〉〉 Automotive Products・Electronics

Influence of the Crystal Orientation and the Grain Sizeon the Flexing Property of Tough Pitch Copper
Ryosuke Matsuo*
We researched the influence of the crystal orientation and the grain size on theflexing property of tough pitch copper (C1100). As a result of the Institute ofInterconnecting and Packaging Electronic Circuits (IPC) bending tests under the same conditions,a sample oriented to a {001}<100> orientation (W-orientation) had a better life than a sample oriented to a {001}<110> orientation (NDW-orientation). As a result of a surface observation and ananalysis after the tests, the surface of the sample oriented to a {001}<110> orientation (NDWorientation) was confirmed to have a surface roughness and some cracks which was assumed tobe the starting point of fracture, which is contrary to the sample oriented to a {001}<100>(W-orientation). In addition, in the case of a random orientation, it was clarified that the smaller
the crystal grain size, the better the bending performance. In addition, in the case of a randomorientation, it was clarified that the smaller the crystal grain size, the better the flexing property.

ABSTRACTINTRODUCTION
1.1. INTRODUCTION
Tough pitch copper (C1100) having a {001}<100> recrystallized texture is known for its excellent flexing property1),
and is used for flat cables, etc. To make the tough pitch
copper, a cold working with a large area reduction is performed at first to sufficiently develop a β fiber rolled texture, and then a recrystallization heat treatment is performed, thereby obtaining a structure which is oriented to
the W-orientation and coarsely developed.
The reasons for the excellent flexing property are; theW-orientation effectively contributes to the flexibility 2), thehighly oriented texture that does not depend on the specific orientation leads to high flexibility 3), 4), regardless ofthe orientation accumulation itself, a remarkable coarsenTable 1

ing of the crystal grains which occurs with the accumulation leads to high flexibility 5). However, the degree of each
impact is not clear. In this report, we researched the factors affecting the flexing life, especially in tough pitch
copper with coarse W-orientation grains, and studied the
crystal orientation, the crystal grain size and their interrelationship.

EXPERIMENTAL
PROCEDURE
2.2.EXPERIMENTAL
PROCEDURE
Rolled strip samples were mainly used for the research of acrystal orientation, and samples of rolled round wires,
which are easy to control, were used for the experiment targeting a grain size. Table 1 shows the trial processes. No.1
are strip samples, and No.2 are rolled round wire samples.

Processes of test pieces.

Sample number

1: Strip

Post Process

Sampling Derections

1-1

CR (0.17 mmt) → HT (200℃, 2 h)
→ CR (0.035 mmt) → HT (200℃, 2 h)0°(Longitudinal is parallel to LD)

1-2

CR (0.45 mmt) → HT (200℃, 2 h)
→ CR (0.035 mmt) → HT (200℃, 2 h)0°

CR (0.035 mmt) → HT (200℃, 2 h)

22.5°(rotated on ND axis from 0°)

1-3
1-4

Previous Process

150 mmt → HR and CR (12 mmt)
→ HT (general)

0°

1-5

45.5°(rotated on ND axis from 0°)

1-6
2-1
2: Drawing
and rolling

2-2
2-3
2-4

CR (0.45 mmt) → HT (200℃, 2 h)
→ CR (0.035 mmt) → HT (700℃, 2 h)

0°

-

0°

→ HT (400℃, 2 h)

0°

→ HT (500℃, 2 h)

0°

→ HT (600℃, 2 h)

0°

9 mm φ→ CD (0.22 mm φ ) →HT (general) →CR (0.035 mmt, 0.8 mmw)
→ RT

HR: Hot Rolling CR: Cold Rolling CD: Cold Drawing HT: Heat Treatment RT: Recrystallization Treatment
mmt: millimeter thickness mmw: millimeter width LD: longitudinal direction ND: normal direction*

Automotive Products & Electronics Laboratories, R&D Division

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Influence of the Crystal Orientation and the Grain Size on the Flexing Property of Tough Pitch Copper

For sample No.1 (strip), a softening heat treatment was
performed by general hot rolling and followed by coldrolling. Then, to produce recrystallized materials with different W-orientation ratios, they were subjected to a final
cold rolling with the area reductions of 79, 92, and 97%,
and the thickness was set to 35 μm. Finally, they were
subjected to a recrystallization heat treatment. The test
pieces cut out from the strips in the rolling direction wereidentified as samples No.1-1, No.1-2 and No.1-3.
Furthermore, in order to obtain different orientations,strips were cut out at 22.5 degrees and 45 degrees in therolling direction of the strips with an area reduction rate of
97%, and they were identified as samples No.1-4 andNo.1-5, respectively. Figure 1 shows the relationshipbetween the sampling directions of the strips and thesamples oriented to the W-orientation (sample No.1-1 tosample No.1-3), the {001} <210> orientation (W/NDWorientation) (sample No.1-4), and the NDW-orientation(sample No.1-5).
TD（Transverse direction）
NDW-orientation{001}<110>
LD（Longitudinal direction）

W/NDW-orientation{001}<210>
W-orientation{001}<100>

Microscopy v5”. The tolerance angle was set to 12.5
degrees in the orientation analysis. The grain sizes were
the average values of the grain diameters on a transverse
direction-normal direction (TD-ND) plane or a longitudinal
direction-transverse direction (LD-TD) plane by the cutting method of the Inverse Pole Figure (IPF) map.
Tensile tests were performed on samples No.1-3, No.14, No.1-5, and No.1-6, but the width of the test pieces
was 12.75 mm, which did not comply with JIS Z 2241.
The bending tests were performed using Ueshima
Seisakusho’s flexing tester, FT-2130 (the test method of
this tester conforms to the standard of the Institute ofInterconnecting and Packaging Electronic Circuits (IPC))
with 12.75 mm width and 120 mm length for sample No.1
and 0.8 mm width and 120 mm length for sample No.2.
The test temperature was 85°C, and the test conditions
were a bending radius of 6.3 mm and a stroke of ±13 mm.
The life until break was defined as the life, and eachtest piece was tested repetitively from N=1 to 4 forobtaining the average values. Figure 2 shows the simplified schematic of the flexion movement part.
The surfaces of the flexing test samples were observedwith a scanning electron microscope (SEM), and the surface roughness was measured with a laser microscope(KEYECE VK8510).

3
1：Movable plate
2：Fixed plate
3：Test sample
4：Bending radius
4 5

Figure 1 Relationship between the sampling directions and theoriented samples of the strips.

In order to suppress the orientation in the W-orientation,a cold rolling and a heat treatment with low area reductions were repeated, and finally, a recrystallization heat
treatment was performed to make sample No.1-6. It was
subjected to a high-temperature heat treatment to coarsen the recrystallized grains to match the mechanicalproperties of the samples No.1-3 to No.1-5 as much as
possible.
For sample No.2 (rolled round wire), after drawing andannealing were repeated, the final rolling was performed
to a thickness of 0.035 mm and a width of 0.8 mm, andfinally, a recrystallization heat treatment was performed(sample No.2-1). After that, an additional heat treatment
was performed at 400°C, 500°C, and 700°C to change
the grain sizes (samples. No.2-2, No.2-3 and No.2-4,
respectively).
The crystal orientations and the grain sizes of all samples were measured by the Electron BackScatter
Diffraction (EBSD) method. The analysis was conductedby EDAX TSL’s software, “Orientation Imaging

2

1

5：Stroke

Figure 2 Simplified schematic of the flexion movement.

RESULTANDDISCUSSION
3.3.RESULT
AND
STUDY
3.1

Effect of the Crystal Orientation on the Flexing
Life of Recrystallized Heat Treatment Materials
Figure 3 shows the area fractions and the IPF maps ofsample No.1 in the W-orientation.
The area fractions in the W-orientation were 48, 73, 97
and 19% in samples No.1-1, No.1-2, No.1-3 and No.1-6,
respectively. In samples No.1-1, No.1-2 and No.1-3, it
was confirmed that the higher the degree of orientation,
the larger the proportion of coarse grains in which theW-orientation preferentially grew. It was also found thatsample No.1-3 with 97% of the W-orientation had coarse
grains of 100 to 300 μm on the LD plane and 30 to 100 μm
on the TD plane. From these results, samples No.1-3,
No.1-4, and No.1-5 have the strong W-orientation, the W/
Furukawa Electric Review, No. 51 202034〉〉 Automotive Products・Electronics

Influence of the Crystal Orientation and the Grain Size on the Flexing Property of Tough Pitch Copper

SampleNumber

No.1-1

No.1-2

No.1-3

No.1-6

Area fraction ofW-orientation{001}<100>（%）

48

73

97

19

IPF MAP

70 µm

70 µm

70 µm

70 µm

Figure 3 Area fractions in the W-orientation and the IPF maps of the LD-TD plane of sample No.1.

NDW, and the NDW-orientation, respectively, whereas
sample No. 1-6 has a weak orientation, that is, the orientation was random. The average grain size was about 50 μm.
Figure 4 shows the relationship between the flexing life
and the area fraction of the W-orientation in samples
No.1-1, No.1-2 and No.1-3. The life of sample No. 1 was
540,000 times, that of sample No.2 was 570,000 times,
and that of sample No.1-3 was one million times or more(the test was terminated because it had not been broken
when reaching one million times). The degree of orientation and the flexing life were not necessarily in a proportional relationship, and sample No.1-3, in which theW-orientation was most strongly oriented, showed a sig-

Average life of IPC ﬂexing test ×104/strokes

Average life of IPC ﬂexing test ×104/strokes

120
100
80
60
40
20
0

40

100
50
60
70
80
90
Area fraction of W-orientation{001}<100>（%）

Figure 4 Relationship between the average life measured
by the IPC flexing tests and the area fraction of the6
W-orientation {001}<100>(force-quit at 1.0×10 strokes).

Table 2nificantly longer life compared to others. From theseresults, it is assumed that there are other effects such asa crystal orientation or a grain size other than theW-orientation.
Table 2 shows the mechanical properties of samples
No.1-3, No.1-4, No.1-5 and No.1-6. Comparing the samples, the difference in the strength was small but the difference in the elongation was large.
Figure 5 shows the flexing lives of samples No.1-3,
No.1-4, No.1-5 and No.1-6.
The flexing life of the sample with the W-orientation(sample No.1-3) was 10 times and more than that of sample No.1-4 (W/NDW-orientation) and sample No.1-5
100

10

1

No.1-3oriented to W{001}<100>No.1-4No.1-5

No.1-6oriented tooriented to non-oriented
W/NDW
NDW
{001}<210> {001}<110>

Figure 5 Average flexing lives measured by the IPC flexing
tests on the differently oriented samples
6(force-quit at 1.0×10 strokes).

Mechanical properties of sample No.1.
Elongation（%）

Sample Number

Oriented Crystal

Yield Strength / MPa

Tensile Strength / MPa

No.1-3W-orientation {001}<100>

40

122

6

No.1-4W/NDW-orientation {001}<210>

35

133

43

No.1-5

NDW-orientation {001}<110>

36

132

31

No.1-6

Non-oriented

43

143

12

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Influence of the Crystal Orientation and the Grain Size on the Flexing Property of Tough Pitch Copper(NDW-orientation) (the test on sample No.1-3 was terminated during test). From this result, it is considered thatthe flexing life was greatly improved by the W-orientation,
but the W/NDW and the NDW-orientations did not contribute to it. In other words, it is concluded that the flexing
life depends on the high orientation of specific crystal
grains (in this case, the W-orientation), and even if thegrain size is coarse, it does not necessarily improve.
3.2 Effect of the Grain Size on the Flexing Life of
Recrystallized Heat Treatment Materials
Figure 6 shows the IPF maps, the crystal orientations andthe measurement results of the grain size (LD plane andTD plane) of sample No.2. The average grain sizes of thesample subjected to the recrystallization heat treatment
alone and the ones with an additional heat treatment at
400°C, 500°C and 700°C for two hours were 4, 10, 18

and 35 µm, respectively. Also, as the average grain size
increased, the orientation in the <100> direction tended
to increase. However, as the degree of orientation (areafraction) in a specific orientation was much lower thanthat of samples No.1-3 to No.1-5, which were close to100%, it was regarded as a random orientation.
Figure 7 shows the flexing life of sample No.2. As it canbe seen from the figure, the flexing life was improved as
the grain size became finer. When large grains wereinvolved, it is considered that the flexing life was
improved only in the case when the W-orientation wasoriented as shown in Figure 4 within the range of the conditions of this test. From these results, it is consideredthat the coarse grain structure oriented to theW-orientation was reverified to be largely influenced by
the crystal orientation.

(a)Sample Number

No.2-1

No.2-2

No.2-3No.2-4

Average grain
size/µm（TD-ND）

4

10

18

35

IPF MAP（LD-TD）

100 µm

100 µm

100 µm

100 µmIPF MAP（TD-ND）

(b)

<123>

Area fraction of crystal direction（%）

100

35 µm

<111>

<101>

60

40

20

No.2-1

No.2-2

No.2-3

35 µm

<100>

80

0

35 µm

No.2-4

Sample number
Figure 6 (a) Average grain sizes on the TD-ND plane and the
IPF map on the LD-TD plane and the TD-ND plane ofsample No.2.
(b) Crystal directions on the LD-TD plane of sample
No.2.

Average life of IPC ﬂexing test ×104/strokes

35 µm

1000

100

10

1

No.2-14 µm

No.2-2

No.2-310 µm
18 µm
Average grain size

No.2-435 µm

Figure 7 Average flexing lives of sample No. 2 after the IPC
flexing tests
6(force-quit at 3.0×10 strokes).

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36〉〉 Automotive Products・Electronics

Influence of the Crystal Orientation and the Grain Size on the Flexing Property of Tough Pitch Copper

3.3 Discussion
Figure 8 shows the SEM images of the surface of thesamples after bending 200,000 times in samples No.1-1,
No.1-2 and No.1-3. The growth of undulations on the surface layers was confirmed, and in connection with the
Figure 2, the area was clearly larger as the orientation of
the W-orientation was lower. Figure 9 shows the SEM
images of the surface of the sample with theW-orientation (after bending 200,000 times) and the sample with the NDW-orientation (after bending 90,000 times,
which was the breaking point) to consider the effect of
the crystal orientation. When the NDW-orientation wasoriented, a microscopic surface roughness was observed

Sample number

on the entire surface, but when the W-orientation was oriented, the surface roughness was minor.
From these results, it is considered that a crystal orientation had a large effect on the plastic deformation
behavior during bending. This roughness on the surface
is assumed to be due to a extrusion and an intrusion of
the slip surface formed by a slip of the crystal, and it isalso assumed that the differences in the relative relationship between the stress and the crystal direction, such as
the number of main slip directions considered to be
active in the stress direction or the Young’s modulus, had
an effect.

No.1-1

No.1-2

No.1-3

SEM Images（Low-power
×120）
300 µmsurface after
2.0×106
strokes

300 µm300 µm

50 µm

50 µm

SEM Images（High-power
×1000）
50 µm

Figure 8 SEM images of the surface of samples No.1-1, No.1-2 and No.1-3 after the IPC flexing tests.

No.1-3：Oriented to W{001}<100>surface after 2.0×105 strokes

SEM Images（Low-power
×120）

No.1-5：Oriented to NDW{001}<110>surface after 9.0×104 trokes

stress direction
longitudinal direction
and stress direction

300 µm

SEM Images（high-power
×1000）

longitudinal direction

300 µmstress direction
longitudinal direction
and stress direction

50 µm

longitudinal direction

50 µm

Figure 9 SEM images of the surface of samples No.1-3 and No.1-5 after the IPC
flexing tests.

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Influence of the Crystal Orientation and the Grain Size on the Flexing Property of Tough Pitch Copper

Figure 10 shows the surface roughness of the samples
measured by a laser microscope. It can be seen thatwhen the W-orientation was oriented, the surface
became relatively flat, but when the NDW-orientation wasoriented, the unevenness was remarkably formed. Figure
11 shows the surface appearance of a sample in which

the NDW-orientation was oriented. Since the cracks
observed on the surface were along the valleys of theirregularities, it is considered that the stress concentration
might have increased in the concave portions of the valleys to generate cracks, which is considered to be one of
the focuses of the destruction process.

No.1-3

No.1-5

Oriented to W {001}<100>
Surface after 2.0×105 strokes

Oriented to NDW {001}<110>
Surface after 9.0×104 strokes

A

B
A

B

LD
100 µmTD

A

TD

100 µmB

298 µm

A

ND

ND

3 µm

3 µm

TD

298 µmB

Figure 10 Roughness on the surfaces of samples No.1-3 and No.1-5 after the IPC flexing tests.

No.1-5：Oriented to NDW {001}<110>
Surface after 9.0×104 strokes

LD
TD

Figure 11 SEM image of a surface crack of sample No.1-5 after
the IPC flexing tests.

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Influence of the Crystal Orientation and the Grain Size on the Flexing Property of Tough Pitch Copper

sample Number
Average Grain
Size/µm
strokesNo.2-1

No.2-2

No.2-3No.2-4

4

10

18

35

2.0×105

2.0×105

1.5×105

6.0×104

SEM Images（Low-power
×120）

SEM Images（High-power ×1000 or ×3000）

Figure 12 SEM images of the surfaces of sample No.2 after the IPC flexing tests.

Figure 12 shows surface SEM images of sample No.2
having relatively random crystal orientations and different
grain sizes after bending 200,000 times or the ones fractured before that. In sample No.2-1, which has fine crystal grains, the growth of surface roughness due to crystal
slip across the grain boundaries was suppressed, and thegeneration range was also narrow. This is considered tobe the reason for the longer life.
In this study, the surface state changed depending on
the crystal orientation in the surface layer, and the cracks
that were likely to have been affected by the change weregenerated. However, the change in the underlying structure is unknown, and further investigation is needed.
This study is focused on the relationship between the
crystal orientation, the grain size and the flexing life.
However, the effects of the degree of crystal orientationand the characteristics of the grain boundaries associated with them, or the shape of the crystal grains (such as
the aspect ratio, etc.) were not considered. Therefore, wewill work on it as a future issue.

CONCLUSION
4.4.CONCLUSION
We investigated the dependence of a crystal orientation
and a grain size on the flexing life of tough pitch copperand obtained the following conclusions.
(1) The flexing life is longer in the sample oriented inthe {001}<100> orientation (W-orientation) than in
the sample oriented in other than the {001} <100>orientation (W-orientation). That is, the flexing life do
not necessarily improve only by the coarsening of
the crystal grains, but the orientation in a specificorientation contributes strongly.
(2) When the crystal grains are randomly oriented, theflexing life tends to be longer as the crystal grain
size is finer.

(3) When the flexing life is excellent, the undulation
growth on the surface after the test is minor, butwhen the flexing life is inferior, the undulation
growth is remarkable. This suggests that the difference in the crystal orientation affects each phenomenon. This is caused by the extrusion and the intrusion on the surface due to the crystal slip caused bybending, and it is considered that it eventually
becomes the starting point of a crack.
In the future, to investigate the detailed mechanism, theinfluence of the state of the roughened substructure, of
the coincidence boundary caused by the degree of crystal orientation or the grain shape, and of the grain shape(aspect ratio, etc.) will be investigated.

REFERENCES
1) Y.Yamamoto, H.Abe, S.Sakai, N.Oya: Journal of the Japan Copperand Brass Research Association, 31 (1992), 65-71.
2) K.Kanmuri: Thesis for Tokyo Institute of Technology: “Effect of acrystal orientation on the thickness dependence of the repetitive
deformation behavior in copper foil”, (2015) (in Japanese).
3) T.Muroga, K.Yokomizo, Y.Yamamoto, G.Sasaki, C.Tong: J.JRICu,
47 (2008), 208-213.
4) H.Nagai, T.Hatano, J.Miyake, M.Kato: J.JRICu, 41 (2002), 251-255.
5) K.Yamazaki, R.Takeda, M.Takeda: J.JRICu, 45 (2006), 27-30.

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