WO2011039875A1 - すずめっきの耐熱剥離性に優れるCu-Ni-Si系合金すずめっき条 - Google Patents
すずめっきの耐熱剥離性に優れるCu-Ni-Si系合金すずめっき条 Download PDFInfo
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- WO2011039875A1 WO2011039875A1 PCT/JP2009/067100 JP2009067100W WO2011039875A1 WO 2011039875 A1 WO2011039875 A1 WO 2011039875A1 JP 2009067100 W JP2009067100 W JP 2009067100W WO 2011039875 A1 WO2011039875 A1 WO 2011039875A1
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/48—After-treatment of electroplated surfaces
- C25D5/50—After-treatment of electroplated surfaces by heat-treatment
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C9/00—Alloys based on copper
- C22C9/06—Alloys based on copper with nickel or cobalt as the next major constituent
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C9/00—Alloys based on copper
- C22C9/10—Alloys based on copper with silicon as the next major constituent
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/34—Pretreatment of metallic surfaces to be electroplated
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D7/00—Electroplating characterised by the article coated
- C25D7/06—Wires; Strips; Foils
- C25D7/0614—Strips or foils
Definitions
- the present invention relates to a Cu—Ni—Si alloy tin-plated strip having good heat-resistant peelability, which is suitable as a conductive spring material for connectors, terminals, relays, switches and the like.
- solid solution strengthened copper alloys represented by phosphor bronze and brass have been used as copper alloys for electronic materials such as connectors and terminals.
- the amount of precipitation hardening type copper alloys having higher strength and higher electrical conductivity is increasing in place of conventional solid solution strengthened copper alloys.
- precipitation-hardened copper alloys by aging the supersaturated solid solution that has undergone solution treatment, fine precipitates are uniformly dispersed, increasing the strength of the alloy and reducing the amount of solid solution elements in the copper. , Electrical conductivity is improved. For this reason, precipitation hardening type copper alloys are excellent in strength and electrical conductivity.
- a typical precipitation hardening type copper alloy is a Cu—Ni—Si alloy, which has been put to practical use as a copper alloy for electronic materials.
- this copper alloy the strength and electrical conductivity are increased by the precipitation of fine Ni—Si intermetallic particles in the copper matrix.
- melting in the atmosphere is performed to cast an ingot having a desired composition.
- hot rolling, cold rolling and aging heat treatment are performed to finish the strip or foil having a desired thickness and characteristics.
- the Cu—Ni—Si based alloy Sn plated strip obtained by applying Sn plating to the Cu—Ni—Si based alloy strip manufactured as described above makes use of the excellent solder wettability and electrical connectivity of Sn. It is used as a consumer connector and terminal. Therefore, the Cu—Ni—Si based alloy Sn plating strip is required to have excellent strength, high electrical / thermal conductivity, and excellent properties such as heat-resistant peelability of tin plating.
- the Sn-plated strip of Cu-Ni-Si alloy is generally degreased and pickled in a continuous plating line, followed by electroplating and then Sn plating by electroplating. Finally, Manufactured in a process of reflow treatment and melting the Sn plating layer.
- Cu base plating of the Cu—Ni—Si based alloy Sn plating strip As the base plating of the Cu—Ni—Si based alloy Sn plating strip, Cu base plating is generally used, and Cu / Ni two-layer base plating may be applied for applications requiring heat resistance.
- the Cu / Ni two-layer undercoat is obtained by performing reflow treatment after performing electroplating in the order of Ni undercoat, Cu undercoat, and Sn plating. This technique is disclosed in Patent Documents 1 to 3 (Japanese Patent Laid-Open Nos. 6-196349, 2003-293187, and 2004-68026).
- Patent Document 4 Japanese Patent Laid-Open No. 9-209062 limits the size of the Si oxide in order to improve solder wettability and heat swell resistance of Ag plating.
- Patent Document 5 Japanese Patent Laid-Open No. 2007-39789 describes that it is effective to suppress the Si concentration at the interface between the plating and the base material.
- Patent Document 4 relates to Ag plating, not Sn plating, and is not economically preferable.
- Patent Document 5 describes that it is effective to suppress the Si concentration at the interface between the plating and the base material in order to obtain good heat-resistant peelability. There is no description of the concentration of the element. Therefore, the present inventors have improved the heat peelability of the Cu—Ni—Si based alloy tin plating strip from a viewpoint completely different from the above prior art.
- the present inventors pay attention to the Si concentration and Zn concentration at the interface between the base material of the Cu-Ni-Si-based alloy Sn plating strip subjected to the reflow treatment and the plating layer immediately above it, The following knowledge was obtained by investigating the relationship with the heat-resistant peelability of plating.
- the Cu—Ni—Si based alloy is subjected to an aging treatment on the solution-treated supersaturated solid solution, whereby fine Ni—Si compound particles are precipitated and contribute to an increase in strength.
- the solid solution Si precipitates as a Ni—Si compound, and a part remains in the Cu matrix.
- the remaining solid solution Si naturally remains even after plating, and moves to the interface between the base material and the plating phase after plating to generate a Si concentrated layer at the interface.
- the Si concentrated layer formed at the base material / plating phase interface causes plating peeling. Therefore, in order to obtain good heat-resistant peelability of plating, it is necessary to prevent the Si concentration from increasing under the interface between the base material after the reflow treatment and the plating phase.
- the interface between the base material and the plating phase is in a Si deficient state.
- a plating strip excellent in heat-resistant peelability can be produced.
- a plating strip having further excellent heat-resistant peelability is manufactured by defining the Zn concentration in the Si-deficient layer. Can do.
- the present invention is made by paying attention to the Si concentration and the Zn concentration under the interface between the copper base material and the plating phase in order to improve the heat release property of Sn plating, and provides the following plating strips. To do.
- concentration profile of the base material after the aging treatment of this invention It is a density
- FIG. It is a density
- Ni and Si are subjected to an aging treatment to precipitate Ni and Si compound particles in a Cu matrix, thereby obtaining high strength and electrical conductivity.
- Ni is added in the range of 1.0 to 4.5% by mass. If Ni is less than 1.0, sufficient strength cannot be obtained. When Ni exceeds 4.5 mass%, a crack generate
- the additive concentration (mass%) of Si is in the range of 1/6 to 1/4, preferably 1/5 to 1/4 of the additive concentration (mass%) of Ni. If Si deviates from this range, the conductivity decreases.
- the “Si deficient layer” refers to a portion that is continuously lower than the Si concentration of the copper alloy composition, specifically, a portion where the Si concentration is less than 100% of the Si concentration of the copper alloy composition, Particularly, it refers to a portion of 95% or less.
- the base material contains Zn and, if necessary, at least one selected from the group of Sn, Mg, Co, Ag, Cr and Mn in order to improve properties such as heat peelability and strength. ing. These are contained in a total of 2.0% by mass or less because the conductivity decreases as the amount added increases.
- the "interface between the copper alloy and the plating phase” means the Sn plating strip after reflow by GDS (glow discharge issuance spectroscopy analyzer). From the concentration profile in the depth direction of Sn, Cu, Ni, and Si, it is obtained as follows. (A) In the case where the Cu plating layer remains on the Cu base, a position where the Cu concentration is intermediate between the Cu concentration of the base material and the maximum value of the Cu concentration profile is defined as the interface. (A) When the Cu plating layer does not remain on the Cu base, the plating layer immediately above the base material is Cu 6 Sn 5 .
- the position at which the Cu concentration is intermediate between the Cu concentration of the base material and the Cu concentration of Cu 6 Sn 5 (39.1 wt%) is defined as the interface.
- the interface In the case of a Cu / Ni base, in the Ni concentration profile, the position where the Ni concentration is intermediate between the Ni concentration of the base material and the maximum value of the Ni concentration profile is defined as the interface.
- the “Si concentration at the interface between the copper alloy and the plating phase” refers to the maximum value of the Si concentration within a depth range of 0.5 ⁇ m from the interface.
- the Si concentration at the interface between the copper alloy and the plating phase must be less than 100% of the Si concentration of the copper alloy composition in order to obtain excellent tin plating heat-resistant peelability. If it is 100% or more, plating peeling may occur after long-term storage and / or heating conditions.
- the “Zn concentration at the interface between the copper alloy and the plating phase (in the Si-deficient layer)” refers to the maximum value of the Zn concentration within a depth of 0.5 ⁇ m from the interface. Zn contributes to good heat-resistant peelability of plating at the interface between the plating and the base material.
- this maximum value that is, the Zn concentration at the interface between the copper alloy and the plating phase is 90% or more of the Zn concentration of the copper alloy composition, preferably 95. It is important to be at least%.
- the Cu—Ni—Si based alloy of the present invention is produced, for example, by appropriately changing and adjusting “melting, casting ⁇ homogenization ⁇ hot rolling ⁇ cold rolling 1 ⁇ solution forming ⁇ cold rolling 2 ⁇ aging”.
- a thick Si-enriched layer is formed intentionally on the surface of the base material, and at the same time an Si-deficient layer is formed.
- the aging treatment is carried out in the presence of oxygen or other compounds that easily bind to Si, not in a conventional reducing atmosphere, a Si concentrated layer with a Si deficient layer shown in FIG. 1 can be formed.
- the Si concentration has a constant copper alloy composition.
- the oxygen concentration in the ambient atmosphere of the aging treatment is adjusted to 5 to 50 ppm and the formation of the Si oxide layer on the alloy surface is promoted, a target Si concentrated layer is generated.
- the oxygen concentration can be appropriately changed depending on the aging temperature, time, and degree of surface layer removal.
- the Si concentrated layer on the surface of the base material copper alloy obtained by the aging treatment is removed by polishing, buffing, pickling or the like.
- a plating treatment is performed to obtain the alloy tin plating strip of the present invention.
- the plating process is performed within a temperature range of 20 to 80 ° C. and a plating time of 3 to 120 seconds.
- a reflow process is performed in two stages.
- the first-stage reflow treatment is for diffusing Zn at the interface between the plating and the base material, and is performed at 250 ° C. for 3 to 10 seconds.
- the second stage reflow treatment is for obtaining a desired plating film structure, and is performed at 550 ° C. for 3 to 10 seconds.
- the plating strip of this invention is manufactured by the said process.
- Plating thickness (3-1) Cu underlayer reflow Sn From the surface to the base material, a plating film is composed of layers of Sn phase, Cu—Sn alloy phase, and optionally remaining Cu phase.
- This plating film structure is obtained by performing electroplating on the base material in the order of Cu base plating and Sn plating, and performing reflow treatment.
- the thicknesses of the Sn phase and the Cu—Sn phase are determined by an electrolytic film thickness meter.
- the thickness of the Sn phase after the reflow treatment is 0.1 to 1.5 ⁇ m. When the thickness is less than 0.1 ⁇ m, solder wettability and contact resistance deterioration under high temperature environment are remarkably accelerated.
- the thickness of the Cu—Sn alloy phase after the reflow treatment is 0.1 to 1.5 ⁇ m. Since the Cu—Sn alloy phase is hard, if it exists in a thickness of 0.1 ⁇ m or more, it contributes to a reduction in insertion force. On the other hand, when the thickness of the Cu—Sn alloy phase exceeds 1.5 ⁇ m, the thermal stress generated inside the plating layer when heated is increased, and the plating peeling is promoted.
- the thickness of the Cu plating phase formed by electroplating is 0 to 0.8 ⁇ m.
- a preferable thickness of the Cu plating layer is 0.4 ⁇ m or less. However, it is more preferable that the thickness of the Cu plating layer is zero because the Cu—Sn alloy phase is consumed during the reflow process.
- the Sn plating layer thickness is appropriately adjusted so as to be formed in the range of 0.5 to 2.0 ⁇ m, and the Cu plating layer thickness in the range of 0.1 to 1.5 ⁇ m. Then, the said plated structure is obtained by performing a reflow process on suitable conditions.
- a plating film is composed of layers of Sn phase, Cu—Sn alloy phase and Ni phase from the surface to the base material.
- This plating film structure is obtained by performing electroplating on the base material in the order of Ni base plating, Cu base plating, and Sn plating, and performing reflow treatment.
- the reflow process Cu and Sn between the plating layers react to form a Cu—Sn alloy layer.
- the Ni plating layer remains almost in the state (thickness) after electroplating.
- the thickness of the Ni phase is determined by SEM observation from the cross section.
- the thickness of the Sn phase and the thickness of the Cu—Sn alloy phase after the reflow treatment are the same as those of the Cu underlayer reflow Sn.
- the thickness of the Ni phase after the reflow treatment is 0.1 to 1.0 ⁇ m. When the thickness of the Ni phase is less than 0.1 ⁇ m, the corrosion resistance and heat resistance of the plating deteriorate. On the other hand, when the thickness of the Ni phase after the reflow treatment exceeds 1.0 ⁇ m, the thermal stress generated inside the plating layer when heated is increased, and the plating peeling is promoted.
- the Sn plating layer thickness is in the range of 0.5 to 2.0 ⁇ m
- the Cu plating layer thickness is in the range of 0.1 to 1.0 ⁇ m
- the Ni plating layer thickness is in the range of 0.1 to 0.8 ⁇ m. Adjust as appropriate. Then, the said plated structure is obtained by performing a reflow process on suitable conditions.
- excellent in heat-resistant peelability means that after heating, 90 ° bending with a bending radius of 0.5 mm and bending back are performed, and plating peeling does not occur.
- Step 1 After covering the molten metal surface with a piece of charcoal, a predetermined amount of Ni, Si, Zn and other additive elements were added, and the molten metal temperature was adjusted to 1200 ° C. Thereafter, the molten metal was cast into a mold to produce an ingot having a width of 60 mm and a thickness of 30 mm, and processed into a Cu base reflow Sn plating material and a Cu / Ni base reflow Sn plating material in the following steps.
- Step 2 After heating at 950 ° C. for 3 hours, hot rolling to a thickness of 8 mm.
- Step 2 The oxidized scale on the surface of the hot rolled plate is ground and removed with a grinder.
- Step 3 Cold rolling to a sheet thickness of 0.3 mm.
- Step 4 As a solution treatment, the solution is heated at 800 ° C. for 1 minute and then rapidly cooled in water.
- Step 5 The electric furnace is evacuated to a vacuum degree of 10 ⁇ 4 Pa or less and replaced with nitrogen gas having a purity of 99.99998%. This operation is repeated twice or more. Thereafter, oxygen gas having a purity of 99.9999% is injected and controlled to a predetermined oxygen concentration.
- As an aging treatment after holding at 460 ° C. for 6 hours in an electric furnace controlled to a predetermined oxygen concentration, cooling is performed as it is.
- Step 6 Cold rolling to a plate thickness of 0.25 mm.
- Step 7) After holding at 500 ° C. for 10 seconds in an electric furnace in a nitrogen atmosphere, buffing is performed in a 10 vol% sulfuric acid-1 vol% peroxide aqueous solution to remove the Si concentrated layer on the copper alloy surface.
- Ni foundation plating is performed under the following conditions (only Cu / Ni foundation reflow Sn plating).
- -Plating bath composition nickel sulfate 250 g / L, nickel chloride 45 g / L, boric acid: 30 g / L.
- -Plating bath temperature 50 ° C.
- Current density 5A / dm 2.
- Cu base plating is performed under the following conditions.
- -Plating bath composition copper sulfate 200 g / L, sulfuric acid 60 g / L. Plating bath temperature: 25 ° C. Current density: 5A / dm 2.
- Sn plating is performed under the following conditions.
- Plating bath composition stannous oxide 41 g / L, phenol sulfonic acid 268 g / L, surfactant 5 g / L.
- Plating bath temperature 50 ° C.
- Current density 9A / dm 2.
- the substrate is held for 10 seconds in a heating furnace adjusted to a nitrogen atmosphere and a temperature of 250 ° C.
- Step 12 As the second-stage reflow treatment, it is kept in a heating furnace adjusted to a nitrogen atmosphere and a temperature of 550 ° C. for 5 seconds, and then cooled with water.
- the above-mentioned process 11 was performed only about the invention example, and was not performed about the comparative example. The following evaluation was performed about the sample produced in this way.
- FIG. 2 is a concentration profile with respect to the depth direction of Si and Zn in the Cu-based Sn-plated copper alloy according to Invention Example 1.
- FIG. 3 is a concentration profile of Sn and Cu in the Cu base Sn-plated copper alloy according to Invention Example 1 with respect to the depth direction.
- FIG. 4 is a concentration profile with respect to the depth direction of Si and Zn in the Cu / Ni underlayer Sn-plated copper alloy according to Invention Example 8.
- FIG. 5 is a concentration profile of Sn, Cu, and Ni in the Cu / Ni underlayer Sn-plated copper alloy according to Invention Example 8 in the depth direction.
- the copper alloy according to Invention Example 1 shown in FIG. 3 is a Cu underlayer with no Cu plating layer remaining. Therefore, according to the above definition, “Cu concentration is the Cu concentration of the base material in the Cu concentration profile”. And the “intermediate position between the Cu concentration of Cu 6 Sn 5 (39.1 wt%)” is the interface. Accordingly, it was determined that the interface between the plating phase and the copper alloy exists at a depth of 1.4 ⁇ m.
- FIG. 2 is a concentration profile of Si and Zn with respect to the depth direction of the same sample.
- the maximum value of the Si concentration in the range from the interface having the depth of 1.4 ⁇ m to the depth of 0.5 ⁇ m (that is, the depth from the surface of 1.4 to 1.9 ⁇ m) is 0.29 mass%. . Therefore, the Si concentration at the interface between the copper alloy and the plating phase was 93% of the copper alloy, which was less than 100% of the Si concentration of the copper alloy composition.
- the maximum value of the Zn concentration in the range from the interface having the depth of 1.4 ⁇ m to the depth of 0.5 ⁇ m (that is, the depth from the surface of 1.4 to 1.9 ⁇ m) is 0.36 mass%. It becomes. Therefore, the Zn concentration at the interface between the copper alloy and the plating phase was 100% of the copper alloy.
- FIG. 4 is a concentration profile of Si and Zn with respect to the depth direction of the same sample.
- the maximum value of the Si concentration in the range from the interface having the determined depth of 1.65 ⁇ m to the depth of 0.5 ⁇ m is 0.32 mass%. .
- the Si concentration at the interface between the copper alloy and the plating phase was 92% of the copper alloy, which was less than 100% of the Si concentration of the copper alloy composition.
- the maximum value of Zn concentration in the range from the interface having the depth of 1.5 ⁇ m to the depth of 0.5 ⁇ m (that is, the depth from the surface of 1.65 to 2.15 ⁇ m) is 0.52 mass%. It becomes. Therefore, the Zn concentration at the interface between the copper alloy and the plating phase was 95% of the copper alloy.
- the Si concentration ratio at the interface between the base material and the plating phase of Invention Examples 1 to 14 is less than 100% of that of the base material immediately after plating and after the heat test at 2000 ° C. or 3000 h at 150 ° C.
- the Zn concentration ratio at the interface between the material and the plating phase was 90% or more, and plating peeling did not occur even when heated at 150 ° C. for 2000 h or 3000 h regardless of the Cu base or Cu / Ni base.
- the Si concentration ratio at the interface between the base material and the plating phase was less than 100% of that of the base material immediately after plating and after the heat resistance test at 150 ° C. for 2000 h or 3000 h.
- Comparative Examples 10 to 12 and 22 to 24 were 100% or more of that of the base material immediately after plating and after the heat resistance test heated at 150 ° C. for 2000 h or 3000 h, and the first stage reflow treatment was not performed.
- the Zn concentration ratio at the interface was less than 90%, and plating peeling occurred.
- the plating peeling time was shorter than those of Comparative Examples 1 to 9 and 13 to 21.
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Abstract
Description
析出硬化型銅合金の代表的なものにCu-Ni-Si系合金があり、電子材料用銅合金として実用化されている。この銅合金では、銅マトリックス中に微細なNi-Si系金属間化合物粒子が析出することにより強度と導電率が上昇する。Cu-Ni-Si系合金の一般的な製造プロセスは、通常の析出硬化型銅合金と同様に、まず大気溶解を行い、所望の組成のインゴットを鋳造する。その後、熱間圧延、冷間圧延および時効熱処理を行い、所望の厚みおよび特性を有する条や箔に仕上げる。
Cu-Ni-Si系合金のSnめっき条は、一般的に、連続めっきラインにおいて、脱脂および酸洗後、電気めっき法により下地めっきを施し、次に電気めっき法によりSnめっきを施し、最後にリフロー処理を施し、Snめっき層を溶融させる工程で製造される。
Cu-Ni-Si系合金Snめっき条の下地めっきとしては、Cu下地めっきが一般的であり、耐熱性が求められる用途に対してはCu/Ni二層下地めっきが施されることもある。ここで、Cu/Ni二層下地めっきとは、Ni下地めっき、Cu下地めっき、Snめっきの順に電気めっきを行った後にリフロー処理を行ったものである。この技術は特許文献1~3(特開平6-196349、特開2003-293187、特開2004-68026号公報)等に開示されている。
又、上記特許文献4はSnめっきではなくAgめっきに関するものであり経済的に好ましくなく、耐加熱膨れ性を改善するために同文献で採用されているSiの酸化物の大きさの限定をそのままSnめっきへ適用してもめっき成分が異なるため優れた効果は望めない。
また、特許文献5には、良好な耐熱剥離性を得るために、めっきと母材との界面のSi濃度を抑えることが有効であることは記載されているが、耐熱剥離性を促進させる他の元素の濃度についての記載は無い。
そこで、本発明者らは、上記従来技術とは全く別の観点から、Cu-Ni-Si系合金すずめっき条の耐熱剥離性の改善を行った。
Cu-Ni-Si系合金は前述したように、溶体化処理された過飽和固溶体を時効処理することにより、微細なNi-Si化合物粒子が析出して強度上昇に寄与する。しかし、固溶Si全てがNi-Si化合物として析出するわけではなく、一部はCuマトリックス中に固溶して残存する。この残存した固溶Siは当然めっき後も残存しており、めっき後に母材とめっき相との界面へ移動して界面でSi濃化層を生成する。この母材/めっき相界面に生成するSi濃化層は、めっき剥離の原因となる。従って、良好なめっきの耐熱剥離性を得るためには、リフロー処理後の母材とめっき相との界面下のSi濃度の上昇を防止する必要がある。
本発明者は、めっき処理前の母材合金表面に厚いSi濃化層を比較的短時間で形成するとSi濃化層の下側にSi欠乏層が形成される(図1参照)ことに着目し、本発明を完成させた。即ち、所定の条件で母材表面に作為的に厚いSi濃化層を形成後、そのSi濃化層の大部分を除去してからめっきすると、母材とめっき相の界面下はSi欠乏状態となり、長期保存後及び/又は加熱条件下でも母材/めっき相界面下のSi濃化層の形成が防止できるため、耐熱剥離性に優れためっき条を製造することができる。また、めっきと母材との界面におけるZnの存在がめっきの耐熱剥離性に有効であるため、上記Si欠乏層におけるZn濃度を規定することによってさらに耐熱剥離性に優れためっき条を製造することができる。
このように、本発明は、Snめっきの耐熱剥離性を改善するために、銅母材/めっき相界面下のSi濃度及びZn濃度に着目して成されたものであり、下記めっき条を提供する。
(2)前記Si欠乏層のSi濃度が銅合金組成のSi濃度の95%以下であることを特徴とする(1)のCu-Ni-Si系合金すずめっき条。
(3)前記Si欠乏層におけるZn濃度が銅合金組成のZn濃度の95%以上であることを特徴とする(1)又は(2)のCu-Ni-Si系合金すずめっき条。
NiおよびSiは、時効処理を行うことによりCuマトリックス中にNiとSiの化合物粒子が析出し、高い強度と導電率が得られる。
Niは1.0~4.5質量%の範囲で添加する。Niが1.0を下回ると充分な強度が得られない。Niが4.5質量%を超えると、鋳造や熱間圧延で割れが発生する。
Siの添加濃度(質量%)は、Niの添加濃度(質量%)の1/6~1/4、好ましくは1/5~1/4の範囲とする。Siがこの範囲から外れると、導電率が低下する。特に、Siの添加量がNiの1/4を超えると、固溶Siが増え、銅合金とめっき相の界面のSi濃度が高くなり、銅合金とその直上のめっき相との界面にSi濃化処理に伴うSi欠乏層が形成されなくなり、耐熱剥離性が低下する。
なお、本発明において「Si欠乏層」とは、銅合金組成のSi濃度よりも連続的に低い部分をいい、具体的にはSi濃度が銅合金組成のSi濃度の100%未満である部分、特に95%以下の部分をいう。
また、母材には、耐熱剥離性や強度等の特性を改善するために、Znと必要に応じてSn、Mg、Co、Ag、Cr及びMnの群から選ばれた少なくとも一種とを含有している。これらは添加量が増えると導電率が低下するため合計で2.0質量%以下含まれている。
本発明においては、「銅合金とめっき相の界面」とは、GDS(グロー放電発行分光分析装置)により、リフロー後のSnめっき条のSn、Cu、Ni、Siの深さ方向の濃度プロファイルから下記のように求められる。
(ア)Cu下地でCuめっき層が残存している場合、Cuの濃度プロファイルにおいて、Cu濃度が、母材のCu濃度とCuの濃度プロファイルの最大値の中間になる位置を界面とする。
(イ)Cu下地でCuめっき層が残存していない場合、母材直上のめっき層はCu6Sn5である。従って、Cuの濃度プロファイルにおいて、Cu濃度が、母材のCu濃度とCu6Sn5のCu濃度(39.1wt%)の中間になる位置を界面とする。
(ウ)Cu/Ni下地の場合、Niの濃度プロファイルにおいて、Ni濃度が、母材のNi濃度とNiの濃度プロファイルの最大値の中間になる位置を界面とする。
本発明においては、「銅合金とめっき相の界面のSi濃度」とは、上記界面から0.5μmの深さの範囲内におけるSi濃度の最大値を指す。優れたすずめっきの耐熱剥離性を得るためには、この最大値が、つまり、銅合金とめっき相の界面のSi濃度が、銅合金組成のSi濃度の100%未満でなければならない。100%以上であると、長期保存後及び/又は加熱条件下でめっき剥離が発生するおそれがある。
また、本発明においては、「銅合金とめっき相の界面の(Si欠乏層における)Zn濃度」とは、上記界面から0.5μmの深さの範囲内におけるZn濃度の最大値を指す。Znはめっきと母材との界面において、めっきの良好な耐熱剥離性に寄与する。このため、優れたすずめっきの耐熱剥離性を得るためには、この最大値が、つまり、銅合金とめっき相の界面のZn濃度が、銅合金組成のZn濃度の90%以上、好ましくは95%以上であることが重要である。
例えば、時効処理の周囲雰囲気の酸素濃度を5~50ppmに調整して、合金表面でのSi酸化物層形成を促進すると、目的とするSi濃化層が生成する。上記酸素濃度は時効温度、時間、表面層除去の程度により適宜変更可能である。
上記時効処理で得られた母材銅合金表面のSi濃化層を、研磨、バフ研磨、酸洗等により除去する。
上記処理により、本発明のめっき条が製造される。
(3-1)Cu下地リフローSn
表面から母材にかけて、Sn相、Cu-Sn合金相、場合により残存するCu相の各層でめっき皮膜が構成される。母材上にCu下地めっき、Snめっきの順に電気めっきを行い、リフロー処理を施すことにより、このめっき皮膜構造が得られる。Sn相及びCu-Sn相の厚みは電解式膜厚計により求められる。
リフロー処理後のSn相の厚みは0.1~1.5μmとする。厚みが0.1μm未満となると高温環境下における半田濡れ性や接触抵抗の劣化が著しく促進され、1.5μmを超えると、加熱した際にめっき層内部に発生する熱応力が高くなり、めっき剥離が促進される。
リフロー処理後のCu-Sn合金相の厚みは0.1~1.5μmとする。Cu-Sn合金相は硬質なため、0.1μm以上の厚さで存在すると、挿入力の低減に寄与する。一方、Cu-Sn合金相の厚さが1.5μmを超えると、加熱した際にめっき層内部に発生する熱応力が高くなり、めっき剥離が促進される。
電気めっきで形成したCuめっき相の厚みは0~0.8μmであり、0.8μmを超えると、加熱された際にめっき層内部に発生する熱応力が高くなり、めっき剥離が促進される。好ましいCuめっき層の厚みは0.4μm以下であるが、リフロー処理時にCu-Sn合金相形成に消費され、その厚みがゼロになるのが更に好ましい。
表面から母材にかけて、Sn相、Cu-Sn合金相、Ni相の各層でめっき皮膜が構成される。母材上にNi下地めっき、Cu下地めっき、Snめっきの順に電気めっきを行い、リフロー処理を施すことにより、このめっき皮膜構造が得られる。リフロー処理により、めっき層間のCuとSnが反応してCu-Sn合金層が形成される。一方、Niめっき層は、ほぼ電気めっき上がりの状態(厚み)で残留する。Ni相の厚みは、断面からのSEM観察により求める。
リフロー処理後のSn相の厚み及びCu-Sn合金相の厚みは、上記Cu下地リフローSnと同様である。
リフロー処理後のNi相の厚みは0.1~1.0μmとする。Ni相の厚みが0.1μm未満では、めっきの耐食性や耐熱性が低下する。一方、リフロー処理後のNi相の厚みが1.0μmを超えると加熱した際にめっき層内部に発生する熱応力が高くなり、めっき剥離が促進される。
市販の電気銅をアノードとして、硝酸銅浴中で電解を行い、カソードに高純度銅を析出させた。この高純度銅中のP、As、Sb、Bi、Ca、Mg及びS濃度は、いずれも1質量ppm未満であった。以下、この高純度銅を下記インゴット製造材料に用いた。
高周波誘導炉を用い、内径60mm、深さ200mmの黒鉛るつぼ中で、2kgの高純度銅を溶解した。溶湯表面を木炭片で覆った後、所定量のNi、Si、Zn及びその他の添加元素を投入し、溶湯温度を1200℃に調整した。
その後、溶湯を金型に鋳込み、幅60mm、厚み30mmのインゴットを製造し、以下の工程で、Cu下地リフローSnめっき材およびCu/Ni下地リフローSnめっき材に加工した。
(工程1)950℃で3時間加熱した後、厚さ8mmまで熱間圧延する。
(工程2)熱間圧延板表面の酸化スケールをグラインダーで研削、除去する。
(工程3)板厚0.3mmまで冷間圧延する。
(工程4)溶体化処理として800℃で1分加熱し、水中で急冷する。
(工程5)電気炉を真空度10-4Pa以下まで真空引きし、純度99.9998%の窒素ガスで置換する。この操作を2回以上繰り返す。その後、純度99.9999%の酸素ガスを注入し、所定の酸素濃度に制御する。時効処理として、この所定の酸素濃度に制御した雰囲気の電気炉中で460℃で6時間保持後、そのまま冷却する。
(工程6)板厚0.25mmまで冷間圧延する。
(工程7)窒素雰囲気の電気炉中に500℃で10秒保持した後、10vol%硫酸―1vol%過酸化水溶液中で、バフ研磨を行い、銅合金表面のSi濃化層を除去する。
・めっき浴組成:硫酸ニッケル250g/L、塩化ニッケル45g/L、ホウ酸:30g/L。
・めっき浴温度:50℃。
・電流密度:5A/dm2。
(工程9)次の条件でCu下地めっきを施す。
・めっき浴組成:硫酸銅200g/L、硫酸60g/L。
めっき浴温度:25℃。
・電流密度:5A/dm2。
(工程10)次の条件でSnめっきを施す。
・めっき浴組成:酸化第1錫41g/L、フェノールスルホン酸268g/L、界面活性剤5g/L。
めっき浴温度:50℃。
・電流密度:9A/dm2。
(工程11)第1段リフロー処理として、窒素雰囲気、温度250℃に調整した加熱炉中に、10秒間保持する。
(工程12)第2段リフロー処理として、窒素雰囲気、温度550℃に調整した加熱炉中に、5秒間保持した後、水冷する。
なお、上述の工程11は発明例のみについて行い、比較例については行わなかった。
このように作製したサンプルにつき、次の評価を行った。
機械研磨と化学エッチングによりめっき層を完全に除去した後、Cu以外の添加元素につき、ICP-発光分光法で測定した。
(b)酸洗研磨量
酸洗研磨を行う前後のサンプルの板厚をマイクロメータで測定し、酸洗研磨前後の板厚の差から酸洗研磨量を求めた。
(c)Si及びZn濃度プロファイル、及び、界面Si及びZn濃度
試料をアセトン中で超音波脱脂した後、表面からのGDS(グロー放電発光分光分析装置)分析により、Si及びZnの深さ方向の濃度プロファイルを求めた。測定条件は次の通りである。
装置:JOBIN YBON社製JY5000RF-PSS型
Current Method Program:CNBinteel-12aa-0
Mode:設定電力=40W
気圧:775Pa
電流値:40mA(700V)
フラッシュ時間:20s
予備加熱(Preburn)時間:2s
測定(分析)時間=30s、サンプリング時間=0.020s/point
GDSによる濃度プロファイルデータの代表的なものを図2~5に示す。図2は、発明例1に係るCu下地Snめっき銅合金におけるSi及びZnの深さ方向に対する濃度プロファイルである。図3は、発明例1に係るCu下地Snめっき銅合金におけるSn及びCuの深さ方向に対する濃度プロファイルである。図4は、発明例8に係るCu/Ni下地Snめっき銅合金におけるSi及びZnの深さ方向に対する濃度プロファイルである。図5は、発明例8に係るCu/Ni下地Snめっき銅合金におけるSn、Cu及びNiの深さ方向に対する濃度プロファイルである。
また、上記決定された深さ1.4μmの界面から0.5μmの深さ迄の間(即ち表面から深さ1.4~1.9μm)の範囲におけるZn濃度の最大値は0.36mass%となる。従って、当該銅合金とめっき相との界面のZn濃度は当該銅合金の100%であった。
また、上記決定された深さ1.5μmの界面から0.5μmの深さ迄の間(即ち表面から深さ1.65~2.15μm)の範囲におけるZn濃度の最大値は0.52mass%となる。従って、当該銅合金とめっき相との界面のZn濃度は当該銅合金の95%であった。
幅10mmの短冊試験片を採取し、150℃の温度で、大気中2000時間(Cu下地に係る発明例及び比較例)又は3000時間(Cu/Ni下地に係る発明例及び比較例)まで加熱した。その間、50時間毎にサンプルを加熱炉から取り出し、曲げ半径0.5mmの90°曲げと曲げ戻しを行った。そして、曲げ内周部表面を光学顕微鏡(倍率50倍)で観察し、めっき剥離の有無を調べた。
上記試験条件及び試験結果を表1に示す。
比較例1~9及び13~21は、母材とめっき相との界面のSi濃度割合は、めっき直後も150℃で2000h又は3000h加熱の耐熱試験後も、母材のそれの100%未満であったが、第1段リフロー処理を行っておらず、前記界面におけるZn濃度割合が90%未満であり、めっき剥離が発生した。
比較例10~12及び22~24は、めっき直後も150℃で2000h又は3000h加熱の耐熱試験後も、母材のそれの100%以上であり、さらに第1段リフロー処理を行っておらず、前記界面におけるZn濃度割合が90%未満であり、めっき剥離が発生した。また、そのめっき剥離時間は比較例1~9及び13~21よりも短かった。
Claims (3)
- 1.0~4.5質量%のNiを含有し、Niの質量%に対し1/6~1/4のSiを含有し、さらにZnと必要に応じてSn、Mg、Co、Ag、Cr及びMnの群から選ばれた少なくとも一種とを合計で2.0質量%以下含有し、残部が銅および不可避的不純物から構成される銅合金すずめっき条であり、銅合金とその直上のめっき相との界面に、Si濃度が銅合金組成のSi濃度の100%未満であるSi欠乏層を有し、該Si欠乏層におけるZn濃度が銅合金組成のZn濃度の90%以上であることを特徴とするCu-Ni-Si系合金すずめっき条。
- 前記Si欠乏層のSi濃度が銅合金組成のSi濃度の95%以下であることを特徴とする請求項1に記載のCu-Ni-Si系合金すずめっき条。
- 前記Si欠乏層におけるZn濃度が銅合金組成のZn濃度の95%以上であることを特徴とする請求項1又は2に記載のCu-Ni-Si系合金すずめっき条。
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