NewNew Products
Products

Development of a High Performance Copper Alloy
EFCUBE-ST for Connectors

INTRODUCTION

In recent years, small-sized B to B connectors which areused for the connection between circuit boards andbetween modules, have been being downsized and compacted in association with the performance advancementin small-sized electronic devices such as smart phones
and tablet-type terminals. Copper alloy strips used forsmall-sized connectors require conflicting characteristics
of a high spring characteristic and of a good bendingworkability. Moreover, copper alloys which are less prone
to permanent deformation with a good elasticity (a lowYoung’s modulus) and have a high electric conductivity,
are in demand because connectors are becoming shorterand smaller, and are reduced in their cross sectional
areas. Cu-Ti alloys and phosphor bronze alloys have been
mainly used for high mechanical strength copper alloys
for connectors. However, in those cases, their Young’s
modulus and electric conductivity do not meet therequirements. To fulfill all the required characteristics in agood balance, we have developed a new copper alloy“EFCUBE-ST (UNS: C64790)” using a texture control
technology. As Figure 1 shows, in EFCUBE-ST, the crystal
orientations of a highly-concentrated Colson alloy inwhich Ni and Si density is concentrated, are controlledunidirectionally. In addition, as Table 1 shows, this product is suitable for the customers who are promoting green
procurement because it doesn’t include harmful elements.
Apply texture
control technology
NormalDirection
LongitudinalDirection

Crystal grain

Characteristics of EFCUBE-ST.
EFCUBE-ST
TemperEH

Tensile strength

MPa

910

950

0.2% proof stress

MPa

880

930

5Elongation%Young’s modulus

GPaVickers hardness

Hv

Evaluation method

SHTensile test
JIS Z 2241
compliant

3―110275

Electric conductivity %IACS

295

JIS Z 2244 compliant

35JIS H 0505 compliant(Bending workability)
Figure 2 shows the correlation between the strength andthe bending workability. The EFCUBE-ST has higher
mechanical strength (0.2% proof stress: 880-930 MPa)
than the general Colson alloy and the 10% phosphor
bronze alloy, while keeping a good bending workability(10 mm width, 0.15 mmt board thickness, 90°W bend: 2to 5 t). That is comparable to the Cu-Ti alloy. Figure 3
shows the observation results of the cross sectional areas
after 90°W bending. It shows that the EFCUBE-ST wasprocessed without having a crack as well as in the Cu-Ti
alloy, while the 10% phosphor bronze alloy generated acrack.
t: board thickness
10 mm
0.15 mmFigure 1

TD

Bend radiusLD

Crystal orientations arecontrolled unidirectionally.

Crystal orientations are random.

Texture control of EFCUBE-ST.

Chemical composition of EFCUBE-ST.

Elements

NiSiZnSnMg

CrCu

Content (mass%)

3.8

0.9

0.5

0.1

0.1

0.2

Bal.

2.

Table 2NDTransverse
Direction

Table 1

Therefore, we have two types of product lines dependingon the mechanical strength.

← GoodBending workability(Minimum bend radius:multiples of board thickness)

1.

5t
4t
3t

SH

EFCUBE-ST
EH

2t

Cu-Ti alloy

1t
0t
650

EFCUBE-820

700

750

800

850

900

950

1000

0.2% proof stress/MPa(Rolling direction)

CHARACTERISTICS

Figure 2 shows the basic characteristics of the EFCUBEST. The EFCUBE-ST has two tempers, EH and SH.

10% phosphor
bronze alloy

General Colson
Alloy

Figure 2

Correlation between strength andbending workability.

Furukawa Review, No. 42

201218

Development of a High Performance Copper Alloy EFCUBE-ST for Connectors

EFCUBE-ST

Cu-Ti alloy 10% phosphor
bronze alloy

High strength(0.2% proof stress)-ST
EFCUBE-ST）（EH）

880MPa840
800

100GPaLow elasticity
Figure 3110760120(Young s modulus)

Cross sectional areas of bend specimens.

130

140

720

3ｔ

4ｔ

2ｔ

1ｔ

Bendingworkability(Marginal bend radius)

5010(Young’s modulus)
Figure 4 shows the stress-strain curves (S-S curves) ofthe EFCUBE-ST, the Cu-Ti alloy and the 10% phosphor
bronze alloy. The EFCUBE-ST shows a low Young’s modulus which is comparable to the 10% phosphor bronze
alloy. Compared to the materials with high Young’s modulus within the same strength zone, it can keep a wide
elastic area and is not prone to permanent deformationeven when a certain amount of displacement occurs.
Therefore, it meets the trend of downsizing in the springparts which is required in the downsizing of connectors.
In addition, because the low Young’s modulus brings theelimination of size variation in the way of processing connectors, etc., the contact pressure (spring load) of theconnectors’ electric contacts stabilizes. Thus, it contributes to the connection reliability of connectors.

1100
1000
Nominal stress /MPa

90010%Phosphor bronze

2010High electric conductivity(Electric conductivity)

Figure 5

3.

30
2030

40%IACS

Cu-Ti
Cu-Ti alloy

400%

Heat resistance(Stress relaxation rate (1000 hours at 150 ℃)

Characteristics of EFCUBE-ST and other alloys.

CONCLUSIONThe EFCUBE-ST is suitable as a material for connectors
which have been being downsized and highly-functionalized because of its high reliability in terms of strength,
bending workability and high temperature environment.
For more information, please contact:
Sales Management Division
Metals Company
TEL: +81-3-3286-3866 FAX: +81-3-3286-3289
UNS number: C64790

EFCUBE-ST(EH)
Cu-Ti alloy

800700

10% Phosphor bronze alloy

600
500
400
300
200
100
00.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
Nominal strain(%)
Figure 4

Stress-strain curves in rolling directions.

Figure 5 is the cobweb chart in which the characteristicsof the EFCUBE-ST and other copper alloys are compared. The EFCUBE’s Young’s modulus is lower than thatof the Cu-Ti alloy, and its strength, bending workability
and heat-resisting characteristic are superior to those of
the 10% phosphor bronze. Its electric conductivity ismore than three times greater than that of the Cu-Ti alloy
and that of the 10% phosphor bronze, which means it ishighly superior to others.
As stated above, the EFCUBE-ST fulfills all the characteristics in a good balance compared to the existing copper alloys, thus contributes to the designing of the ultracompact connectors in the next generation and the technical innovation of connectors.

Furukawa Review, No. 42201219