Walsin Rare Case Size: 4 of 234,815 Chip Resistors Sit at 0815

We counted the case size on all 234,815 rows of Walsin’s chip resistor export. The rarest Walsin case size is 0815, with exactly four part numbers. The second rarest is 0306, with ten. If your layout commits to either footprint, your entire choice is four parts or ten.

---

Venatech Limited, an authorised Walsin distributor in Hong Kong, holds all 203 of Walsin Technology (Walsin) parametric export files. This post is measured from two of them — Thick_Film_Low_Ohm_Current_Sense_Chip_Resistor__1of1.xlsx and Metal_Low_Ohm_Current_Sense_Chip_Resistor__1of1.xlsx — and every part number below was pulled out of those files, not written from memory. Every figure is a count of part numbers, never a count of pieces.

Which Walsin chip resistor case size has the fewest part numbers?

0815, metric 2037, with four part numbers. We grouped all 234,815 chip resistor rows by the Size column and found 19 distinct case size strings. The largest, 0603, carries 42,374 rows. The smallest, 0815, carries four. That is a ratio of 10,593 to one between the deepest footprint in Walsin’s chip resistor catalogue and the thinnest, and the thin end is where a layout decision quietly becomes a sourcing decision.

Case size (imperial/metric)	Part numbers	Series present	Distinct resistance values
0815 (2037)	4	1 of 58	2
0306 (0816)	10	1 of 58	10
1225 (3263)	47	1 of 58	47
02012 and 02014 arrays	194 each	1 each	—
0602*8 array	555	2 of 58	—
01005 (0402)	755	1 of 58	94
2512 (6432)	22,154	23 of 58	1,075

All four 0815 rows belong to one series — Thick Film Power Low ohm Current Sense Chip Resistor — and all four are rated 1 W. We have not seen this counted anywhere. The honest reading is not that 0815 is a bad footprint; it is that 0815 is a footprint with no bench behind it.

What is the second rarest Walsin case size, and what sits on it?

0306, metric 0816, with ten part numbers, all Metal Foil Low Ohm Power Sensing parts. We read every one of the ten. They run from 0.001 Ω to 0.010 Ω in exact 1 mΩ steps, every one at ±1% tolerance and 1/2 W. Nothing else in the whole 234,815-row export uses that case code. It is a ten-rung ladder with no sideways move available on it at all.

The temperature coefficient runs the opposite way to intuition. The four lowest values — 0.001 Ω through 0.004 Ω — are graded ≦±100 ppm/°C, and the six from 0.005 Ω up are graded ≦±50. So on this footprint the better TCR grade sits at the higher resistances, which is the reverse of what the thick film shelf does.

One formatting detail will bite a script. Nine of the ten write the resistance with three decimal places — 0.001Ω through 0.009Ω — and the tenth, WW06YR010FTL, writes 0.01Ω with two. A string sort puts it in the wrong place. We checked: the metal file does this nowhere else.

Does the tolerance letter in the 0815 part numbers agree with the tolerance column?

On two of the four, no. We read the four 0815 rows field by field. WW15WR005JTL carries a J where the conventional thick film reading is ±5%, and its Tolerance column states ±1%. WW15WR010FTL carries an F, conventionally ±1%, and its Tolerance column states ±5%. Both letters are contradicted by their own row, so we are flagging this rather than publishing a decode.

Part number	Size	Resistance	Tolerance (export)	Letter in code	TCR	Match / mismatch vs 0.010 Ω ±1% 1 W
WW15WR010FTL	0815 (2037)	0.010 Ω	±5%	F	≦±100	Match on resistance, size, 1 W; mismatch — ±5%, and the letter reads ±1%
WW15WR010JTL	0815 (2037)	0.010 Ω	±5%	J	≦±100	Match on resistance, size, 1 W; mismatch — ±5% tolerance
WW15WR005FTL	0815 (2037)	0.005 Ω	±1%	F	≦±200	Mismatch — half the resistance, twice the TCR
WW15WR005JTL	0815 (2037)	0.005 Ω	±1%	J	≦±200	Mismatch — half the resistance, and the letter reads ±5%
WW25WR010FTL	2512 (6432)	0.010 Ω	±1%	F	≦±1000	Match on resistance, tolerance, 1 W; mismatch — 2512 footprint, 10× the TCR
WW06YR010FTL	0306 (0816)	0.01 Ω	±1%	F	≦±50	Match on resistance and tolerance; mismatch — 0306 footprint, 1/2 W

Look down the Tolerance column rather than the letters and a cleaner pattern appears: the exported tolerance tracks the resistance value, not the code. Both 0.005 Ω rows read ±1% whatever the letter, and both 0.010 Ω rows read ±5% whatever the letter. The two F/J pairs are otherwise identical in every exported field — same size, same resistance, same TCR, same 1 W, same 7" reel taping, same Sn base (Lead free) termination.

How much choice do you actually lose at a rare footprint?

Almost all of it. We counted distinct resistance values per case size: 2512 offers 1,075, and 0815 offers two — 0.005 Ω and 0.010 Ω. That is a 537-to-1 collapse in the value ladder for a footprint change most layout reviews treat as cosmetic. 0306 offers ten values, every one of them below 0.011 Ω.

The practical consequence is that at 0815 you cannot re-tune the shunt value after the board is cut. Your sense amplifier gain, your ADC full-scale point and your shunt dissipation all have to land on 5 mΩ or 10 mΩ, and the only other lever you have is the tolerance, which on this footprint is tied to the value you picked. At 2512 the same decision has 1,075 landing spots.

That is the argument for checking footprint depth at schematic stage rather than at first build. A thin footprint is not a defect. It is a constraint that is invisible in a parametric selector, because a selector that lets you filter by resistance first will happily show you one row and never tell you it was the only one.

Does a four-part case size tell you anything about a part’s lifecycle?

No, and we will not assert it either way. We hold no affected-part list from any manufacturer, including Walsin, so we cannot tell you whether anything in this post is obsolete, nor would we guess. What we counted is a population: four rows at one case code on the day we parsed the export. That is a supply-breadth observation, not a lifecycle one.

The two are routinely confused, and the confusion is expensive in both directions. A footprint with four part numbers behind it is a single point of failure in a design because there is nowhere to move sideways, not because anything is going away. Walsin’s own full catalogue carries the standing line that products “may be discontinued without advance notice” — and we hold no record of what that line has ever been applied to, so read it as a policy rather than a warning about anything specific. It is exactly why a design that depends on one footprint and two resistance values deserves a second look, whoever makes the part.

Which rare footprint did we get wrong in our own published count?

0815, in our own post on current sense TCR. That post said the metal low-ohm export carries four footprints the thick film export does not, and named 1225, 0612, 0306 and 0815 across 74 rows. We re-measured it for this post. The 74-row figure is right and so are three of the four names — but 0815 sits in the thick film file, not the metal one. The metal-only footprints are 1225 (3263) with 47 rows, 0612 (1632) with 17 and 0306 (0816) with 10, which is 74 exactly.

While re-measuring we found something the first pass missed. 1225 appears in the chip resistor export under two different metric codes: 1225(3264) on 1,708 wide-terminal rows, and 1225(3263) on the 47 metal foil rows. Same imperial footprint, one digit apart in the metric code, and a text filter on either string silently drops the other set. We have not seen this counted anywhere, and it is the kind of defect that makes a parametric search look complete when it is not.

Publishing a correction to our own count is cheaper than letting it stand. It is also the reason we put the export filename next to every figure: so a reader can re-run the count and tell us when we are wrong.

What should a buyer in the United States or Germany check before design-in?

Check footprint depth before you check availability. A buyer in Michigan or Baden-Württemberg typically reaches for stock first, but on a four-part case size the binding question is whether a second value even exists. We checked the Venatech Hong Kong snapshot as at 23 September 2026: it holds 254 chip resistor codes, three of them WW low-ohm current sense parts, and none at 0815, 0306 or any wide-terminal footprint.

1. Ask how many part numbers share your footprint, not just whether yours is available. If the answer is four, the footprint is the risk, not the part.
2. Cross the whole list in one pass. Paste up to 500 part numbers or drop an Excel or CSV file into the free cross-reference tool. It is matched against Walsin’s published catalogue and states every difference from your original rather than hiding it, with filters for commercial or automotive grade and for soft termination, high temperature, safety certified, high Q / low ESR and low profile.
3. Check what is physically in Hong Kong on ready stock before you commit a build slot. It is a dated snapshot, not a live feed.

We will not tell you a part is equivalent. We will show you where it differs — and on a four-part footprint, telling you that the difference has nowhere to go is the more useful half.

For the two shelves these parts come from, see low ohm current sense: thick film vs metal. For the 1225, 1020 and 0612 family that shares the wide-terminal geometry, see wide terminal power resistors. The full range is on the Walsin chip resistor page.

The short version

Walsin’s rarest chip resistor case size is 0815, with four part numbers out of 234,815, all 1 W thick film low-ohm current sense. The second rarest is 0306 with ten, all metal foil, 1 mΩ to 10 mΩ in 1 mΩ steps. 0815 offers two distinct resistance values where 2512 offers 1,075. On two of the four 0815 codes the tolerance letter contradicts the Tolerance column, and across all four the exported tolerance tracks the resistance value rather than the letter — flagged, not decoded, because we hold no datasheet for the series. 1225 appears under two metric codes, 3264 and 3263, and a text filter on one drops 47 parts. And our own earlier post put 0815 in the wrong file; it is corrected above.

Send us the footprint, not just the value. We will tell you how many Walsin part numbers share it, what the second and third choices are, and where each one differs — and if the answer is four, we will say so plainly. Which of your current footprints have you never counted?

---

Frequently asked questions

<!– wp:rank-math/faq-block {"questions":[{"id":"faq-question-01","title":"What is the rarest case size in Walsin's chip resistor catalogue?","content":"0815, metric 2037, with exactly four part numbers out of 234,815. We counted the Size column on every row. All four are 1 W Thick Film Power Low ohm Current Sense parts offering only two resistance values, 0.005 Ω and 0.010 Ω. No other series in the catalogue uses that case code.","visible":true},{"id":"faq-question-02","title":"How many Walsin chip resistors use the 0306 case size?","content":"Ten, all Metal Foil Low Ohm Power Sensing parts. We read every row. They run 0.001 Ω to 0.010 Ω in 1 mΩ steps at ±1% and 1/2 W. The four lowest values are graded ≦±100 ppm/°C and the six above 0.004 Ω are graded ≦±50, so the better grade sits at the higher resistances.","visible":true},{"id":"faq-question-03","title":"Does the tolerance letter in a Walsin 0815 part number mean what it usually means?","content":"Not on two of the four. WW15WR005JTL carries a J and its Tolerance column reads ±1%; WW15WR010FTL carries an F and reads ±5%. The exported tolerance appears tied to the resistance value rather than the letter. We hold no datasheet for this series, so we flag it rather than publishing a decode.”,”visible”:true},{“id”:”faq-question-04″,”title”:”Does a case size with four parts mean those parts are being withdrawn?”,”content”:”No. We hold no affected-part list from any manufacturer and we will not infer one from a row count. A four-part footprint is a supply-breadth constraint, not a lifecycle signal. Walsin’s exports carry no lifecycle or status column anywhere in the 203 files we hold, so any such question goes to Walsin directly.”,”visible”:true},{“id”:”faq-question-05″,”title”:”Why does 1225 appear twice in Walsin’s chip resistor export?”,”content”:”Because the metric code differs between two files. We found 1225(3264) on 1,708 wide-terminal rows and 1225(3263) on 47 metal foil rows. Same imperial footprint, one digit apart. A text filter on either string silently drops the other 47 or 1,708 parts.”,”visible”:true},{“id”:”faq-question-06″,”title”:”Are any 0815 or 0306 parts in Venatech’s Hong Kong stock?”,”content”:”Not on the snapshot as at 23 September 2026. We checked it: 254 of the 1,125 codes are chip resistors and three of those are WW low-ohm current sense parts, none at 0815, 0306 or a wide-terminal footprint. Stock is always a dated snapshot, so ask us before you plan around it.”,”visible”:true},{“id”:”faq-question-07″,”title”:”How do I find out how many Walsin parts share my footprint?”,”content”:”Send the footprint with the BOM. The free cross-reference tool takes up to 500 pasted part numbers or an Excel or CSV file, matches them against Walsin’s published catalogue, and states every difference from your original. We will add the footprint count by hand where it matters, because no selector reports it.”,”visible”:true}],”listStyle”:””,”titleWrapper”:”h3″,”titleCssClasses”:””,”contentCssClasses”:””,”sizeSlug”:””} –>

---