Patent Application
20130075272
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.
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.
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.
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.
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.
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.
Patent Document 1: Japanese Patent (Granted) Publication No. 4011336
Patent Document 2: Japanese Unexamined Patent Application, Second Publication No. 2001-240949
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.
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.
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.
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.
Namely, the inventors of the present invention increased a formation ratio of the special grain boundary and controlled the ratio of LσN to LN to be 0.35 or higher (LσN/LN≧0.35), LσN being a unit total special grain boundary length and LN 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.
Here, the special grain boundary is the corresponding interface having the Σ value of 3≦Σ≦29, the Σ 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≦15°/Σ1/2.
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° C. to 900° 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 (LσN/LN≧0.35).
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 (Lσ/L≧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.
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:
Lσ
N
/L
N≧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° or more is defined as the crystal grain boundary, and a unit total crystal grain boundary length LN being a converted value corresponding to a unit area of 1 mm2 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 Lσ 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 LσN being a converted value corresponding to a unit area of 1 mm2 from the total special crystal grain boundary length Lσ, and
(c) LσN/LN being a ratio of LσN, which is the measured unit total special crystal grain boundary length, to LN, which is the measured unit total crystal grain boundary length.
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 μm to 1000 μm.
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:
imparting machining stress by machining the highly pure copper anode for electrolytic copper plating; and
performing recrystallization heat treatment at 250° C. to 900° C. after the step of imparting machining stress, wherein
the special grain boundary length ratio LaN/LN is 0.35 or more.
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.
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 LσN/LN becomes 0.35 or more.
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° C. to 900° C., and
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.
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
the step of performing recrystallization heat treatment may be carried out by heating the anode within a temperature range of 250° C. to 900° 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.
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: LaN/LN≧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° or more is defined as the crystal grain boundary, and a unit total crystal grain boundary length LN being a converted value corresponding to a unit area of 1 mm2 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 LσN being a converted value corresponding to a unit area of 1 mm2 from the total special crystal grain boundary length Lσ; and (c) LσN/LN being a ratio of LσN, which is the measured unit total special crystal grain boundary length, to LN, which is the measured unit total crystal grain boundary length.
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.
(a) to (d) of
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.
As shown in the schematic drawings of (a) to (d) of
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 LσN/LN≧0.35. LσN/LN is a length ratio of special grain boundaries, which is defined by the description above (the corresponding interface having the Σ value of 3≦Σ≦29, and the intrinsic corresponding site lattice orientation defect Dq of the corresponding interface satisfying the relationship Dq≦15°/Σ1/2). LσN is the total special crystal grain boundary length in a unit area, and LN 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.
The unit total crystal grain boundary length LN 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° 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 mm2 to obtain the unit total crystal grain boundary length LN.
If the special grain boundary length ratio LσN/LN 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 LσN/LN is set to be 0.35 or higher.
The highly pure copper anode of the first aspect of the present invention is an anode made of the copper defined by the
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 μm to 1000 μm. If the average diameter of the crystal grains deviates from this range, a large amount of anode slime is formed.
The highly pure copper anode having a crystal grain boundary structure in which the special grain boundary length ratio LσN/LN of the unit total special boundary length LσN to unit total grain boundary length LN satisfies the relationship of LσN/LN≧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° C. to 900° C.
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 LσN/LN≧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° C. to 900° 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.
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 LσN/LN≧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° C. to 900° 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.
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 LσN can be enhanced, and the value of the special grain boundary length ratio LσN/LN can be adjusted to 0.35 or more.
In addition, a crystal grain boundary structure may also be obtained in which LσN/LN≧0.35 by repeatedly carrying out the aforementioned cold working or hot working as well as the recrystallization heat treatment multiple times.
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 LσN/LN of the unit total special boundary length LσN of crystal grain boundaries to the total crystal grain boundary length LN of crystal grain boundaries satisfies the relationship of LσN/LN≧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.
Locating the crystal grain boundary on the highly pure copper anode and the measurement of the unit total grain boundary length LN 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° 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 LN corresponding to a unit area of 1 mm2 Similarly, locating the special crystal grain boundary on the highly pure copper anode and the measurement of the unit total special grain boundary length LσN 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 Lσ within the measured area is measured. Then, the total special crystal grain boundary length Lσ is divided by the measured area, converting the value to the unit total special grain boundary length LσN corresponding to a unit area of 1 mm2.
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.).
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.
The following provides a more detailed explanation of the present invention through examples thereof.
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.
In the wire-drawing-cold-working process shown in Table 1, a wire-shaped sample having a cross-sectional shape of φ60 mm is turned into a shape having a cross-sectional shape of φ30 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 φ30 mm is transformed into a sphere with a diameter of about 40 mm by mold forging.
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.
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 LN and the unit total special grain boundary length Lσ.
The values of LN, LσN and special grain boundary length ratio LσN/LN are shown in Table 3.
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.
In addition, results of EBSD analysis for anodes 3, 5, 8, 10, 13 and 20 of the present invention are respectively shown in
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).
In addition, the unit total grain boundary length LN, the unit total special grain boundary length LσN, the special grain boundary length ratio LσN/LN, 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.
Those values are shown in Table 4.
In addition, results of EBSD analysis for comparative example anodes 1 and 4 are respectively shown in
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 cm2) as anodes and using the printed wiring boards as cathodes.
Plating solution: Copper pyrophosphate 80 g/L
Plating conditions: Solution temperature: 50° C.
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.
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 μm or more was counted.
These measurement results are shown in Tables 5 and 6.
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.
It was also demonstrated that in the comparative example anodes, in which the special grain boundary length ratio LON/LN 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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-077215 | Mar 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/057450 | 3/25/2011 | WO | 00 | 12/5/2012 |
