A single mistyped character turns a Walsin thick film resistor into a thin film one. We measured every pair of part numbers in the catalogue that differ by exactly one character and cross a family boundary: there are 6,836 of them, all between thick film and thin film, and all 6,836 differ at position 5.
Venatech Limited, an authorised Walsin distributor in Hong Kong, holds all 203 parametric export files published by Walsin Technology (Walsin). This post is written from the 114 of those files that hold parts — 390,465 part rows resolving to 359,135 distinct part numbers. We compared every part number against every other part number of the same length, position by position, and kept the pairs that belong to different product families. Every part number below is real. The thick film side comes from Thick_Film_High_Power_Chip_Resistor_1_1_2W.xlsx and Thick_Film_Anti_Surge_Chip_Resistor_1.xlsx; the thin film side from Tantalum_nitride_Thin_Film_Chip_Resistor_MF_Series_1.xlsx.
Does any Walsin part number appear in two product families?
No — zero of 359,135, across all 28 family pairs. We intersected the distinct part-number sets of the eight families pairwise and every one of the 28 intersections is empty. That is the good news and we have published it before: the complete code is a clean key, so a lookup on the full string can never return two different components. The bad news is what sits one character away from it.
| Family pair | Part numbers compared | Shared part numbers | Deepest shared prefix | Pairs one character apart | Match / mismatch for a cross-reference key |
|---|---|---|---|---|---|
| Chip resistor x thin film | 234,401 x 93,914 | 0 | 4 characters (MF12) |
6,836 | Mismatch — unique as a key, one keystroke apart in practice |
| Chip resistor x varistor | 234,401 x 379 | 0 | 4 characters (SR10) |
0 | Match — lengths differ, 12 against 9 |
| Thin film x RF | 93,914 x 457 | 0 | 3 characters (SF1) |
0 | Match |
| MLCC x RF | 23,601 x 457 | 0 | 2 characters (RF) |
0 | Match |
| MLCC x antenna | 23,601 x 44 | 0 | 2 characters (RF) |
0 | Match |
| RF x antenna | 457 x 44 | 0 | 3 characters (RFA) |
0 | Match |
| The other 22 pairs | — | 0 each | 0 to 2 characters | 0 each | Match |
6,836 cross-family pairs sit at a Hamming distance of one, and every single one of them is a chip resistor against a thin film resistor. No other family pair produces a single one. We have not seen this counted anywhere. 6,273 distinct part numbers are involved — 4,560 thin film and 1,713 thick film chip resistor — which is 1.7 percent of the catalogue carrying a one-character neighbour in a different product family.
How close do the eight families actually get to colliding?
Four characters, and only twice. We computed the deepest shared prefix for every one of the 28 family pairs. The record is 4 characters, reached by exactly two pairs: MF12 shared by the chip resistor and thin film exports, and SR10 shared by the chip resistor and varistor exports. Twenty-two of the 28 pairs never share more than 2 characters, and 5 pairs share none at all.
SR10 is the harmless one, and it shows why length matters. SR10W1005FTL is a 12-character anti-sulfuration thick film chip resistor from Thick_Film_General_Purpose_1_1_2W.xlsx; SR101K05D is a 9-character varistor from Walsin_MOV_ALL.xlsx. They share four opening characters and can never be confused by a full-string match, because no fixed-width or truncation rule in a BOM tool would bring a 9-character code and a 12-character code into contact.
MF12 is the dangerous one, because both sides are 12 characters, both sides end FTL, and both sides carry the same resistance in the same case size. We checked all 2,460 chip resistor codes beginning MF12 against all 20,520 thin film codes beginning MF12. None of them collide. Thousands of them are one character apart.
What changes when that one character changes?
The resistor technology, the temperature coefficient and the power rating — while the resistance, the tolerance and the case size stay identical. That is what makes it worth a post. We pulled the full export row for six real part numbers, three thick film and three thin film, each pair differing only at position 5.
| Part number | Family and series | Size | Resistance | Tolerance | TCR, ppm per degree Celsius | Rated power | Match / mismatch against its one-character neighbour |
|---|---|---|---|---|---|---|---|
MF12P1651FTL |
chip resistor — Thick Film High Power (Automotive) | 1206 (3216) | 1,650 ohm | plus or minus 1% | not more than plus or minus 100 | 1/2 W | reference |
MF12F1651FTL |
thin film — Tantalum nitride MF Series | 1206 (3216) | 1,650 ohm | plus or minus 1% | not more than plus or minus 15 | 2/5 W | Match on size, resistance, tolerance. Mismatch on film type, TCR (15 against 100) and rated power |
MF12E5361FTL |
chip resistor — Thick Film Triple Power Surge (Automotive) | 1206 (3216) | 5,360 ohm | plus or minus 1% | not more than plus or minus 100 | 3/4 W | reference |
MF12R5361FTL |
thin film — Tantalum nitride MF Series | 1206 (3216) | 5,360 ohm | plus or minus 1% | not more than plus or minus 25 | 2/5 W | Match on size, resistance, tolerance. Mismatch on film type, TCR and rated power — 3/4 W down to 2/5 W |
MF12Q1782FTL |
thin film — Tantalum nitride MF Series | 1206 (3216) | 17,800 ohm | plus or minus 1% | not more than plus or minus 50 | 2/5 W | reference |
MF12W1782FTL |
thin film — Tantalum nitride MF Series | 1206 (3216) | 17,800 ohm | plus or minus 1% | not more than plus or minus 10 | 2/5 W | Match on everything published except TCR — 10 against 50, a 5x difference from one character |
Read the first pair again. MF12P1651FTL and MF12F1651FTL are both 1206, both 1,650 ohm, both plus or minus 1 percent. One is thick film rated at 1/2 W with a temperature coefficient of not more than plus or minus 100 ppm per degree Celsius. The other is tantalum nitride thin film rated at 2/5 W with not more than plus or minus 15. A circuit that needs the 15 and receives the 100 does not fail on the bench; it drifts in the field. We hold a datasheet for neither of these series — our two resistor datasheets cover the WR and MR series only — so confirm both against Walsin’s own site before you commit.
The last pair is inside the thin film family and shows the same mechanism at full strength: MF12Q1782FTL and MF12W1782FTL publish identical size, resistance, tolerance and power, and differ only in TCR, 50 against 10.
Which character position carries the risk, and why always the same one?
Position 5, on all 6,836 pairs, with no exceptions. We recorded which index differed on every cross-family pair at Hamming distance one. The distribution is not a distribution: 6,836 of 6,836 differ at character 5, and 0 differ at any of the other 11 positions. Characters 1 to 4 carry the series stem and the case size; characters 6 to 12 carry the resistance value and the termination and packaging suffix. Position 5 is the field that moves.
This is a measurement, not a decode, and we will not tell you what Walsin intends position 5 to mean. What we can say is checkable: across the thin film MF export, position 5 takes the values that separate the TCR grades we tabulated above — F, R, Q and W map to not more than plus or minus 15, 25, 50 and 10 respectively on the rows we pulled — while on the thick film side the same slot holds P and E on parts whose TCR is not more than plus or minus 100.
The operational consequence is narrow and sharp. An optical character recognition pass over a reel label, a hand-retyped line on a BOM, or a find-and-replace across a part-number column has exactly one place it can go wrong and produce another real, orderable, in-catalogue part. Not an error. A different component. For the wider structural argument about why no parser can rescue you here, see 10 lengths across 8 Walsin families.
How do I tell thick film from thin film when the code looks identical?
By the export file the row came from, and by the TCR, because the part number string will not tell you. We checked: MF is used as an opening prefix by both the thin film export, on 20,520 part numbers, and the chip resistor export, on 14,791. Neither side carries a column stating the film type. The thin film rows name it in the free-text Series field — “Tantalum nitride Thin Film Chip Resistor / MF Series” — and the thick film rows name a different series string in the same column.
Three checks, in order:
- Read the TCR. Thin film MF rows in our extract publish not more than plus or minus 10, 15, 25 or 50. Thick film MF rows publish not more than plus or minus 100 or 200. There is no overlap in the pairs we pulled.
- Read the rated power. Every thin film MF row we pulled is 2/5 W. The thick film neighbours are 1/2 W and 3/4 W.
- Read the
Seriesstring, not the part number. It is the only field in either export that names the technology, and it is free text.
For the specification-level comparison of the two technologies, see thin film against thick film chip resistors. The precision end of that argument is in where the TCR curves cross over.
What should I send us if I am not sure which one I have?
The whole line as it appears on your BOM, including whatever your system did to it. Paste up to 500 part numbers, or drop your Excel or CSV, into the free cross-reference tool — matched against Walsin’s published catalogue, with every difference from your original stated rather than hidden, and a filter for commercial or automotive grade. We will tell you which family the code resolves to and which neighbours sit one character away.
We will not tell you a part is equivalent. We will show you where it differs — and in this family, the difference is one character and a 5x change in temperature coefficient. What is physically 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 thin film range sits on the thin film page. We hold 28 Walsin datasheets, 451 pages; ask for the one covering your part number and it will be in your inbox, and if we hold none for your series we will say so on the same day.
The short version
Zero of 359,135 Walsin part numbers appear in two product families, and all 28 pairwise intersections are empty, so the full code is a clean key. 6,836 cross-family pairs are one character apart, every one of them a thick film chip resistor against a thin film resistor, and every one of them differing at position 5. 6,273 distinct part numbers are involved. One character changes the film type, the temperature coefficient and the rated power while the case size, resistance and tolerance stay identical: MF12P1651FTL and MF12F1651FTL are both 1206, 1,650 ohm, plus or minus 1 percent, and their TCR figures are not more than plus or minus 100 and not more than plus or minus 15. We hold no datasheet for either series and we say so. Qualification stays with you — our job is to make sure the part number you qualify is the part number you ordered.
Send us the resistor lines off your BOM and we will return, for each one, the family it resolves to, the TCR the export publishes, and any part number in the catalogue that sits one character away from it. And a question back: if your goods-in check reads the reel label by eye, which character is the person checking?
Frequently asked questions
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Can the same Walsin part number belong to two different product families?
No. We intersected the distinct part-number sets of all eight families pairwise and every one of the 28 intersections is empty: zero of 359,135 part numbers appears twice. A lookup on the complete code can never return two different components. The risk is not collision, it is near-collision.
How many Walsin part numbers are one character away from a part in another family?
6,836 pairs, involving 6,273 distinct part numbers — 4,560 thin film and 1,713 thick film chip resistor. Every one of the 6,836 pairs is a chip resistor against a thin film resistor, and every one differs at character position 5. No other family pair in the catalogue produces a single one-character neighbour.
What is the difference between MF12P1651FTL and MF12F1651FTL?
Both are 1206 case size, 1,650 ohm, plus or minus 1 percent. The thick film part is rated 1/2 W with a temperature coefficient of not more than plus or minus 100 ppm per degree Celsius. The tantalum nitride thin film part is rated 2/5 W with not more than plus or minus 15. The film type, TCR and power all change on one character.
Does the Walsin export have a column that says thick film or thin film?
No. Neither the chip resistor export nor the thin film export carries a film-type column. The technology is named only inside the free-text Series string — the thin film rows read “Tantalum nitride Thin Film Chip Resistor / MF Series”. The most reliable published discriminator is the TCR figure, which does not overlap between the two.
Which part of a Walsin resistor part number should I check most carefully?
Position 5. On all 6,836 cross-family one-character pairs we measured, position 5 is the character that differs, and no other position differs on any of them. Characters 1 to 4 hold the series stem and case size; characters 6 to 12 hold the resistance value and the suffix. Position 5 is where a transcription error produces another real part.
Do you hold a datasheet for the Walsin MF series?
No. We hold 28 Walsin datasheets, 451 pages, of which 2 are chip resistor documents covering the WR and MR series only. There is no MF datasheet in our library, thick film or thin film. Confirm every specification on those lines against Walsin’s own site and ask us for the sheet if one is issued.
How close do any two Walsin families get to sharing a part number?
Four characters of shared prefix, reached by exactly two family pairs: MF12 between chip resistor and thin film, and SR10 between chip resistor and varistor. Twenty-two of the 28 pairs never share more than two opening characters, and five pairs share none at all.