Copper alloy sheet, copper alloy sheet with plating film, and manufacturing method thereof

Abstract

To provide: a copper alloy sheet including Zn and capable of enhancing solder wettability and the adhesion of a plating film; a copper alloy sheet having the plating film; and methods for manufacturing them.SOLUTION: The copper alloy sheet includes Zn of more than 2.0% (mass%, the same hereinafter) and 32.5% or less, Sn of 0.1% or more and 0.9% or less, Ni of 0.05% or more and less than 1.0%, Fe of 0.001% or more and less than 0.1%, P of 0.005% or more and 0.1% or less and the remainder consisting of Cu and inevitable impurities in the central part in the sheet thickness direction. A surface Zn concentration in the surface is 60% or less of that in the central part, and a surface layer part to a depth having 90% of the central Zn concentration from the surface has a Zn concentration increasing toward the central part in the sheet direction from the surface at a concentration gradient of 10 mass% / μm or more and 1000 mass% / μm or less.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a copper alloy sheet containing Sn, Ni, Fe, and P in brass (Cu-Zn alloy), a plated copper alloy sheet obtained by plating the copper alloy sheet, and a method for producing the same. This application claims priority based on Japanese Patent Application No. 2019-144181, filed in Japan on August 6, 2019, the contents of which are incorporated herein by reference. [Background technology]

[0002] Copper or copper alloys are used for electronic and electrical conductive parts such as terminals of connectors in semiconductor devices or movable conductive pieces of electromagnetic relays, and among them, brass (Cu-Zn alloy) has been widely used from the viewpoints of strength, workability, cost balance, etc. In addition, in the case of terminals of connectors, etc., mainly to improve the reliability of contact with the conductive member of the counterpart side, it has become common to use a Cu-Zn alloy substrate (base plate) with tin (Sn) plating on its surface, and in consideration of recyclability, etc., there has been an increase in the use of Cu-Zn-Sn-based alloys in which Sn is added to the Cu-Zn alloy substrate itself.

[0003] However, these Cu-Zn-Sn based alloys have a problem in that they have low stress relaxation resistance, and in order to improve this stress relaxation resistance, measures such as those described in Patent Documents 1 to 5 have been proposed.

[0004] Patent Document 1 describes that the stress relaxation resistance can be improved by adding Ni to a Cu-Zn-Sn based alloy to form a Ni-P based compound. Patent Document 2 describes that the strength, elasticity, and heat resistance can be improved by adding Ni and Fe together with P to a Cu-Zn-Sn alloy to form a compound. Although Patent Document 2 does not directly describe stress relaxation resistance, the above-mentioned improvements in strength, elasticity, and heat resistance are considered to mean improvements in stress relaxation resistance.

[0005] Patent Document 3 describes that the stress relaxation resistance can be improved by adding Ni to a Cu-Zn-Sn alloy and adjusting the Ni / Sn ratio within a specific range, and also describes that the addition of a small amount of Fe is effective in improving the stress relaxation resistance.

[0006] Patent Document 4 is directed to lead frames, and describes that it is possible to improve stress relaxation resistance by adding Ni, Fe, and P to a Cu-Zn-Sn alloy and simultaneously adjusting the atomic ratio of (Ni+Fe) / P to within the range of 0.2 to 3 to generate an Fe-P compound, a Ni-P compound, or an Fe-Ni-P compound.

[0007] Although the proposals in Patent Documents 1 to 4 have made it possible to improve the stress relaxation resistance to some extent, it is still difficult to say that it is sufficient, and further improvement has been desired. Under these circumstances, as described in Patent Document 5, it has been discovered that the stress relaxation resistance can be further improved by adjusting the total amount of Fe, Ni, and P, the (Ni+Fe) / P, the Fe / Ni ratio, and further Sn / (Ni+Fe) in a well-balanced manner.

[0008] As described above, copper alloys for conductive parts of electronic and electrical equipment, which are made of brass (Cu-Zn alloy) containing Sn, Ni, Fe, and P, are capable of providing excellent stress relaxation resistance properties, particularly in parts such as connectors, which have bent parts that are rolled into thin plates (strips) and bent, and which are used in such a way that the bent part comes into contact with a mating conductive material and maintains contact with the mating conductive material due to the springiness of the bent part. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 5-33087 [Patent Document 2] JP 2006-283060 A [Patent Document 3] Patent No. 3953357 [Patent Document 4] Patent No. 3717321 [Patent Document 5] Patent No. 5303678 Summary of the Invention [Problem to be solved by the invention]

[0010] By the way, copper alloys containing Zn have a good balance between excellent mechanical strength and good electrical conductivity due to the addition of Zn. However, there is a risk that the solder wettability will deteriorate and the electrical connection reliability will be deteriorated. In particular, in order to further improve the electrical connection reliability of conductive parts of electronic and electrical equipment, a heating and melting treatment (reflow treatment) is often performed after applying Sn plating to the base material. However, when copper alloys containing Zn are subjected to such treatment, the solder wettability of the Sn-plated surface is significantly reduced, and there is also a risk that the adhesion of the plating film will also be reduced.

[0011] The present invention has been made in view of the above circumstances, and has an object to improve the solder wettability and the adhesion of a plating film in a copper alloy sheet containing Zn. [Means for solving the problem]

[0012] In view of these circumstances, the inventors conducted extensive research and discovered that the decrease in solder wettability is caused by the oxidation of Zn present on the surface of the base material, and that in particular, when a base material is plated with Sn and then subjected to a heat melting process, the Zn in the base material diffuses due to heating and reaches the surface of the plating film, causing a significant decrease in solder wettability. In this case, Cu in the copper alloy base material is alloyed with Sn to form an Sn-Cu alloy layer, and Zn is taken into this Sn-Cu alloy layer, which makes it easier for Zn to diffuse to the surface of the Sn layer (plating film surface) above it.

[0013] Because Zn is an active element, the Zn on the surface of the copper alloy sheet before plating immediately becomes Zn oxide. When plating a copper alloy sheet with a large amount of Zn on the surface, the Zn oxide on the base material surface and the metal in the plating film cannot easily form a metallic bond, so the adhesion of the plating film is poor and it is prone to peeling when heated, etc.

[0014] Based on such knowledge, the present invention aims to suppress surface oxidation by appropriately controlling the Zn concentration in the surface layer of a copper alloy sheet, and to reduce the Zn concentration in a plating film even when a plating film is formed, thereby improving solder wettability and adhesion.

[0015] The copper alloy sheet of the present invention contains, in the central portion in the thickness direction, Zn of more than 2.0% (mass%, the same applies below) and not more than 32.5%, Ni of 0.1% or more and not more than 0.9%, Sn of 0.05% or more and less than 1.0%, Fe of 0.001% or more and less than 0.1%, P of 0.005% or more and not more than 0.1%, and the balance being Cu and unavoidable impurities, and has a surface layer portion whose Zn concentration at the surface is 60% or less of the central Zn concentration at the central portion, and whose Zn concentration is 90% of the central Zn concentration from the surface, and the Zn concentration in the surface layer portion increases from the surface toward the central portion with a concentration gradient of 10 mass% / μm or more and 1000 mass% / μm or less.

[0016] This copper alloy sheet has a surface Zn concentration of 60% or less of the central Zn concentration, and since the surface Zn concentration is low, Zn oxide is unlikely to occur on the surface. Therefore, it has excellent electrical connection reliability and can be used as a contact as is, and when a plating film is formed on the surface, peeling of the plating film can be prevented. In addition, even if a heat treatment is performed after the plating film is formed, diffusion of Zn into the plating film can be suppressed. Therefore, the plating film surface also has excellent solder wettability.

[0017] From the viewpoint of preventing oxidation of the copper alloy sheet surface and suppressing Zn diffusion into the plating film, the surface Zn concentration is preferably 60% or less of the central Zn concentration. In addition, since the Zn concentration changes rapidly in the surface layer, the surface layer is thin and the excellent mechanical properties of the copper alloy are maintained.

[0018] In the surface layer, if the Zn concentration gradient from the surface is less than 10 mass% / μm, the above-mentioned Zn diffusion suppression property is saturated, but the desired Zn concentration does not reach a considerable depth, and the properties as a Zn-containing copper alloy sheet are impaired. On the other hand, if the Zn concentration gradient exceeds 1000 mass% / μm, the surface layer with a low Zn concentration becomes too thin, and the effect of suppressing Zn diffusion is poor.

[0019] In one embodiment of the copper alloy sheet, the thickness of the surface layer is 0 μm or more and 1 μm or less. If the thickness of the surface layer exceeds 1 μm, the proportion of the range with low Zn concentration in the entire sheet thickness increases, and the mechanical properties of the Zn-containing copper alloy may be impaired. This deterioration of properties is particularly noticeable when the sheet thickness is thin.

[0020] The copper alloy sheet with a plated layer of the present invention comprises the copper alloy sheet and a plated layer formed on the surface layer portion of the copper alloy sheet. This copper alloy sheet with a plating film has a low Zn concentration on the surface of the copper alloy sheet and little Zn oxide on the surface of the copper alloy sheet, so the plating film has excellent adhesion. In addition, the amount of Zn diffusing from the copper alloy sheet into the plating film can be reduced, and the copper alloy sheet has excellent solder wettability.

[0021] In one embodiment of the copper alloy sheet having a plating film, the average concentration of Zn in the plating film is 10% or less of the central Zn concentration.

[0022] When the average Zn concentration in the plating film exceeds 10% of the Zn concentration at the center of the copper alloy sheet, the effect of surface diffusion of Zn on the contact resistance becomes large.

[0023] In another embodiment of the copper alloy sheet with a plating film, the plating film is made of one or more layers selected from tin, copper, zinc, nickel, gold, silver, palladium, and alloys thereof. By making the plating film of these metals or alloys, it can be suitably used as a connector terminal.

[0024] The method for producing a copper alloy sheet of the present invention includes a Zn enrichment treatment in which Zn is diffused onto the surface to form a surface portion enriched in Zn, and a surface portion removal treatment in which the surface portion is removed to form a surface layer portion.

[0025] In this manufacturing method, Zn in the Zn-containing copper alloy is first diffused and concentrated in the surface portion, and then the concentrated surface portion is removed. The surface layer portion formed after removing the surface portion has a low Zn concentration and generates little oxide film, and therefore has excellent solder wettability.

[0026] In the method for producing a copper alloy sheet having a plating film of the present invention, the plating film is applied to a copper alloy sheet having a current density of 0.1 A / dm 2 More than 60A / dm 2 The copper alloy plate is formed by the following electrolytic plating process. The current density during electrolytic plating is 0.1 A / dm 2 If the current density is less than 60 A / dm, the deposition rate is slow and it is not economical. 2 If it exceeds this value, the diffusion limit current density is exceeded, and a film without defects cannot be formed.

[0027] For example, when electrolytic tin plating is performed as the electrolytic plating, a reflow treatment may be performed to improve whisker resistance. That is, in one embodiment of the method for producing a copper alloy sheet with a plating film, the plating film contains tin, and after the electrolytic plating, a reflow treatment is performed at a heating peak temperature of 230°C to 330°C, preferably 300°C or less, and a heating time at the heating peak temperature of 0.5 seconds to 30 seconds, preferably 1 second to 20 seconds.

[0028] If the peak heating temperature during processing is less than 230°C or the heating time is less than 0.5 seconds, the tin will not melt. If the heating temperature exceeds 330°C or the heating time exceeds 30 seconds, excessive heating will cause Zn to diffuse into the plating film surface, reducing solder wettability. Effect of the Invention

[0029] According to the present invention, it is possible to suppress surface oxidation, improve the electrical connection reliability and the solder wettability of the surface of a copper alloy sheet, and even if a plating film is formed, to reduce the Zn concentration in the plating film, thereby improving the solder wettability of the surface of the plating film and the adhesion between the plating film and the copper alloy sheet. [Brief description of the drawings]

[0030] [Figure 1] 1 is a cross-sectional view showing a schematic diagram of one embodiment of a copper alloy sheet having a plating film according to the present invention. [Diagram 2] FIG. 2 is an analysis diagram of the Zn component in the depth direction of the copper alloy sheet measured by XPS. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] An embodiment of the present invention will be described. In the plated copper alloy sheet 1 of this embodiment, as shown in FIG. 1, a plated copper alloy sheet 10 containing Zn, Sn, Ni, P, and Fe has a plated copper alloy sheet 20 formed on a surface 10a thereof, the plated copper alloy sheet 10 comprising a Cu layer 21, a Sn—Cu alloy layer 22, and a Sn layer 23 laminated in that order.

[0032] [Copper alloy plate] The copper alloy sheet 10 contains, at the center in the sheet thickness direction, in mass % (the same applies to the following element contents), Zn from more than 2.0% to 32.5%, Sn from 0.1% to 0.9%, Ni from 0.05% to less than 1.0%, Fe from 0.001% to less than 0.1%, P from 0.005% to 0.1%, and the balance is Cu and unavoidable impurities.

[0033] (Zn) Zn (zinc) is a basic alloying element in the copper alloy (brass) targeted in the present invention, and is an element effective in improving the strength and springiness of the copper alloy sheet 10. In addition, Zn is cheaper than Cu, so it is also effective in reducing the material cost of the copper alloy sheet 10. If the Zn concentration is 2.0% or less, the effect of reducing the material cost is not sufficiently obtained. In addition, the effect of improving the strength and springiness is insufficient. On the other hand, if the Zn concentration exceeds 32.5%, the stress relaxation resistance property is reduced, and even if Fe, Ni, and P are added, it becomes difficult to ensure sufficient stress relaxation resistance property, and the corrosion resistance is reduced, and a large amount of β phase is generated, so that the cold rolling property and bending workability are also reduced. Therefore, the Zn concentration is set to be in the range of more than 2.0% and not more than 32.5%. In addition, even within the above range, the Zn concentration is preferably in the range of 4.0% to 32.5%, more preferably in the range of 8.0% to 32.0%, and particularly preferably in the range of 8.0% to 27.0%.

[0034] In this case, the Zn concentration at the center of the sheet thickness (central Zn concentration) is more than 2.0% and not more than 32.5% as described above, but the Zn concentration at the surface 10a (surface Zn concentration) is 60% or less (0% or more) of the central Zn concentration. Also, the Zn concentration has a concentration gradient of 10 mass% / μm or more and 1000 mass% / μm or less from the surface to the center of the sheet thickness.

[0035] Since the surface Zn concentration of this copper alloy sheet 10 is 60% or less of the central Zn concentration, Zn oxide is unlikely to occur on the surface 10a, and even if plating is subsequently performed and then heat treated, diffusion of Zn into the plating film 20 can be suppressed. Therefore, the solder wettability is excellent, and peeling of the plating film 20 can be prevented.

[0036] From the viewpoints of preventing oxidation of the surface 10a and suppressing Zn diffusion into the plating film 20, it is sufficient that the surface 10a does not contain Zn (the surface Zn concentration is 0% of the central Zn concentration). However, if the surface Zn concentration is 60% or less of the central Zn concentration, the properties of a Zn-containing copper alloy are imparted to a certain degree to the surface, which is preferable. The surface Zn concentration is more preferably 40% or less of the central Zn concentration, and even more preferably 30% or less.

[0037] If the Zn concentration gradient occurring from the surface 10a in the sheet thickness direction is less than 10 mass% / μm, the desired Zn concentration is not reached until a considerable depth is reached, and the properties of the Zn-containing copper alloy sheet are impaired. On the other hand, if the Zn concentration gradient exceeds 1000 mass% / μm, the portion where the concentration gradient occurs (the surface portion described below) becomes too thin, and the effect of suppressing Zn diffusion becomes poor. This Zn concentration gradient is preferably 20 mass% / μm or more and 500 mass% / μm or less, more preferably 50 mass% / μm or more and 200 mass% / μm or less.

[0038] In the portion where this concentration gradient occurs, the range from the depth position where the Zn concentration is 90% of the central Zn concentration to the surface 10a is defined as the surface layer 11. The thickness of this surface layer 11 is 0 μm or more and 1 μm or less, preferably 0.3 μm or less, and more preferably 0.2 μm or less. The portion inside the surface layer 11 is defined as the inside 12 of the base material.

[0039] 2 is a graph showing the results of analyzing the Zn content in the depth direction of a sample obtained by thinning the copper alloy sheet 10 in the sheet thickness direction using an X-ray photomolecular spectroscopy (XPS), where the horizontal axis is the depth from the surface 10a and the vertical axis is the XPS spectrum intensity. The Zn concentration measured at the center in the sheet thickness direction of the base material is stable, and the arithmetic average of the maximum and minimum values ​​is taken as the "center Zn concentration," and the depth (from the surface 10a) to the position where the Zn concentration, which changes from the surface 10a toward the center in the sheet thickness direction, first reaches 90% of the center Zn concentration, is taken as the "surface layer thickness."

[0040] (Sn, Ni, Fe, P) The addition of Sn (tin) is effective in improving the strength of the copper alloy sheet 10, and the addition of Sn to a brass alloy as the base material for electronic and electrical equipment materials to be used after Sn plating is advantageous in improving the recyclability of the Sn-plated brass material. Furthermore, the present inventors have found that the coexistence of Sn with Ni and Fe also contributes to improving the stress relaxation resistance of the copper alloy sheet 10. If the Sn content is less than 0.1%, these effects cannot be sufficiently obtained, while if the Sn content exceeds 0.9%, the hot workability and cold rolling properties are reduced, and there is a risk of cracks occurring during hot rolling or cold rolling, and the electrical conductivity is also reduced.

[0041] Therefore, the amount of Sn added is set to the range of 0.1% to 0.9%. The Sn concentration is preferably within the above range, particularly within the range of 0.2% to 0.8%.

[0042] Ni (nickel) is a characteristic additive element in the present invention, along with Fe and P. By adding an appropriate amount of Ni to a Cu-Zn-Sn alloy and allowing Ni to coexist with Fe and P, [Ni,Fe]-P-based precipitates can be precipitated from the parent phase (mainly α-phase). Also, by allowing Ni to coexist with Fe, Co, and P, [Ni,Fe,Co]-P-based precipitates can be precipitated from the parent phase (mainly α-phase).

[0043] The presence of these [Ni,Fe]-P-based precipitates or [Ni,Fe,Co]-P-based precipitates can pin the grain boundaries during recrystallization, thereby reducing the average grain size of the copper parent phase. As a result, the strength of the copper alloy sheet 10 can be increased. In addition, by reducing the average grain size in this way, bending workability and stress corrosion cracking resistance can also be improved. Furthermore, the presence of these precipitates can significantly improve the stress relaxation resistance. In addition, the coexistence of Ni with Sn, Fe, Co (cobalt), and P is effective not only in improving the stress relaxation resistance due to the precipitates, but also in improving strength through solid solution strengthening. Here, if the amount of Ni added is less than 0.05%, the stress relaxation resistance cannot be sufficiently improved. On the other hand, if the amount of Ni added is 1.0% or more, the amount of Ni dissolved in the parent phase increases, reducing the electrical conductivity, and increasing the amount of expensive Ni raw material used, resulting in an increase in cost.

[0044] Therefore, the amount of Ni added is set to the range of 0.05% or more and less than 1.0%. Even within the above range, the amount of Ni added is particularly preferably set to the range of 0.05% or more and less than 0.8%.

[0045] Fe (iron) is a characteristic additive element in the present invention, and by adding an appropriate amount of Fe to a Cu-Zn-Sn alloy and allowing Fe to coexist with Ni and P, it is possible to cause [Ni,Fe]-P-based precipitates to precipitate from the parent phase (mainly α-phase). Also, by allowing Fe to coexist with Ni, Co, and P, it is possible to cause [Ni,Fe,Co]-P-based precipitates to precipitate from the parent phase (mainly α-phase).

[0046] The presence of these [Ni,Fe]-P-based precipitates or [Ni,Fe,Co]-P-based precipitates can reduce the average grain size of copper by pinning the grain boundaries during recrystallization, and as a result, the strength of the copper alloy sheet 10 can be increased. In addition, by reducing the average grain size in this way, bending workability and stress corrosion cracking resistance can also be improved. Furthermore, the presence of these precipitates can significantly improve the stress relaxation resistance. Here, if the amount of Fe added is less than 0.001%, the effect of pinning the grain boundaries is not sufficiently obtained, and therefore sufficient strength cannot be obtained. On the other hand, even if the amount of Fe added is 0.10% or more, no further improvement in strength is observed, and the amount of Fe dissolved in the parent phase increases, resulting in a decrease in electrical conductivity and a decrease in cold rolling ability.

[0047] Therefore, the amount of Fe added is set to the range of 0.001% or more and less than 0.10%. Even within the above range, the amount of Fe added is preferably set to the range of 0.002% or more and 0.08% or less.

[0048] P (phosphorus) has a strong bond with Fe, Ni, and even Co, so that when an appropriate amount of P is added together with Fe and Ni, it is possible to form [Ni,Fe]-P type precipitates. Also, when an appropriate amount of P is added together with Fe, Ni, and Co, it is possible to form [Ni,Fe,Co]-P type precipitates.

[0049] The presence of these precipitates can improve the stress relaxation resistance of the copper alloy sheet 10. Here, if the P content is less than 0.005%, it becomes difficult to sufficiently precipitate the [Ni,Fe]-P precipitates or the [Ni,Fe,Co]-P precipitates, and the stress relaxation resistance cannot be sufficiently improved. On the other hand, if the P content exceeds 0.10%, the amount of P dissolved in the matrix increases, so that the electrical conductivity decreases and the rollability decreases, making it easier for cold rolling cracks to occur.

[0050] Therefore, the P content is set to the range of 0.005% or more and 0.10% or less. Furthermore, within the above range, the P content is particularly preferably in the range of 0.01% or more and 0.08% or less.

[0051] Incidentally, P is an element that is often inevitably mixed in from the raw materials used to melt the copper alloy. Therefore, in order to regulate the P content as described above, it is desirable to appropriately select the raw materials used to melt the copper alloy.

[0052] The remainder of the above elements is basically Cu (copper) and unavoidable impurities. Examples of unavoidable impurities include Mg, Al, Mn, Si, (Co), Cr, Ag, Ca, Sr, Ba, Sc, Y, Hf, V, Nb, Ta, Mo, W, Re, Ru, Os, Se, Te, Rh, Ir, Pd, Pt, Au, Cd, Ga, In, Li, Ge, As, Sb, Ti, Tl, Pb, Bi, S, O, C, Be, N, H, Hg, B, Zr, and rare earth elements, and the total amount of these unavoidable impurities is preferably 0.3 mass% or less.

[0053] Incidentally, Co may be intentionally contained in an amount of 0.001% or more and less than 0.10%. If Co is added together with Ni, Fe, and P in this range, [Ni, Fe, Co]-P-based precipitates are generated, and the stress relaxation resistance of the copper alloy sheet 10 can be further improved. Here, if the amount of Co added is less than 0.001%, the effect of further improving the stress relaxation resistance by adding Co cannot be obtained, while if the amount of Co added is 0.10% or more, the amount of solid-solubilized Co increases, the electrical conductivity decreases, and the cost increases due to the increased amount of expensive Co raw material used.

[0054] Therefore, when Co is added, the amount of Co added is set to be within the range of 0.001% or more and less than 0.10%. The amount of Co added is preferably within the above range, particularly within the range of 0.002% or more and 0.08% or less. Even if Co is not actively added, it goes without saying that less than 0.001% Co may be contained as an impurity.

[0055] [Plating film] The plating film 20 is composed of, from the surface 10a of the copper alloy sheet 10 to the surface 20a of the plating film 20, a Cu layer 21 having a thickness of 0 μm to 1 μm, a Sn—Cu alloy layer 22 having a thickness of 0.1 μm to 1.5 μm, and a Sn layer 23 having a thickness of 0.1 μm to 3.0 μm, in that order.

[0056] If the thickness of the Cu layer 21 exceeds 1 μm, high thermal stress is generated inside the plating film layer during heating, which may cause peeling of the plating film 20. This Cu layer 21 may not even be present.

[0057] The Sn-Cu alloy layer 22 is hard, and if its thickness is less than 0.1 μm, the effect of reducing the insertion force during use as a connector is reduced, resulting in a decrease in strength. If the thickness of the Sn-Cu alloy layer 22 exceeds 1.5 μm, the thermal stress generated in the plating film 20 during heating increases, and there is a risk of the plating film 20 peeling off.

[0058] If the thickness of the Sn layer 23 is less than 0.1 μm, the solder wettability decreases, and if the thickness exceeds 3.0 μm, there is a risk of high thermal stress occurring inside the plating film 20 when heated.

[0059] The average concentration of Zn in the plating film 20 having the above-mentioned layer structure is 10% or less (0% or more) of the Zn concentration at the center of the copper alloy sheet 10.

[0060] If the average Zn concentration in the plating film 20 exceeds 10% of the central Zn concentration in the copper alloy sheet 10, the Zn in the plating film may diffuse to the surface 20a, reducing the solder wettability. The average Zn concentration in the plating film 20 is more preferably 5% or less of the central Zn concentration in the copper alloy sheet 10, and even more preferably 3% or less.

[0061] [Manufacturing method] A method for producing the plated copper alloy sheet 1 having the above-mentioned configuration will be described.

[0062] This plated copper alloy sheet 1 is produced by producing a copper alloy base material having a composition containing more than 2.0% and not more than 32.5% Zn, 0.1% or more and not more than 0.9% Sn, 0.05% or more and less than 1.0% Ni, 0.001% or more and less than 0.1% Fe, 0.005% or more and 0.1% or less P, with the balance being Cu and unavoidable impurities (copper alloy base material production process), subjecting the obtained copper alloy base material to a surface treatment (surface treatment process), followed by plating (plating treatment process) and reflow treatment (reflow treatment process).

[0063] (Copper alloy base material manufacturing process) The copper alloy base material is manufactured by melting and casting the materials mixed in the above-mentioned composition ranges to produce a copper alloy ingot, and then subjecting the copper alloy ingot to a process including hot rolling, cold rolling, continuous annealing, and finish cold rolling in this order. In this embodiment, the thickness of the copper alloy base material is 0.2 mm.

[0064] (Surface treatment process) The obtained copper alloy base material is subjected to a surface treatment, which includes a Zn enrichment treatment for diffusing Zn in the copper alloy base material to the surface portion to enrich it, and a surface portion removal treatment for removing the Zn-enriched surface portion.

[0065] In the Zn enrichment treatment, the copper alloy base material is heated to a predetermined temperature for a predetermined time in an oxidizing atmosphere such as oxygen or ozone. The heating temperature and heating time in this case may be 100°C or higher within a time period in which recrystallization does not occur, and may be any temperature within this range, taking into consideration equipment restrictions and economic efficiency. For example, a long time may be used at a low temperature, such as 1 minute at 300°C, 2 hours at 250°C, or 5 hours at 200°C, and a short time may be used at a high temperature.

[0066] The oxidizing substance concentration in the oxidizing atmosphere may be, for example, 5 to 4000 ppm in the case of ozone, preferably 10 to 2000 ppm, and more preferably 20 to 1000 ppm. When oxygen is used without ozone, the atmospheric concentration is preferably at least twice as high as that when only ozone is used. An oxidizing substance such as ozone may be mixed with oxygen. Before the Zn enrichment treatment, a treatment for promoting the diffusion of Zn, such as the introduction of strain or vacancies by mechanical polishing, may be performed.

[0067] The surface removal treatment can be carried out by applying chemical polishing, electrolytic polishing, mechanical polishing, or the like, either alone or in combination, to the copper alloy base material that has been subjected to Zn enrichment treatment.

[0068] The chemical polishing can be performed by selective etching, etc. The selective etching can be performed by etching using an acidic or alkaline liquid containing a component capable of suppressing copper corrosion, such as a nonionic surfactant, a heterocyclic compound having a carbonyl group or a carboxyl group, an imidazole compound, a triazole compound, or a tetrazole compound.

[0069] Electrolytic polishing can be carried out, for example, by using an acid or alkaline liquid as an electrolyte and by electrolysis of components that tend to segregate at the grain boundaries of copper, thereby preferentially etching the grain boundaries.

[0070] Mechanical polishing can be performed using various commonly used methods such as blasting, lapping, polishing, buffing, grinder polishing, and sandpaper polishing.

[0071] In this manner, the copper alloy base material is subjected to Zn enrichment treatment and surface portion removal treatment to form the copper alloy sheet 10. As described above, the copper alloy sheet 10 has a lower Zn concentration in the surface layer portion 11 than the central Zn concentration, and the Zn concentration increases at a predetermined concentration gradient from the surface 10a toward the center in the sheet thickness direction.

[0072] (Plating process) Next, a plating process is performed to form a plating film 20 on the surface 10a of the copper alloy sheet 10.

[0073] The surface 10a of the copper alloy sheet 10 is cleaned by removing dirt and natural oxide films by degreasing, pickling, etc., and then a Cu plating layer is formed on the surface 10a of the copper alloy sheet 10, and then a Sn plating layer is formed on the surface of the Cu plating layer by Sn plating. The Cu plating layer and the Sn plating layer are preferably pure copper and pure tin plating layers, respectively, but may be Cu alloy plating layers and Sn alloy plating layers containing other elements, respectively, as long as the effects of the present invention are not impaired.

[0074] Each plating layer is plated with a current density of 0.1A / dm 2 More than 60A / dm 2 The plating is performed using the following electrolytic plating method. The current density during electrolytic plating is 0.1A / dm 2 If the current density is less than 60 A / dm, the deposition rate is slow and it is not economical. 2 If the current density exceeds the diffusion limit, a film without defects cannot be formed.

[0075] Table 1 shows an example of plating conditions for Cu or Cu alloy, and Table 2 shows an example of plating conditions for Sn or Sn alloy.

[0076] [Table 1]

[0077] [Table 2]

[0078] (Reflow processing process) Next, the copper alloy sheet 10 on which these plating layers are formed is subjected to a reflow treatment in which the peak heating temperature is set to 230°C or more and 330°C or less, the peak heating temperature is held for 0.5 seconds or more and 30 seconds or less, and then the temperature is cooled to 60°C or less.

[0079] By carrying out this reflow treatment, a plating film 20 is formed which is configured in this order from the surface 10a of the copper alloy sheet 10, including a Cu layer 21 having a thickness of 0 μm to 1 μm, a Sn-Cu alloy layer 22 having a thickness of 0.1 μm to 1.5 μm, and a Sn layer 23 having a thickness of 0.1 μm to 3.0 μm. Note that in this reflow treatment, all of the Cu in the Cu plating layer may be alloyed with the Sn in the Sn plating layer, and the Cu layer 21 may not be formed.

[0080] This reflow treatment may cause some Cu on the surface 10a of the copper alloy sheet 10 to diffuse into the plating film 20 and be alloyed with Sn that constitutes the plating film 20. In that case, Zn contained in the copper alloy sheet 10 may also diffuse into the plating film 20 together with Cu. However, since the Zn concentration on the surface 10a of the copper alloy sheet 10 is made low, the amount of Zn taken into the plating film 20 is also very small, and the surface diffusion of Zn can be effectively suppressed.

[0081] In addition, since the surface of the copper alloy sheet 10 contains very little Zn, there is also little surface oxide, and even if a small amount of oxide is present, it can be easily removed by normal cleaning before plating. Therefore, the copper alloy sheet 1 with a plating film has excellent adhesion between the plating film 20 and the copper alloy sheet 10.

[0082] Furthermore, since Zn oxide is unlikely to occur on the surface 20a of the plating film 20, the plating film 20 also has excellent solder wettability.

[0083] In the above embodiment, the plating film 20 consisting of the Cu layer 21, the Sn-Cu alloy layer 22, and the Sn layer 23 in this order is formed on the copper alloy sheet 10. However, the plating film is not limited to this and may be composed of one or more layers selected from tin, copper, zinc, nickel, gold, silver, palladium, and alloys thereof. EXAMPLES

[0084] [Example 1] A copper alloy ingot containing more than 2.0% and not more than 32.5% Zn, 0.1% to 0.9% Sn, 0.05% to less than 1.0% Ni, 0.001% to less than 0.1% Fe, 0.005% to 0.1% P, with the balance being Cu and unavoidable impurities, was prepared, and a plate-shaped copper alloy mother plate was produced by conventional hot rolling, intermediate annealing, cold rolling, etc. Some of the ingots further contained 0.001% to less than 0.1% Co.

[0085] Next, this copper alloy mother plate was subjected to a Zn enrichment treatment by heating under various conditions in an oxidizing atmosphere at a heating temperature of 200 to 300°C for a heating time of 1 minute to 5 hours, and then subjected to a surface removal treatment to produce copper alloy plates having various Zn concentration gradients in the surface layer.

[0086] The surface portion removal treatment was carried out by any one of the following polishing treatments. Physical polishing: Buff polishing Chemical polishing: Immersion in a polishing solution of sulfuric acid, hydrogen peroxide and polyoxyethylene dodecyl ether Electrolytic polishing: Pass electricity through a phosphoric acid solution using SUS304 as the counter electrode As a comparative example, a sample (a sample of the copper alloy mother plate as it is) that was not subjected to the Zn enrichment treatment and the surface portion removal treatment was also prepared.

[0087] Then, the Zn concentration on the surface and at each portion in the thickness direction of each of these copper alloy sheets was measured. The Zn concentration in each portion in the thickness direction was measured from the concentration profile in the depth direction by X-ray photoelectron spectroscopy (XPS). The measurement conditions for XPS were as follows:

[0088] (Measurement conditions) Pretreatment: Immerse in acetone solvent and pretreat using an ultrasonic cleaner at 38 kHz for 5 minutes. Equipment used: ULVAC PHI Inc. X-ray photoelectron spectrometer PHI5000 VersaProbe Sputtering rate: 100Å / min Sputtering time: 100 minutes

[0089] Since the depth in the above XPS is an SiO2 equivalent depth, the SiO2 equivalent depth in the XPS depth direction concentration profile was converted to an actual depth by comparing it with data measured by TEM-EDX (Energy Dispersive X-ray Spectroscopy) from a separate cross-sectional direction.

[0090] The central Zn concentration of the copper alloy sheet was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) using a sample taken from the central part of the thickness where the Zn concentration was stable.

[0091] Next, each copper alloy sheet was subjected to treatments such as degreasing and pickling to remove dirt and natural oxide films, and then a Cu plating layer was formed under the Cu plating conditions shown in Table 1, and then a Sn plating layer was formed under the Sn plating conditions shown in Table 2. The copper alloy sheets on which these plating layers were formed were then subjected to a reflow treatment to produce copper alloy sheets with a plating film.

[0092] In the reflow treatment, the plating layer was heated to a temperature within a range of 230° C. to 330° C., and then cooled to a temperature of 60° C. or less.

[0093] Then, a sample was cut out from each of the copper alloy sheets having a plating film, and the Zn concentration in the plating film was measured. The Zn concentration in the plating film was measured from the concentration profile in the depth direction from the surface by XPS, in the same manner as in the case of the above copper alloy sheet.

[0094] In addition, for each sample of bare copper alloy sheet (copper alloy sheet on which no plating film was formed) and copper alloy sheet with a plating film, the solder wettability of the surface was measured, and the surface hardness of the bare material (copper alloy sheet) and the adhesion of the plating film for the copper alloy sheet with a plating film were also measured.

[0095] <Solder wettability> The solder wettability was evaluated in accordance with the soldering test method (balance method) of JIS-C60068-2-54 using a 5200TN solder checker made by Rhesca Corporation. After removing dirt by degreasing, the wettability of each sample with lead-free solder was evaluated under the following flux application and soldering conditions.

[0096] (Flux application) Flux: 25% rosin-ethanol Flux temperature: room temperature Flux depth: 8mm Flux immersion time: 5 seconds Drip-cutting method: Place the edge against filter paper for 5 seconds to remove flux, then fix it to the device and hold for 30 seconds.

[0097] (Soldering) Solder composition: Sn-3.0%Ag-0.5%Cu manufactured by Senju Metal Industry Co., Ltd. Solder temperature: 240℃ Solder immersion speed: 10±2.5mm / sec Solder immersion depth: 2mm Solder immersion time: 10 seconds

[0098] From the obtained load / time curve, the time from the start of immersion until the buoyancy due to surface tension became zero (i.e. the contact angle between the solder and the sample became 90°) was taken as the zero-cross time (seconds). Solder wettability was rated as A (good) when the zero-cross time was less than 2 seconds, B (fair) when it was 2 to 4 seconds, and C (poor) when it was 4 seconds or more.

[0099] <Adhesion> Adhesion was evaluated by a cross-cut test on a sample that had been heated for 1000 hours at 120°C. A cutter knife was used to cut the sample to create 100 1mm square grids, and cellophane tape (Nichiban Co., Ltd. #405) was then pressed against the grids with finger pressure. After the cellophane tape was peeled off, if no peeling of the plating film occurred, it was rated A; if 3 or fewer grids peeled off, it was rated B; and if 4 or more grids peeled off, it was rated C.

[0100] <Surface hardness> Surface hardness was measured on bare materials (copper alloy sheets) without a plating film. Using a Vickers hardness tester, hardness was measured at loads of 1gf and 10gf, and hardness measured at a load of 1gf that was 80% or more of the hardness measured at a load of 10gf was rated A (good), hardness measured at a load of 70% or more but less than 80% was rated B (passable), and hardness measured at less than 70% was rated C (unacceptable).

[0101] Tables 3A, 3B and Tables 4A, 4B and 4C show the evaluation results for each bare material (copper alloy sheet) sample, and Tables 5A, 5B and Tables 6A, 6B and 6C show the evaluation results for each plated copper alloy sheet sample.

[0102] In both tables, "central Zn concentration" is the Zn concentration at the center of the sheet thickness, "central Sn, Ni, Fe, P, Co concentrations" are the concentrations of Sn, Ni, Fe, P, Co at the center of the sheet thickness, "surface Zn concentration" is the Zn concentration on the surface of the copper alloy sheet at the stage where the surface removal process has been performed, and the unit is mass%. "Ratio to center concentration" is the ratio of the surface Zn concentration to the central Zn concentration, and the unit is %. "Surface layer thickness" is the depth from the surface of the copper alloy sheet to the point where the Zn concentration first reaches 90% of the central Zn concentration, and the unit is μm, and "concentration gradient" is the gradient of the Zn concentration in the surface layer, and the unit is mass% / μm.

[0103] The surface layer thickness and concentration gradient are calculated from the depth direction concentration profile of the Zn component by XPS. Figure 2 shows an example of the profile, which is related to a sample in Table 4 with a central Zn concentration of 10 mass% and a concentration gradient of 130 mass% / μm. For each sample in Tables 3 and 4, including this example, copper alloy sheets with various surface Zn concentrations were produced. For each sample in Tables 5 and 6, a plating film was formed on each copper alloy sheet in Tables 3 and 4.

[0104] The concentration gradient means the gradient of a straight line connecting the surface concentration in the profile and the point where the concentration first reaches 90% of the concentration at the center of the sheet thickness. In other words, when the change in Zn concentration from the surface of the copper alloy sheet to the point where the concentration first reaches 90% of the concentration at the center of the sheet thickness in the depth direction concentration profile can be regarded as a straight line with a generally constant gradient even if there are local fluctuations, the gradient of the profile is defined as the concentration gradient.

[0105] Each table is organized by the central Zn concentration, which is 2.1 mass% for Table 3A, 10 mass% for Table 3B, 20 mass% for Table 4A, 32.5 mass% for Table 4B, 20 mass% for Table 4C, 2.1 mass% for Table 5A, 10 mass% for Table 5B, 20 mass% for Table 6A, 32.5 mass% for Table 6B, and 2.1 mass% for Table 6C.

[0106] In Tables 5A, 5B and 6A, 6B, and 6C, the unit of the thickness of the Cu plating layer is μm, and the thickness of the Cu plating layer is "0" means that only Sn plating was performed without Cu plating. The thickness of the Sn plating layer was 1 μm.

[0107] [Table 3A]

[0108] [Table 3B]

[0109] [Table 4A]

[0110] [Table 4B]

[0111] [Table 4C]

[0112] [Table 5A]

[0113] [Table 5B]

[0114] [Table 6A]

[0115] [Table 6B]

[0116] [Table 6C]

[0117] As shown in Tables 3 and 4, the copper alloy sheets that were not subjected to Zn enrichment treatment and surface removal treatment (the concentration gradient is "∞ (untreated)" and the Zn concentration gradient from the sheet surface is extremely steep) and those with a Zn concentration gradient of more than 1000 mass% / μm had poor solder wettability. Regarding surface hardness, in materials with a central Zn concentration of 20 mass%, those with a Zn concentration gradient of less than 10 mass% / μm showed a significant decrease in surface hardness.

[0118] Furthermore, as shown in Tables 5 and 6, the copper alloy sheets that were not subjected to the Zn enrichment treatment and the surface removal treatment (the concentration gradient was "∞ (untreated)" and the Zn concentration gradient from the sheet surface was extremely steep) and the sheets with a Zn concentration gradient of more than 1000 mass% / μm had poor adhesion even when a plating film was formed.

[0119] [Example 2] Copper alloy sheets having various concentration gradients were prepared using a method similar to that of Example 1 for a material with a central Zn concentration of 32.5 mass%, and then plated using a method similar to that of Example 1 to prepare copper alloy sheets with a plated film.

[0120] The Zn concentration in the Sn plating layer of the prepared copper alloy sheet with plating film and the solder wettability were confirmed. The Zn concentration in the Sn plating layer was measured by XPS under the same conditions as in Example 1. The results are shown in Table 7.

[0121] [Table 7]

[0122] As shown in Table 7, in samples in which the concentration gradient exceeded 1000 mass % / μm, the solder wettability deteriorated as the Zn concentration ratio to the center in the plating exceeded 10%.

[0123] [Example 3] A copper alloy sheet sample with a central Zn concentration of 20 mass% and a concentration gradient of 10 mass% / μm was prepared in the same manner as in Example 1. During preparation, the amount of removal in the surface removal treatment was varied to produce samples with the same concentration gradient but different surface Zn concentrations. The prepared sample was plated in the same manner as in Example 1 to produce a copper alloy sheet with a plated film, and the plating adhesion and solder wettability were measured. The results are shown in Table 8.

[0124] [Table 8]

[0125] As shown in Table 8, in samples in which the surface Zn concentration exceeded 60% of the center Zn concentration, plating adhesion and solder wettability deteriorated.

[0126] [Example 4] In the same manner as in Example 1, a copper alloy sheet (bare material) was prepared in which the Zn concentration at the center of the thickness of the copper alloy sheet (central Zn concentration) was 32.5 mass%, various Zn concentration gradients were present at the surface layer, and the surface Zn concentration was adjusted to 0 mass%, and then only one layer of each of the metal plating layers shown in Table 9 was formed. In this example, only the plating process was performed, and no reflow process was performed.

[0127] The plating metals were Sn, Cu, Zn, Ni, Au, Ag, and Pd. The plating current density was 3A / dm 2 The thickness of the plating film was 1 μm. Although any of commonly used acidic, neutral, or alkaline plating baths may be used as the various plating baths, in this embodiment, an acidic bath was used for Sn, Cu, Zn, Ni, and Pd, and an alkaline bath was used for Au and Ag.

[0128] The solder wettability and plating film adhesion of the samples prepared by the above procedure were evaluated. The evaluation and judgment methods were the same as those in Example 1. The evaluation results are shown in Table 9.

[0129] [Table 9]

[0130] As shown in Table 9, the solder wettability was good in both the examples and the comparative examples. However, as shown in the comparative examples, in the samples that had not been subjected to the Zn concentration treatment and surface removal treatment (those with a concentration gradient of "∞ (untreated)") and the samples with a Zn concentration gradient of more than 1000 mass% / μm, peeling of the plating film occurred after heating.

[0131] In the examples, a plating film having only one layer is shown, but this is not intended to limit the embodiments. For the purpose of reducing costs and further improving characteristics, various metals may be alloyed by a process such as heating, or a multi-layer plating film structure may be used.

[0132] For example, in the combination of the above-mentioned Cu plating layer and Sn plating layer, if reflow treatment cannot be performed due to some characteristic reasons, the pure tin plating layer may form an unintended alloy layer over time with the underlying copper (copper alloy sheet or Cu plating layer), and whiskers may occur due to factors such as internal stress of the plating layer caused by the alloy layer. In that case, the Sn plating layer can be made into an alloy plating layer of Sn and Cu or Ag to suppress whiskers. Also, in order to prevent the copper of the copper alloy sheet from diffusing into the plating layer (for example, the tin layer) and forming an alloy, an intermediate layer (for example, an electrolytic nickel plating layer) that suppresses diffusion can be formed. [Industrial Applicability]

[0133] It suppresses surface oxidation, improves electrical connection reliability, and even if a plating film is formed, it reduces the Zn concentration in the plating film, reduces the contact electrical resistance on the plating film surface, and improves the adhesion between the plating film and the copper alloy sheet. [Explanation of symbols]

[0134] 1. Copper alloy plate with plating film 10 Copper alloy plate 11 Surface layer 12 Inside the base material 20 Plating film 21 Cu layer 22 Sn-Cu alloy layer 23 Sn layer

Claims

1. A copper alloy sheet comprising, at a central portion in a thickness direction, more than 2.0% (mass%, the same applies below) and not more than 32.5% Zn, 0.1% or more and not more than 0.9% Sn, 0.05% or more and less than 1.0% Ni, 0.001% or more and less than 0.1% Fe, 0.005% or more and not more than 0.1% P, and the balance being Cu and unavoidable impurities, wherein a surface Zn concentration at a surface is 40% or less of a central Zn concentration at the central portion, and the copper alloy sheet has a surface layer portion having a depth from the surface to a depth where the Zn concentration is 90% of the central Zn concentration, and the copper alloy sheet has a concentration gradient of 10% by mass / μm or more and 1000% by mass / μm or less from the surface toward the central portion.

2. The copper alloy sheet according to claim 1, further comprising 0.001% or more and less than 0.1% of Co.

3. 3. The copper alloy sheet according to claim 1, wherein the surface layer has a thickness of 1 μm or less.

4. The copper alloy sheet according to any one of claims 1 to 3, a plating film formed on the surface layer portion of the copper alloy sheet.

5. 5. The copper alloy sheet having a plating film according to claim 4, wherein an average concentration of Zn in the plating film is 10% or less of the central Zn concentration.

6. 6. The copper alloy sheet with a plating film according to claim 4 or 5, characterized in that the plating film is made of one or more layers selected from tin, copper, zinc, nickel, gold, silver, palladium, and alloys thereof.

7. A method for producing the copper alloy sheet according to any one of claims 1 to 3, comprising: a Zn concentration treatment for diffusing and concentrating Zn on a surface to form a Zn-concentrated surface portion; and a surface portion removal treatment for removing the surface portion to form the surface layer portion.

8. A method for producing a copper alloy sheet having a plating film according to any one of claims 4 to 6, comprising the steps of: applying a current density of 0.1 A / dm ２ More than 60A / dm ２ A method for producing a copper alloy sheet having a plating film, comprising the steps of:

9. The plating film contains tin, 9. The method for producing a copper alloy sheet having a plating film according to claim 8, characterized in that after the electrolytic plating treatment, a reflow treatment is performed at a heating peak temperature of 230° C. or more and 330° C. or less, and a heating time at the heating peak temperature is 0.5 seconds or more and 30 seconds or less.

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