Patent Application
20100000637
The present invention relates to Cu—Ni—Si system alloys suitable for use in a variety of electronic components such as a lead frame, connector, pin, terminal, relay and switch. Further, the present invention relates to a method for manufacturing the alloys. Further, the present invention relates to electronic components made of the alloys.
A copper alloy for electronic materials used in electronic components and the like is required to satisfy both high strength and high electrical conductivity (or thermal conductivity) as a basic characteristic. Further, the copper alloy is also required to have bending workability, stress relaxation performance, thermal resistance, thermal peel resistance of plating, solderability, etching workability, press punching quality, corrosion resistance and the like.
In the above background, as a copper alloy for electronic materials, the usage of age hardened copper alloys superior to solid-solution hardened copper alloys in strength, electrical conductivity and stress relaxation performance has been increasing instead of solid-solution hardened copper alloys typified by existing phosphor bronze, brass and the like in recent years. In the age hardened copper alloys, the age hardening of supersaturated solid solution, which underwent solution treatment beforehand, disperses fine precipitates uniformly, thereby increases the strength of the alloys. At the same time, it also reduces the amount of solved elements contained in the copper, thereby improves the electrical conductivity.
Among age hardened copper alloys, A Cu—Ni—Si system alloy is a copper alloy having relatively high electrical conductivity and strength, and therefore it is one of the alloys that have been actively developed in the industry in these days. In the copper alloy, fine particles of Ni—Si intermetallic compounds are precipitated in the copper matrix, thereby the strength and electrical conductivity increase.
For example, Japanese patent laid-open publication No. 2002-266042 (Patent document 1) discloses Cu—Ni—Si system alloys aiming high strength and excellent bending workability. It also discloses that, in preparing the copper alloys, a summation of reduction ratios of cold rolling before and after conducting the age hardening should be 40% or less, heat conditions where a diameter of recrystallized grains is 5 to 15 μm should be selected in the solution treatment, and the age hardening should be conducted for 30 to 300 minutes at 440 to 500° C. The copper alloys that are specifically described in Patent document 1 do not generate cracks by W-bending, the tensile strength is 520 MPa when the electrical conductivity is at its highest point of 53% IACS, and the electrical conductivity is 46% IACS when the tensile strength is at its highest point of 710 MPa (see Table 2 of working examples).
Japanese patent laid-open publication No. 2001-207229 (Patent document 2) discloses examples of development of Cu—Ni—Si system alloys having excellent bending workability in addition to high strength and electrical conductivity. It discloses that excellent bending workability is provided by bringing the mass ratio of Ni and Si in an alloy close to the concentration of the intermetallic compound, Ni2Si, namely, by adjusting the mass ratio of Ni and Si such that the ratio Ni/Si becomes 3 to 7. Further, it discloses that suitable materials as a copper alloy for electronic materials are obtainable by adding Fe and/or one or more selected from Zr, Cr, Ti and Mo to a Cu—Ni—Si system alloy, conducting quality governing and then adding Mg, Zn, Sn, Al, P, Mn, Ag or Be as needed. The copper alloys that are specifically described in Patent document 2 do not generate cracks by 90°-bending (not 180°-bending), the tensile strength is 640 MPa when the electrical conductivity is at its highest point of 56% IACS, and the electrical conductivity is 44% IACS when the tensile strength is at its highest point of 698 MPa (see Table 1 of working examples). Further, reduction ratios of cold rolling before and after conducting the ge hardening are 60% and 37.5% (a summation of those rates is 97.5%).
Japanese patent laid-open publication No. 61-194158 (Patent document 3) discloses Cu—Ni—Si system alloys having excellent electrical conductivity of 60% IACS or more, high strength, excellent stiffness strength and repetitive bending workability, and high thermal resistance. It discloses that the alloys should contain 0.02 to 1.0 wt % Mn, 0.1 to 5.0 wt % Zn, 0.001 to 0.01 wt % Mg, and 0.001 to 0.01 wt % elements selected one or more from Cr, Ti and Zr. In working examples of the document, data of 51.0 kgf/mm2 (500 MPa) tensile strength and 67.0% IACS electrical conductivity, and data of 62.0 kgf/mm2 (593 MPa) tensile strength and 64.0% IACS electrical conductivity (see Table 2). The Cu—Ni—Si system alloys whose thickness is 10 mm after hot rolling are conducted cold rolling until its thickness reaches 0.25 mm without recrystallization annealing along the way. A reduction ratios in this case is 97.5% that is notably-high, and it is inferable that the bending workability extremely deteriorates. In addition, annealing at 450° C. is conducted along the way and after cold rolling. However, in the case of Cu—Ni—Si system alloys, a precipitation reaction proceeds whereas a recrystallization reaction does not proceed.
Japanese patent laid-open publication No. 11-222641 (Patent document 4) discloses Cu—Ni—Si system alloys having excellent mechanical characteristics, electrical conductivity, stress relaxation performance and bending workability by adding specified amount of Sn, Mg, or additionally Zn, limiting contained amount of 5 and 0, and adjusting crystal grain size to more than 1 μm and equal to or less than 25 μm. Further, it discloses that recrystallization after cold rolling should be conducted at 700 to 920° C. in order to adjust the crystal grain size within the above range. Working examples of the document disclose Cu—Ni—Si system alloys that have 610 to 710 MPa tensile strength and could be conducted 180° bending test of 0 radius. The electrical conductivity of the alloys is 31 to 42% IACS and a rate of the stress relaxation is 14 to 22% by heating at 150° C. for 1000 hours.
Japanese patent No. 3520034 (Patent document 5) discloses Cu—Ni—Si system alloys, wherein specified amount of Mg, Sn, Zn and S is contained, a crystal grain size is more than 0.001 mm and 0.025 mm or less, the ratio (a/b) which is a major axis (a) of the crystal grain in its cross-section parallel to a final work processing way to a major axis (b) of the crystal grain in its cross-section transverse to the final work processing way is 0.8 or more and 1.5 or less, and the bending workability and stress relaxation performance are excellent. Working examples of the document disclose Cu—Ni—Si system alloys that have 685 to 710 MPa tensile strength, 32 to 40% IACS electrical conductivity and could be conducted 180° bending test of 0 radius.
Further, as recent studies of characteristic improvements of Cu—Ni—Si system alloys, remediation technologies of the strength and bendability focusing on the precipitate-free zone (PFZ) are reported in non-patent documents 1 and 2. The precipitate-free zone is a band-like zone that is formed near a crystal grain boundary by a grain boundary reactive deposition at age hardening (discontinuous precipitation) and does not have fine precipitates. If an external force is applied, a plastic deformation occurs in the precipitate-free zone by priority because fine precipitates contributing to strength are not in the zone, and as a result, the tensile strength and bending workability are deteriorates. Non-patent document 1 discloses an addition of P and Sn and a double age hardening are effective for restraining an emergence of the precipitate-free zone. It discloses the strength increases considerably without diminishing elongation by adding preliminary age hardening at 250° C. for 48 hours prior to age hardening at 450° C. for 16 hours in the double age hardening. In particular, it discloses Cu—Ni—Si system alloys having 770 to 900 MPa tensile strength and 34 to 36% IACS electrical conductivity. Non-patent document 2 discloses a range of PFZ increases in association with an increase of time of age hardening.
Patent document 1: Japanese patent laid-open publication No. 2002-266042
Patent document 2: Japanese patent laid-open publication No. 2001-207229
Patent document 3: Japanese patent laid-open publication No. 61-194158
Patent document 4: Japanese patent laid-open publication No. 11-222641
Patent document 5: Japanese patent No. 3520034
Non-patent document 1: Chizuru WATANABE, Masaru MIYAKOSHI, Fumiya NISHIJIMA, Ryoichi KADOMAE: “Improvement of mechanical characteristics of Cu-4.0 mass % Ni-0.95 mass % Si-0.02 mass % P alloys”, Cu and Cu alloys, Japan Copper and Brass Association, 2006, Vol. 45, Number 1, page 16 to 22.
Non-patent document 2: Goro ITO, Shunsuke SUZUKI, Yoshihira TOU, Yoshinori YAMAMOTO, Nobuhide ITO, “Influence of the amount of Ni and Si and the condition of age hardening to bending workability of plate materials of Cu—Ni—Si system alloys”, Cu and Cu alloys, Japan Copper and Brass Association, 2006, Vol. 45, Number 1, page 71 to 75.
As discussed previously, a variety of methods for a characteristic improvement of Cu—Ni—Si system alloys are developed, and so far, a method for a characteristic improvement of Cu—Ni—Si system alloys with adding other alloy elements has been a main method. However, additive elements to alloys are recently being requested due to problems of the recyclability.
Further, an improvement of the electric conductivity of Cu—Ni—Si system alloys is requested in association with a development of high integration, miniaturization and lamination of electronic components in recent years. This is because the smaller a cross-section area of a current-carrying part becomes, the higher thermal elevation of parts by Joule heat becomes.
ΔT=J2·L2/(2·E·H·S2)
“ΔT” stands for the thermal elevation, “J” stands for the current of electricity, “E” stands for the electric conductivity, “H” stands for the heat thermal conductivity, and “L” and “S” each stands for the length and the cross-section area of the current-carrying part. The thermal elevation is inversely related to square of the electric conductivity because “H” is proportional to “E”. If the cross-section area of parts diminishes, the strength of a spring deteriorates in the use of connectors and the like. Accordingly, characteristics of the strength of a spring such as the tensile strength and stress relaxation performance are attached a high value. Therefore, it is unacceptable to deteriorate the tensile strength and stress relaxation performance in exchange for improving the electric conductivity. In a similar way, it is also unacceptable to deteriorate the bendability because a miniaturization of parts complicate processes of parts.
The object of the invention is to provide Cu—Ni—Si system alloys for electronic materials that are added other alloy elements as little as possible, and have improved electric conductivity, strength, bendability and stress relaxation performance. Another object of the invention is to provide a method for manufacturing the alloys. A further object of the invention is to provide wrought copper product and electronic components made of the alloys.
The inventor has diligently studied to cope with the requirements, and eventually have found out that Cu—Ni—Si system alloys having excellent electric conductivity, tensile strength, stress relaxation performance and bendability are provided by adding particular conditions to a rate of temperature increase of age hardening, maximum reaching temperature of materials and time of age hardening, and by correcting conditions of solution treatment and a reduction ratio of before and after conducting age hardening in a manufacturing process for Cu—Ni—Si system alloys that contain impurities as little as possible.
In one aspect, the present invention that has been made based on these findings is the Cu—Ni—Si system alloy comprising 1.2 to 3.5 mass % Ni, Si in a concentration (mass %) of ⅙ to ¼ of Ni concentration (mass %) and the balance Cu and impurities whose total amount is 0.05 mass % or less, and having the following characteristics:
(A) electric conductivity: 55 to 62% IACS
(B) tensile strength: 550 to 700 MPa
(C) bendability: free from cracking at 180° bending test of 0 radius
(D) stress relaxation performance: 30% or less as measured on heating at 150° C. for 1000 hr.
The electric conductivity slightly deteriorates by an addition of Zn to the alloy. However, if excellent thermal peel resistance of Sn plating is particularly needed, Zn may be added up to a ceiling of 0.5 mass % to the alloy because the addition of Zn has a profound effect on the improvement of thermal peel resistance of Sn plating. Accordingly, in another aspect, the present invention is the Cu—Ni—Si system alloy comprising 1.2 to 3.5 mass % Ni, Si in a concentration (mass %) of ⅙ to ¼ of Ni concentration (mass %), 0.5 mass % or less of Zn and the balance Cu and impurities whose total amount is 0.05 mass % or less, and having the following characteristics:
(A) electric conductivity: 55 to 62% IACS
(B) tensile strength: 550 to 700 MPa
(C) bendability: free from cracking at 180° bending test of 0 radius
(D) stress relaxation performance: 30% or less as measured on heating at 150° C. for 1000 hr
(E) thermal peel resistance of plating: Peeling of plating could not be seen after thermal peel resistance test of Sn plating.
In an embodiment of the copper alloy according to the present invention, when an average grain size transverse to a rolling way is set to “a” and an average grain size parallel to the rolling way is set to “b” in a crystal structure whose cross-section is parallel to a rolling direction,
“a” is 1 to 15 μm, “b/a” is 1.05 to 1.67, and
an average range of precipitate-free zone in metal structure is 10 to 100 nm.
In a further aspect, the present invention is wrought copper product made of the alloys.
In a further aspect, the present invention is electronic components such as a lead frame, a connector, pin, a terminal, a relay, switch, foil materials for a secondary battery and the like made of the alloys.
In a further aspect, the present invention is a method for manufacturing Cu—Ni—Si system alloys comprising steps of solution treatment, cold rolling, age hardening and cold rolling in this order, wherein the each step is conducted on the following condition:
(solution treatment) The average grain size is adjusted within 1 to 15 μm.
(age hardening) The maximum temperature of materials during heat treating is 550° C. or less, the temperature of materials is maintained within 450 to 550° C. for 5 to 15 hours. The average rate of temperature increase of materials is 50° C./h or less in each temperature province of 200 to 250° C., 250 to 300° C. and 300 to 350° C. during a temperature increase process.
(cold rolling) The sum of a reduction ratio of the cold rolling before age hardening and a reduction ratio of the cold rolling after age hardening is 5 to 40%.
The invention could provide Cu—Ni—Si system alloys for electronic materials that are not added alloy elements other than Ni and Si or alloy elements other than Ni, Si and Zn, and have improved excellent electric conductivity, strength, bending workability and stress relaxation performance.
In the present invention, Si concentration (mass %) of copper alloys is ⅙ to ¼ of Ni concentration (mass %). This is because excellent electric conductivity (for example, 55% IACS or more) could not be provided if Si concentration is not in the range. Si concentration is preferably 1/5.5 to 1/4.2, and more preferably 1/5.2 to 1/4.5 of Si concentration.
Ni concentration is 1.2 to 3.5 mass %. If Ni concentration is below 1.2 mass %, excellent tensile strength (for example, 550 MPa) could not be provided. If Ni concentration is over 3.5 mass %, excellent bending workability could not be provided (for example, cracks are generated by 180° bending test of 0 radius). Ni concentration is preferably 1.4 to 2.5 mass %, and more preferably 1.5 to 2.0 mass %.
It has been a main procedure to improve characteristics of Cu—Ni—Si system alloys with adding various alloy elements. However, in accordance with the object of the present invention, other alloy elements (they are described “impurities” in the present invention) are excluded as much as possible. A sufficient electric conductivity tends not to be provided if other alloy elements are significantly contains, and it has been found difficult to provide Cu—Ni—Si system alloys having excellent strength, electric conductivity, bendability and stress relaxation performance. Accordingly, the total amount of concentrations of impurities is controlled to 0.05 mass % or less, preferably 0.02 mass % or less and more preferably 0.01 mass % or less in the present invention. Therefore, in preferred embodiments of the present invention, alloy elements other than Ni and Si except unavoidable impurities are not contains in Cu—Ni—Si system alloys.
However, if excellent thermal peel resistance of Sn plating is particularly needed, Zn may be contained in the alloys because its effect on the electrical conductivity is relatively small and its effect on the improvement of thermal peel resistance of Sn plating is profound. A decreasing rate of the electrical conductivity per 0.1 mass % of Zn is about 0.5% IACS. However, if Zn concentration is over 0.5 mass %, it is difficult to obtain sufficient electrical conductivity (for example, 55% IACS or more), and if Zn concentration is below 0.5 mass %, the effect on the improvement of thermal peel resistance of Sn plating could hardly be seen. Accordingly, Zn concentration is preferably 0.05 to 0.5 mass % and more preferably 0.1 to 0.3 mass %.
(Crystal Structure)
When an average grain size transverse to a rolling way is set to “a” and an average grain size parallel to the rolling way is set to “b” in a crystal structure whose cross-section is parallel to a rolling direction,
“a” is 1 to 15 μm, “b/a” is 1.05 to 1.67.
If “a” is less than 1 μm, excellent stress relaxation performance could not be provided (for example, stress relaxation performance is more than 30%), and excellent tensile strength could not be provided due to a shortage of precipitate Ni2Si at aging. Meanwhile, if “a” is more than ˜15 μm, excellent bending workability could not be provided (for example, cracks are generated by 180° bending test of 0 radius). “a” is preferably 2 to 10 μm, more preferably 2 to 5 μm when the bendability is attached a high value, and more preferably 5 to 10 μm when the strength and stress relaxation performance are attached a high value.
If “b/a” is less than 1.05, excellent tensile strength could not be provided (for example, tensile strength is less than 550 MPa). Meanwhile, if “b/a” is more than 1.67, excellent bendability could not be provided (for example, cracks are generated by 180° bending test of 0 radius). “b/a” is preferably 1.10 to 1.40, and more preferably 1.20 to 1.30.
An average range of the precipitate-free zone of the crystal structure is set to 10 to 100 nm in the crystal structure whose cross-section is parallel to a rolling direction. If the range of the precipitate-free zone is large, sufficient bendability, stress relaxation performance and tensile strength could not be provided. If the range of precipitate-free zone is more than 100 nm, excellent bendability could not be provided (for example, cracks are generated by 180° bending test of 0 radius), and excellent stress relaxation performance could not either (for example, stress relaxation performance is more than 30%). It is preferable that the range of precipitate-free zone is small. However, if the range is restricted to less than 10 nm, excellent electrical conductivity (for example, 55IACS % or more) could not be provided even if a characteristic age hardening of the present invention mentioned below is conducted. Accordingly, the average range of the precipitate-free zone to advance electrical conductivity, bending workability and stress relaxation performance in proper balance is preferably 20 to 90 nm, and more preferably 30 to 80 nm.
In addition, by adjusting to the above composition, fine Ni—Si intermetallic compound grains, whose grain size are in nm order and contribute to the increase of the strength, also precipitate frequently.
(Characteristics of Alloy)
The copper alloy of the present invention has the following characteristics at the same time in one embodiment.
(A) electric conductivity: 55 to 62% IACS
(B) tensile strength: 550 to 700 MPa
(C) bendability: free from cracking at 180° bending test of 0 radius
(D) stress relaxation performance: 30% (15 to 30% in exemplification) or less as measured on heating at 150° C. for 1000 hr
The copper alloy of the present invention has the following characteristics at the same time in a preferable embodiment.
(A) electric conductivity: 56 to 60% IACS.
(B) tensile strength: 600 to 660 MPa
(C) bendability: free from cracking at 180° bending test of 0 radius
(D) stress relaxation performance: 25% or less (15 to 25% in exemplification) as measured on heating at 150° C. for 1000 hr
The copper alloy of the present invention has the following characteristics at the same time in another preferable embodiment.
(A) electric conductivity: 60 to 62% IACS
(B) tensile strength: 600 to 610 MPa
(C) bendability: free from cracking at 180° bending test of 0 radius
(D) stress relaxation performance: 25% or less (20 to 25% in exemplification) as measured on heating at 150° C. for 1000 hr
The copper alloy of the present invention containing Zn has the following characteristics at the same time in another embodiment.
(A) electric conductivity: 55 to 62% IACS
(B) tensile strength: 550 to 700 MPa
(C) bendability: free from cracking at 180° bending test of 0 radius
(D) stress relaxation performance: 30% or less (15 to 30% in exemplification) as measured on heating at 150° C. for 1000 hr
(E) thermal peel resistance of plating: Peeling of plating could not be seen after thermal peel resistance test of Sn plating
The copper alloy of the present invention containing Zn has the following characteristics at the same time in a preferable embodiment.
(A) electric conductivity: 56 to 60% IACS
(B) tensile strength: 600 to 660 MPa
(C) bendability: free from cracking at 180° bending test of 0 radius
(D) stress relaxation performance: 25% or less (15 to 25% in exemplification) as measured on heating at 150° C. for 1000 hr
(E) thermal peel resistance of plating: Peeling of plating could not be seen after thermal peel resistance test of Sn plating
The copper alloy of the present invention containing Zn has the following characteristics at the same time in another preferable embodiment.
(A) electric conductivity: 56 to 60% IACS
(B) tensile strength: 640 to 660 MPa
(C) bendability: free from cracking at 180° bending test of 0 radius
(D) stress relaxation performance: 20% or less (15 to 20% in exemplification) as measured on heating at 150° C. for 1000 hr
(E) thermal peel resistance of plating: Peeling of plating could not be seen after thermal peel resistance test of Sn plating
The above “thermal peel resistance test” indicates a method for evaluation of the peeling of Sn plating of a test piece in the following way.
The test piece is under-plated with Cu 0.3 μm thick and upper-plated with Sn 1 μm thick, and heated at 300° C. for 20 seconds as a reflow process.
Then 90°-bending of 0.5 mm in radius to Good Way (GW: a direction where the bending axis is transverse to the rolling direction) and returning of the bend (go back and forth) are conducted, and s adhesive tape (a masking tape for plating, for example: #851A of SUMITOMO 3M) is attached to a surface of a bending inner periphery part and peeled from the surface.
Then the surface of the bending inner periphery part is examined with a microscope (20 magnifications) and the presence or absence of peelings of the plating is measured.
As far as the inventor of the present invention knows, there have never been examples of providing copper alloys having the same composition as the present invention and the characteristics coming up to those of the copper alloys of the present invention, that is, the characteristics of the electrical conductivity, strength, bending workability and stress relaxation performance in proper balance to the levels of the present invention.
(Method for Manufacturing)
In a general manufacturing process of Cu—Ni—Si system alloys, first, raw materials such as electrolytic cathode copper, Ni and Si are dissolved by the atmospheric melting furnace coated with charcoal. Then the molten metal is cast to ingots. After that, a hot rolling is conducted, and threads or foils having intended thickness (for example, 0.08 to 0.64 mm thick) and characteristics are produced by repeating the cold rolling and heat treatments. The heat treatments are a solution treatment and an age hardening. In the solution treatment, rough and large Ni—Si compounds produced in the molding process and the like solute into Cu to form a solid solution by heating at about 700 to about 1000° C., and recrystallize the Cu matrix at the same time. The hot rolling may introduce as the solution treatment. In the age hardening, Ni and Si in the solid solution in the solution treatment are precipitated as fine Ni—Si particles by heating at about 350 to about 550° C. for 1 hour. The strength and electrical conductivity increase by the age hardening. The cold rolling may be conducted before and/or after the age hardening in order to provide higher strength. In the case of conducting the cold rolling after the age hardening, the annealing to remove strains (low temperature annealing) may be conducted after cold rolling.
In the age hardening, if a heat time is changed in a fixed heat temperature, the electrical conductivity monotonously increases with the time. Meanwhile, the tensile strength generally increases to relative maximum at a certain temperature, and after that, decreases with the time. Even in the case of changing a heat temperature in a fixed heat time, the electrical conductivity monotonously increases with the time, and the tensile strength increases to relative maximum and then decreases. The aging conducted on the condition that the tensile strength is at relative maximum is called a peak aging. The aging conducted on the range that the tensile strength increases with the time or the temperature is called an overaging.
The overaging could be conducted in order to increase the electrical conductivity of Cu—Ni—Si system alloys. That is, the excellent electrical conductivity (for example, about 60% IACS) could be provided with relative ease if appropriate aging times and temperatures are selected. However, the tensile strength decreases (for example, to about 500 MPa), and in addition, the stress relaxation performance and the bendability deteriorate. If the cold rolling with high reduction ratio is conducted after that, the tensile strength makes a recovery to about 600 MPa. However, the bendability deteriorates significantly due to processing strains and the improvement of the stress relaxation performance could not be desired. The existing highly conductive Cu—Ni—Si system alloys described in Patent document 3 and the like were techniques basically applying the excessive aging.
The inventor of the present invention has examined in order to advance the electrical conductivity, bendability and stress relaxation performance in proper balance, and found out that Cu—Ni—Si system alloys having excellent electric conductivity, tensile strength, stress relaxation performance and bending workability are provided by adding particular conditions to a rate of temperature increase of the age hardening, maximum reaching temperature of materials and times of the age hardening, and by correcting conditions of the solution treatment and a reduction ratio of the cold rolling before and after conducting the age hardening in a manufacturing process for Cu—Ni—Si system alloys that contain impurities as little as possible.
Accordingly, in order to manufacture Cu—Ni—Si system alloys of the present invention, series of characteristic process flows are necessary in processes after the solution treatment, that is, the cold rolling (intermediate rolling), the age hardening and the cold rolling (last rolling). Particularly, the characteristic age hardening is essential.
(Age Hardening)
The rate of temperature increase, the maximum reaching temperature, the time of maintaining the temperature of materials at 450 to 550° C. and the rate of temperature increase of materials are regulated as conditions of the aging.
(A) The rate of temperature increase: If the temperature of materials increases mildly, fine cores of precipitation are produced in crystal grains in the temperature increase process, and a grain boundary reactive deposition after that, that is, a growth of the precipitate-free zone is restrained. Accordingly, even if a long-time aging is conducted in order to provide the high electrical conductivity, the precipitate-free zone does not grow so much and mechanical characteristics (such as strength, bendability and stress relaxation) do not deteriorate. That is, previously, the high electrical conductivity could not been provided if the aging time is reduced and the growth of the precipitate-free zone is restrained in order to improve the mechanical characteristics. Further, the precipitate-free zone grows and the excellent mechanical characteristics could not be provided if the aging time is prolonged in order to improve the electrical conductivity. The present invention has high significance in that it has the above two conflicting characteristics in the same time. The above mechanism presumed in the present invention does not restrict the present invention.
In particular, it is necessary that the average rate of temperature increase of materials is 50° C./h or less in each temperature province of 200 to 250° C., 250 to 300° C. and 300 to 350° C. The average rate of temperature increase is preferably 10° C./h or more in the light of the manufacturing efficiency. The average rate of temperature increase is typically 20 to 40° C./h.
A certain degree of restrictive effect of the precipitate-free zone could be provided by adding preliminary heat treatment at 250° C. for 48 hr described in Non-patent document 1. However, the manufacturing efficiency deteriorates significantly by the preliminary heat treatment. The method of controlling the rate of temperature increase of the present invention hardly deteriorates the manufacturing efficiency. Therefore, it is an industrially extremely useful method.
(B) The maximum reaching temperature of materials: The temperature is set to 550° C. or less, because the range of the precipitate-free zone broadens (for example, over 100 nm) regardless of controlling the rate of temperature increase if the temperature is over 550° C. The temperature is preferably 530° C. or less, and more preferably 500° C. or less. Meanwhile, if the maximum reaching temperature is less than 450° C., the excellent electrical conductivity could not be provided. Accordingly, the maximum reaching temperature is preferably 450° C. or more, and more preferably 480° C. or more.
(C) The time of maintaining the temperature at 450 to 550° C.: The time is set to 5 to 15 hours. If the heat time is less than 5 hours, the range of the precipitate-free zone narrows (for example, less than 10 nm). However, sufficient electrical conductivity could not be provided even if the rate of temperature increase is controlled. If the time is over 15 hours, the range of the precipitate-free zone broadens (for example, over 100 nm). The preferable time is 6 to 10 hours in consideration of the manufacturing efficiency additionally.
(Solution Treatment)
In the solution treatment, the average grain size is regulated to 1 to 15 μm. The average grain size after the solution treatment is substantively same as “a” regulated above in the stage of products. Accordingly, “a” derived from a crystal structure is less than 1 μm if the average grain size is less than 1 μm, and “a” will be more than 15 μm if the average grain size is more than 15 μm. The average grain size is preferably 2 to 10 μm, and in this case, “a” of 2 to 10 μm can be obtained.
The heat temperature and the heat conditions of the solution treatment for providing the above grain size are the public knowledge themselves. A person skilled in the art could set them appropriately. For example, the temperature of materials is maintained in an appropriate temperature of 700 to 800° C. for appropriate times of 5 to 600 seconds, air cooling or water cooling is conducted shortly thereafter, and the above grain size could be provided.
(Cold Rolling)
The summation of reduction ratios of the intermediate rolling and the last rolling is set to 5 to 40%. “b/a” derived from a metal structure of products is less than 1.05 if the summation of reduction ratios will be less than 5%, and “b/a” will be more than 1.67 if the summation of reduction ratios is more than 40%. The summation of reduction ratios is more preferably 10 to 25%, and in this case, “b/a” of 1.10 to 1.40 can be obtained. In addition, there is no problem even if either the reduction ratio of the intermediate rolling or that of the last rolling is 0.
The reduction ratio “R” is defined by the following formula.
R(%)=(t0−t)/t0×100
(t0: thickness before rolling, t: thickness after rolling)
When the thickness in the intermediate rolling is set to t1 as substitute for t0 and the thickness in the last rolling is set to t2 as substitute for t1, “the summation of reduction ratio Rsum(%)” is provided by the following formula.
Rsum(%)=(t0−t1)/t0×100+(t1−t2)/t1×100
(Annealing to Remove Strains)
The annealing to remove strains may be conducted after the last cold rolling in order to improve a spring limit value. The annealing to remove strains may be conducted at low temperature for long time (for example, 300° C.×30 minutes), and may be conducted at high temperature for short time (for example, 500° C.×30 seconds). If the temperature is too high or the time is too long, the tensile strength extremely decreases. It is preferable to set the decreasing amount of the tensile strength to 10 to 50 MPa and set the conditions.
Further, the effect of the present invention is also maintained if Cu—Ni—Si system alloys of the present invention are conducted the surface treatment with Sn plating or gold plating.
Accordingly, a method for manufacturing copper alloys of the present invention comprises the following steps in this order in a preferable embodiment:
the step of melt cast to make ingots comprising 1.2 to 3.5 mass % Ni, Si in a concentration (mass %) of ⅙ to ¼ of Ni concentration (mass %), 0.5 mass % or less Zn as an optional ingredient, the balance Cu and impurities whose total amount is 0.05 mass % or less,
the step of hot rolling,
the step of cold rolling,
the step of solution treatment to adjust an average grain size within 1 to 15 μm,
the step of cold rolling whose reduction ratio is 0 to 40%,
the step of age hardening wherein the maximum temperature of materials during heat treating is 550° C. or less, the temperature of materials is maintained within 450 to 550° C. for 5 to 15 hours, and an average rate of temperature increase of materials is 50° C./h or less in each temperature province of 200 to 250° C., 250 to 300° C. and 300 to 350° C. during a temperature increase process,
the step of cold rolling wherein a reduction ratio is 0 to 40% (a sum of said rate and the reduction ratio at the cold rolling before age hardening is 5 to 40%), and
optionally, the step of annealing to remove strains.
A person skilled in the art would be able to understand that processes such as grinding, polishing, shot-blasting and pickling for removal of oxidized scale could be properly conducted between each step mentioned above.
Cu—Ni—Si system alloys of the present invention could be processed to various sorts of wrought copper product such as plates, stripes, tubes, bar and wires. Further, Cu—Ni—Si system alloys of the present invention could be preferably used as, in particular, conductive spring components such as connector, pin, relay, switch, and lead frame components of semiconductor devices such as transistors and integrated circuits.
Hereinafter, working examples will be described in order to understand the present invention and advantages thereof better. However, the present invention is not limited to these examples.
2 kg electrolytic cathode copper was solved by a high-frequency induction furnace in a graphite crucible with 60 mm inside diameter and 200 mm depth. The surface of the molten metal in the crucible was covered with a charcoal chip, specified quantity of Ni, Si and if needed, Zn were added to the molten metal, then a temperature of the molten metal was adjusted to 1200° C. Then the molten metal was cast into a mold and an ingot with 60 mm width and 30 mm thickness was produced. A concentration of elements except Ni, Si and Zn, that is, impurities in the ingot was examined by the all elements semi-quantitative analysis of the glow-discharge mass spectrometry. As a result, the concentration was totally about 0.01 mass %. Fe (0.005 mass %), S (0.001 mass %) and C (0.001 mass %) were contained as comparatively highly-concentrated elements.
The ingot was heated at 950° C. for 3 hours, hot-rolled to 8 mm thickness, and oxidized scales on the surface were removed by grinding with a grinder. Then the cold rolling, the solution treatment, the cold rolling (intermediate rolling), the age hardening, the cold rolling (last rolling), and the annealing to remove strains as processes and the heat treatments were conducted in this order. The degree of processing and the board thickness at the heat treatments in each rolling were adjusted in order that the board thickness may be 0.25 mm after the last rolling. A pickling with 10 mass % sulfuric acid and 1 mass % hydrogen peroxide solution and a machine polish with #1200 emery papers were conducted in sequence in order to remove surface oxide films produced by the heat treatment after the solution treatment, after the age hardening and after the annealing to remove strains.
In the solution treatment, the sample was set in an electric furnace adjusted to a predetermined temperature for a predetermined time, then was instantly ejected from the electric furnace and air-cooled.
In the age hardening, the sample was heated on the conditions of different temperatures with the electric furnace. During the age hardening, the sample was contacted with a thermocouple and changes of the temperature of the sample were examined.
In the annealing to remove strains, the sample was set in the electric furnace adjusted to 300° C. for 30 minutes, then was ejected from the electric furnace and air-cooled. The annealing to remove strains was not conducted in the case where the last rolling was not conducted.
The following evaluation tests were conducted on the provided samples.
A crystal structure whose cross-section is parallel to a rolling direction was examined for the sample after the solution treatment and the sample after the annealing to remove strains or the sample after the last rolling if the annealing to remove strains was not conducted (hereinafter called “products”). The rolling direction was conducted mirror finishing with a mechanical polish and an electrolytic polish, a crystal grain boundary was produced by an etching, and then a picture of the crystal structure was taken. A solution mixed with ammonia water and hydrogen peroxide solution was used as the etching liquid. A light microscope and an electron scanning microscope were accordingly used for taking pictures of the crystal structure. In the case that the grain size was too small to discriminate the crystal grain boundary by the etching, an orientational map image of the sample with mirror surfaces after the electrolytic polish was taken with an EBSP method (Electron Backscattering Pattern), and the grain shapes was examined by using the image.
Three random straight lines transverse to a rolling direction were drawn on the above picture of the crystal structure and the number of crystal grains parted by the lines was counted. The value of a total length of the lines divided by the number of the crystal grains was set to “a”. In the same way, three random straight lines parallel to a rolling direction were drawn on the above picture of the crystal structure and the number of crystal grains parted by the lines was counted. The value of a total length of the lines divided by the number of the crystal grains was set to “b”.
The value of (a+b)/2 was calculated about the sample after the solution treatment and the value was set to the average grain size. The value of b/a was calculated about the products.
The vicinity of the crystal grain boundary of the products in the cross-section parallel to a rolling direction was examined by the transmission electron microscope of about one hundred thousand magnifications, and the average width of the precipitate-free zone (the average width about random 30 points) was calculated.
The electric conductivity of the products was examined by the four terminal method with reference to JIS-H0505.
The test piece of JIS13B was produced by press that a tensile direction may be parallel to a rolling direction. The tension test of the test piece was conducted with reference to JIS-Z2241 and the tensile strength was examined.
A test piece with 10 mm width was obtained from the products, and a 180° bending test of 0 radius test was conducted to Good Way (GW: a direction where the bending axis is transverse to the rolling direction) and Bad Way (BW: a direction where the bending axis is parallel to the rolling direction) with reference to JIS-Z2248. The presence or absence of cracks was examined from the surface and cross-section of the bending part of the sample after bending. The case where the cracks were not seen was set to ◯ and the case where the cracks were seen was set to X. In this case, cracks with over 10 μm depth were qualified as the cracks.
A test piece with 10 mm width and 100 mm length was obtained from the products in order that a longer direction of the test piece may be parallel to the rolling direction. As shown in
y
0=(⅔)·2·σ0/(E·t)
“E” is Young's modulus and “t” is a thickness of the test piece. The stress was unloaded after heating at 150° C. for 1000 hours, the amount of permanent set (height “y”) was measured as shown in
The test piece was degreased by alkali and pickled by 10% sulfuric acid, under-plated with Cu 0.3 μm thick, upper-plated with Sn 1 μm thick, and then heated at 300° C. for 20 seconds as a reflow process. The condition of the plating is as follows:
Plating bath composition: 200 g/L copper sulfate and 60 g/L sulfuric acid
Plating bath temperature: 25° C.
Current density: 5 A/dm2
Plating bath composition: 41 g/L stannous oxide, 268 g/L phenolsulfonic acid and 5 g/L surface active agent
Plating bath temperature: 50° C.
Current density: 9 A/dm2
A test piece with 10 mm width was obtained from the sample after the reflow process and heated at 150° C. for 1000 hours in the atmosphere. Then 90-bending of 0.5 mm in radius to Good Way (GW: a direction where the bending axis is transverse to the rolling direction) and returning of the bend (a both-way 90-bending) were conducted, and the adhesive tape (#851A of SUMITOMO 3M) was attached to a surface of a bending inner periphery part and peeled from the surface. Then the surface of the bending inner periphery part was examined with a light microscope (20 magnifications) and the presence or absence of peelings of the plating was measured. The case where the peelings of the plating were not seen at all was set to ◯. The case where the plating was detached in sheet shapes was set to X. The case where the plating was locally detached in point shapes was set to Δ. From a practical standpoint for applications of a connector and the like, the level of Δ has no problem.
Effects on crystal structures and characteristics of the products by the manufacturing condition are explained as follows. Sample compounds are set to Cu-1.60 mass % Ni-0.35 mass % Si alloy, the products are produced by changing conditions of the solution treatment, the age hardening and the rolling.
In (a), materials are set in the electric furnace adjusted to 200° C., and the temperature is maintained for 1 hour. Then the temperature of the electric furnace is increased from 200° C. to 350° C. in 5 hours. Next, the temperature of the electric furnace is increased to 500° C. in 1 hour and maintained for 8 hours, and then ejected from the electric furnace and air-cooled.
In (b), materials are set in the electric furnace adjusted to 200° C., and the temperature is maintained for 1 hour. Then the temperature of the electric furnace is increased from 200° C. to 250° C. in 3 hours, increased to 300° C. in 2 hours and then increased to 350° C. in 1 hour. Next, the temperature of the electric furnace is increased to 490° C. and maintained for 10 hours, and then ejected from the electric furnace and air-cooled. In (c), materials are set in the electric furnace adjusted to 500° C., and ejected from the electric furnace after 9 hours and air-cooled. These correspond to steps of a conventional heating procedure.
The average rate of temperature increase in each temperature province of 200 to 250° C., 250 to 300° C. and 300 to 350° C., the maximum reaching temperature of materials and the time of maintaining the temperature at 450 to 550° C. were measured. The products were produced on the conditions of the solution treatment and rolling of the present invention, and the crystal structures and the characteristics were examined. No. 1 to 3 of Table 1 show the results. The (a), (b) and (c) of
No. 1 and 2 produced on the conditions of the present invention fill the requirements of the crystal structures and the characteristics regulated in the present invention.
The rate of temperature increase of No. 3 that is the conventional example is larger than that of the present invention, and the conditions except that are same as those of No. 1. The precipitate-free zone was significantly over 100 nm. Accordingly, the tensile strength was below 550 MPa, cracks were generated by the 180° bending test of 0 radius and the stress relaxation performance was over 30%.
No. 4 is also the conventional example and conducted the high degree reduction ratio of cold rolling, to increase the tensile strength of No. 3 up to 550 MPa. The reduction ratio was high, and in addition, the precipitate-free zone was over 100 nm. Accordingly, the heavy shaking at the level where the test piece was broken by the 180° bending test of 0 radius was generated, and the stress relaxation performance was over 30%.
No. 5 is the conventional generic Cu—Ni—Si system alloys, conducted the peak aging and produced characteristics improving the tensile strength. Though the bendability and the stress relaxation performance were excellent, the electrical conductivity was less than 50% IACS.
(The Rate of Temperature Increase in Aging)
Table 2 shows the data in the case where the rate of temperature increase in aging in No. 1 is changed. It shows that the width of the precipitate-free zone is narrowed by reducing the rate of temperature increase. The tensile strength, bendability and stress relaxation performance improve because of the narrowed width of the precipitate-free zone. The rate of temperature increase was over 50° C./h in some temperature provinces in the comparative examples No. 9 and 10. Accordingly, the precipitate-free zone was over 100 nm, the tensile strength was below 550 MPa, cracks were generated by the 180° bending test of 0 radius and the stress relaxation performance was over 30%.
(Maximum Reaching Temperature and Time of Maintaining 450 to 550° C. in Aging)
Table 3 shows the data in the case where the maximum reaching temperature and the time of maintaining 450 to 550° C. in aging in No. 2 is changed.
When the time of maintaining 450 to 550° C. is long, the electrical conductivity improves. However, the precipitate-free zone broadens. With respect to the comparative example No. 11 where the aging time is less than 5 hours, the width of the precipitate-free zone is less than 10 nm and the electrical conductivity is less than 55% IACS. With respect to the comparative example No. 14 where the aging time is more than 15 hours, the width of the precipitate-free zone is more than 100 nm, the tensile strength is less than 550 MPa, cracks are generated by the 180° bending test of 0 radius and the stress relaxation performance is more than 30%.
When the maximum reaching temperature is high, the electrical conductivity improves. However, the width of the precipitate-free zone broadens. With respect to the comparative example No. 16 where the maximum reaching temperature is more than 550° C., the width of the precipitate-free zone is more than 100 nm, the tensile strength is less than 550 MPa, cracks are generated by the 180° bending test of 0 radius and the stress relaxation performance is more than 30%.
(Rolling Reduction Ratio)
Table 4 shows the data in the case where the rolling reduction ratio in No. 1 is changed. It shows that “b/a” which is calculated from the metal structure of the products and the tensile strength increase as the reduction ratio increases. The b/a in No. 17, where the total amount of the intermediate reduction ratio and the last reduction ratio is less than 5%, is less than 1.05, and the tensile strength is less than 550 MPa. The “b/a” in No. 23, where the total amount of the intermediate reduction ratio and the last reduction ratio is more than 40%, is more than 1.67, and the tensile strength is more than 700 MPa and cracks are generated by the 180° bending test of 0 radius.
(Grain Size after the Solution Treatment)
Table 5 shows the data in the case where the grain size after the solution treatment in No. 2 is changed. It shows that “a” which is calculated from the crystal structure of the products increases and the stress relaxation performance decreases as the grain size after the solution treatment increases. The “a” in No. 24, where the grain size after the solution treatment is less than 1 μm, is less than 1 μm, the stress relaxation performance is more than 30% and the tensile strength is less than 550 MPa due to insufficient solution treatment. The “a” in No. 29, where the grain size after the solution treatment is more than 15 μm, is more than 15 μm, and cracks are generated by the 180° bending test of 0 radius.
Effects on crystal structures and characteristics of the products by the alloy contents are explained as follows. Cu—Ni—Si system alloys containing different contents were processed to products on the same manufacturing conditions as the above invention example No. 1. When the solution treatment was conducted at 750° C. for 60 seconds, the grain sizes of all test pieces were within the preferable range of the present invention though the grain sizes slightly changed due to their contents.
(Effect of Ni Concentration/Si Concentration)
Table 6 shows the data in the case where Ni concentration is fixed to 1.60 mass % and Si concentration is changed. The test pieces of No. 1 and 5 are same as that of Table 1. The test piece of No. 5 is the conventional alloy whose electrical conductivity is less than 55% IACS and its manufacturing condition is different from those of other test pieces.
When Ni concentration/Si concentration is out of the range of 4 to 6, the electrical conductivity is less than 55% IACS. When Ni concentration/Si concentration decreases, the tensile strength increases. This is because the amount of precipitation of Ni2Si increased due to the increase of Si concentration.
The result of the evaluation for the thermal peel resistance of Sn plating of the alloys in the present invention is Δ (detached in point shapes). The results of the evaluation for No. 5 and 34 are X. This is because the solid solution of Si deteriorates the thermal peel resistance. That is, the solid solution of Si increased because the amount of precipitation of Ni2Si in No. 5 was small and Si was added excessively compared to Ni in No. 34.
(Effect of Ni)
Table 7 shows the data in the case where Ni concentration/Si concentration is maintained within the range of that in the present invention and Ni concentration is changed. The tensile strength in No. 35, where Ni concentration is less than 1.2 mass %, is less than 550 MPa. The tensile strength in No. 41, where Ni concentration is more than 3.5 mass %, is more than 700 MPa and cracks are generated by the 180° bending test of 0 radius.
(Effect of Zn)
As the effect of addition of Zn, Table 8 shows the data in the case where Zn of different concentrations is added in No. 1. The result of the evaluation for the thermal peel resistance of Sn plating of the alloys in the present invention became ◯ (no peeling) by adding more than 0.05 mass % Zn. The electrical conductivity decreased as the amount of Zn increased. However, the electrical conductivity was more than 55% IACS in the range of less than 0.5 mass % Zn.
(Effect of Impurities)
As the effect of impurities, Table 9 shows the data in the case where the impurities in No. 43 increased. The total amount of the impurities is changed by adding Sn for supposed interfusion of Sn plated Cu materials and adding Mg for supposed residual deoxidation elements at melting. The electrical conductivity is less than 55% IACS in the case where the impurities is more than 0.05 mass %.
330
390
580
330
390
580
70
330
390
580
160
521
X
37
160
3.35
X
X
35
85
80
60
120
542
31
140
530
33
3
16
560
50.6
110
62.5
545
31
115
63.4
538
35
45
1.01
1.80
707
0.8
17.4
0.8
545
35
17.5
6.15
3.90
54.2
46.5
1.15
3.60
545
704
X
X
0.60
54.4
54.5
54.2
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-259294 | Sep 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/068420 | 9/21/2007 | WO | 00 | 3/25/2009 |
