U.S. patent application number 10/976818 was filed with the patent office on 2005-05-05 for softening-resistant copper alloy and method of forming sheet of the same.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). Invention is credited to Aruga, Yasuhiro, Kajihara, Katsura.
Application Number | 20050092404 10/976818 |
Document ID | / |
Family ID | 34544313 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050092404 |
Kind Code |
A1 |
Aruga, Yasuhiro ; et
al. |
May 5, 2005 |
Softening-resistant copper alloy and method of forming sheet of the
same
Abstract
A softening-resistant copper alloy contains Fe in an Fe content
in the range of 0.01 to 4.0% by mass. The copper alloy has a cube
orientation density of 50% or below and a mean grain size of 30
.mu.m or below after being annealed at 500.degree. C. for 1 min. A
copper alloy sheet forming method of forming a copper alloy sheet
comprises, in successive steps: a hot rolling process for
hot-rolling a copper alloy sheet of the copper alloy according to
any one of claims 1 to 4, at least two working cycles each of a
cold rolling process and an annealing process, and a finish cold
rolling process. Reduction ratio for each of the cold rolling
processes of the working cycles is in the range of 50 to 80%, and
reduction ratio for the finish cold rolling process is in the range
of 30 to 85%.
Inventors: |
Aruga, Yasuhiro; (Kobe-shi,
JP) ; Kajihara, Katsura; (Kobe-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd.)
Kobe-shi
JP
651-8585
|
Family ID: |
34544313 |
Appl. No.: |
10/976818 |
Filed: |
November 1, 2004 |
Current U.S.
Class: |
148/681 ;
148/432; 420/496 |
Current CPC
Class: |
C22C 9/00 20130101; C22F
1/08 20130101 |
Class at
Publication: |
148/681 ;
148/432; 420/496 |
International
Class: |
C22C 009/00; C22F
001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 5, 2003 |
JP |
2003-376122 |
Claims
1. A softening-resistant copper alloy containing Fe, and having a
cube orientation density of 50% or below after being annealed at
500.degree. C. for 1 min.
2. A softening-resistant copper alloy containing Fe, and having a
cube orientation density of 50% or below after being annealed at
500.degree. C. for 1 min and a mean grain size of 30 .mu.m or
below.
3. The copper alloy according to claim 1, wherein the Fe content is
in the range of 0.01 to 4.0% by mass.
4. The copper alloy according to claim 2, wherein the Fe content is
in the range of 0.01 to 4.0% by mass.
5. A softening-resistant copper alloy sheet forming method of
forming a copper alloy sheet comprising, in successive steps: a hot
rolling process for hot-rolling a copper alloy sheet of the copper
alloy containing Fe; at least two working cycles each of a cold
rolling process and an annealing process; and a finish cold rolling
process; wherein reduction ratio for each of the cold rolling
processes of the working cycles is in the range of 50 to 80%, and
reduction ratio for the finish cold rolling process is in the range
of 30 to 85%.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a softening-resistant
copper alloy having high softening resistance and a method of
forming a sheet of the softening-resistant copper alloy. The
softening-resistant copper alloy having high softening resistance
can be effectively applied to various fields including the
electric, the electronic and the mechanical field.
[0003] 2. Description of the Related Art
[0004] The recent progressive advancement of device
miniaturization, device thinning and weight reduction of various
devices including electronic devices has urged the rapid progress
of the miniaturization and weight reduction of copper alloy parts
including lead frames, terminals and connectors for those small,
lightweight devices.
[0005] For example, a copper alloy containing Fe in a small Fe
content is sued widely for forming lead frames for semiconductor
devices. A copper alloy designated by CDA194 excellent in strength,
electric conductivity and thermal conductivity is used widely as an
international standard copper alloy. The alloy CDA194 contains 2.1
to 2.8% by mass (hereinafter, referred to simply as "%") Fe, 0.015
to 0.15% P, and 0.05 to 0.20% Zn.
[0006] Generally, lead frames having a plurality of leads are
fabricated by subjecting a copper alloy sheet of the foregoing
chemical composition to a stamping process. Recently, thickness
reduction of copper alloy sheets and increase in the number of
leads of each lead frame have progressively advanced to cope with
device miniaturization, device thinning and weight reduction of
electric and electronic devices. Residual stresses are liable to be
induced in such thin lead frames having a large number of leads
formed by the stamping process and the leads of such thin lead
frames tend to be arranged irregularly. Therefore, the lead frame
with many leads formed by subjecting the copper alloy sheet to the
stamping process is subjected to a heat treatment, such as an
annealing process, to remove residual stresses. Such a heat
treatment often softens the workpiece, and the workpiece treated by
the heat treatment is unable to maintain its initial mechanical
strength. The heat treatment is desired to be carried out at a
higher process temperature in a shorter time to improve
productivity. Therefore, there is a strong demand for
heat-resistant materials capable of maintaining its high strength
after being heat-treated.
[0007] Alloy elements including Fe, P and Zn and additional trace
elements including Sn, Mg and Ca are added to copper alloys or the
contents of those alloy elements and additional trace elements are
adjusted to meet such a demand. However, it is impossible to
achieve the miniaturization, weight reduction and improvement of
softening resistance of copper alloy parts satisfactorily simply
through the adjustment of the chemical composition of the copper
alloy. Therefore, studies have been made in recent years to develop
techniques of controlling the texture of copper alloys.
[0008] A technique disclosed in JP-A No. 2003-96526 (Patent
document 1) increases strength by controlling intensity ratio of
diffraction after finish rolling and grain size before finish
rolling. A technique disclosed in JP-A No. 2002-339028 (Patent
document 2) improves workability by controlling cube orientation
density in addition to controlling intensity ratio of
diffraction.
[0009] The technique disclosed in Patent document 1 increases the
strength of a copper alloy sheet of a copper alloy produced by
adding a trace of Ag to oxygen-free copper by subjecting a copper
alloy sheet to a hot rolling process, subjecting the hot-rolled
copper alloy sheet to a plurality of working cycles each of a cold
rolling process and a recrystallization annealing process, and
subjecting the copper alloy sheet to finish rolling process,
wherein the reduction ratio of the finish cold rolling is
controlled, mean grain size after the recrystallization annealing
process immediately before the finish cold rolling process and the
reduction ratio of the cold rolling process subsequent to the last
recrystallization annealing process are controlled to control
intensity ratio of diffraction after finish cold rolling process
and grain size before finish cold rolling process.
[0010] According to Patent document 1, x-ray diffraction strength
must be properly controlled because strength decreases and an
anisotropic etching character appears as cubic orientation density
increases. Patent document 1 mentions about the high softening
resistance of this copper alloy. However, high softening resistance
intended by the present invention cannot be achieved by simply
applying rolling and annealing conditions to processing the copper
alloy sheet and hence further improvement is desired.
[0011] According to Patent document 2, a copper alloy suitable for
forming electronic parts and having improved workability and
formability can be obtained by properly controlling the intensity
of diffraction of (200) and (220), and cube orientation density.
However, high softening resistance intended by the present
invention cannot be guaranteed by the technique disclosed in Patent
document 2.
SUMMARY OF THE INVENTION
[0012] The present invention has been made in view of those
problems in the prior art techniques an it is an object of the
present invention to provide a copper alloy suitable for the
miniaturization and weight reduction of copper alloy parts for
electric and electronic devices and capable of maintaining high
strength even if the copper alloy is processed by a heat treatment,
such as an annealing process, and a method of forming a sheet of
the copper alloy.
[0013] A copper alloy having high softening resistance in one
aspect of the present invention contains Fe, has a cube orientation
density of 50% or below after being annealed at 500.degree. C. for
1 min, and, preferably, a mean grain size of 30 Km or below.
[0014] The copper alloy of the present invention contains
inexpensive Fe as an essential alloy element in a small Fe content.
Although there is not any particular restriction, a desirable Fe
content is in the range of 0.01% to 4%. Other possible alloy
elements are 0.03% or below P and about 1% Zn. Desirable respective
contents of other elements are limited to those of unavoidable
impurities.
[0015] A copper alloy sheet forming method in another aspect of the
present invention includes, in successive steps, a hot rolling
process for hot-rolling a copper alloy sheet of a copper alloy
containing Fe, at least two working cycles each of a cold rolling
process and an annealing process, and a finish cold rolling
process; wherein reduction ratio for each of the cold rolling
processes of the working cycles is in the range of 50 to 80%, and
reduction ratio for the finish cold rolling process is in the range
of 30 to 85%.
[0016] According to the present invention, a stable copper alloy
having high softening resistance can be produced by controlling
cube orientation density after annealing at 500.degree. C. for 1
min to 50% or below. Reduction of strength that occurs in the sheet
of the conventional material when the sheet is treated by a heat
treatment for annealing or the like can be suppressed to the least
unavoidable extent. Consequently, even in a case where decrease in
dimensional accuracy of parts due to residual stress induced in the
parts by a stamping process or the like is expected, strength
reduction due to annealing can be suppressed, decrease in
dimensional accuracy can be prevented, and copper alloy parts of
stable quality can be produced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above and other objects, features and advantages of the
present invention will become more apparent from the following
description taken in connection with the accompanying drawings, in
which:
[0018] FIG. 1 is a cube orientation mapping of a copper alloy sheet
in a preferred embodiment according to the present invention
produced by using "EBSP measuring and analyzing system OIM; and
[0019] FIG. 2 is a grain size histogram of the copper alloy sheet
obtained by using "EBSP measuring and analyzing system OIM".
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] A copper alloy having high softening resistance in a
preferred embodiment according to the present invention contains Fe
in a small Fe content. The copper alloy has a cube orientation
density of 50% or below after annealing at 500.degree. C. for 1 min
and, preferably, the copper alloy has a mean grain size of 30 Km or
below after annealing at 500.degree. C. for 1 min for the following
reasons.
[0021] The inventors of the present invention found through
experiments that the higher the cube orientation density of a
copper alloy containing Fe in a small Fe content after annealing,
the higher the rate of reduction of the strength of the copper
alloy due to heat treatment, that the lower the cube orientation
density, the less is strength reduction and the higher is the
softening resistance, that the orientation density can be
quantitatively evaluated on the basis of cube orientation density
after annealing under specific conditions of 500.degree. C. and 1
min, that the rate of strength reduction due to heat treatment
becomes obviously high when the cube orientation density is greater
than 50%, and that copper alloys having orientation densities of
50% or below, preferably, 40% or below exhibit stable, high
softening resistance.
[0022] Mean grain size after annealing at 500.degree. C. for 1 min,
as well as cube orientation density, is closely related with
softening resistance. Copper alloys having mean grain sizes of 30
.mu.m or below have particularly high softening resistance.
[0023] The term "Cube orientation" signifies a state where the
<001> direction of crystals is parallel to rolling direction,
a normal to a rolled surface and width. In a rolled surface, a
(100) plane is oriented. The ratio of grains having the cube
orientation increases as cube orientation develops. If cube
orientation develops excessively, the strength of the copper alloy
decreases. High softening resistance intended by the present
invention can be secured if the cube orientation density is
controlled to 50% or below.
[0024] The cube orientation density can be measured by an EBSP
(electron back-scatter diffraction pattern) method. The EBSP method
projects an electron beam on the surface of a specimen, and obtains
a Kikuchi pattern (cube orientation mapping) as shown in FIG. 1
formed by reflected electrons. The crystal orientation in a part on
which the electron beam falls can be known through the analysis of
the Kikuchi pattern. A crystal orientation distribution is measured
by two-dimensionally scanning the surface of the specimen with the
electron beam and measuring crystal orientation at predetermined
pitches.
[0025] However, if the specimen has many defects, such as strain
fields and deformation bands formed by machining, such as stamping,
and dislocation, it is difficult to obtain a Kikuchi pattern. A
copper alloy sheet of the copper alloy of the present invention is
finished by cold rolling by high reduction. Therefore, the cube
orientation density of the copper alloy sheet as finished by cold
rolling cannot be measured by the EBSP method. Therefore, the cube
orientation density of the copper alloy sheet is measured after
annealing the cold rolled copper alloy sheet at 500.degree. C. for
1 min.
[0026] Crystal grains of the same orientation increase as cube
orientation develops. Consequently, irregularity of atoms in grain
boundaries decreases and grain obviously tend to grow. It was
confirmed that the copper alloy sheet maintains high strength after
annealing at 500.degree. C. for 1 min when grain sizes are 30 Km or
below, preferably 25 .mu.m or below.
[0027] The copper alloy of the present invention contains Fe as an
essential component. Although there are not particular restrictions
on the Fe content and the composition of the copper alloy, it is
desirable that the Fe content is between 0.01% and 4.0% to make the
copper alloy exhibit its characteristics effectively. If the Fe
content is less than 0.01%, the amount of Fe precipitates or
Fe-base intermetallic compounds is small and the strength of the
copper alloy sheet is insufficient for forming lead frames,
terminals and connectors, and the softening resistance of the
copper alloy sheet is insufficient. Strength does not increase and
softening resistance does not improve even if the Fe content is
increased beyond 4.0%, and a large amount of coarse dispersoids
containing Fe adversely affecting the castability and workability
of the copper alloy. Therefore, it is desirable that the Fe content
of the copper alloy is 4.0% or below. Amore desirable Fe content is
between 0.03% and 3.5%, more preferably, between 0.05% and 3.0% to
provide a copper alloy satisfactory in strength, softening
resistance, castability and hot-workability.
[0028] The copper alloy of the present invention may contain P and
Zn in addition to Fe. A suitable P content is about 1% or below.
Because when the P content is increased beyond 1%, a large amount
of coarse dipersoids generate and they deteriorate castability. Zn
is an element effective in preventing the separation of Sn and
solder. The effect of Zn saturates at certain Zn content. Excessive
Zn content deteriorates the wettability of molten Sn and molten
solder. A desirable Zn content is about 1.0% or below. Other
elements do not need to be added intentionally. The copper alloy
may contain unavoidable impurities, such as Pb, Ni, Mn, Cr, Al, Mg,
Ca, Be, Si, Zr and In, and some of those impurities may be
intentionally added to the copper alloy without departing from the
scope of the present invention.
[0029] A method of forming a copper alloy sheet of a copper alloy
conforming to the foregoing cube orientation density and mean grain
size and high in softening resistance will be described.
[0030] A method of forming a copper alloy sheet of the copper alloy
of the present invention includes, in successive steps, a hot
rolling process for hot-rolling a copper alloy sheet of a copper
alloy, at least two working cycles each of a cold rolling process
and an annealing process, and a finish cold rolling process. The
copper alloy sheet is finished in a desired thickness by the finish
cold rolling process. A generally used conventional copper alloy
forming method includes the least necessary processes, such as a
hot rolling process, a cold rolling process, an annealing process
and a finish rolling process from the viewpoint of productivity and
cost. The inventors of the present invention found that nuclei of
cube orientation are formed if the reduction ratio in one cold
rolling pass is excessively high and cube orientation is liable to
develop during the annealing of the copper alloy sheet and that the
development of rolling textures in B orientation ({011} and
<211>) and S orientation ({123} and <634>) is
suppressed when the reduction ration in one cold rolling pass is
excessively low and cube orientation and many nuclei of cube
orientation existed in the copper alloy sheet before the cold
rolling process, i.e., after the hot rolling, remains in the copper
alloy sheet.
[0031] When the copper alloy sheet is processed by at least two
working cycles each of the cold rolling process and the annealing
process, and reduction ratio for each cold rolling process is
properly controlled, the development of cube orientation and the
formation of nuclei can be effectively suppressed. If the reduction
ratio for each cold rolling process is below 50% or greater than
80%, cube orientation grows easily when the copper alloy sheet is
annealed and the cube orientation density increases beyond the
foregoing desirable upper limit when the copper alloy sheet is
annealed at 500.degree. C. for 1 min. Grains grow abnormally as
cube orientation develops, the mean grain size exceeds 30 .mu.m and
the softening resistance of the copper alloy sheet deteriorates.
Thus the reduction ratio for each cold rolling process in the range
of 50 to 80%, and the execution of at least two working cycles each
of the cold rolling process and the annealing process are essential
conditions of the present invention.
[0032] Although the repetition of the working cycle of the cold
rolling process and the annealing process to suppress the
development of cube orientation and the formation of nuclei
effectively widens the allowable reduction ratio range for the
finish cold rolling, it is desirable that reduction ratio for the
finish cold rolling process is between 30% and 85%, more desirably,
between 35% and 80%.
[0033] The present invention requires the cube orientation density
of the copper alloy sheet controlled under predetermined conditions
to be 50% or below. Thus the strength of the copper alloy sheet is
decreased scarcely by annealing, and the copper alloy sheet has
high softening resistance. A copper alloy sheet having high
softening resistance can be surely manufactured by subjecting the
copper alloy sheet to the working cycles each of the cold rolling
process for rolling the copper alloy sheet at the predetermined
reduction ratio and the annealing process, and properly controlling
the reduction ratio for the finish cold rolling process.
[0034] The copper alloy sheet of the present invention thus
manufactured has high softening resistance and strength that is
scarcely decreased by heat treatment, such as annealing. The copper
alloy sheet can be effectively used for forming copper alloy parts
that are subjected to a heat treatment, such as annealing, after a
final machining process, such as IC lead frames, terminals and
connectors.
EXAMPLES
[0035] Examples of the present invention and comparative examples
will be described.
[0036] Copper alloys of chemical compositions shown in Table 1 were
melted in a coreless low-frequency induction furnace and copper
alloy ingots of 50 mm in thickness, 200 mm in width and 500 mm in
length were produced by a semicontinuous casting process. Each of
the ingots was heated and the thickness was reduced to 12 mm by hot
rolling and the sheet was machined by facing. Then the ingot was
processed by a plurality of working cycles each of a cold rolling
process and an annealing process, and the sheet was rolled in a
copper alloy sheet of about 0.2 mm in thickness by finish cold
rolling.
[0037] The copper alloy sheets were annealed at 500.degree. C. fore
1 min in a salt bath. Specimens were sampled from the annealed
copper alloy sheets. The specimens were ground and buffed. The
surfaces of the specimens were finished by electrolytic polishing.
A region of 500 .mu.m.times.500 .mu.m in the surface of each of the
test specimens was measured at pitches of 1 .mu.m by a scanning
electron microscope (Model JEOL JSM 5410, Nippon Denshi) and an
EBSP measuring and analyzing system OIM (orientation imaging
macrograph) (TSL). Cube orientation densities (within 150 from an
ideal orientation) and mean grain sizes were determined by using
analyzing software "OIM Analysis" of the EBSP measuring and
analyzing system.
[0038] FIG. 1 is a cube orientation mapping of the copper alloy
sheet in Specimen 1 specified in Table 1 obtained by using the EBSP
measuring and analyzing system OIM. In FIG. 1, black parts are cube
orientation. Cube orientation density can be determined by
analyzing the cube orientation mapping by the analyzing software.
FIG. 2 is a grain size histogram of the copper alloy sheet in
Specimen 1 obtained by the analyzing software. Mean grain size can
be determined from the grain size histogram showing area fractions
for grain sizes.
[0039] The softening resistance of each specimen was evaluated on
the basis of the rate of reduction of hardness due to annealing.
Test pieces of 0.2 mm in thickness, 10 mm in width and 10 mm in
length were sampled from both a copper alloy sheet finished by the
finish cold rolling and a copper alloy sheet obtained by annealing
the copper alloy sheet finished by finish cold rolling at
500.degree. C. for 1 min. The hardnesses of those test pieces were
measured by a micro-Vickers hardness meter ("Bishyo Kodo-kei",
Matuzawa Seiki). The measuring load was 0.5 kg.
1 TABLE 1 Number of cold rolling Maximum Minimum Finish After
annealing (500.degree. C. .times. 1 min) cycles between cold
rolling cold rolling cold rolling Cube Mean hot rolling reduction
reduction reduction Initial Hardness orientation grain Specimen
Chemical composition and finish ratio ratio ratio hardness Hardness
reduction density size No. Fe P Zn cold rolling (%) (%) (%) (Hv)
(Hv) (Hv) (%) (.mu.m) 1 1.8 -- -- 2 70 60 60 128 105 23 19 12 2 0.5
-- -- 2 75 55 70 123 96 27 31 19 3 2.1 0.03 -- 2 65 60 50 140 120
20 7 9 4 2.1 0.03 -- 2 75 60 75 156 123 33 34 21 5 2.1 0.03 0.1 2
78 55 83 159 121 38 43 26 6 2.1 0.03 0.1 2 70 60 65 148 122 26 22
15 7 2.1 0.03 0.1 3 70 60 55 143 126 17 5 7 8 1.6 -- -- 2 88 60 55
124 72 52 57 34 9 0.3 -- -- 2 93 60 88 130 70 60 70 42 10 2.1 0.03
0.1 2 95 60 60 147 90 57 64 38 11 2.1 0.03 0.1 2 70 30 80 151 96 55
61 36 12 2.1 0.03 0.1 2 70 60 95 157 99 58 65 40 13 2.1 0.03 0.1 2
92 60 90 161 99 62 72 43 14 2.1 0.03 0.1 2 50 20 20 125 65 60 69 42
15 2.1 0.03 0.1 2 90 40 90 160 95 65 75 46 16 2.1 0.03 0.1 1 75 70
50 142 94 48 52 31
[0040] The copper alloy sheets in Specimens 1 to 7 are those
meeting requirements specified by the present invention. Every one
of the copper alloy sheets in Specimens 1 to 7 has a cube
orientation density of 50% or below and a mean grain size of 30 Km
or below. Hardness reductions in all the copper alloy sheets in
Specimens 1 to 7 due to annealing were 40 Hv or below. It is known
from data shown in Table 1 that the copper alloy sheets according
to the present invention are high in softening resistance.
[0041] The copper alloy sheets in Specimens 8 to 16 are comparative
examples not meeting all the requirements specified by the present
invention. All the copper alloy sheets in comparative examples have
cube orientation densities exceeding 50% and mean grain sizes
greater than 30 .mu.m. The strength of the copper alloy sheets in
comparative examples was decreased greatly by annealing and copper
alloy sheets in comparative examples were unsatisfactory in
softening resistance.
[0042] Specimen 8: Maximum reduction ratios for the cold rolling
processes between the hot rolling process and the finish cold
rolling process are higher than 80%.
[0043] Specimen 9: Maximum reduction ratios for the cold rolling
processes between the hot rolling process and the finish cold
rolling process are higher than 80% and reduction ratio for the
finish cold rolling is higher than 85%.
[0044] Specimen 10: Maximum reduction ratios for the cold rolling
processes between the hot rolling process and the finish cold
rolling process are higher than 80%.
[0045] Specimen 11: Minimum reduction ratios for the cold rolling
processes between the hot rolling process and the finish cold
rolling process are lower than 50%.
[0046] Specimen 12: Reduction ratio for the finish cold rolling is
higher than 85%.
[0047] Specimen 13: Maximum reduction ratios for the cold rolling
processes between the hot rolling process and the finish cold
rolling process are higher than 80% and reduction ratio for the
finish cold rolling is higher than 85%.
[0048] Specimen 14: Minimum reduction ratios for the cold rolling
processes between the hot rolling process and the finish cold
rolling process are lower than 50%. Reduction ratio for the finish
cold rolling is lower than 30%.
[0049] Specimen 15: Minimum reduction ratios for the cold rolling
processes between the hot rolling process and the finish cold
rolling process are lower than 50%. Reduction ratio for the finish
cold rolling is higher than 85%.
[0050] Specimen 16: The working cycle including the cold rolling
process and the annealing process is performed only once between
the hot rolling process and the finish cold rolling process.
[0051] Although the invention has been described in its preferred
embodiments with a certain degree of particularity, obviously many
changes and variations are possible therein. It is therefore to be
understood that the present invention may be practiced other wise
than as specifically described herein without departing from the
scope and spirit thereof.
* * * * *