Walsin MLCC Ordering Key: 26 Keys, Four Different Position Counts, and 30 Part Numbers That Disagree With Their Own Data Row

The Walsin MLCC ordering key is not one key. We read all 28 datasheets we hold and found 26 separate keys running 6, 7, 8 or 9 positions. We then decoded all 24,026 export rows against them. 30 part numbers state a dielectric or a tolerance their own data row contradicts.

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Venatech Limited, an authorised Walsin distributor in Hong Kong, holds 28 Walsin Technology (Walsin) datasheets totalling 451 pages, plus all 203 parametric export files. This post is written from the page-2 ordering key of every MLCC approval sheet and from 00_ALL_MLCC_parts_combined.xlsx. Every part number below is real and sits in that export. We decoded each one character by character rather than trusting a column.

How many positions does the Walsin MLCC ordering key have, and do the 26 keys agree?

They do not. 27 of the 28 documents we hold publish at least one part-number key, and the 26 distinct keys take four different position counts. Five MLCC keys open on the case size and run 7 positions. Seventeen open on a two-letter series prefix and run 8. The two Mega Cap keys run 9. Both chip resistor sheets run 6, under a different heading. Only 00_MLCC_Application_Guide.pdf, 12 pages, publishes none.

Key, and the document it sits in	Positions	Position 1	The two positions at the end	Match / mismatch against the 8-position house pattern
5 sheets, 01_General_Purpose.pdf to 05_Surface_Coating_Type.pdf	7	case size, four characters	Termination, Packaging	Mismatch — no series prefix, so the code starts with a number
17 sheets, 06_Microwave_RF.pdf to 22_Feed_Through_FT.pdf	8	two-letter series	Termination, Packaging	Match — this is the pattern
23_Mega_Cap_M_Series.pdf, 24_Mega_Cap_V_Series_Vertical_Stacked.pdf	9	series letter, then a chip-count digit	Thickness, Control code	Mismatch — no termination and no packaging position at all
Walsin_MR_Automotive_Thick_Film_Chip_Resistor.pdf, Walsin_WR_General_Purpose_Chip_Resistor.pdf	6	size code	Packaging, Termination	Mismatch — the last two positions are in the opposite order

The heading differs too. The 24 MLCC sheets head the block HOW TO ORDER on page 2; the two resistor sheets head it CATALOGUE NUMBERS, on page 4 of the MR sheet and page 6 of the WR sheet; and the 65-page 00_MLCC_Full_Catalogue.pdf repeats a key on 21 of its pages under a third heading, EXPLANATION OF PART NUMBERS.

Which single letters carry more than one meaning inside the same key?

Several, and the worst of them carries three. We checked all 24 MLCC keys letter by letter. In the General Purpose key alone, five letters — A, B, C, F and G — are each defined twice in the same eight characters. A is the X7S dielectric in position 3 and plus or minus 0.05 picofarad in position 5. F is Y5V and plus or minus 1 percent. We have not seen this counted anywhere.

Letter	Meaning in one position	Meaning in another position	Keys where both definitions appear	Match / mismatch
C	plus or minus 0.25 pF, tolerance	Cu/Ni/Sn termination	12 of 24 MLCC keys	Mismatch — position decides, not the letter
G	plus or minus 2 percent, tolerance	13-inch reel, packaging	13 of 24	Mismatch
G	also the X8G dielectric	—	4 of 24 — RF, RH, MT, HT	Mismatch — three meanings in one code
B	X7R dielectric	plus or minus 0.1 pF, tolerance	6 of 24	Mismatch
M	plus or minus 20 percent, tolerance	surface coating, termination	5 of 24	Mismatch
K	plus or minus 10 percent, tolerance	Non Coating, termination	2 of 24 — the S2 and S3 safety keys	Mismatch
T	X7T dielectric (SH key)	7-inch reel, packaging	1 of 24	Mismatch
L	13-inch reel on 03_Large_Size_1825_2220_2225.pdf	9.00 plus or minus 0.35 mm chip thickness on both Mega Cap keys	—	Mismatch — 19 other keys write a 13-inch reel as G

That last row is the one to carry away. L is the 13-inch reel code on exactly one of the 26 keys. Nineteen MLCC keys and both resistor keys use G. A script that learned G from the General Purpose sheet will silently mis-read a large-size code, and a human skim-reading the 1825 sheet will not notice.

The Mega Cap keys are the densest: their thickness position draws on a 21-letter table from A to W, and six of those letters — N, B, T, J, K and M — already mean something else in the same nine-position code. SH55T225K251 shows the same trap in the 8-position family.

Which part numbers disagree with their own data row?

Thirty of them, out of 24,026. We decoded position 3 and position 5 of every part number in 00_ALL_MLCC_parts_combined.xlsx and compared each against the Dielectric and Tolerance columns on the same row. 6 rows disagree on dielectric and 24 disagree on tolerance — ignoring the 656 MG rows where the column holds a bare signed decimal rather than a tolerance at all, and ignoring pure formatting differences such as ±0.5pF against +-0.50pF.

Part number	Letter in the code	Key says that letter means	Export column says	Which looks right	Match / mismatch
MT15B102K101	B, position 3	X7R	NPO	the code — 1000 pF NP0 at 0402 and 100 V is a tall order	Mismatch
MG18N1R6B500	N, position 3	NP0	X7R	the column is the doubtful one — 1.6 pF in X7R is not a normal part	Mismatch
ST31N103J631	N, position 3	NP0	X7R	the column — 10 nF NP0 at 1206 and 630 V is not credible	Mismatch
0201B8R2B250	B, position 3	X7R	NPO	the column — 8.2 pF is an NP0 value	Mismatch
0805A105M101	A, position 3	X7S	X5R	unresolved from the data we hold	Mismatch
0603B225J160	J, position 5	plus or minus 5 percent	+-20%	the column — 2.2 µF X7R at 5 percent is not offered	Mismatch
MT21B101M101	M, position 5	plus or minus 20 percent	+-5%	unresolved	Mismatch
RF15N0R1P500	P, position 5	plus or minus 0.02 pF	+-5%	the catalogue restricts P to UF items, so the code is the doubtful one	Mismatch
1206N101F631	F, position 5	plus or minus 1 percent	+-1% on one row, +-5% on a second	neither — this code appears twice with different data	Mismatch, twice over
MT15N0R5C500	N and C	NP0, plus or minus 0.25 pF	NPO, +-0.25pF	both	Match — this is what a clean row looks like
0201B102K160	B and K	X7R, plus or minus 10 percent	X7R, +-10%	both	Match

Thirty rows in 24,026 is 0.12 percent, and that is exactly why it is dangerous: it is rare enough that nobody checks and common enough to land on your board. The honest position is that for those 30 we will not tell you which half is right from the export alone. We will send you the governing datasheet page and let you decide, and we will say so in writing.

MT18N391J101 is a thirty-first case of the same shape, already published by us: its Dielectric column reads 390 instead of NP0. For the capacitance field’s version of this argument, see the MLCC capacitance code that 28 rows disagree with.

Why does position six read Impulse voltage on three keys and Rated voltage on twenty-one?

Because on the safety series it is not the working voltage, and Walsin says so in the key itself. Three of the 24 MLCC keys — 16_Safety_X1Y2_General_S2.pdf, 17_Safety_X1Y2_Automotive_S2_H.pdf and 18_Safety_X2_S3.pdf — label position 6 “Impulse voltage”. The remaining 21 label it “Rated voltage”. The S2 key then spells the codes out: 502 is 5000 V impulse, 602 is 6000 V impulse.

S242B101K502 ends in 502, and all 173 S2 rows in the export carry 5000 or 6000 Vdc in the Rated Voltage column. That number is the impulse figure the key names, not a working voltage. The working rating — X1 at 310 Vac, Y2 at 250 Vac, 1500 Vdc — is in the datasheet and in no export column. Anyone selecting a mains-facing part from the export alone will read the voltage field by a factor of sixteen too high.

Where do the last two positions go when a part number reaches the export?

They vanish. Every one of the 24,026 part numbers in the MLCC export is exactly 12 characters long. Not one carries a termination position or a packaging position, so a 7-position key arrives with 5 positions filled and an 8-position key with 6. We measured the length of all 24,026 and the distribution has a single value.

The export does carry a Termination column, so you might expect it to make up the difference. It does not. We checked all 24,026 rows: the Termination column states a metal finish on zero of them. It is populated on 1,106 rows and every one of those values is a tolerance or a bare decimal that has landed in the wrong column — 784 of the 788 MG rows hold a value identical to their own Tolerance cell. That defect has its own post: the termination column that contains tolerances.

So the two positions that decide what you can actually buy — the plating and the reel — are in the key, absent from the code, and absent from the column named after one of them. That is the single most common reason a Walsin code pasted straight from a catalogue will not be accepted as an orderable line.

Which case size exists in the export and in no ordering key at all?

0306. Three General Purpose part numbers use it — 0306B225J4R0, 0306B225K4R0 and 0306B225M4R0, all X7R, 2.2 µF, 4 Vdc — and the General Purpose key’s size list runs 0201, 0402, 0603, 0805, 1206, 1210, 1812 and stops. 0306 is not in it. It is not in the packaging table on page 11 either. We checked all 24 keys; no Walsin MLCC key we hold defines a 0306 size field.

The three rows also carry L 0.8 mm and W 1.6 mm, which is the reverse-geometry convention — the part is wider than it is long. A selector that assumes L is the longer dimension will sort these wrongly. 0306 appears on 3 of the 24,026 rows and in no other series.

What should you check before you paste a Walsin ordering code into a BOM?

Four things, in this order, and all four take under a minute each once you know the key is series-specific. Walsin publishes 26 of them and they do not share a position count.

1. Which key governs your code. A letter pair in the first two characters means an 8-position series key; four digits mean a 7-position key; a letter and a digit mean a 9-position Mega Cap key.
2. Decode position 3 and position 5 yourself and compare them with the data row. Thirty rows in 24,026 disagree. It is faster to check than to find out at first article inspection.
3. Add the termination and packaging positions back. They are not in the export and the code is not orderable without them. For the suffix argument in full, see the CT suffix and orderable part numbers.
4. Cross the whole list in one pass instead of decoding by hand. Paste up to 500 part numbers, or drop your Excel or CSV, into the free cross-reference tool, and read every stated difference. Then check what is physically on the shelf at ready stock — 1,125 part numbers as at 23 September 2026, a dated snapshot and not a live feed.

The whole MLCC line sits on the Walsin MLCC page. We hold 28 Walsin datasheets, 451 pages. Ask for the one covering your part number and it will be in your inbox, not in a brochure. (852) 2628 4777.

The short version

There is no single Walsin MLCC ordering key. There are 26, running 6, 7, 8 or 9 positions under three different headings, and the last two positions are reversed between the capacitor and resistor families. Inside one key a letter can mean three things: on the RF, RH, MT and HT keys, G is the X8G dielectric, plus or minus 2 percent, and a 13-inch reel. L is a 13-inch reel on one key of 26 and a chip thickness on two others. Thirty of 24,026 export rows contradict their own code, and we will not guess which half is right. Every 12-character export code is missing its termination and packaging positions. 0306 exists as three real part numbers and in no key at all. Qualification stays with you — our job is to make sure the code you send to purchasing decodes to the part you drew.

Send us the Walsin codes off your BOM and we will return a position-by-position decode of each one, including which of the 26 keys governs it and whether its own data row agrees. And a question back: when your MRP system learned that G means a 13-inch reel, who told it that on one Walsin sheet it means 9 millimetres of chip?

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Frequently asked questions

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