MLCC Ageing Rate: Zero of Walsin’s 26 Datasheets Publish One, and the Word Decade Appears on 0 of 451 Pages

No Walsin MLCC datasheet we hold publishes an ageing rate. We searched all 451 pages of all 28 documents: the word “decade” returns zero pages. The phrase “aging rate” returns exactly one hit in 451 pages, and it is a chart caption. Twenty-three of the 26 MLCC documents specify the heat treatment that resets ageing.

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Venatech Limited, an authorised Walsin distributor in Hong Kong, holds 28 Walsin Technology (Walsin) datasheets, 451 pages. This post is written from the full extracted text of every one of them and from 00_ALL_MLCC_parts_combined.xlsx. Every part number below is real. We rejoined words the PDF had broken across a line before matching, because a naive search under-counts, and we checked both the British and the American spelling.

How many of Walsin’s 26 MLCC datasheets publish an ageing rate?

None. We searched all 451 pages for “decade”, for “per decade hour”, for “%/decade” and for any percent figure attached to the word ageing. “Decade” returns 0 pages and 0 documents. No numeric ageing rate appears in any of the 26 MLCC documents or either chip resistor sheet. The one thing we did find is a caption.

What we searched 451 pages for	Pages that return it	Documents that return it	Match / mismatch against a tolerance budget
decade	0	0	Mismatch — the unit an ageing rate is quoted in is not in the library
a numeric ageing rate, any form	0	0	Mismatch
the phrase aging rate	1 of 451	1 of 28	Mismatch — a chart caption, with no value in the text layer
the de-ageing heat treatment	85	23 of 26 MLCC	Match — the reset is fully specified
Preconditioning for Class II MLCC, the page-3 footnote	17	16 of 26 MLCC	Match, on the sheets that carry it
a rest period before measurement	—	25 of 26 MLCC	Match, but in two different lengths

The single hit is on page 8 of 65 in 00_MLCC_Full_Catalogue.pdf, where the General Purpose block lists four electrical characteristic charts and names the second “Capacitance Change – Typical aging rate”. The text layer of that page carries axis values for the temperature chart and the DC bias chart and none for the ageing chart. The page closes with Walsin’s own footnote: “All above typical electronic characteristics are for reference only.” Only 3 of the 65 catalogue pages carry an electrical-characteristics block at all, and only that one names ageing. We have not seen this counted anywhere.

That is the whole published position. A chart with no numbers, on one page in 451, under a disclaimer.

What do the datasheets publish instead of a rate?

The procedure that erases it, in full, three times over. 23 of the 26 MLCC documents specify a heat treatment at 150 °C for one hour before a Class II part is measured, across 85 of the 451 pages. The three that do not are 00_MLCC_Application_Guide.pdf at 12 pages, 09_Microwave_Automotive_RT.pdf at 10 pages — an NP0-only series, so correctly silent — and 16_Safety_X1Y2_General_S2.pdf at 14 pages, which is not NP0-only and is dealt with below.

Walsin states it three different ways, and all three appear in our library:

• The page-3 footnote, on 16 documents, verbatim: “Preconditioning for Class II MLCC: Perform a heat treatment at 150±10°C for 1 hour, then leave in ambient condition for 24±2 hours before measurement.”
• Inside the reliability tables, on 19 documents, as “To apply de-aging at 150°C for 1hr then set for 24±2 hrs at room condition”.
• On the automotive and Mega Cap sheets, on 6 documents, as “Perform 150 +0/-10°C for 1 hr and then set for 24±2 hrs at room temp.”

Read those together and the gap is obvious. Walsin tells you exactly how to put the capacitance back where the datasheet measured it, and not how far it will have moved by the time the part reaches your board. The tolerance in the ordering key — K for plus or minus 10 percent, M for plus or minus 20 percent — carries no reference time anywhere in 451 pages.

Which Walsin part numbers does this actually touch?

8,479 of 24,026 — every Class II part in the catalogue. That is a count we have already published, in MLCC shelf life, storage and handling, and we re-ran it for this post and got the same number: 7,544 X7R, 751 X5R, 133 X6S, 26 X8R, 21 X7S, 2 Y5V and 2 X7T. The other 15,546 are NP0 or X8G and do not carry the question.

Part number	Dielectric	Governing sheet	Ageing rate in it	De-ageing step in it	Rest before measurement	Match / mismatch
0201B102K160	X7R	01_General_Purpose.pdf, 21 pp	none	yes, both wordings	24 ± 2 hrs	Mismatch — reset specified, drift not
MT15B104K500	X7R	11_Automotive_MT.pdf, 29 pp	none	yes, page-3 footnote	24 ± 2 hrs	Mismatch
ST18B473K500	X7R	12_Soft_Term_Automotive_ST.pdf, 23 pp	none	yes, page-3 footnote	24 ± 2 hrs	Mismatch
SH18B101K100	X7R	19_Soft_Term_SH.pdf, 27 pp	none	yes	24 ± 2 hrs	Mismatch
MG15B101J160	X7R	14_MG_Series_High_Reliability.pdf, 23 pp	none	yes	24 ± 2 hrs	Mismatch
TT31X225K100	X5R	21_Low_Profile_TT.pdf, 9 pp	none	yes	24 ± 2 hrs	Mismatch
FT21B103M500	X7R	22_Feed_Through_FT.pdf, 9 pp	none	yes	48 ± 4 hrs	Mismatch, and a different rest period
S242B101K502	X7R	16_Safety_X1Y2_General_S2.pdf, 14 pp	none	no — not stated anywhere in 14 pages	48 ± 4 hrs for Class II	Mismatch — neither the rate nor the reset
HH15N0R2A500	NPO	10_High_Q_Low_ESR_HH.pdf, 11 pp	none needed	yes, for Class II generally	24 ± 2 hrs	Match — Class I, no ageing question
RF03N0R1A250	NPO	06_Microwave_RF.pdf, 19 pp	none needed	yes, for Class II generally	24 ± 2 hrs	Match — Class I
UF03N0R1A101	NPO	08_Microwave_Narrow_Tolerance_UF.pdf, 9 pp	none needed	yes, for Class II generally	24 ± 2 hrs	Match — Class I

The three Match rows are the point as much as the eight mismatches. For an NP0 part the absence of an ageing rate is correct and complete. For an X7R part it is a missing term. That is the real reason a Class I to Class II substitution is never a like-for-like swap, and it has nothing to do with the temperature coefficient everyone argues about — see NP0 against X7R and X5R.

Why does one safety sheet omit the de-ageing step its automotive twin states?

We do not know, and the asymmetry matters because the two sheets cover the same construction. 16_Safety_X1Y2_General_S2.pdf, 14 pages, is 1 of only 3 MLCC documents in 26 that never state the heat treatment — and the only one of those 3 that carries a Class II dielectric. We searched all 14 pages for de-ageing, for a heat treatment at 150 °C and for “150 +0/-10°C”; all three return nothing. Its automotive counterpart 17_Safety_X1Y2_Automotive_S2_H.pdf, 12 pages, states it on pages 5 and 6 as “Perform 150 +0/-10°C for 1 hr and then set for 24±2 hrs at room temp.”

Both sheets cover X1/Y2 class capacitors at 1808 to 2220, both offer NP0 and X7R, and the S2 export holds 173 part numbers of which 86 are X7R and 87 are NPO — so the Class II half of the series is governed by the one sheet that omits the Class II preconditioning. The S2 sheet does distinguish the two classes elsewhere: it is one of four documents that write “24±2 hrs (Class I) and 48±4 hrs (Class II)” for the post-test recovery. It knows the distinction exists and does not apply it to the preconditioning.

S242B101K502 is a real part on that sheet. If you are qualifying it, the pre-measurement condition has to come from the automotive sheet or from Walsin directly, and we will say that in writing rather than quietly lend you the other document’s wording.

Must a Class II part rest 24 hours before measurement, or 48?

Both, depending on which sheet governs your part. 25 of the 26 MLCC documents state a rest period and they do not agree. 19 state only 24 ± 2 hours. Six state 48 ± 4 hours for Class II: the three safety sheets, the feed-through sheet and both Mega Cap sheets. Four of those six print the split explicitly as “24±2 hrs (Class I) and 48±4 hrs (Class II)”.

Rest period stated	Documents	Named
24 ± 2 hours only	19	the General Purpose, high voltage, microwave, automotive, soft termination, high temperature and low profile sheets
48 ± 4 hours for Class II	6	16, 17, 18, 22, 23, 24
48 ± 4 hours and no 24 ± 2 anywhere	1	22_Feed_Through_FT.pdf
explicit Class I against Class II split	4	16, 18, 23, 24

A factor of two in the settling time matters for anyone writing an incoming inspection procedure. Measure an FT21B103M500 at 24 hours against a sheet that asks for 48 and you are not measuring what Walsin measured. We have published the related count of which sheets state their capacitance test conditions at all in MLCC capacitance test conditions.

Does the parametric export say anything about ageing?

Nothing at all. 00_ALL_MLCC_parts_combined.xlsx carries 16 columns across 24,026 rows: Part Number, Series, Size, Dielectric, Capacitance, Tolerance, Rated Voltage, L, W, T, Termination, Packing, SPQ, Remark, Thickness and Symbol. We checked all 16. None names ageing, de-ageing, a reference time or an age-related capacitance figure. Nor does any of the other 202 export files.

So the only field in the export that signals the question at all is Dielectric, and it signals it by implication: an X7R row carries a time term and an NPO row does not. That implication is doing a lot of work for a selector filter, and nothing in the file tells the reader it is there.

What should you ask for before you cross a Class II capacitor?

Three questions, in this order, and not one of them is answered anywhere in the 451 pages we hold.

1. Ask for the ageing rate and the reference time for your exact part number. Not for the series. We hold 28 Walsin datasheets, 451 pages, and the figure is in none of them. Ask us and we will ask Walsin and send you what comes back, including the answer “we do not have it” if that is the answer.
2. Ask which rest period the governing sheet uses before you write an incoming inspection step. 24 ± 2 hours on 18 documents, 48 ± 4 on six.
3. Cross field by field rather than on a dielectric letter. Two X7R parts from different manufacturers can share case size, capacitance, tolerance and voltage and still differ on a term neither datasheet states. Paste up to 500 part numbers or drop your Excel or CSV into the free cross-reference tool, 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 line sits on the Walsin MLCC page.

Check us while you are here. UL file E182369 is in UL’s own public database, and we are an authorised Walsin Technology distributor in Hong Kong — confirm it with Walsin. (852) 2628 4777.

The short version

Walsin publishes no MLCC ageing rate. We searched all 451 pages of all 28 datasheets: “decade” returns zero, and “aging rate” returns one hit, a chart caption on page 8 of 65 of the catalogue, on a page whose own footnote calls the characteristics reference only. Against that, 23 of the 26 MLCC documents specify the heat treatment that resets ageing across 85 pages, 16 carry it as a page-3 footnote, and 25 state a rest period before measurement — 24 ± 2 hours on 19 documents and 48 ± 4 on six. The general X1/Y2 safety sheet omits the preconditioning its automotive twin states, and 86 of the 173 S2 part numbers are X7R. 8,479 of 24,026 Walsin MLCC part numbers are Class II and carry the question; 15,546 are not and do not. We will not tell you a crossed part is a like-for-like swap on a dielectric letter. We will show you which term neither datasheet states. Qualification stays with you.

Send us the Class II lines off your BOM and we will tell you, part number by part number, which sheet governs it, whether that sheet states the de-ageing step, and which rest period it asks for — and we will put the ageing-rate request to Walsin in writing. And a question back: when your tolerance budget allowed plus or minus 10 percent for an X7R, what number did it use for the time term, and where did that number come from?

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Frequently asked questions

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