Furukawa ElectricNewNew Products
Products

Development of High-Performance Alloys forElectronic Connectors

1.

2.

INTRODUCTION

In recent years there have been rapid advances in mobileequipment and digital home appliances, as well as in thetrend to automotive electronics, leading to improved performance and increased density of electronic components and the use of large numbers of miniaturized connectors. Figure 1 shows connectors that illustrate thistrend. The example shown in Figure 1 (a), known as a Bto-B connector, is formed in a complex “bellows” bend,
while the FPC connector in Figure 1 (b) is the type connected via a flat cable. The technological issues involved
with the most advanced connectors are small size, low
profiled, narrow pitch, increased number of poles, andhigher transmission speeds. Further requirements arelower cost and higher quality.
The copper alloys used in the miniaturized connectors
for electronic components need to have strength, conductivity, stress relaxation properties and bending workability, and as high-performance alloys that satisfy theserequirements, we have developed EFTEC-97 and EFTEC98S, as well as F5218 and F5248S.
Table 1 shows the composition (typical values), andTable 2 selected mechanical and physical properties forthese new alloys. EFTEC-97 and -98S are materials witha Cu-Ni-Si (Corson) alloy base, to which trace amountsof Zn, Sn, Mg and Cr have been added. These are materials in which the stress relaxation properties and bending
workability have been improved by heat treatment control
technology to effect the nano-level fine precipitation of
Ni2Si compound. F5218 and F5248S, on the other hand,
are materials with a base of spring phosphor bronze withtrace amounts of Fe and Ni in which crystal grain diameter is controlled, thereby increasing strength and improving bending workability. None of these materials contains
any substance that imposes environmental load as regulated by RoHS directive or similar standards.

（a）

BENDING WORKABILITY

Bellows connectors like that shown in Figure 1 (a) musthave superior bending workability to accommodate to complex bends, and the material must also be strong. Figure 2
shows the relationship between bending workability (90°Wbend) parallel to the rolling direction (BW) and 0.2 % yieldstrength (YS). Workability in the longitudinal axis is normalized for sheet thickness (t). Comparing with the workabilityof C5210 (Spring phosphor bronze), all the new alloys show
improved strength while bending workability is also satis-

Table 1EFTEC-97

Cu-2.3Ni-0.55Si-0.15Sn-0.5Zn-0.1Mg

EFTEC-98S

Cu-3.75Ni-0.9Si-0.15Sn-0.5Zn-0.1Mg-0.2Cr

F5218

Cu-8Sn-0.1Fe-0.15Ni-0.03P

F5248S

Cu-10Sn-0.1Fe-0.15Ni-0.03P

Table 2

EFTEC-98S

F5218

F5248S(a) Bellows connector
Figure 11 mm(b) FPC connector

Typical miniaturized connectors.

Selected properties of copper alloys developed here
(typical values for each quality level).

EFTEC-97（b）

0.5 mmChemical composition of copper alloys developed
here (typical values). (mass %)TemperTS(MPa)YS(MPa)

Hv

HC

690

600

205

EH

740

660

225

SH

780

750

235

H

810

725

245

EH

850

750

265

SH

910

870

280

ESH

980

950

300

H

775

730

230

EH

800

750

250

SH

850

810

260

ESH

900

860

265

XSH

940

910

270

H

810

780

230

EH

855

810

250

SH

930

885

260

ESH

965

920265XSH

1020

980

270E(GPa)

EC(%IACS)

132

40

132

3511013109

12

TS: Tensile strength YS: Yield strength (0.2 %) Hv: Hardness
E: Young's modulus EC: Electrical conductivity

Furukawa Review, No. 32

2007

87

Development of High-Performance Alloys for Electronic Connectors

factory, and at YS≒680 MPa, all the alloys show R/t≒0.
Further, while increased strength does produce deterioration in workability, EFTEC-98S workability at YS≒750
MPa shows R/t≒1, a satisfactory level of bending workability equivalent to C1720 (HM temper).

3.

STRENGTH AND YOUNG’S MODULUS

FPC connectors like that shown in Figure 1 (b) requirematerials of high contact pressure, that is to say, highstrength. (It is considered that of the materials shown inTable 2, the higher quality categories--SH, ESH andXSH--are suitable.) Among these, F5218 and F5248S,
because of their characteristically low Young’s modulus,
undergo greater sag (displacement) when subjected tothe same contact pressure and have less change in displacement with respect to changes in contact pressure,so as a result reliability is higher. EFTEC-97 and -98S, on
the other hand, have a higher Young’s modulus, giving
them the advantage that at displacements limited by low
profiled, high contact pressure can be obtained with only
slight sag (displacement).

4.

STRESS RELAXATION PROPERTIES

Figure 3 shows the results of an investigation of stressrelaxation properties*. Since EFTEC-97 and 98S haveexcellent stress relaxation properties, they suffer a smaller
long-term drop in contact pressure, even in higher-temperature environments, contributing to the reliability ofelectrical contact. F5218 and F5248S, for their part, haveproperties equal or superior to spring phosphor bronze(C5210).
Figure 4 shows simulation of actual connectors, plotting
the results of direct measurement of changes in the contact pressure (load) when heated at 150°C for (1) cantilever beam test pieces, and (2) 90°V-bent test pieces towhich a load stress of 0.8 x YS has been applied. The rateof change in longitudinal contact pressure is normalized
to initial contact pressure and the relationship to heat
treatment time is shown. For C5210, contact pressure
dropped by approximately 40-50 % over 200 hr for bothtest pieces (1) and (2), but with EFTEC-97 higher contactpressure was maintained, the rate of drop being in theorder of 10-20 % for both test pieces (1) and (2).
* Test method: in conformity to EMAS-3003, cantilever beam
method, test temperature: 150°C, applied stress: 0.8 x YS.

EFTEC－97

EFTEC-98S

F5218

F5248S

C1720

C5210

4120Better

32

10600

650

700

750

800

850900

Yield strength (MPa)Figure 2Contact pressure drop rate (%)

Bending workability R/t

51008060
40
200Relationship between bending workability (90°Wbend) and 0.2 % yield strength.

0Figure 4110

EFTEC-98S(H)F5218(EH)

F5248S(EH)

C5210(EH)

C1720(HM)100BetterStress relaxation (%)

Electrical conductivity (%IACS)

EFTEC-97(EH)

Stress relaxation properties.

C5210 ②1101001000

Change in contact pressure drop rate (stress relaxation properties).

60

C17510EFTEC-97E
EFTEC-97

40

C17530C17200

C2680

20

EFTEC-98S

F5218/F5218S
F5248S

C5210

C1990

0400

1000

500

600

700

800

1000

900

Tensile strength (MPa)Heat treatment time (hr)Figure 3

C5210 ①EFTEC-97 ②

Heat treatment time (hr)100

10EFTEC-97 ①

Figure 5

Relationship between tensile strength and electricalconductivity.

Furukawa Review, No. 32

2007

88

Development of High-Performance Alloys for Electronic Connectors

5.

CONCLUSION

Figure 5 shows the relationship between tensile strengthand electrical conductivity for selected connector materials (JIS alloys and the alloys developed by us). For
EFTEC-97 and 98S, strength and electrical conductivity
are in good balance, and stress relaxation properties aresuperior. F5218 and F5248S, for their part, exhibit both

high strength and good bending workability. These materials are thus well suited to low profiled, narrow pitch miniaturized connectors.
For more information, please contact:
No.1 Sales Division, Metals Company, Furukawa
Electric		 TEL: +81-3-3286-3866 FAX: +81-3-3286-3289

Furukawa Review, No. 32

200789