Development of TEX-B Solderable, Heat-Resistant,Triple-Insulated Winding Wireby Tadashi Ishii *, Yong Hoon Kim *, Atsushi Higashiura *2,Kunihiko Mori *3 and Isamu Kobayashi *4

Furukawa Electric's TEX-E general-purpose triple-insulated winding wire hascome into wide use due to the trend toward decreasing the size and cost ofswitching power supply transformers, and to the fact that transformers are easier to recycle. It
also makes possible the design of transformers that are environment-friendly. It is expected, however, that the trend in power supply units toward downsizing and higher efficiency will continue,
and this will raise problems with respect to heat generated by the component parts and theeffects of heat dissipation due to smaller size and higher mounting densities. It is essential thatthe materials used be of higher heat resistance.
To meet these needs we have developed TEX-B solderable, heat-resistant (Class B), tripleinsulated winding wire. Among the technologies employed were those of polymer alloying, polymer evaluation, and thin coating. Approvals have been obtained from certification authorities
world wide with respect to important safety standards relating to switching power supply transformers. This report describes the development of TEX-B wire, together with its characteristics.

ABSTRACT1.

INTRODUCTION

In recent years there have been advances in downsizing
electronic and electrical equipment, presenting various
needs with respect to power supply units--namely smallersize, lighter weight, higher efficiency, lower noise levels
and lower cost. The mainstream means used in the downsizing of power supply units is known as the switching
power supply, which is a type of DC stabilized power supply controlled by the switching method. Input from commercial-frequency AC power supply or DC power supply isconverted into power of a frequency above the audio frequencies and then controlled and rectified to provide thedesired DC output. The conversion into high-frequency
power is accomplished by high-speed switching of semiconductors. In a power supply unit of this type, increasing
the switching frequency allows a reduction in the numberof transformer windings, resulting in a smaller unit. When
it is desired to have an even slimmer unit or attain higherdensity mounting, materials of higher heat resistance must
be used, since heat generation from the component partsand poorer heat dissipation will cause problems.
We have accordingly developed the TEX-B solderable,
heat-resistant, triple-insulated winding wire, which meetsthese requirements. Each of the three layers of insulation
over the conductor of the TEX-B winding wire is approxi* Polymer Engineering Center, Ecology and Energy Lab.
*2 Organic Analysis Sec., Ecology and Energy Lab.
*3 Engineering Dept., Magnet Wire Div.
*4 Hiratsuka Plant, Magnet Wire Div.

mately 33 µm thick, or about 100 µm in total. In responseto the requirements of the safety standards, any two of theinsulation layers can withstand a voltage of 3000 Vrms for
1 min. TEX-B also has Class B heat resistance, and features better electrical endurance and a higher voltage forthe inception of partial discharge. This report describes
the development of TEX-B wire, together with its characteristics.

2.

SAFETY STANDARDS AND THE ROLE
OF TRIPLE-INSULATED WIRE

There are two important safety standards for final products that use switching power supplies: IEC 60065 "Safety
Requirements for Mains Operated Electronic and Related
Apparatus for Household and Similar General Use" andIEC 60950 "Safety of Information Technology Equipment"
issued by the International Electrotechnical Commission.
The primary aspects of safety requirements for transformers are the insulating characteristics between the primary and secondary coils, and the provision of creepage
distance. When enameled wire is used (an enamel film is
not recognized as an insulator), an interleaving tape orbarrier must be interposed between the primary or secondary coils. When Furukawa Electric's triple-insulatedwire is used, on the other hand, the insulation layer fulfills
that role so there is no need for interleaving tape or a barrier, simplifying the structure and reducing the size of thetransformer.

13.

DEVELOPMENT OF TEX-B

When it is desired to achieve an even thinner profile, higher efficiency and greater mounting density, a material withhigher heat resistance is required. This is because of theproblem posed by heat generated from the component
parts and a deterioration of heat dissipation performance.
An investigation was therefore conducted drawing on thetechnologies of polymer alloying, polymer evaluation, andthin coating.

Continuous operating temperature (°C)

3.1 Polymer Alloying Technology
The basic requirement for any polymer to be used intransformers is that it possess the various characteristics
required for winding wire. Of these the primary objective
was Class B heat resistance, and solderability and resistance to chemical attack were also identified as important.
It is difficult for a winding wire to achieve both Class B
heat resistance and solderability. Let us consider one of
the mechanisms of solderability. When the triple-insulated
wire is dipped in the solder melt the insulation either melts
or decomposes from the heat. The solder then instantly
enters into the space between the insulation layer and theconductor, the conductor is wetted with solder and in aSuper-engineering
plastics
200

Fluoride-andpolysulfide-based
Target
range

150
130
Class B

Engineering plastics:
Polyamide-andpolyester-based

100

Polyolefin-based
50
05

10

1520

⇒No adhesion

Soldering time (s)Figure 1

short time the solder adheres to the conductor.
On the other hand the insulation layer must be sufficiently heat resistant. It is essential that the heat of thesolder not melt or decomposes the insulation too easily,
and we have accordingly investigated the relationshipbetween heat resistance and solderability for heat-resistant thermoplastic resins. As a result, it was found that all
resins having good solderability were lower in heat resistance than Class B (see Figure 1).
It was here that the techniques of polymer alloying wereemployed to combine resins with the mutually exclusive
properties of heat resistance and solderability to produce
a resin that has both. A variety of resins were combinedand the proportions optimized until a specially modified
polyethersulfone resin was found that satisfied therequirements. It has a morphology in which a resin having
the property of solderability forms a fine dispersion evenly
through a heat-resistant matrix resin (Photo 1).
A number of heat-resistant thermoplastic resins wereconsidered for use as a resin resistant to heat and chemical attack, and from among them we selected polyphenylenesulfide which is capable of high-speed thin coating. It
was decided that the basic structure of TEX-B heat-resistant triple-insulated winding wire would be a 1st and 2nd
layer of modified polyethersulfone and a 3rd layer ofpolyphenylenesulfide.
3.2 Thin Coating Technology
Thin coating technology is used in TEX-E general-purpose
triple-insulated winding wire, and was also adopted indeveloping TEX-B. High-speed thin coating of resin withhigh heat resistance and thermoplasticity requires that theresin have a suitable melt viscosity and the melt tensile
strength required for high-speed coating. The coating
characteristics of a resin can be found by establishing themelt viscosity of the resin and its viscosity behavior whenmelted. The process involved repeated comparisons ofactual coating characteristics and optimization of coatingconditions.

Solderability of engineering plastics.

4.

TEX-B CHARACTERISTICS

In this section we will discuss the properties of TEX-B,
including the basic characteristics of winding wire plus
electrical properties and solderability. The electrical properties deserve particular attention.

Photo 1

2

Morphology of modified polyethersulfone (by SEM).

4.1 General Characteristics
The main characteristics of TEX-B are shown in Table 1,and compared with those of TEX-E general-purpose tripleinsulated winding wire which has Class E heat resistance.
It can be confirmed that in each of the characteristics
there is virtually no difference between the two. It was also
confirmed that, of the safety standards relating to switching power supplies, the conditions for Class B are satisfied
with respect to Annex U and Modified Annex C of IEC
60950. The surface hardness of the TEX-B insulation
layer, however, was lower than that of enameled wire. Full

Furukawa Review, No. 222002

Comparison of Characteristics of TEX-B and TEX-E.
TEX-B

TEX-EConductor diameter (mm)

0.400

0.400

Overall diameter (mm)

0.600

0.600

Insulation thickness (mm)

0.100

0.100

Dielectric breakdown Voltage

(kV)

26.0

23.4

Solderability [420°C](sec)< 103.0

Solderability [450°C]

(sec)

5.0

—

1D

1D

Dimensions

Heat shock [150°C ✕1 hr]
Cut-through

(°C)

245

231

Unidirectional abrasion

(N)

21.57

19.31

Reciprocated abrasion(times)Static friction coefficient

285
0.085(mm)

4.0

< 0.5

Xylene4H

3H

Styrene3H

3H

Annex U.2.1

PassPassAnnex U.2.2

PassPass

Adherence
Chemical resistanceIEC 60950

2600.11

Annex U.2.3[Class E]

Pass

PassAnnex U.2.3[Class B]

Pass—

Pass

Pass

Modified Annex C[Class E]

Pass

Pass

Modified Annex C[Class B]

Pass—Annex U.2.4

TEX-B
2000

Voltage (V0-peak)

Characteristics

2500

TEX-E
1500

1000

500

0050

100

150

Temperature (°C)

Figure 3

Comparison between partial discharge inception
voltages of TEX-B and TEX-E at 10 kHz.

10000010000

Life (hr)Table 1

1000

10010120

140160200240

Temperature (°C)

Figure 4

Temperature index for TEX-B.

Applied voltage (kV/0.1 mm)

104.3TEX-B
TEX-E

1110100

1000

10000

Time (hr)Figure 2

Comparison between V-t characteristic of TEX-B andTEX-E at 50 Hz.

attention must be paid to tension during winding. On theother hand TEX-B is solderable, but requires a slightly
higher solder melt temperature than TEX-E.
4.2 V-t Characteristic
Figure 2 shows the results of measurement of V-t characteristics at room temperature for commercial-frequency(50 Hz) AC. The lifetime is considerable longer for TEX-B
than for general-purpose TEX-E. It was confirmed thatelectrical endurance is improved, and this is attributed tothe improved heat resistance of the insulation layers ofwhich TEX-B is made, so that it was able to withstand theheat generated when the voltage was applied.

Temperature Dependence of Partial Discharge
Inception Voltage
Figure 3 shows the results of measurements of the temperature dependence of the partial discharge inception
voltage with a straight-polarity rectangular wave of 10kHz, a pulse width of 10 µs and a detection sensitivity of
10 pC. For TEX-B wire the rated temperature is 130°C,but even at 140°C the same level of partial discharge
inception voltage was maintained as for room temperature, whereas for the general-purpose TEX-E wire there
was a tendency for the voltage to decrease as temperature rose. One reason for this superiority of TEX-B overTEX-E is thought to be the higher glass transformation
temperature Tg of the resins used in the insulation layersof TEX-B.
4.4 Thermal Endurance Characteristic
The thermal endurance characteristic was investigated inconformance to the standard for establishing the temperature index for enameled wire (IEC 60172), and Figure 4shows the results obtained. It was confirmed by an
Arrhenius plot that a temperature index corresponding to alife of 20,000 hours satisfies the level of Class B heatresistance.

3Table 2

Safety codes certifying TEX-B wire.

Test-house

Country

CSA

CanadaSafety CodeCAN/CSA-C22.2 No.1-98
CSA Std C22.2 No.66-1988
CAN/CSA-C22.2 No.223-M91
No.234-M90
No.60950-00
CAN/CSA-E60065-00
IEC No.60065 (6th Ed)
UL 506, 1310, 1585, 1411, 1950, 3rd Ed

NEMKO

NorwayIEC60950 3rd
IEC60950/FDIS 4th Ed
IEC60065/FDIS 7th Ed

Photo 2

TEX-B wire after soldering.

ULUSAVDE

GermanyUL1950 (OBJT2)DIN EN 60950 (VDE 0805):2001-12
EN 60950:2000
IEC 60950:1999+corr.2000 modif.
DIN EN 60065:1998 (VDE 0860:1999-10)

4.5 Solderability
A 40-mm length of TEX-B wire was immersed in a solder
melt and the length to which solder adhered was measured. It was found that at 450°C solder adhered over 30
mm or more within 5 sec (Table 1), a result that was
somewhat inferior to that of TEX-E wire. Solderability wasthen confirmed for TEX-B when wound onto phenol resinbobbin material. Observation of the adherence of solder tothe bobbin showed virtually no damage with respect to theTEX-B wire, confirming the feasibility of highly reliable soldering (Photo 2).

5.

OBTAINING SAFETY CERTIFICATION

TEX-B wire has received approval from certification bodies in several countries as complying with safety standards for switching power supplies (Table 2). Approvals
were received in October 2001 from CSA (Canada), andfrom NEMKO (Norway) in November, from UL (USA) inDecember, from VDE (Germany) in January 2002, andfrom BSI (UK) in March.

4

IEC 60065:1998 mod.
BSI

UK

BS EN60065:1998
IEC 60065 6th Ed:1998
BS EN 60950:2000

6.

CONCLUSION

We have developed TEX-B solderable, heat-resistant(Class B), triple-insulated winding wire. TEX-B wire hasreceived approval under important safety standards relating to switching power supplies from certification authorities in several nations. It is proposed that UL1446(Systems of Insulation Material - General) will be obtainedfor insulation systems including bobbin materials.
In terms of trends in switching power supply technologies, investigations are being actively carried out onachieving slimmer profiles and higher efficiency, as wellas greater mounting density. It is anticipated that
Furukawa Electric's triple-insulated winding wire will play arole in a widening range of fields.

Furukawa Review, No. 222002