U.S. patent application number 13/637842 was filed with the patent office on 2013-03-28 for highly pure copper anode for electrolytic copper plating, method for manufacturing same, and electrolytic copper plating method.
This patent application is currently assigned to MITSUBISHI MATERIALS CORPORATION. The applicant listed for this patent is Naoki Kato, Koichi Kita, Satoshi Kumagai, Kiyotaka Nakaya, Mami Watanabe. Invention is credited to Naoki Kato, Koichi Kita, Satoshi Kumagai, Kiyotaka Nakaya, Mami Watanabe.
Application Number | 20130075272 13/637842 |
Document ID | / |
Family ID | 44712199 |
Filed Date | 2013-03-28 |
United States Patent
Application |
20130075272 |
Kind Code |
A1 |
Nakaya; Kiyotaka ; et
al. |
March 28, 2013 |
HIGHLY PURE COPPER ANODE FOR ELECTROLYTIC COPPER PLATING, METHOD
FOR MANUFACTURING SAME, AND ELECTROLYTIC COPPER PLATING METHOD
Abstract
Provided are a highly pure copper anode for electrolytic copper
plating, a method for manufacturing the same, and an electrolytic
copper plating method using the highly pure copper anode. The
highly pure copper anode obtains a crystal grain boundary structure
having a special grain boundary ratio L.sigma..sub.N/L.sub.N of
0.35 or more. L.sub.N is a unit total special grain boundary
length. L.sigma..sub.N is a unit total special boundary length. By
having the configuration described above, plating defect can be
reduced by suppressing the occurrence of the particles, such as the
slime or the like, which are generated on the anode side in the
plating bath.
Inventors: |
Nakaya; Kiyotaka; (Naka-shi,
JP) ; Kita; Koichi; (Susono-shi, JP) ;
Kumagai; Satoshi; (Iwaki-shi, JP) ; Kato; Naoki;
(Naka-shi, JP) ; Watanabe; Mami; (Naka-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nakaya; Kiyotaka
Kita; Koichi
Kumagai; Satoshi
Kato; Naoki
Watanabe; Mami |
Naka-shi
Susono-shi
Iwaki-shi
Naka-shi
Naka-shi |
|
JP
JP
JP
JP
JP |
|
|
Assignee: |
MITSUBISHI MATERIALS
CORPORATION
Tokyo
JP
|
Family ID: |
44712199 |
Appl. No.: |
13/637842 |
Filed: |
March 25, 2011 |
PCT Filed: |
March 25, 2011 |
PCT NO: |
PCT/JP2011/057450 |
371 Date: |
December 5, 2012 |
Current U.S.
Class: |
205/292 ;
148/432; 148/680; 148/684 |
Current CPC
Class: |
C22F 1/08 20130101; C22F
1/00 20130101; C25D 17/10 20130101 |
Class at
Publication: |
205/292 ;
148/684; 148/680; 148/432 |
International
Class: |
C25D 17/10 20060101
C25D017/10; C22F 1/08 20060101 C22F001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2010 |
JP |
2010-077215 |
Claims
1. A highly pure copper anode for electrolytic copper plating
comprising a grain boundary structure satisfying the following
relationship: L.sigma..sub.N/L.sub.N.gtoreq.0.35, wherein (a) a
total crystal grain boundary length L within a measurement area
being measured with a scanning electron microscope by irradiating
an electron beam to individual crystal grains on a surface of the
anode under a condition that an interface between crystal grains
laying side-by-side having a mutual crystal orientation difference
of 15.degree. or more is defined as the crystal grain boundary, and
a unit total crystal grain boundary length L.sub.N being a
converted value corresponding to a unit area of 1 mm.sup.2 from the
total crystal grain boundary length L; (b) locations of special
crystal grain boundaries, where a special grain boundary is formed
between an interface between crystal grains laying side-by-side,
being determined, a total special crystal grain boundary length
L.sigma. of the special crystal grain boundaries being measured
with a scanning electron microscope by irradiating an electron beam
to individual crystal grains on the surface of the anode, and a
unit total special crystal grain boundary length L.sigma..sub.N
being a converted value corresponding to a unit area of 1 mm.sup.2
from the total special crystal grain boundary length L.sigma.; and
(c) L.sigma..sub.N/L.sub.N being a ratio of L.sigma..sub.N, which
is the measured unit total special crystal grain boundary length,
to L.sub.N, which is the measured unit total crystal grain boundary
length.
2. The highly pure copper anode for electrolytic copper plating
according to claim 1, wherein the average diameter of crystal grain
is 3 .mu.m to 1000 .mu.m.
3. A method for manufacturing the highly pure copper anode for
electrolytic copper plating according to claim 1 comprising the
steps of: imparting machining stress by machining the highly pure
copper anode for electrolytic copper plating; and performing
recrystallization heat treatment at 250.degree. C. to 900.degree.
C. after the step of imparting machining stress, wherein the
special grain boundary length ratio L.sigma..sub.N/L.sub.N is 0.35
or more.
4. The method for manufacturing the highly pure copper anode for
electrolytic copper plating according to claim 3, wherein the
machining is carried out by either cold working or hot working at
least.
5. The method for manufacturing the highly pure copper anode for
electrolytic copper plating according to claim 3, wherein a process
having the cold working and the recrystallization heat treatment, a
process having the hot working and the recrystallization heat
treatment, or a combination of the two processes is carried out
repeatedly until the special grain boundary length ratio
L.sigma..sub.N/L.sub.N becomes 0.35 or more.
6. The method for manufacturing the highly pure copper anode for
electrolytic copper plating according to claim 4, wherein a process
having the cold working and the recrystallization heat treatment, a
process having the hot working and the recrystallization heat
treatment, or a combination of the two processes is carried out
repeatedly until the special grain boundary length ratio
L.sigma..sub.N/L.sub.N becomes 0.35 or more.
7. The method for manufacturing the highly pure copper anode for
electrolytic copper plating according to claim 3, wherein the step
of imparting machining stress is carried out by hot working at a
rolling reduction of 5% to 80% within a temperature range of
350.degree. C. to 900.degree. C., and the step of performing
recrystallization heat treatment is carried out by statically
holding the highly pure copper anode for 3 to 300 seconds free of
imparting the machining stress after the step of imparting
machining stress.
8. The method for manufacturing the highly pure copper anode for
electrolytic copper plating according to claim 3, wherein the step
of imparting machining stress is carried out by cold working at a
rolling reduction of 5% to 80%, and the step of performing
recrystallization heat treatment is carried out by heating the
anode within a temperature range of 250.degree. C. to 900.degree.
C. and statically holding the highly pure copper anode for 5
minutes to 5 hours free of imparting the machining stress after the
step of imparting machining stress.
9. An electrolytic copper plating method wherein the highly pure
copper anode for electrolytic copper plating according to claim 1
is used.
10. A method for manufacturing the highly pure copper anode for
electrolytic copper plating according to claim 2 comprising the
steps of: imparting machining stress by machining the highly pure
copper anode for electrolytic copper plating; and performing
recrystallization heat treatment at 250.degree. C. to 900.degree.
C. after the step of imparting machining stress, wherein the
special grain boundary length ratio L.sigma..sub.N/L.sub.N is 0.35
or more.
11. The method for manufacturing the highly pure copper anode for
electrolytic copper plating according to claim 10, wherein the
machining is carried out by either cold working or hot working at
least.
12. The method for manufacturing the highly pure copper anode for
electrolytic copper plating according to claim 10, wherein a
process having the cold working and the recrystallization heat
treatment, a process having the hot working and the
recrystallization heat treatment, or a combination of the two
processes is carried out repeatedly until the special grain
boundary length ratio L.sigma..sub.N/L.sub.N becomes 0.35 or
more.
13. The method for manufacturing the highly pure copper anode for
electrolytic copper plating according to claim 11, wherein a
process having the cold working and the recrystallization heat
treatment, a process having the hot working and the
recrystallization heat treatment, or a combination of the two
processes is carried out repeatedly until the special grain
boundary length ratio L.sigma..sub.N/L.sub.N becomes 0.35 or
more.
14. The method for manufacturing the highly pure copper anode for
electrolytic copper plating according to claim 10, wherein the step
of imparting machining stress is carried out by hot working at a
rolling reduction of 5% to 80% within a temperature range of
350.degree. C. to 900.degree. C., and the step of performing
recrystallization heat treatment is carried out by statically
holding the highly pure copper anode for 3 to 300 seconds free of
imparting the machining stress after the step of imparting
machining stress.
15. The method for manufacturing the highly pure copper anode for
electrolytic copper plating according to claim 10, wherein the step
of imparting machining stress is carried out by cold working at a
rolling reduction of 5% to 80%, and the step of performing
recrystallization heat treatment is carried out by heating the
anode within a temperature range of 250.degree. C. to 900.degree.
C. and statically holding the highly pure copper anode for 5
minutes to 5 hours free of imparting the machining stress after the
step of imparting machining stress.
16. An electrolytic copper plating method wherein the highly pure
copper anode for electrolytic copper plating according to claim 2
is used.
Description
TECHNICAL FIELD
[0001] The present invention relates to a highly pure copper anode
for electrolytic copper plating, a method for manufacturing the
highly pure copper anode, and an electrolytic copper plating method
using the highly pure copper anode. According to the highly pure
copper anode, the method for manufacturing the copper anode,
formation of particles, such as slimes or the like, which are
generated on the anode side in an electrolytic plating bath, can be
prevented during electrolytic plating using a copper pyrophosphate
bath. Also, according to the electrolytic plating method using the
highly pure copper anode, plating defect can be reduced due to
formation of the particles.
[0002] The present application claims priority on the basis of
Japanese Patent Application No. 2010-077215, filed in Japan on Mar.
30, 2010, the contents of which are incorporated herein by
reference.
BACKGROUND ART
[0003] Confectionary, a highly pure copper is used as an anode
electrode for copper plating during electrolytic plating in a
copper pyrophosphate bath used for plating on a through-hole on a
printed-wiring board.
[0004] However, in the above-mentioned electrolytic copper plating,
slimes whose major components are copper powders or metal salts are
formed on the surface of the anode during dissolution of the anode.
Such slimes are peeled off from the anode, and drift into the bath.
The slimes drifted into the bath adhere to the surface of cathode
electrode, increasing occurrence of plating defects, such as
nodules or the like.
[0005] In order to solve the problem, the electrolytic copper
plating shown in Patent Document 1 is proposed, for example. In the
electrolytic copper plating shown in Patent Document 1, a pure
copper anode, in which the oxygen content in the anode is
appropriately defined and the grain size in the anode electrode is
also appropriately defined, is used.
[0006] As an alternative method, the electrolytic copper plating
shown in Patent Document 2 is proposed, for example. In the
electrolytic copper plating shown in Patent Document 2, the crystal
grains of the pure copper anode are miniaturized by hot-forging,
cold-working, and strain relief annealing the highly pure copper
ingot.
RELATED ART DOCUMENTS
Patent Documents
[0007] Patent Document 1: Japanese Patent (Granted) Publication No.
4011336
[0008] Patent Document 2: Japanese Unexamined Patent Application,
Second Publication No. 2001-240949
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
[0009] The formation of the slimes whose major components are
copper powders or metal salts is not prevented in a satisfactory
level during the electrolytic copper plating in the copper
pyrophosphate bath using the conventional copper plating anode.
Especially, occurrence of plating defects due to the formation of
the particles, such as the slimes or the likes, is not suppressed
in a satisfactory level in a case where an elaborate plating, such
as a plating on a through-hole on a printed-wiring board, is
required.
[0010] Under the circumstance explained above, the purpose of the
present invention is to provide a highly pure copper anode for
electrolytic copper plaiting and a method of manufacturing the
highly pure copper anode. By using the anode, and performing the
method, the formation of the particles, such as the slimes or the
like, generated on the anode side in the electrolytic plating bath,
can be prevented during electrolytic copper plating using a copper
pyrophosphate bath. Also, an electrolytic copper plating method
using the highly pure copper anode is provided. By performing the
electrolytic copper plating method, occurrence of the plating
defects due to the formation of the above-mentioned particles can
be reduced.
Means for Solving the Problems
[0011] The inventors of the present invention obtained the
following findings as a result of conducting extensive studies on
the correlation between the structure of the crystal grain boundary
of a highly pure copper anode, and the anode slime formation and
formation of the plating defects during electrolytic copper plating
using a copper pyrophosphate bath.
[0012] In the case of conventional electrolytic copper plating
using a copper pyrophosphate bath and a highly pure copper anode,
copper dissolves as the electrolysis proceeds. This dissolution of
copper in the anode proceeds unevenly. Particularly, the
dissolution proceeds selectively and preferentially at a crystal
boundary, causing the partial dislodgement or the like of the
crystal grains. Such an event can be one of triggers of the slime
formation.
[0013] Namely, the inventors of the present invention increased a
formation ratio of the special grain boundary and controlled the
ratio of L.sigma..sub.N to L.sub.N to be 0.35 or higher
(L.sigma..sub.N/L.sub.N.gtoreq.0.35), L.sigma..sub.N being a unit
total special grain boundary length and L.sub.N being a unit total
grain boundary length, in order to allow the dissolution from the
surface of the anode to proceed evenly in a highly pure copper
anode for electrolytic copper plating. As a result, the dissolution
from the surface of the anode proceeds evenly, and the formation of
the particles, such as the slimes, is reduced. In other words, the
inventors of the present invention found that the plating defects
due to the slime formation on the anode can be reduced
significantly by controlling appropriately the formation ratio of
the special grain boundary.
[0014] Here, the special grain boundary is the corresponding
interface having the .SIGMA. value of 3.ltoreq..SIGMA..ltoreq.29,
the .SIGMA. value being defined based on "Trans. Met. Soc. AIME,
185, 501 (1949)". The special grain boundary is also defined as a
crystal grain boundary in which the intrinsic corresponding site
lattice orientation defect Dq at the corresponding grain boundary
as described in "Acta. Metallurgica Vol. 14, p. 1479 (1966)"
satisfies the following relationship,
Dq.ltoreq.15.degree./.SIGMA..sup.1/2.
[0015] In addition, the inventors of the present invention found
that, during the manufacturing of a highly pure copper anode for
electrolytic copper plating, by carrying out recrystallization heat
treatment over a predetermined temperature range (250.degree. C. to
900.degree. C.) after imparting machining stress by carrying out
prescribed cold working and hot working, a highly pure copper anode
for electrolytic copper plating can be manufactured having a high
formation rate of the so-called special grain boundary among the
crystal grain boundaries present on the surface of the copper anode
(L.sigma..sub.N/L.sub.N.gtoreq.0.35).
[0016] Moreover, the inventors of the present invention found that,
in the case of plating onto a through-hole on a printed-wiring
board, for example, using the highly pure copper anode having a
high special grain boundary formation ratio
(L.sigma./L.gtoreq.0.35), fine copper plating layers can be formed
that is free of contamination on the inner surface of the
through-hole of the printed-wiring board and formation of plating
defects such as nodular deposits.
[0017] A first aspect of the present invention is a highly pure
copper anode for electrolytic copper plating including a grain
boundary structure satisfying the following relationship:
L.sigma..sub.N/L.sub.N.gtoreq.0.35, wherein
[0018] (a) a total crystal grain boundary length L within a
measurement area being measured with a scanning electron microscope
by irradiating an electron beam to individual crystal grains on a
surface of the anode under a condition that an interface between
crystal grains laying side-by-side having a mutual crystal
orientation difference of 15.degree. or more is defined as the
crystal grain boundary, and a unit total crystal grain boundary
length L.sub.N being a converted value corresponding to a unit area
of 1 mm.sup.2 from the total crystal grain boundary length L;
[0019] (b) locations of special crystal grain boundaries, where a
special grain boundary is formed between an interface between
crystal grains laying side-by-side, being determined, a total
special crystal grain boundary length L.sigma. of the special
crystal grain boundaries being measured with a scanning electron
microscope by irradiating an electron beam to individual crystal
grains on the surface of the anode, and a unit total special
crystal grain boundary length L.sigma..sub.N being a converted
value corresponding to a unit area of 1 mm.sup.2 from the total
special crystal grain boundary length L.sigma., and
[0020] (c) L.sigma..sub.N/L.sub.N being a ratio of L.sigma..sub.N,
which is the measured unit total special crystal grain boundary
length, to L.sub.N, which is the measured unit total crystal grain
boundary length.
[0021] In the highly pure copper anode for electrolytic copper
plating of the first aspect of the present invention, the average
diameter of crystal grain may 3 .mu.m to 1000 .mu.m.
[0022] A second aspect of the present invention is a method for
manufacturing the highly pure copper anode for electrolytic copper
plating of the first aspect of the present invention including the
steps of:
[0023] imparting machining stress by machining the highly pure
copper anode for electrolytic copper plating; and
[0024] performing recrystallization heat treatment at 250.degree.
C. to 900.degree. C. after the step of imparting machining stress,
wherein
[0025] the special grain boundary length ratio La.sub.N/L.sub.N is
0.35 or more.
[0026] In the method for manufacturing a highly pure copper anode
for electrolytic copper plating of the second aspect of the present
invention, the machining may be carried out by either cold working
or hot working at least.
[0027] In the method for manufacturing a highly pure copper anode
for electrolytic copper plating of the second aspect of the present
invention, a process having the cold. working and the
recrystallization heat treatment, a process having the hot working
and the recrystallization heat treatment, or a combination of the
two processes may be carried out repeatedly until the special grain
boundary length ratio L.sigma..sub.N/L.sub.N becomes 0.35 or
more.
[0028] In the method for manufacturing a highly pure copper anode
for electrolytic copper plating of the second aspect of the present
invention, the step of imparting machining stress may be carried
out by hot working at a rolling reduction of 5% to 80% within a
temperature range of 350.degree. C. to 900.degree. C., and
[0029] the step of performing recrystallization heat treatment may
be carried out by statically holding the highly pure copper anode
for 3 to 300 seconds free of imparting the machining stress after
the step of imparting machining stress.
[0030] In the method for manufacturing a highly pure copper anode
for electrolytic copper plating of the second aspect of the present
invention, the step of imparting machining stress may be carried
out by cold working at a rolling reduction of 5% to 80%, and
[0031] the step of performing recrystallization heat treatment may
be carried out by heating the anode within a temperature range of
250.degree. C. to 900.degree. C. and statically holding the highly
pure copper anode for 5 minutes to 5 hours free of imparting the
machining stress after the step of imparting machining stress.
[0032] An electrolytic copper plating method of a third aspect of
the present invention is an electrolytic copper plating method in
which the highly pure copper anode of the first aspect of the
present invention. The highly pure copper anode of the first aspect
of the present invention is the highly copper anode for
electrolytic copper plating including a grain boundary structure
satisfying the following relationship:
La.sub.N/L.sub.N.gtoreq.0.35, wherein (a) a total crystal grain
boundary length L within a measurement area being measured with a
scanning electron microscope by irradiating an electron beam to
individual crystal grains on a surface of the anode under a
condition that an interface between crystal grains laying
side-by-side having a mutual crystal orientation difference of
15.degree. or more is defined as the crystal grain boundary, and a
unit total crystal grain boundary length L.sub.N being a converted
value corresponding to a unit area of 1 mm.sup.2 from the total
crystal grain boundary length L; (b) locations of special crystal
grain boundaries, where a special grain boundary is formed between
an interface between crystal grains laying side-by-side, being
determined, a total special crystal grain boundary length La of the
special crystal grain boundaries being measured with a scanning
electron microscope by irradiating an electron beam to individual
crystal grains on the surface of the anode, and a unit total
special crystal grain boundary length L.sigma..sub.N being a
converted value corresponding to a unit area of 1 mm.sup.2 from the
total special crystal grain boundary length L.sigma.; and (c)
L.sigma..sub.N/L.sub.N being a ratio of L.sigma..sub.N, which is
the measured unit total special crystal grain boundary length, to
L.sub.N, which is the measured unit total crystal grain boundary
length.
Effects of the Invention
[0033] According to the highly pure copper anode for electrolytic
copper plating, the method for manufacturing the same, and the
electrolytic copper plating method of the present invention, the
anode slime formation can be suppressed, the contamination at the
inner circumferential surface of the through-hole due to the slime
can be prevented, and formation of plating defects, such as the
nodular deposits, can be prevented, even in a case of elaborate
plating onto a through-hole on a printed-wiring board.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] (a) to (d) of FIG. 1 is a schematic drawing showing the
progression of the dissolving of an anode surface by electrolysis.
(a) of FIG. 1 indicates the initial state at the start of
electrolysis. (b) of FIG. 1 indicates the state at the start of
selective dissolution of a grain boundary after a fixed amount of
time has elapsed from the start of electrolysis. (c) of FIG. 1
indicates the state where current density disproportionation by a
shape factor occurs due to a selective dissolving of the grain
boundary, and an accelerated selective dissolving of the grain
boundary is occurring consequently. (d) of FIG. 1 indicates the
state of separation and falling off of undissolved crystal grains
due to dissolution of the grain boundary.
[0035] FIG. 2 shows the results of EBSD analysis of the anode 3 of
the present invention in which thick lines indicate special grain
boundaries and narrow lines indicate ordinary grain boundaries
(same as FIGS. 3 to 9).
[0036] FIG. 3 shows the results of EBSD analysis the anode 5 of the
present invention.
[0037] FIG. 4 shows the results of EBSD analysis of the anode 8 of
the present invention.
[0038] FIG. 5 shows the results of EBSD analysis of the anode 10 of
the present invention.
[0039] FIG. 6 shows the results of EBSD analysis of the anode 13 of
the present invention.
[0040] FIG. 7 shows the results of EBSD analysis of the anode 20 of
the present invention.
[0041] FIG. 8 shows the results of EBSD analysis of the anode 1 of
a comparative example.
[0042] FIG. 9 shows the results of EBSD analysis of the anode 4 of
a comparative example.
BEST MODE FOR CARRYING OUT THE INVENTION
[0043] The inventors of the present invention obtained the
following findings as a result of investigating the progression of
dissolution of the surface of a highly pure anode during
electrolytic copper plating.
[0044] As shown in the schematic drawings of (a) to (d) of FIG. 1,
during the initial state at the start of electrolysis (FIG. 1(a)),
there are no major changes in the anode surface. However, in a
state when a fixed amount of time has elapsed from the start of
electrolysis (FIG. 1(b)), crystal grains on the anode surface begin
to be selectively dissolved from chemically unstable grain
boundaries within the grains. In a state in which electrolysis has
progressed further (FIG. 1(c)), the current density
disproportionation by a shape factor occurs due to a selective
dissolving of the grain boundary, and an accelerated selective
dissolving of the grain boundary is occurring consequently. In a
state in which electrolysis has progressed further (FIG. 1(d)), due
to the progression of dissolution of grain boundaries on the anode
surface along with undissolved crystal grains separate and fall
off, thereby causing the formation of anode slime and the
occurrence of plating defects. In addition, a newly formed surface
is formed on those portions of the anode where undissolved crystal
grains have separated and fallen off, thereby causing the
occurrence of voltage fluctuations and making it difficult to carry
out stable electrolysis operation.
[0045] The inventors of the present invention further conducted
research on an anode that prevents the occurrence of selective
dissolution (non-uniform dissolution) from grain boundaries as the
duration of electrolysis progresses for use as a highly pure copper
anode for electrolytic copper plating. The following findings were
obtained as a result of that research. The ratio of the special
grain boundary, which is stable crystal-structurally and
chemically, is increased in a case where the anode has a specific
crystal grain structure. The specific crystal grain structure
satisfies the relationship L.sigma..sub.N/L.sub.N.gtoreq.0.35.
L.sigma..sub.N/L.sub.N is a length ratio of special grain
boundaries, which is defined by the description above (the
corresponding interface having the .SIGMA. value of
3.ltoreq..SIGMA..ltoreq.29, and the intrinsic corresponding site
lattice orientation defect Dq of the corresponding interface
satisfying the relationship Dq.ltoreq.15.degree./.SIGMA..sup.1/2).
L.sigma..sub.N is the total special crystal grain boundary length
in a unit area, and L.sub.N is the total crystal grain boundary
length in the unit area. When the proportion of these special grain
boundaries increases, the occurrence of the aforementioned
selective dissolution of grain boundaries is reduced, the
separation and falling off of undissolved crystal grains are
suppressed. As a result, the anode slime formation is reduced, and
at the same time, the formation of the plating defect due to the
slime is reduced.
[0046] The unit total crystal grain boundary length L.sub.N can be
determined using a scanning electron microscope. First, individual
crystal grains of the anode surface are irradiated with an electron
beam, and crystal orientation data is obtained from the resulting
electron backscatter diffraction pattern. Next, the total grain
boundary length L of crystal grains within the measuring range is
determined under a condition that an interface between crystal
grains laying side-by-side having a mutual crystal orientation
difference of 15.degree. or more is defined as the crystal grain
boundary. Lastly, the total grain boundary length L is divided by a
measurement area, converting it to the unit total crystal grain
boundary length corresponding to the unit area of 1 mm.sup.2 to
obtain the unit total crystal grain boundary length L.sub.N.
[0047] If the special grain boundary length ratio
L.sigma..sub.N/L.sub.N is less than 0.35, the formation of anode
slime cannot be reduced, and the formation of plating defects due
to the anode slime cannot be reduced since selective dissolution of
crystal grain boundaries during electrolysis cannot be suppressed.
Therefore, the special grain boundary length ratio
L.sigma..sub.N/L.sub.N is set to be 0.35 or higher.
[0048] The highly pure copper anode of the first aspect of the
present invention is an anode made of the copper defined by the
FIG. 2 of JIS-H2123. Copper content of the copper is 99.96% by mass
or higher. For the highly pure copper anode of the first aspect of
the present invention, a highly pure copper belonging to the first
grade or the second grade can be used. The copper content of the
first grade highly pure copper is 99.99% by mass or higher. Upper
limits of phosphorous and oxygen are 0.0003% by mass and 0.001% by
mass, respectively. In addition, Pb, Zn, Bi, Cd, Hg, S, Se and Te
contents have to be equal to or lower than the predetermined upper
limit values. The copper content of the second grade highly pure
copper is 99.96% by mass or higher. Its oxygen content is 0.001% by
mass or lower.
[0049] In addition, the average diameter of the crystal grains of
the highly pure copper anode of the present invention (as
determined by counting twin crystals as crystal grains) is
preferably 3 .mu.m to 1000 .mu.m. If the average diameter of the
crystal grains deviates from this range, a large amount of anode
slime is formed.
[0050] The highly pure copper anode having a crystal grain boundary
structure in which the special grain boundary length ratio
L.sigma..sub.N/L.sub.N of the unit total special boundary length
L.sigma..sub.N to unit total grain boundary length L.sub.N
satisfies the relationship of L.sigma..sub.N/L.sub.N.gtoreq.0.35
can be manufactured by imparting mechanical stress by carrying out
working (cold working and/or hot working) when manufacturing the
highly pure copper anode for electrolytic plating, followed by
carrying out recrystallization heat treatment at 350.degree. C. to
900.degree. C.
[0051] In a specific example of manufacturing referred to as
Manufacturing Example (A), a method for manufacturing a highly pure
copper anode having the crystal grain boundary structure satisfying
the relationship L.sigma..sub.N/L.sub.N.gtoreq.0.35 can be
exemplified. In the method, first, hot working is performed on the
highly pure copper for electrolytic plating at a rolling reduction
of 5% to 80% within a temperature range of 350.degree. C. to
900.degree. C. Then, and then recrystallization heat treatment is
carried out by statically holding the copper anode free of
imparting mechanical stress for 3 seconds to 300 seconds.
[0052] In addition, in another example of manufacturing referred to
as Manufacturing Example (B), another method for manufacturing a
highly pure copper anode having the crystal grain boundary
structure satisfying the relationship
L.sigma..sub.N/L.sub.N.gtoreq.0.35 can be exemplified. In the
method, first, cool working is performed on the highly pure copper
for electrolytic plating at a rolling reduction of 5% to 80% within
a temperature range of 350.degree. C. to 900.degree. C. Then, and
then recrystallization heat treatment is carried out by statically
holding the copper anode free of imparting mechanical stress for 5
minutes to 5 hours.
[0053] As a result of imparting stress by the hot working or the
cold working at the specific rolling reduction as described in the
aforementioned Manufacturing Examples (A) and (B), followed by
recrystallization in a state of statically holding free of
imparting stress within the predetermined temperature ranges, the
formation of special grain boundaries can be promoted.
Consequently, the ratio of the unit total special grain boundary
length L.sigma..sub.N can be enhanced, and the value of the special
grain boundary length ratio L.sigma..sub.N/L.sub.N can be adjusted
to 0.35 or more.
[0054] In addition, a crystal grain boundary structure may also be
obtained in which L.sigma..sub.N/L.sub.N.gtoreq.0.35 by repeatedly
carrying out the aforementioned cold working or hot working as well
as the recrystallization heat treatment multiple times.
[0055] As a result of carrying out electrolytic plating using as
the anode for electrolytic plating a highly pure copper anode
having a crystal grain boundary structure in which the special
grain boundary length ratio L.sigma..sub.N/L.sub.N of the unit
total special boundary length L.sigma..sub.N of crystal grain
boundaries to the total crystal grain boundary length L.sub.N of
crystal grain boundaries satisfies the relationship of
L.sigma..sub.N/L.sub.N.gtoreq.0.35, the anode slime formation can
be reduced. Moreover, in the case where copper plating is formed on
the inner surface of the through-hole of a printed wiring board,
fine copper plating layers that are free of the contamination and
the formation of plating defect can be formed on the surface of the
through-hole.
[0056] Locating the crystal grain boundary on the highly pure
copper anode and the measurement of the unit total grain boundary
length L.sub.N are carried out with a scanning electron microscope.
First, an electron beam is irradiated to individual crystal grains
on the anode surface with a scanning electron microscope. Then, an
interface between crystal grains laying side-by-side having mutual
crystal orientation difference of 15.degree. or more is defined as
the crystal grain boundary based on the crystal orientation data
obtained from the acquired electron backscatter diffraction
pattern. Then, the total crystal grain boundary length L within the
measured area is measured. Lastly, the total crystal grain boundary
length L is divided by the measured area, converting the value to
the unit total grain boundary length L.sub.N corresponding to a
unit area of 1 mm.sup.2 Similarly, locating the special crystal
grain boundary on the highly pure copper anode and the measurement
of the unit total special grain boundary length L.sigma..sub.N are
carried out as explained below. First, an electron beam is
irradiated to individual crystal grains on the anode surface with a
scanning electron microscope. Then, an interface between crystal
grains laying side-by-side having the special crystal grain
boundary is located. Then, the total special crystal grain boundary
length L.sigma. within the measured area is measured. Then, the
total special crystal grain boundary length L.sigma. is divided by
the measured area, converting the value to the unit total special
grain boundary length L.sigma..sub.N corresponding to a unit area
of 1 mm.sup.2.
[0057] More specifically, crystal grain boundaries and special
grain boundaries can be located and their lengths can be calculated
with an EBSD measuring device that uses a field emission-scanning
electron microscope (S4300-SE manufactured by Hitachi, Ltd., OIM
Data Collection manufactured by EDAX/TSL Inc.) and analytical
software (OIM Data Analysis Ver. 5.2 available from EDAX/TSL
Inc.).
[0058] In addition, measurement of average diameter of the crystal
grains of the highly pure copper anode (as determined by counting
twin crystals as crystal grains) can be carried out by determining
crystal grain boundaries from results obtained with the
aforementioned EBSD measuring device and analytical software,
calculating the number of crystal grains within the measured area,
calculating the crystal grain area by dividing the area of the
measured area by the number of the crystal grains, and determining
the average diameter of the crystal grains by converting on the
basis of a circle.
[0059] The following provides a more detailed explanation of the
present invention through examples thereof.
EXAMPLES
[0060] Highly pure copper anodes (referred to as anodes of the
present invention) 1 to 20 having the prescribed sizes shown in
Table 3 were manufactured. The anodes of the present invention 1 to
20 were manufactured by carrying out hot working (temperature,
processing method, processing rate), cold working (processing
method, processing rate) and/or recrystallization heat treatment
(temperature, time) under the conditions shown in Table 1, or
repeating these processes on recrystallized materials or cast
materials of highly pure copper of the tough pitch pure copper
(TPC) with a purity of 99.9% by mass or higher, the highly pure
copper (4N OFC) with a purity of 99.99% by mass or higher, the
highly pure copper (5N OFC) with a purity of 99.999% by mass or
higher, and the highly pure copper (6N OFC) with a purity of
99.9999% by mass or higher shown in Table 1. After the heat
treatment, the anodes 1 to 20 of the present invention were
water-cooled.
[0061] In the wire-drawing-cold-working process shown in Table 1, a
wire-shaped sample having a cross-sectional shape of .phi.60 mm is
turned into a shape having a cross-sectional shape of .phi.30 mm by
drawing process. In the ball shaping process shown in Table 1, a 47
mm length cylindrical-shaped sample having a cross-sectional shape
of .phi.30 mm is transformed into a sphere with a diameter of about
40 mm by mold forging.
[0062] In the examples shown in Table 1, repetitions of a process
having hot working and heat treatment, a process having cold
working and heat treatment, or the combination of the two processes
performed in an identical condition are shown. However, it is not
necessary to repeat the processes in the identical condition, and
the processes can be repeated in different conditions (processing
temperature, processing method, processing rate, holding
temperature, holding time), as long as it is within the condition
range defined by each of the claims.
[0063] The crystal grain boundaries and special grain boundaries of
the anodes of the present invention manufactured in the manner
describe above were identified with the aforementioned EBSD
measuring device (S4300-SE manufactured by Hitachi, Ltd., OIM Data
Collection manufactured by EDAX/TSL Inc.) and analytical software
(OIM Data Analysis Ver. 5.2 available from EDAX/TSL Inc.), followed
by determination of the unit total grain boundary length L.sub.N
and the unit total special grain boundary length L.sigma..
[0064] The values of L.sub.N, L.sigma..sub.N and special grain
boundary length ratio L.sigma..sub.N/L.sub.N are shown in Table
3.
[0065] The values of average crystal grain diameter determined from
results obtained with the aforementioned EBSD measuring device and
analytical software are also shown in Table 3.
[0066] In addition, results of EBSD analysis for anodes 3, 5, 8,
10, 13 and 20 of the present invention are respectively shown in
FIGS. 2 to 7.
[0067] Highly pure copper anodes 1 to 5 of the comparative examples
shown in Table 4 (to be referred to as comparative examples anodes)
were manufactured for comparative purposes by carrying out hot
working (temperature, processing method, processing rate), cold
working (processing method, processing rate) and recrystallization
heat treatment (temperature, time) on highly pure copper anode
materials fabricated in the manner previously described under the
conditions shown in Table 2 (with at least one of these conditions
being conditions outside the scope of the present invention).
[0068] In addition, the unit total grain boundary length L.sub.N,
the unit total special grain boundary length L.sigma..sub.N, the
special grain boundary length ratio L.sigma..sub.N/L.sub.N, and the
average diameter of the crystal grains were determined in the same
manner as in the examples for the comparative example anodes
manufactured as described above.
[0069] Those values are shown in Table 4.
[0070] In addition, results of EBSD analysis for comparative
example anodes 1 and 4 are respectively shown in FIGS. 8 and 9.
TABLE-US-00001 TABLE 1 Process 1 Heat treatment Process 2 Heat
treatment Cu Temp. Processing Temp. Time Temp. Processing Temp.
Time No. Purit Starting material (.degree. C.) method/conditions
(.degree. C.) (min) Repeat (.degree. C.) method/conditions
(.degree. C.) (min) Repeat 1 TPC Casting 900 Rolling-reduction- 900
15 5 -- -- -- -- -- hot-working, 20% 2 4N Recrystallization 650
Rolling-reduction- 650 2 7 -- -- -- -- -- OFC hot-working, 12% 3 4N
Casting 800 Extrusion- 750 100 1 -- -- -- -- -- OFC hot-working,
Area reduction rate 90% 4 6N Recrystallization 580 Hot-forging 450
10 1 -- -- -- -- -- OFC (Ball shaping) 5 4N Casting 630
Hot-forging, 630 5 3 -- -- -- -- -- OFC Forging rate 2.0 6 TPC
Recrystallization Room Rolling-reduction- 550 5 5 -- -- -- -- --
Temp. cold-working, 18% 7 5N Recrystallization Room Cold-forging,
420 15 4 -- -- -- -- -- OFC Temp. Forging rate 3.0 8 4N
Recrystallization Room Cold-forging 600 30 1 -- -- -- -- -- OFC
Temp. (Ball shaping) 9 6N Recrystallization Room Rolling-reduction-
880 100 1 -- -- -- -- -- OFC Temp. cold-working, 7% 10 4N Casting
750 Rolling-reduction- 750 2 3 680 Rolling-reduction- 680 2 3 OFC
hot-working, hot-working, 25% 15% 11 TPC Recrystallization 800
Extrusion- 800 10 1 650 Hot-forging 650 5 1 hot working, (Ball
shaping) Area reduction rate 90% 12 4N Recrystallization 780
Rolling-reduction- 780 5 2 500 Rolling-reduction- 500 5 3 OFC
hot-working, hot-working, 30% 35% 13 5N Casting 720 Hot-forging,
720 5 3 620 Rolling-reduction- 620 5 4 OFC Forging rate 3.0
hot-working, 8% 14 6N Casting 760 Hot-forging, 760 3 3 350
Rolling-reduction- 350 30 1 OFC Forging rate 2.5 hot-working, 25%
15 TPC Casting 800 Rolling-reduction- 800 5 5 Room
Rolling-reduction- 470 60 3 hot-working, Temp. cold-working, 20%
20% 16 4N Recrystallization 900 Rolling-reduction- 900 5 3 Room
Cold-forging, 400 10 1 OFC hot-working, Temp. Forging rate 2.5 25%
17 6N Recrystallization 650 Hot-forging, 650 30 1 Room
Rolling-reduction- 280 120 1 OFC Forging rate 3.0 Temp.
cold-working, 75% 18 4N Casting 880 Rolling-reduction- 880 10 4
Room Cold-forging, 800 60 1 OFC hot-working, Temp. Forging rate 3.0
20% 19 TPC Casting 600 Hot-forging, 600 5 4 Room Rolling-reduction-
450 30 2 Forging rate 3.0 Temp. cold-working, 15% 20 5N Casting 850
Extrusion- 850 2 4 Room Wire-drawing- 300 10 1 OFC hot-working,
Temp. cold-working + Area reduction rate forging 90% (ball
shaping)
TABLE-US-00002 TABLE 2 Process 1 Heat treatment Process 2 Heat
treatment Cu Temp. Processing Temp. Time Temp. Processing Temp.
Time No. Purity Starting material (.degree. C.) method/conditions
(.degree. C.) (min) Repeat (.degree. C.) method/conditions
(.degree. C.) (min) Repeat 1 4N Recrystallization Room
Wire-drawing- -- -- 1 -- -- -- -- -- OFC Temp. cold-working + cold
forging (ball shaping) 2 4N Recrystallization 350 Hot-forging, 350
2 1 -- -- -- -- -- OFC Forging rate 2.0 3 TPC Recrystallization
Room Cold-forging, -- -- 1 Room Cold-forging, 250 30 1 Temp.
Forging rate 3.0 Temp. Forging rate 3.0 4 TPC Casting 850
Extrusion- 850 5 1 Room Cold-forging 200 15 1 hot-working, Temp.
(Ball shaping) Area reduciton rate 90% 5 4N Casting 900
Rolling-reduction- 900 5 3 Room Rolling-reduction- 250 30 1 OFC
hot-working, Temp. cold-working, 30% 40%
TABLE-US-00003 TABLE 3 Avg. diameter L L.sigma. L(.sigma.)/L
.times. of crystal grains No. (mm/mm.sup.2) (mm/mm.sup.2) 100
(.mu.m) 1 111.2 64.4 57.9% 19.0 2 72.1 37.8 52.5% 27.1 3 15.5 7.8
50.6% 102.5 4 46.5 28.5 61.3% 45.6 5 133.6 84.8 63.5% 15.4 6 52.0
35.0 67.4% 38.9 7 153.8 88.4 57.5% 14.1 8 24.3 12.3 50.8% 89.2 9
2.3 1.6 70.1% 865.0 10 82.3 62.6 76.1% 21.5 11 98.0 52.8 53.9% 21.0
12 45.2 25.1 55.6% 42.3 13 27.6 18.4 66.6% 68.9 14 64.8 40.6 62.7%
29.4 15 123.9 59.0 47.6% 17.8 16 79.3 35.1 44.3% 28.3 17 61.7 41.6
67.5% 35.2 18 10.1 6.4 62.6% 202.7 19 94.1 69.2 73.6% 21.3 20 233.2
90.5 38.8% 7.5
TABLE-US-00004 TABLE 4 L L.sub..sigma. L(.sigma.)/L .times. Avg.
diameter No. (mm/mm.sup.2) (mm/mm.sup.2) 100 of crystal grains
(.mu.m) 1 661.5 153.5 23.2% 3.3 2 30.5 8.8 29.0% 67.1 3 111.0 37.1
33.4% 19.0 4 211.0 59.3 28.1% 6.7 5 130.3 41.0 31.5% 15.8
[0071] Electrolytic copper plating was carried out under the
conditions indicated below on through-holes of five printed wiring
boards using the anodes 1 to 20 of the present invention and the
comparative example anodes 1 to 5 (each having an anode surface
area of 400 cm.sup.2) as anodes and using the printed wiring boards
as cathodes.
[0072] Plating solution: Copper pyrophosphate 80 g/L [0073]
Potassium pyrophosphate 400 g/L [0074] pH 8.5 (adjusted by
ammonia)
[0075] Plating conditions: Solution temperature: 50.degree. C.
[0076] Cathode current density: 3 A/dm.sup.2 [0077] Plating time:
20 min/board
[0078] The amount of anode slime formed from the start of
electrolytic copper plating to completion of electrolytic copper
plating of the fifth printed wiring board was measured for the
aforementioned anodes 1 to 20 of the present invention and the
comparative example anodes 1 to 5.
[0079] In addition, the inner surfaces of the through-hole on the
printed wiring boards were observed with a light microscope, and
the number of nodular defects formed on the inner surface of the
through-holes having a height of 3 .mu.m or more was counted.
[0080] These measurement results are shown in Tables 5 and 6.
TABLE-US-00005 TABLE 5 Amt. of anode No. of defects (no./wafer)
slime 1st 2nd 3rd 4th 5th formed Type board board board board board
(mg) Anodes 1 0 0 0 0 1 <10 of 2 0 0 0 0 0 <10 Present 3 0 0
0 0 0 <10 Invention 4 0 0 0 0 1 <10 5 0 0 0 0 1 <10 6 0 0
0 0 1 <10 7 0 0 0 0 0 <10 8 0 0 0 0 1 <10 9 0 0 0 0 0
<10 10 0 0 0 0 0 <10 11 0 0 0 0 0 <10 12 0 0 0 0 0 <10
13 0 0 0 0 1 <10 14 0 0 0 0 1 <10 15 0 0 0 0 1 <10 16 0 0
0 0 0 <10 17 0 0 0 0 1 <10 18 0 0 0 0 1 <10 19 0 0 0 0 0
<10 20 0 0 0 0 0 <10 Note: The amount of anode slime formed
indicates the total amount formed at completion of plating the
fifth board.
TABLE-US-00006 TABLE 6 Amt. of anode No. of defects (no./wafer)
slime 1st 2nd 3rd 4th 5th formed Type board board board board board
(mg) Anodes of 1 0 0 0 2 2 32 Comparative 2 0 0 0 2 3 38 Example 3
0 0 0 3 3 31 4 0 0 0 2 3 35 5 0 0 0 3 2 34 Note: The amount of
anode slime formed indicates the total amount formed at completion
of plating the fifth board.
[0081] Based on the results shown in Tables 5 and 6, followings
were demonstrated. According to the highly pure copper anode for
electrolytic copper plating, the method for manufacturing the
highly pure copper anode for electrolytic copper plating, and the
electrolytic copper plating method of the present invention, for
example even in the case where fine copper plating layers are
formed on an inner surface of a through-hole of a printed wiring
board, the anode slime formation can be suppressed. At the same
time, the contamination on the inner surface, and the formation of
plating defect, such as the nodular deposit or the like, can be
prevented.
[0082] It was also demonstrated that in the comparative example
anodes, in which the special grain boundary length ratio
LO.sub.N/L.sub.N was less than 0.35, large amounts of anode slime
were formed. Furthermore, there were large numbers of plating
defects due to the anode slime.
INDUSTRIAL APPLICABILITY
[0083] The present invention has a significantly high industrial
applicability, since it shows excellent effects of being able to
suppress the anode slime formation and to prevent the formation of
plating defect on the surface of a plated material in an
electrolytic copper plating. Particularly, in the case where it is
applied to formation of a copper plating layer on an inner surface
of a through-hole on a printed-wiring board, the contamination on
the inner surface of the through- hole on the printed-wiring board
and formation of plating defect, such as the nodular deposit or the
like, can be prevented.
* * * * *