The MLCC preheat limit for a 2220 part is printed twice by Walsin Technology (Walsin) and the two numbers differ: 130 °C in the application guide, 50 °C in the large-size sheet. Only 7 of the 26 MLCC files we opened give any preheat guidance. The other 19 leave 23,352 of 24,026 export rows to the guide alone.
Venatech Limited, an authorised Walsin distributor in Hong Kong, holds 28 Walsin datasheets, 451 pages in all. This post is written from the 26 MLCC files in that set: 24 series approval sheets, the full catalogue and the 12-page application guide (Jan. 2022), checked against the 24,026-row parametric export. We searched every page for the words preheat and pre-heat and for the symbol ΔT. Every part number below is real. The question is the one a reflow engineer asks before a 2220 goes on a heavy board: how far below the peak may the preheat end?
How many Walsin MLCC files give a preheat limit?
Seven of 26. We opened each file, searched every page and sorted the hits into three kinds. Seven files print process guidance on preheat, 15 print preheat only as a soldering-heat test condition, and 4 never use the word. The 7 are the application guide, the large-size sheet, the three safety sheets and the two Mega Cap sheets. Series sheets that give guidance reach 674 export rows; the guide is the only text that reaches the other 23,352.
| What the file prints | Files | Which | Export rows | Example part | Match / mismatch against the guide |
|---|---|---|---|---|---|
| ΔT limit by case size, no rate | 1 | 00_MLCC_Application_Guide.pdf |
all 24,026 | 1206B102J101 |
reference |
| Rate of 4 °C per second, final preheat within 100 °C or 50 °C of soldering temperature | 1 | 03_Large_Size_1825_2220_2225.pdf |
501 | 2220B102K102 |
Mismatch — different rule, different numbers |
| Rate of 3 °C per second; a ΔT only in the hand-soldering table | 3 | S2, S2-H, S3 safety sheets | 173 (S2 only) | S242B101K502 |
Mismatch — rate, no reflow ΔT |
| Rate of 3 °C per second | 2 | Mega Cap M and V sheets | 0 | no export rows | Mismatch — and no part to test it on |
| Preheat 120 to 150 °C for 1 minute (FT: 150 ±10 °C, 60 to 90 s), inside the test row only | 15 | 14 sheets and the catalogue, including SH, SG, TT and FT | 21,058 | SH21B103K500 |
Mismatch — a test condition, not a process limit |
| No mention of preheat | 4 | RT, MT, ST, VT | 2,294 (MT 2,176, ST 118) | MT21B103K500 |
Mismatch — silent |
The sheets are the General Purpose family and the others listed in the Walsin index; the guide is MLCC_application_guide.pdf. We have not seen this counted anywhere: 674 of 24,026 export rows, 2.8 percent, belong to a series whose own sheet says anything about preheat as a process.
What preheat limit applies to a 2220 part?
Two, and they are 80 °C apart. The application guide’s thermal-shock table limits the temperature difference ΔT to 130 °C for reflow at 1210 or larger. The large-size sheet says the final preheat should be within 50 °C of the soldering temperature for 1210, 1808, 1812, 1825, 2220 and 2225. For a 260 °C peak that is a floor of 130 °C against a floor of 210 °C.
| Case size band | Guide, reflow (Jan. 2022) | Large-size sheet, final preheat (Apr. 2026) | Export rows in the band | Example part | Match / mismatch | Your incumbent part (fill in) |
|---|---|---|---|---|---|---|
| 1206 and smaller | ΔT ≤ 190 °C | within 100 °C | 20,554 | 1206B102J101 |
Mismatch by 90 °C, but the sheet covers no part in this band | |
| 1210 and larger | ΔT ≤ 130 °C | within 50 °C | 3,472 | 2220B102K102 |
Mismatch by 80 °C on the 501 large-size rows |
The large-size sheet’s 100 °C band reads “small chips such as 0402, 0603, 0805 and 1206”. We counted its export series: 501 rows, 118 at 1825, 258 at 2220 and 125 at 2225. No row in it is a small chip, so the 100 °C line applies to no part the sheet covers. Of the 3,472 export rows at 1210 or larger, 501 carry the 50 °C sheet, 173 carry the safety sheet and 2,798 carry the guide alone. The guide does not define ΔT in text; the endpoints are in a figure we did not transcribe. We read both as the gap between the end of preheat and the peak, and that reading is ours.
Can the large-size sheet’s own preheat rules be met together?
Only up to a 250 °C solder temperature. Page 9 of the sheet prints a soak maximum, TS max, of 200 °C in its profile table, and a few lines earlier asks for a final preheat within 50 °C of the soldering temperature. Within 50 °C of 250 °C is 200 °C. Above that the two lines cannot both hold. The same table lists a classification temperature of 260 °C.
| Solder temperature on the sheet | Final preheat needed (within 50 °C) | Soak maximum printed | Match / mismatch |
|---|---|---|---|
| 235 °C (lower bound of “235 – 260 °C”) | 185 °C or above | 200 °C | Match |
| 250 °C | 200 °C or above | 200 °C | Match, no margin |
| 260 °C (classification temperature) | 210 °C or above | 200 °C | Mismatch by 10 °C |
We did the subtraction ourselves, and it rests on reading the soak maximum as the final preheat. That reading is the natural one, and the sheet does not confirm it. A reader qualifying a 2220 such as 2220B103K102 at a 260 °C peak should not take either line as a guaranteed envelope.
Is the MLCC preheat rate 3 or 4 °C per second?
Both appear. The large-size sheet says the rate of preheat should not exceed 4 °C per second; the three safety sheets and the two Mega Cap sheets say 3 °C per second; the guide gives no rate. Counting by file, 1 file says 4, 5 say 3 and 20 say nothing; counting by export row, 501 say 4, 173 say 3 and 23,352 say nothing.
The large-size sheet also prints a ramp-up limit of 3 °C per second from liquidus to peak in its profile table, a different segment of the curve, so its two numbers are not a contradiction. They are two limits on one page that a reader has to keep apart. The sheet’s closing line reads “3°C/sec (heating) and 6°C/sec (heating)”, with the second word apparently meant as cooling; the table above it says ramp-down 6 °C per second, and the cooling paragraph says 4 °C per second when forced cooling is needed. We did not resolve that and we do not quote it.
What does the preheat in a soldering heat test mean?
It is the test setup, not the process. Fifteen files print a preheat inside the Resistance to Soldering Heat row: 120 to 150 °C for 1 minute on the SH, SG and TT sheets, and 150 ±10 °C for 60 to 90 seconds on the FT sheet. These four sheets, SH, SG, TT and FT, cover 1,654 export rows, and none of them gives a preheat limit for your oven. Their soldering pages hold a caption and two pictures, as we found when we compared the soldering pages of the first 12 sheets in our soldering-profile post.
A soak at 150 °C before a 260 °C dip proves the part survives that dip. It does not say a production board may be preheated no higher than 150 °C, or lower. The sheets that state a recommendation say it elsewhere, and the 19 that do not leave the reader on the guide.
What should a process file attach for preheat?
The guide’s thermal-shock table, the large-size sheet’s page 9 for any 1825, 2220 or 2225 part, the safety sheet for S2, and a written answer from Walsin on what ΔT measures. We hold 28 datasheets, 451 pages, and send the file for your part number on request. See also our post on reflow profile and mounting, and the MLCC range page.
Our free cross-reference tool tells you which series a candidate belongs to, and therefore which sheet applies; ready stock shows what is held in Hong Kong as at 23 September 2026. Qualification stays with you: your oven, board and paste decide the profile. Confirm against both datasheets and qualify in your own circuit.
The short version
Seven of 26 Walsin MLCC files give process guidance on preheat. For 1210 and larger the guide limits ΔT to 130 °C and the large-size sheet says within 50 °C: an 80 °C gap on 501 export rows. The sheet’s 100 °C band for small chips applies to none of its parts, and its own 200 °C soak maximum rules out the 50 °C line above 250 °C. Rates are 4 °C per second on one file and 3 on five. 23,352 of 24,026 rows have only the guide.
Send us the part numbers on your BOM and we will tell you which sheet carries any preheat text for each. And a question back: when your process engineer wrote “preheat per datasheet”, which of the three documents was it?
Frequently asked questions
What is the Walsin MLCC preheat limit for reflow?
It depends on the document. The application guide limits ΔT to 190 °C at 1206 or smaller and 130 °C at 1210 or larger. The large-size sheet asks for a final preheat within 100 °C or 50 °C of the soldering temperature. Nineteen of 26 files state no limit.
Is the preheat rate 3 or 4 °C per second?
The large-size sheet says 4 °C per second. The S2, S2-H and S3 safety sheets and the two Mega Cap sheets say 3 °C per second. The application guide and 19 other files give no preheat rate at all.
Does the 50 °C preheat rule apply to every large MLCC?
No. It is printed on the large-size sheet, which covers 501 export rows at 1825, 2220 and 2225. The 2,971 other rows at 1210 or larger have the guide’s 130 °C limit or, for the 173 S2 rows, the safety sheet’s rate.
Why does the large-size sheet’s preheat rule conflict with its own profile?
At a 260 °C peak the rule needs a final preheat of at least 210 °C, but the profile table caps the soak at 200 °C. The two agree only up to a 250 °C solder temperature. This reading is ours; Walsin has not confirmed it.
Is the 120 to 150 °C preheat on a datasheet my reflow preheat?
No. It is the setup for the soldering heat test: 1 minute at 120 to 150 °C before a 260 °C dip, or 60 to 90 seconds at 150 ±10 °C on the FT sheet. It shows what the part survived. It is not a limit for your oven.
Where do I get the preheat limit for my series?
From Walsin, in writing. We hold 28 datasheets, 451 pages, and send the sheet for your part number on request. Ask what ΔT measures, then validate the profile on your own board.