where it does not.

What is inside the suffix of a Walsin chip resistor part number?

Two letters of code, then an optional flag. We read the characters after the tolerance letter on all 234,815 rows and found 48 distinct endings, which collapse to 11 two-letter codes. The first letter is the packaging code and the second the termination code in the two datasheet legends we hold; anything after them is a flag. Length is the only structural variable: 159,228 part numbers are 12 characters, 74,195 are 13 and 1,392 are 15.

We opened both datasheets we hold, the WR general purpose sheet and the MR automotive sheet. Both print the same ordering scheme: size code, type code, resistance code, tolerance code, packaging code, termination code. Their packaging legend lists seven letters (T, Q, G, H, B, D and A) and their termination legend lists one, L, for Sn base, lead-free. The export uses more than that.

How many of the 234,815 part numbers can the datasheets we hold decode?

205,886, or 87.7 percent, carry a packaging letter and a termination letter that both appear in the WR and MR legends. The other 28,929 rows end in a letter neither datasheet defines: 27,218 carry a second letter of R or P, 1,710 a first letter of Z and 1 a first letter of C. The count of 205,886 is TL, AL, DL, GL, HL and QL added together.

The 12.3 percent matters more than it looks, because the undefined letters are not rare codes at the edge of the catalogue. TR alone is 21,269 rows across nine case sizes, and TP is the whole SF anti-sulfuration group at six case sizes. The two datasheets cover the WR and MR series. For the other series in the export we hold no resistor datasheet, so a letter that neither sheet lists is not wrong; it is undefined in the documents we can show you. Ask Walsin, or ask us for the sheet that covers your part number and we will tell you whether we hold it.

There is a second, quieter gap. The datasheets restrict A, D and H to 0402, and 0 of the 4,845 WR 0402 rows carry any of them. All 8,506 WR rows that do carry A, D or H are 0201 or 01005, sizes that appear nowhere in either datasheet. The legend was written for a catalogue that has since grown a smaller case size, and the export followed the part numbers, not the legend.

Does the packaging code agree with the Packaging column?

Not as a lookup. We counted the packaging text under every code. Four of the 11 codes carry more than one packaging text, and the single text 7" reel taping appears under seven different codes: TL, TR, TP, AL, DL, ZL and CL. Eleven codes map to seven texts, and the map is neither one-to-one nor many-to-one in either direction.

The split is not random. AL states 15Kpcs on 2,906 WR rows and nothing on 3,119 WK, MR and WW rows, so the same two letters mean a stated reel count in one series and an unstated one in the next. Inside TL, the 1,938 rows that state 10Kpcs are all 0201, and the 1,142 plain 0201 rows sit beside them under the identical code. This is the same hidden quantity we described in the reel quantity post, now traced back to the letter that causes it.

The thin film export is the opposite extreme. All 93,914 thin film part numbers end in TL and all 93,914 carry 7" reel taping, so for thin film the suffix and the packaging column together carry no information that discriminates one part from another. For the MLCC side, where the export drops the packaging suffix entirely, see the CT suffix.

Does a J at the end of the part number mean automotive?

Usually, and not always: 40,395 of the 46,449 parts ending in J are automotive by series name, and 6,054 are not. We took the series text as the test, counting a row as automotive when the Series column contains the word Automotive, which it does on 102,995 rows. A rule reading a trailing J, V, W or Z as automotive flags 73,640 rows, is right on 63,431, wrong on 10,209 and misses 39,564. A rule reading only J flags 46,449, is right on 40,395 and misses 62,600.

The 6,054 false positives on J sit in five series texts that never use the word Automotive, shown here with the two array texts merged:

The 4,155 false positives on V are all High Power Chip Resistor (Anti-Sulfuration), for example WF12P1432FTLV. We have not seen this counted anywhere: a one-letter suffix rule for automotive is wrong on 10,209 of 234,815 Walsin chip resistor rows, 4.3 percent, and no single rule of either kind reads the grade correctly. The series name says Automotive; it is not a qualification statement. Walsin’s datasheets say compliant, never certified, and the AEC-Q200 qualification report for the exact part number is the document to ask for. That statement is Walsin’s to make, not ours.

What does the prefix add that the suffix cannot?

Coverage without error, but only on some series. Every MR, MF, MK, MA and SR part number is automotive by series name, 49,520 of 49,520, so the prefix is a perfect test where it fires. It fires on 48.1 percent of the automotive rows. The 53,475 automotive rows it misses are all W-prefix parts, where only the trailing flag marks them, and 977 of those carry neither a J, V, W nor Z. All 977 are Power Low-ohm Current Sense parts with the WW prefix, for example WW20PR100FTL, and a decoder that combines the prefix and the flag still misses them.

For the grade split behind MR and SR, see the automotive MR, SR and AEC-Q200 split. The WR and MR datasheet legends define the packaging and termination letters. They do not define J, V, W or Z, and the flag letters are measured from the export, not taken from any Walsin document.

What should a decoder do with a suffix it cannot read?

Keep the original string, decode only what is documented, and report the rest as unread. That is how our free cross-reference tool treats a suffix: the letters are carried through to the result, and a difference from your original is stated, not hidden behind a tick. Three rules, each measured above:

1. Never infer grade from one trailing letter. It is wrong on 10,209 rows.
2. Never infer a reel count from the packaging code alone. Four of 11 codes carry more than one text.
3. Do not match suffixes across manufacturers by letter. Fill the incumbent column above from your own datasheet; other makers print their own packaging legends and we do not reproduce them. Confirm against both datasheets and qualify in your own circuit.

We hold 28 Walsin datasheets, 451 pages, and exactly two of them are chip resistor sheets. We hold none for thin film, so the thin film suffix is read from the export alone. What is in Hong Kong is on ready stock — 1,125 part numbers as at 23 September 2026, a dated snapshot and not a live feed. The range sits on the chip resistor page. Our address is Unit 207, 2/F, Sun Ling Plaza, 30 On Kui Street, Fanling, N.T., Hong Kong, (852) 2628 4777, and our UL file is E182369, which you can look up yourself.

The short version

A Walsin chip resistor suffix is a packaging letter, a termination letter and sometimes a flag. 48 endings reduce to 11 two-letter codes; the two datasheets we hold define 205,886 of 234,815 rows and leave 28,929 undefined. Four of 11 codes carry more than one packaging text and one text sits under seven codes. A trailing-letter rule for automotive is wrong on 10,209 rows, 6,054 on J and 4,155 on V, and the prefix rule never errs but misses 53,475. We will not tell you a suffix means a grade. We will show you the string the file holds. Qualification stays with you.

Send us the chip resistor lines on your BOM and the suffix your decoder reads off them, and we will return what it got wrong. And a question back: when your script flagged a part as automotive from its last letter, did anyone check the series name?

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