Your Incumbent MLCC Just Went End-of-Life: What Do You Actually Do Next? A 7-Step Match Funnel From 23,601 Walsin Part Numbers to 6, and Two Silent Filter Losses That Hide 4 of 18

We hold no maker’s affected-part list, so this is method. For an MLCC end of life replacement, decode the part, fix six match criteria, check the grade, then filter in order. On a generic 0805 X7R 1 µF line we cut 23,601 Walsin part numbers to 6, 2 of them AEC-Q200 compliant. Two filter traps hide 4 of 18.

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Venatech Limited, an authorised Walsin distributor in Hong Kong, wrote this from Walsin Technology (Walsin) 00_ALL_MLCC_parts_combined.xlsx (24,026 rows, 23,601 distinct part numbers), two Walsin approval sheets and our Hong Kong stock snapshot dated 23 September 2026. The worked line is a generic 0805 X7R 1 µF ±10% 25 V specification, not any maker’s part. We hold no manufacturer’s affected-part list and name nobody as discontinued; confirm any notice with its sender in writing. Every part number below is real. Our checklist post, You Have Been Handed an EOL Notice, covers the dates and the bridge buy. This one covers the match.

What do you do first when your incumbent MLCC goes end-of-life?

Pull the notice’s dates, then open the incumbent’s datasheet and stop trusting the part number. Record the notice date, last-time-buy date, last-ship date and any final-order deadline, because they set your runway. Then write down six electrical and mechanical fields plus one grade requirement: seven things to match, and the part number supplies none of them reliably.

The seven: case size, dielectric, capacitance, tolerance, rated voltage, maximum height, and grade (commercial or AEC-Q200). Read each from the datasheet in the datasheet’s own units. Every maker’s code differs, which is why the free cross-reference tool carries decoders for 18 manufacturers’ part numbers decoded, and why you should not decode a competitor code from memory.

How do you decode the part before you search for a replacement?

From the maker’s ordering key, field by field, then test the decode against data. Walsin’s key is in 01_General_Purpose.pdf (21 pages, September 2026). We tested it on all 24,026 export rows: the letter B means X7R on 7,542 of 7,544 rows, and the last three characters decode to the Rated Voltage column on 24,006 of 24,023 testable rows. 17 rows disagree.

Characters in 0805B105K250CT	Field	Reads as	Match / mismatch against the export
0805	Case size	0805 (2012)	Match on every 0805-prefixed row; the automotive and soft-termination prefixes write the size as 21
B	Dielectric	X7R	Match on 7,542 of 7,544; MT15B102K101 and 0201B8R2B250 read NPO
105	Capacitance	10 × 10^5 pF = 1 µF	Match, but the column spells 1 µF two ways (below)
K	Tolerance	±10%	Match by letter; the column fails on 369 K-letter rows
250	Rated voltage	25 × 10^0 = 25 V	Match on 24,006 of 24,023; 17 differ, e.g. MT31B822J631
C	Termination	Cu/Ni/Sn	Match; part of the orderable suffix, not the export key
T	Packaging	7-inch reel	Match; part of the orderable suffix

The 17 voltage disagreements are in Walsin’s own files, and we list one: MT31B822J631 reads 630 V by code and 100 V in the column. We checked every one of these decodes against the column. A decode is a reading, not a proof. Read the datasheet for the exact part.

Which criteria set the match, and in which direction does each one move?

Each criterion moves one way only. Case size, dielectric and capacitance must be equal. Tolerance may be equal or tighter. Voltage may be equal or higher. Height must stay under your drawing’s ceiling at worst case, which is nominal plus the positive thickness tolerance. Grade may be equal or higher. Anything else is a mismatch you accept on purpose.

Criterion	Direction	Worked value	Why it can bite
Case size	Equal	0805	Length and width only; height is separate
Dielectric	Equal	X7R	X5R has a lower temperature ceiling, so we keep X7R strict
Capacitance	Equal	1 µF	Spelled two ways in the export
Tolerance	Equal or tighter	±10% (K); J (±5%) would add 3	The column corrupts on 656 MG rows
Rated voltage	Equal or higher	25 V and up	Higher voltage can change height
Height	At or under ceiling	1.45 mm worst case	Soft termination publishes ±0.30 mm
Grade	Equal or higher	AEC-Q200 compliant	A series name is not a datasheet

We measured the ceiling from the published thickness column. Choose it from your drawing, not from the incumbent’s nominal. We used 1.45 mm because it is 1.25 mm plus the 0.20 mm tolerance the general-purpose 50 V part publishes. A shield can, a stacked board or a conformal window can fix it lower.

How many Walsin parts survive each criterion?

Six of 23,601 survive all six electrical and mechanical criteria, and two of those six carry the AEC-Q200 series. We applied the criteria in order, counted distinct part numbers at each step, and checked each count twice. A naive version of the same filter finds fewer: filtering the Capacitance column on “1000nF” and the Tolerance column on “±10%” returns 14 at the tolerance step, where the true count is 18.

Step	Filter	Part numbers left	What the step removed
0	All Walsin MLCC rows	23,601
1	Case size 0805	4,780	Every other footprint
2	Dielectric X7R	1,474	NP0, X5R, X6S and the rest
3	Capacitance 1 µF, both spellings	36	35 if you filter on “1000nF” only
4	Tolerance ±10%, read from the part-number letter	18	15 if you filter on the column
5	Rated voltage 25 V and up	10	10 V and 16 V parts
6	Worst-case height 1.45 mm or less	6	Four soft-termination parts at 1.55 mm
7	Grade: AEC-Q200 series	2	General-purpose and MG parts

We have not seen this counted anywhere: the export writes 1 µF as 1000nF on 258 rows and as 1uF on 6, and it does this on 19 of 265 capacitance values. A search on “1000nF” silently drops ST21B105K500, the only AEC-Q200 soft-termination part at this value. Separately, the Tolerance column holds -0.1 instead of ±10% on MG21B105K100, MG21B105K250 and MG21B105K500. Combined, the two traps turn 18 candidates into 14, and a tool that filters on those columns loses 4 of 18 (22%) without a warning. The tolerance trap is an extension of a defect we published earlier (656 of 788 MG rows).

Is the replacement automotive grade, and how do you check?

Check the series, then the sheet, then ask for the report. Of the 10 parts at 25 V and up, MT21B105K250 and MT21B105K500 sit in Walsin’s MT series. Walsin’s MT sheet, 11_Automotive_MT.pdf, states “The MT series meet AEC-Q200 requirement”, so we write compliant, never certified. The MG parts sit in a series the export names “Without AEC-Q200 Certification”, so they are not grade matches.

The candidate table below carries a column for your incumbent, and the last column states what differs.

Walsin part number	Series	Voltage	Published thickness (mm), worst case	Your incumbent	Match / mismatch against 0805 X7R 1 µF ±10%, 25 V up, 1.45 mm, AEC-Q200
MT21B105K250	Automotive MT	25 V	1.25 ±0.10 (1.35)		Match on all seven
MT21B105K500	Automotive MT	50 V	1.25 ±0.20 (1.45)		Match; voltage higher, height at the ceiling
0805B105K250	General Purpose	25 V	1.25 ±0.20 and ±0.10 (1.45, 1.35)		Match on six; mismatch on grade; two rows, two tolerances
0805B105K500	General Purpose	50 V	1.25 ±0.20 (1.45)		Match on six; mismatch on grade
MG21B105K250	Automotive MG	25 V	1.25 ±0.10 (1.35)		Match on six; mismatch on grade; hidden by a tolerance-column filter
MG21B105K500	Automotive MG	50 V	1.25 ±0.20 (1.45)		Match on six; mismatch on grade; same filter trap
ST21B105K500	Automotive Soft Term ST	50 V	1.25 ±0.30 (1.55)		Mismatch on height by 0.10 mm; hidden by a “1000nF” filter
SG21B105K250	Soft Termination SG	25 V	1.25 ±0.30 (1.55)		Mismatch on height and termination
SH21B105K250	Soft Termination SH	25 V	1.25 ±0.30 (1.55)		Mismatch on height and termination
SH21B105K500	Soft Termination SH	50 V	1.25 ±0.30 (1.55)		Mismatch on height, voltage and termination

Read the soft-termination rows twice. If your incumbent is soft-terminated and automotive, the one Walsin candidate at this value, ST21B105K500, is 0.10 mm over a 1.45 mm ceiling. That is a decision for your mechanical drawing, and the table makes it in seconds. Our post on soft-termination MLCC series sets out what the polymer adds.

What do you order and what do you ask for?

Order the code with its suffix, ask for the qualification report, and ask what is held. The orderable form of the commercial part is 0805B105K250CT: the C is Cu/Ni/Sn termination and the T a 7-inch reel, per the General Purpose sheet. 0805B105K250 is the only one of the six candidates on our Hong Kong shelf as at 23 September 2026, and its order code in the snapshot is 0805B105K250CT.

Neither automotive-grade candidate was on the shelf that day. We do not hold a qualification report for any part: it is one of the eighteen document types absent from the 451 pages of Walsin sheets we hold, so ask Walsin for the exact part number’s report. Check Hong Kong ready stock for the current snapshot and read the CT suffix post for the encoding. For a whole BOM, the BOM checker takes up to 500 part numbers or an Excel or CSV file. The Walsin MLCC range lists the series.

The short version

Seven things to match: size, dielectric, capacitance, tolerance, voltage, worst-case height and grade. Our funnel on a generic 0805 X7R 1 µF ±10% 25 V line goes 23,601, 4,780, 1,474, 36, 18, 10, 6, with 2 AEC-Q200 compliant. Two traps lose 4 of 18: a 1000nF value filter drops ST21B105K500 and a tolerance-column filter drops three MG parts. One candidate was on the shelf on 23 September 2026. A cross result is a candidate; confirm against both datasheets and qualify in your own circuit.

Paste the incumbent into the free cross-reference tool, or send the BOM line and the notice dates. We will return the Walsin candidates with every difference stated and the shelf position as at 23 September 2026. Qualification stays with you. A question for your own team: if your search tool filters on the value column, how many parts has it already hidden?

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Frequently asked questions

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