Wide Terminal Power Resistors: 1225, 1020 and 0612 Compared

Walsin Technology (Walsin) builds wide terminal power chip resistors in three sizes —
1225 (3264), 0612 (1632) and 1020 (2550). Venatech Limited, an authorised Walsin
distributor in Hong Kong, holds 4,294 of them: 1,708 at 1225, 1,708 at 0612 and 878 at
1020. Power runs 3/4 W to 2 W, and the three sizes are not interchangeable.

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What is a wide terminal chip resistor?

A wide terminal chip resistor puts the terminations on the long sides of the chip instead
of the short ends. The current path across the resistive film gets shorter and wider, and
the thermal path into the board gets broader. The result is more rated power and lower
parasitic inductance in the same board area.

The geometry is the whole point. A 1206 is 3.2 mm long by 1.6 mm wide with terminations at
each 1.6 mm end. Rotate it ninety degrees and you get an 0612: 1.6 mm long by 3.2 mm wide,
terminations along the 3.2 mm edges. Heat leaves through a pad twice as wide.

Which wide terminal sizes does Walsin actually offer?

Three, and they are unevenly populated. Venatech’s extract of Walsin’s own parametric
data returns 4,294 parts in the series group Thick Film Wide Terminal Power
Chip-Resistor: 1,708 at 1225 (3264), 1,708 at 0612 (1632) and 878 at 1020 (2550). The
1020 has roughly half the choice of the other two.

Unique to Venatech’s data. Wide terminal is not one geometry. Walsin files three
different pad arrangements under a single series group — 1,708 parts at 1225 (3264),
1,708 at 0612 (1632) and 878 at 1020 (2550). The 1020 count is not half by accident: it
is the only one of the three sizes with a single rated power and no 100 ppm TCR option
at all. Measured from Walsin’s own export, not published anywhere.

The series group also hides a second series inside it. Of the 4,294 parts, 4,150 sit in
Thick Film Wide Terminal Power Chip-Resistor and 144 in Thick Film Wide Terminal Power
Low Ohm Chip Resistor. The low ohm series is 48 parts per size and covers 0.100 Ω to
0.91 Ω only. Everything from 1.0 Ω up to 1 MΩ is in the main series.

Why does the same 10 kilohm value give 3/4 W at 0612 and 2 W at 1225?

Because the sizes carry different power ratings, and at 0612 the rating also depends on
which part number prefix you pick. A 10 kΩ ±1% wide terminal part exists at 3/4 W, 1 W
and 2 W. The value, tolerance and packaging are identical across all three. Only the size
and the dissipation change.

Part number	Series group	Size	Resistance	Tolerance	TCR	Rated power	Match / mismatch vs WK25L1002FTL
WK25L1002FTL	Wide terminal	1225 (3264)	10 kΩ	±1%	≦±200 ppm	2 W	Reference part
WK20L1002FTL	Wide terminal	1020 (2550)	10 kΩ	±1%	≦±200 ppm	1 W	Value, tolerance, TCR match — size and power mismatch
WK12L1002FTL	Wide terminal	0612 (1632)	10 kΩ	±1%	≦±200 ppm	3/4 W	Value, tolerance, TCR match — size and power mismatch
WF25L1002FTLJ	Wide terminal	1225 (3264)	10 kΩ	±1%	≦±100 ppm	2 W	Size, value, tolerance, power match — TCR mismatch, tighter
WF12L1002FTLJ	Wide terminal	0612 (1632)	10 kΩ	±1%	≦±100 ppm	1 W	Value and tolerance match — size, TCR and power all mismatch
WF25P1002FTL	High power	2512 (6432)	10 kΩ	±1%	≦±100 ppm	2 W	Value, tolerance, power match — size and terminal geometry mismatch
WR25X1002FTL	General purpose	2512 (6432)	10 kΩ	±1%	≦±100 ppm	1 W	Value and tolerance match — size, power and geometry mismatch

Read the 0612 rows together. WK12L1002FTL is 3/4 W. WF12L1002FTLJ is the same size and
the same value at 1 W. The part number prefix, not the case code, carries the rating. A
BOM line that says “0612 10k 1% wide terminal” does not resolve to one part.

The 1225 rows behave differently. Both WK25L1002FTL and WF25L1002FTLJ are 2 W. The
prefix there buys TCR, not power. That asymmetry is the single most useful thing to know
about this series group.

Can I get a 100 ppm TCR wide terminal resistor at 1020?

No. Across the 4,294 parts Venatech holds, the ≦±100 ppm/°C TCR band appears 1,476 times
— 738 at 1225 and 738 at 0612. It appears zero times at 1020. Every 1020 wide terminal
part is ≦±200 ppm, 0 ~ 200 or 0 ~ 350.

Size	Parts held	Rated power options	TCR bands present	≦±100 ppm parts
1225 (3264)	1,708	2 W only	≦±100, ≦±200, 0 ~ 200, 0 ~ 350	738
0612 (1632)	1,708	1 W and 3/4 W	≦±100, ≦±200, 0 ~ 200, 0 ~ 250, 0 ~ 350	738
1020 (2550)	878	1 W only	≦±200, 0 ~ 200, 0 ~ 350	0

The pattern maps onto part number prefixes cleanly. WF25L… and WF12L… are the 830-part
blocks that carry ≦±100 ppm. There is no WF20L… block at all. The 1020 size exists only
as WK20L… at ≦±200 ppm and as 48 WW20L… low ohm parts.

If a design needs the wide terminal thermal path and a 100 ppm coefficient, the choice is
1225 at 2 W or 0612 at 1 W. The 1020 is out.

How does a wide terminal 1225 compare with a 2512 high power part?

Both reach 2 W at 10 kΩ ±1%. WK25L1002FTL is a 1225 wide terminal part; WF25P1002FTL
is a 2512 high power part. Same value, same tolerance, same rated power. The board area
differs, the pad orientation differs, and the TCR differs — the 2512 part is ≦±100 ppm.

The 1225 is 3.2 mm by 6.4 mm. The 2512 is 6.4 mm by 3.2 mm. Identical area, rotated. What
changes is where the heat goes and how long the current loop is. On a 2512 the current
runs the full 6.4 mm; on a 1225 it runs 3.2 mm through a 6.4 mm wide film.

That matters in two places. In a current sense leg the shorter loop lowers parasitic
inductance. In a hot layout the two 6.4 mm wide pads of the 1225 pull heat into the copper
over a longer joint, which is why the wide terminal part hits 2 W in a size the general
purpose series rates at 1 W — compare WR25X1002FTL above.

What does the size code in a Walsin wide terminal part number mean?

It means the reverse of what it means everywhere else in the chip resistor catalogue. In
the general purpose and high power series, 12 is 1206, 20 is 2010 and 25 is 2512. In
the wide terminal group the same two digits mean 0612, 1020 and 1225 — the rotated
geometry with the digits swapped.

Code at characters 3–4	What it means outside the wide terminal group	What it means inside it	Match / mismatch
12	1206 (3216) — 37,468 parts held	0612 (1632) — 1,708 parts held	Mismatch — same two digits, rotated geometry
20	2010 (5025) — 21,228 parts held	1020 (2550) — 878 parts held	Mismatch — same two digits, rotated geometry
25	2512 (6432) — 22,154 parts held	1225 (3264) — 1,708 parts held	Mismatch — same two digits, rotated geometry

The fifth character resolves it. Every one of the 4,294 wide terminal parts carries L in
position five: WK25L…, WF12L…, WW20L…. The general purpose series uses X or W
there, the high power series uses P or A, the high voltage series uses V or N.

So WK12L1002FTL is a 0612 and WR12X1002FTL is a 1206. Two characters apart, two
different footprints.

Which wide terminal part numbers contain an embedded space?

725 of the 4,294. Every one of them is a ±5% part. Walsin’s resistance code for ±5% values
uses two significant digits, then the number of zeros, then a blank — so WK25L103 JTL
carries a real space between 103 and JTL, and WK25L1002FTL does not.

This is documented behaviour, not a data error. Walsin’s own general purpose chip resistor
approval sheet spells out the catalogue number as “2 significant digits followed by no. of
zeros and a blank” for the ±5% E24 series. The ±1% E96 parts use four digits and need no
padding, so they have no space.

The practical effect is a search failure. Paste WK25L103 JTL into a distributor search
box that strips or rejects whitespace and you get nothing. Paste WK25L103JTL and you also
get nothing, because that string is not the part number. Both the space and its position
matter.

Part number as stored	Tolerance	Size	Rated power	Space present
WK25L1002FTL	±1%	1225 (3264)	2 W	No
WK25L103 JTL	±5%	1225 (3264)	2 W	Yes, before JTL
WK12L1002FTL	±1%	0612 (1632)	3/4 W	No
WK12L103 JTL	±5%	0612 (1632)	3/4 W	Yes, before JTL
WF12L103 JTLJ	±5%	0612 (1632)	1 W	Yes, before JTLJ

When should I use the wide terminal low ohm parts?

When you need a shunt under 1 Ω with a wide terminal footprint and 1 W to 2 W of
dissipation, and a metal element part is not required. The 144 WW…L… parts span 0.100 Ω
to 0.91 Ω at ±1% and ±5%, with one-sided TCR bands of 0 ~ 200, 0 ~ 250 and 0 ~ 350 ppm.

Part number	Series group	Size	Resistance	Tolerance	TCR	Rated power	Match / mismatch vs WW25LR100FTL
WW25LR100FTL	Wide terminal low ohm	1225 (3264)	0.100 Ω	±1%	0 ~ 350	2 W	Reference part
WW20LR100FTL	Wide terminal low ohm	1020 (2550)	0.100 Ω	±1%	0 ~ 350	1 W	Value, tolerance, TCR match — size and power mismatch
WW12LR100FTL	Wide terminal low ohm	0612 (1632)	0.100 Ω	±1%	0 ~ 350	1 W	Value, tolerance, TCR match — size and power mismatch
WW25NR100FTL	Metal low ohm current sense	2512 (6432)	0.100 Ω	±1%	≦±50	2 W	Value, tolerance, power match — size, geometry and TCR mismatch
WW25L0R10JTL	Wide terminal low ohm	1225 (3264)	0.100 Ω	±5%	0 ~ 350	2 W	Size, value, TCR, power match — tolerance mismatch

The TCR column is where the decision lands. The wide terminal low ohm parts quote a
one-sided band: 0 ~ 350 ppm means positive drift only, up to 350 ppm/°C. The metal element
part WW25NR100FTL quotes ≦±50 ppm, seven times tighter and two-sided.

Flagged for review. Venatech holds only two Walsin chip resistor datasheets —
Walsin_WR_General_Purpose_Chip_Resistor.pdf and
Walsin_MR_Automotive_Thick_Film_Chip_Resistor.pdf. Neither covers the wide terminal
series, and we hold no public URL for either file. The wide terminal land pattern, body
dimensions, derating curve and maximum working voltage are therefore not in our data.
Confirm the datasheet URL and request the wide terminal approval sheet from Walsin
before publishing any dimensional figure.

Flagged for review. Walsin’s export writes the 1225 metric code two ways: 1225(3264)
on the 1,708 wide terminal rows and 1225(3263) on 47 rows in the Metal Low Ohm Current
Sense group. One of the two is wrong. Confirm which before quoting the metric code to a
customer.

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FAQ

What is a wide terminal chip resistor used for?

Power dissipation and low parasitic inductance in a small board area. Putting the
terminations on the long edges shortens and widens the current path and broadens the
thermal path into the copper. Typical uses are switching regulator sense legs, gate drive
resistors and any node that runs hot in a tight layout.

What sizes does Walsin make wide terminal resistors in?

Three: 1225 (3264), 0612 (1632) and 1020 (2550). Venatech holds 1,708 parts at 1225, 1,708
at 0612 and 878 at 1020, all in the Thick Film Wide Terminal Power Chip-Resistor series
group. Rated power is 2 W at 1225, 1 W or 3/4 W at 0612, and 1 W at 1020.

Is an 0612 the same as a 1206?

No. The two digits are swapped deliberately. An 0612 is 1.6 mm long by 3.2 mm wide with
terminations on the long edges; a 1206 is 3.2 mm by 1.6 mm with terminations on the ends.
Different land pattern, different rated power, different inductance. They do not share a
footprint.

Can I get a 100 ppm TCR wide terminal resistor?

Yes at 1225 and 0612, no at 1020. Of the 4,294 wide terminal parts Venatech holds, 1,476
carry ≦±100 ppm — 738 at 1225 and 738 at 0612. Every 1020 part is ≦±200 ppm or a one-sided
band. The tight-TCR parts all use the WF prefix.

What is the highest power wide terminal resistor Walsin lists?

2 W, at 1225 (3264). Both the WK25L… and WF25L… blocks are rated 2 W, and the 48
low ohm WW25L… parts are also 2 W. The 0612 tops out at 1 W on the WF12L… parts, and
every 1020 part is 1 W.

Why does my Walsin wide terminal part number have a space in it?

Because it is a ±5% part. Walsin’s resistance code for the E24 ±5% series is two
significant digits, the number of zeros, then a blank. 725 of the 4,294 wide terminal part
numbers carry that space, all of them ±5%. The space is part of the part number and must be
reproduced exactly.

What resistance range do Walsin wide terminal resistors cover?

1.0 Ω to 1 MΩ in the main series, at every one of the three sizes. Below that, a separate
144-part low ohm series covers 0.100 Ω to 0.91 Ω, 48 parts per size. There is no wide
terminal part above 1 MΩ and none between 0.91 Ω and 1.0 Ω.

Do wide terminal resistors need a different land pattern?

Yes. The pads run along the long edges rather than the ends, so the footprint is not a
rotated version of the standard one and the paste volume differs. Venatech does not hold
the Walsin wide terminal land pattern drawing; ask us to request the approval sheet before
you commit a layout.

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Next step

Wide terminal selection fails on power and TCR, not on resistance. Send the BOM lines and
Venatech Limited, an authorised Walsin distributor in Hong Kong, will return the size, the
rated power that actually applies to that prefix, the TCR band, and whether the part
number carries an embedded space.

Send your BOM to Venatech · Browse the
Walsin chip resistor range · Read
Chip resistor power rating by case size
and Low-ohm current sense: thick film vs metal.

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