Page 1 of 7 WFxxS_V07 Jan.2011
WF25S, WF20S, WF12S, WF08S, WF06S
±
±±
±5%, ±
±±
±10%, ±
±±
±20%
Power Surge Chip Resistors
Size 2512 , 2010 , 1206 , 0805 , 0603
Page 2 of 7 WFxxS_V07 Jan.2011
FEATURE
1. Power rating and compact size
2. High reliability and stability
3. Reduced size of final equipment
4. Surge protection
APPLICATION
• Power supply
• Measurement instrument
• Automotive industry
• Medical or Military equipment
DESCRIPTION
The resistors are constructed in a high grade ceramic body (aluminum oxide). Internal electrodes are added at
each end and connected by a resistive paste that is applied to the top surface of the substrate. The composition
of the paste is adjusted to request resistance to nominal value within tolerance which controlled by printing
process in this resistive layer.
The resistive layer is covered with a protective coat. Finally, the two external end terminations are added. For
ease of soldering the outer layer of these end terminations is a Tin (Pb free) alloy.
Fig 1. Consctruction of Chip-R
Page 3 of 7 WFxxS_V07 Jan.2011
QUICK REFERENCE DATA
Item General Specification
Series No. WF25S WF20S WF12S WF08S WF06S
Size code 2512(6432 ) 2010 (5025) 1206 ( 3216 ) 0805 (2012) 0603 (1608)
Resistance Tolerance ±5% ±10% ±20% (E24)
Resistance Range 1Ω ~ 1MΩ
TCR (ppm/°C) ± 100 ppm /°C
Max. dissipation at
T
amb
=70°C 1 W 1/2W 1/4W 1/8W 1/10 W
Max. Operation Voltage
(DC or RMS) 200V 200V 200V 150V 50V
Max. Overload Voltage
(DC or RMS) 400V 400V 400V 300V 100V
Climatic category (IEC
60068) 55/155/56
Note :
1. This is the maximum voltage that may be continuously supplied to the resistor element, see “IEC publication
60115-8”
2. Max. Operation Voltage : So called RCWV (Rated Continuous Working Voltage) is determined by
ValueResistancePower RatedRCWV ×=
or Max. RCWV listed above, whichever is lower.
MECHANICAL DATA(unit : mm)
Symbol
WF25S WF20S WF12S WF08S WF06S
L 6.30±0.20 5.00±0.20
3.10±0.15
2.00±0.15
1.60 ± 0.10
W 3.10±0.20 2.50±0.20
1.60±0.15
1.20±0.15
0.80 ± 0.10
T 0.60±0.15 0.60±0.10
0.55±0.10
0.50±0.10
0.45 ± 0.15
Tt 0.60±0.25 0.60±0.25
0.50±0.25
0.40±0.20
0.30 ± 0.15
Tb 0.60±0.25 0.60±0.25
0.50±0.25
0.40±0.20
0.30 ± 0.10
Page 4 of 7 WFxxS_V07 Jan.2011
MARKING
1. Each resistor is marked with a three-digit code on the protective coating to designate the nominal
resistance value.
2. Surge Resistor is prints underline on three-digit code for identification
Example:
472 = 4700Ω
Surge Performance
WFxxS series
.001
.01
.1
1
De-rating curve
The power that the resistor can dissipate depends on the operating temperature; see Fig.2
472
1ms 10ms 100ms 1s
1
1
0
100
10
0
0
2512
1206
Surge duration
Peak power
(Watt)
2010
10000
0603
0805
Page 5 of 7 WFxxS_V07 Jan.2011
MOUNTING
Due to their rectangular shapes and small tolerances, Surface Mountable Resistors are suitable for handling by
automatic placement systems.
Chip placement can be on ceramic substrates and printed-circuit boards (PCBs).
Electrical connection to the circuit is by individual soldering condition.
The end terminations guarantee a reliable contact.
SOLDERING CONDITION
The robust construction of chip
resistors allows them to be completely
immersed in a solder bath of 260°C for
10 seconds. Therefore, it is possible to
mount Surface Mount Resistors on one
side of a PCB and other discrete
components on the reverse (mixed
PCBs).
Surface Mount Resistors are tested for
solderability at 235°C during 2 seconds.
The test condition for no leaching is
260°C for 30 seconds. Typical
examples of soldering processes that
provide reliable joints without any
damage are given in Fig 3.
Fig 3. Infrared soldering profile for Chip Resistors WFxxS
CATALOGUE NUMBERS
The resistors have a catalogue number starting with .
WF20 S 472_ J T L
Size code
WF25 : 2512
WF20 : 2010
WF12 : 1206
WF08 : 0805
WF06 : 0603
Type code
S : surge
Resistance code
E24 : 3 significant digits followed
by no. of zeros and a blank
472 = 4K7
Tolerance
J: ±5%
K:
±10%
M:
±20%
Packaging code
T : 7” Reeled taping
Termination code
L = Sn base (lead
free)
Page 6 of 7 WFxxS_V07 Jan.2011
TEST AND REQUIREMENTS(JIS C 5201-1 : 1998)
TEST PROCEDURE REQUIREMENT
Temperature
Coefficient of
Resistance(T.C.R)
Clause 4.8
Natural resistance change per change in degree centigrade.
( )
6
121
12 10×
−
−
ttR RR
(ppm/°C) t
1
: 20°C+5°C-1°C
R
1
: Resistance at reference temperature
R
2
: Resistance at test temperature
Refer to “QUICK REFERENCE
DATA”
Short time overload
(S.T.O.L)
Clause 4.13
Permanent resistance change after a 5second application of
a voltage 2.5 times RCWV or the maximum overload voltage
specified in the above list, whichever is less.
∆R/R max. ±(1%+0.1Ω)
Resistance to
soldering heat(R.S.H)
Clause 4.18
Un-mounted chips completely immersed for 10±1second in a
solder bath at 260℃±5ºC no visible damage
∆ R/R max. ±(1%+0.05Ω)
Solderability Clause
Clause 4.17 Un-mounted chips completely immersed for 2±0.5second in
a solder bath at 235℃±5℃ good tinning (>95% covered)
no visible damage
Temperature cycling
Clause 4.19
30 minutes at -55°C±3°C, 2~3 minutes at 20°C+5°C-1°C, 30
minutes at +155°C±3°C, 2~3 minutes at 20°C+5°C-1°C, total
5 cycles
no visible damage
∆R/R max. ±(1%+0.05Ω)
Load life (endurance)
Clause 4.25 70±2ºC, 1000 hours, loaded with RCWV or Vmax,1.5 hours
on and 0.5 hours off ∆R/R max. ±(3%+0.1Ω)
Load life in Humidity
Clause 4.24 1000 hours, at rated continuous working voltage in humidity
chamber controller at 40°C±2°C and 90~95% relative
humidity, 1.5hours on and 0.5 hours off
∆R/R max. ±(3%+0.1Ω)
Bending strength
Clause 4.33 Resistors mounted on a 90mm glass epoxy resin PCB(FR4);
bending : 2 mm, once for 10 seconds
∆R/R max. ±(1%+0.05Ω)
Adhesion
Clause 4.32
Pressurizing force: 5N, Test time: 10±1sec. No remarkable damage or
removal of the terminations
Insulation Resistance
Clause 4.6 Apply the maximum overload voltage (DC) for 1minute R≧10GΩ
Dielectric Withstand
Voltage
Clause 4.7
Apply the maximum overload voltage (AC) for 1 minute No breakdown or flashover
Page 7 of 7 WFxxS_V07 Jan.2011
PACKAGING
Plastic Tape specifications (unit :mm)
Series No. A B W F E
WF25S 6.70±0.20 3.50±0.20
WF20S 5.50±0.20 2.80±0.20 12.00±0.30 5.50±0.05 1.75±0.10
WF12S 3.57±0.20 2.00±0.20
WF08S 2.40±0.20 1.65±0.20
WF06S 1.90±0.20 1.10±0.20
8.00±0.30 3.50±0.05 1.75±0.10
Series No. P1 P0 ΦD T
WF25S
WF20S Max. 1.2
WF12S
WF08S Max. 1.0
WF06S
4.00±0.10 4.00±0.10
1.0 0.0
50.1
+
−
Φ
0.65±0.05
Reel dimensions
Reel / Tape A B C D
7” reel for 8mm tape 9.00±0.50
7” reel for 12mm tape
Φ178.0±2.0
Φ60.0±1.0 13.0±0.2 12.4±1.00
Taping quantity
-1206 0805 0603 Chip resistors 5,000 pcs per reel.
-2010 2512 Chip resistors 4,000 pcs per reel.
