JP2008248332A - Tin-plated strip and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tin-plated strip made of copper or a copper alloy which is suitable as various connectors, especially, fitting type connector terminals and can maintain a low contact electrical resistance even under a high temperature condition or under long-term use. <P>SOLUTION: The tin-plated strip made of copper or a copper alloy has a Sn-plated film on its surface and is characterized in that the concentration of Zn existing in the uppermost surface of the Sn-plated film after reflow treatment is 0.1-10 mass% and the concentration of Zn in a depth of ≥0.1 μm (expressed in terms of SiO<SB>2</SB>) from the uppermost surface is ≤0.01 mass%. The tin-plated strip made of a copper alloy is produced by plating a copper alloy with Sn, then performing a surface treatment comprising bringing a solution containing zinc ions into contact with the plated surface, and performing a reflow treatment. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a copper or copper alloy Sn-plated strip that is suitable as various connectors, particularly as a fitting-type connector terminal, having good solder wettability and maintaining a low contact electric resistance even under high temperature conditions or long-term use.

In addition to high strength, high electrical conductivity, and thermal conductivity, copper alloys for electronic materials used for terminals, connectors, etc. have bending workability, stress relaxation resistance, heat resistance, adhesion to plating, solder Wetness, etching processability, press punchability, corrosion resistance, etc. are required.
In addition, in various connectors of electronic components, particularly copper or copper alloy Sn plating materials used for mating connector terminals, tin oxide is formed on the surface over time, while the base material and the components of the base plating are Sn. It is known that when an alloy layer is formed by diffusing into a layer, the pure Sn layer disappears and the contact electrical resistance increases. The deterioration of characteristics with time is accelerated as the temperature increases, and becomes particularly noticeable around an automobile engine. USCAR, which determines the standards for automotive parts, requires the characteristic (heat resistance) that the contact electrical resistance of the connector material does not deteriorate under the strictest usage conditions at the normal usage temperature of 155 ° C and the maximum usage temperature of 175 ° C. Has been.
Furthermore, after the connector terminal material is Sn-plated, surface treatment is performed to remove tin oxide, etc., but after the surface treatment, tin oxide is formed during transportation and storage until the next work step. There is a demand for a material that does not increase the contact electrical resistance even when left for a long period of time. Here, a material that does not increase in contact electrical resistance at high temperatures can be restated as a material that does not increase in contact electrical resistance even when stored for a long period of time.

In general, it is known that the contact electric resistance and solderability of Sn plating show a good correlation with the thickness of the residual pure Sn layer. However, when the Sn plating is thickened, there are problems such as an increase in cost and an increase in force necessary for insertion / extraction.
Therefore, a first plating layer that is Sn and / or Sn—Cu alloy plating is provided around Cu or a Cu alloy, and is composed of an alloy of a third element such as Zn and Sn on the outer surface thereof. Plating provided with a second plating layer in which the concentration of the third element is 0.01 to 80 wt% has been proposed (Patent Document 1).

It has also been proposed to form a plating film containing a first Sn plating film and a metal lower than the second tin on the surface of the electronic component (Patent Document 2). This second plating film is preferably made of Zn or a Zn—Sn alloy, and has a thickness of 50 nm or less and an Sn concentration of less than 60 wt%.
JP 2005-216749 A JP 2006-22345 A

However, the invention of Patent Document 1 is intended to improve whisker resistance in a flat cable, and is manufactured by plating a third element (Zn or the like) and alloying it by heat treatment. Therefore, in order to prevent whisker generation, the second plating layer needs to be plated and alloyed by heat treatment, so special equipment for the plating process of the second plating layer is necessary, and the manufacturing cost increases. However, there is a problem of using a relatively large amount of zinc.
The manufacturing method exemplified in Patent Document 1 is to form the first and second plating films in an inert atmosphere. Therefore, the invention of Patent Document 2 has the same problem as Patent Document 1, and when it is preferably carried out in an inert atmosphere, further equipment cost and manufacturing cost are required.
As described above, there is a need for a copper or copper alloy Sn plating strip that can be economically manufactured without requiring special equipment and that does not increase contact electrical resistance even under long-term and / or high-temperature conditions.

The present invention relates to the following copper alloy Sn plating strip and a method for producing the same.
(1) It has a Sn plating film on the surface, Zn is present at a concentration of 0.1 to 10% by mass on the outermost surface of the Sn plating film after the reflow treatment, and 0.1 μm (in terms of SiO ₂₎ from the outermost surface. ) An Sn plating strip of copper or copper alloy characterized in that the Zn concentration is 0.01% by mass or less at the above depth.
(2) The Sn plating strip according to (1), wherein the thickness of the Sn phase of the Sn plating film is 0.1 to 1.5 μm.
(3) From the surface to the base material, a plating film is constituted by each layer comprising an Sn phase and an Sn—Cu alloy phase, the thickness of the Sn phase is 0.1 to 1.5 μm, and the thickness of the Sn—Cu alloy phase is The Sn plating strip according to (1), which is 0.1 to 1.5 μm.
(4) From the surface to the base material, a plating film is constituted by each layer composed of Sn phase and Ni phase, the thickness of Sn phase is 0.1-1.5 μm, and the thickness of Ni phase is 0.1-2. The Sn plating strip according to (1), which is 0 μm.
(5) From the surface to the base material, a plating film is constituted by each layer composed of Sn phase, Sn—Cu alloy phase, Cu phase, Ni phase, Sn phase thickness is 0.1 to 1.5 μm, Sn—Cu Sn plating as described in said (1) whose thickness of an alloy phase is 0.1-1.5 micrometers, the thickness of Cu phase is 0-1.5 micrometers, and the thickness of Ni phase is 0.1-2.0 micrometers. Article.
(6) The Sn plating according to any one of the above (1) to (5), in which after the Sn plating is performed on the base material, a surface treatment is performed by bringing the plating surface into contact with a solution containing zinc ions and then a reflow treatment is performed. Article manufacturing method.
(7) The said surface treatment is a manufacturing method of the said (6) description performed in the surface treatment tank provided with the solution which added the zinc sulfate.
(8) The manufacturing method according to (6) or (7), wherein the zinc concentration of the solution is 0.1 to 10 g / L.

The copper or copper alloy Sn plating strip of the present invention, in this case, exhibits good solderability and excellent heat resistance even with thin Sn plating, and has a contact electrical resistance even under long-term and / or high-temperature conditions. Does not rise. In addition, the effect can be obtained simply by adding ZnSO ₄ to the sulfuric acid flux solution, which is a commonly used surface treatment solution, so there is no cost for new capital investment, etc., and an excellent effect is achieved with a small amount of Zn. it can. That is, in the manufacturing method of the present invention, Zn can be disposed on the surface during the surface treatment step of removing the oxidized Sn film present on the Sn plating surface of the base material with the acidic solution.

Below, the Sn plating strip of the copper or copper alloy of the present invention will be described together with its production method.
The Sn plating of the present invention is formed on the surface of copper or copper alloy strip. Here, the composition of the copper alloy only has to be used for various connectors of electronic components. For example, brass (Cu-Zn alloy, C2600, C2801, C3604, etc.), phosphor bronze (C5210, C5191, etc.), A Corson alloy (C7025 etc.) is mentioned.

The following plating film is mentioned as an example of the structure of the plating film formed on the surface of the copper or copper alloy strip of this invention. (1) A plating film in which an Sn plating layer is directly formed on the surface of the alloy strip. (2) A plating film in which a Cu plating layer and then a Sn plating layer are formed on the surface of the alloy strip. (3) A plating film in which a Ni plating layer and then a Sn plating layer are formed on the surface of the alloy strip. (4) A plating film formed in the order of a Ni plating layer, a Cu plating layer, and a Sn plating layer on the surface of the alloy strip.
In the plating film, a Cu plating layer, a Ni plating layer, and a Sn plating layer are appropriately formed on the base material in an appropriate order by electroplating.
The thickness of the layer is adjusted by appropriately changing the plating conditions so that the target phase thickness is obtained when the following reflow treatment is performed.

On the outermost surface of the Sn plating film after the reflow treatment of the present invention, Zn is present at a concentration of 0.1 to 10% by mass, and at a depth of 0.1 μm (in terms of SiO ₂ ) or more from the outermost surface, the Zn concentration Is 0.01 mass% or less. When the Zn concentration on the outermost surface is less than 0.1% by mass, good heat resistance is not exhibited. On the other hand, even if it exceeds 10% by mass, no further effect can be expected. Further, Zn concentration further even exceed 0.01 wt% effect 0.1 [mu] m (SiO ₂ basis) or more deep from the outermost surface can not be expected.
The Zn distribution can be analyzed, for example, by sputtering with argon ions using an X-ray photoelectron spectrometer manufactured by ULVAC-PHI.

The Zn distribution on the surface of the Sn plating film of the present invention is very different in quantity and structure from the conventionally known Zn film on the surface of Sn plating (Patent Documents 1 and 2). Instead of plating, the base material having a plating film whose surface is Sn can be manufactured by performing a surface treatment in which a solution containing zinc ions is brought into contact with the plating surface.
Examples of the solution to be contacted include an acidic solution in which zinc sulfate is dissolved and an acidic solution in which zinc phosphate is dissolved. Examples of the contact method include commonly used methods such as immersion in a solution, application of the solution, flow-down, and spraying. Above all, when zinc sulfate is dissolved in the sulfuric acid flux liquid in the surface treatment bath in which the material after the Sn plating treatment is immersed for the purpose of removing tin oxide on the surface of the Sn plating film, the zinc is exposed to the surface during the immersion. Since it adheres and the Sn plating film of this invention is manufactured, a special installation is not required and it is preferable.

The zinc concentration of the solution is preferably 0.1 to 10 g / L, more preferably 0.5 to 5.0 g / L. If it is less than 0.5 g / L, the effect of the present invention cannot be obtained, and even if it exceeds 5.0 g / L, no further effect can be expected.
The immersion temperature and the time temperature depend on each other and can be appropriately changed, but may be, for example, 40 to 60 ° C. for 1 to 10 seconds. Moreover, the pH of an acidic solution is 1-4, for example.

A reflow process is performed on the Sn plating film of the present invention. In the reflow treatment, the electrodeposited Sn plating film is heated once and then rapidly cooled, the stress (distortion) during plating is removed, whisker generation is prevented, and a diffusion layer with the base metal is formed to change over time. The effect of reducing is obtained. By the reflow treatment, the Cu plating layer and the Sn plating layer react to form an Sn—Cu alloy phase. The Cu base plating may be consumed and lost during Sn-Cu alloy phase formation during reflow. That is, the lower limit value of the Cu phase thickness after reflow is not regulated, and the thickness may be zero. The Ni layer remains after electroplating even after reflow.
The conditions for the reflow treatment are adopted according to the thickness of the target strip, the thickness of the Sn phase, the Cu phase, the Ni phase, etc., for example, appropriate conditions in the range of 230 to 600 ° C. and 3 to 30 seconds. The reflow process is performed.

The plated layer structure after the reflow process is (1) Sn phase, (2) Sn phase, Sn-Cu alloy phase, each layer consisting of arbitrary Cu phase, (3) Sn phase, Ni phase from the surface to the base material. (4) Each layer consisting of Sn phase, Sn—Cu alloy phase, arbitrary Cu phase, Ni phase. In the above (3) and (4), the diffusion of the base material Cu into the Sn phase is suppressed by the presence of the Ni phase, and the diffusion of Ni into the Sn phase is suppressed by the presence of the Cu phase or the Cu—Sn alloy phase. Therefore, the disappearance of the pure Sn layer is delayed and the heat resistance is improved. That is, the contact electric resistance does not increase even under a long period and / or high temperature conditions.
Since the surface Sn may be oxidized, the reflow treatment is preferably performed on the Sn plating film in which zinc adheres to the surface by the surface treatment, but in some cases, the reflow treatment may be performed before the surface treatment. .

  The thickness of the Sn phase constituting the plating film of the present invention is preferably 0.1 to 1.5 μm. When the Sn phase is less than 0.1 μm, the solder wettability decreases, and when it exceeds 1.5 μm, the thermal stress generated in the plating layer when heated is increased, and the plating peeling is promoted. A more preferable range is 0.2 to 1.0 μm.

The thickness of the Sn—Cu alloy phase of the present invention is preferably 0.1 to 1.5 μm. When the Sn—Cu alloy phase is less than 0.1 μm, it is impossible to reduce the insertion force derived from the hardness of the Sn—Cu alloy phase. On the other hand, when the thickness exceeds 1.5 μm, the thermal stress generated inside the plating layer when heated is increased, and the plating peeling is promoted. A more preferable thickness is 0.5 to 1.2 μm.
The Cu phase of the present invention may be diffused by reflow to form a Sn—Cu alloy phase, or may remain as a Cu phase. The thickness of the remaining Cu phase is preferably 0 to 0.7 μm. When it exceeds 0.7 μm, when heated, the Sn phase is consumed due to the growth of the Sn—Cu alloy phase, and solder wettability and heat resistance are lowered.
The thickness of the Ni phase of the present invention is preferably 0.1 to 0.8 μm. When the Ni phase is less than 0.1 μm, the corrosion resistance and heat resistance of the plating deteriorate. On the other hand, when it exceeds 0.8 μm, the thermal stress generated inside the plating layer when heated is increased, and the plating peeling is promoted. A more preferable thickness is 0.1 to 0.3 μm.

The plating method, surface treatment method and measurement method employed in the examples of the present invention are shown below.
As a base material, a commercially available brass product, a material symbol C2600, and a thickness of 0.32 mm were used after being degreased and pickled.
(Ni base plating conditions)
Plating bath composition: nickel sulfate 250 g / L, nickel chloride 45 g / L, boric acid 30 g / L.
Plating bath temperature: 55 ° C.
Current density: 4 A / dm ² .
The Ni plating thickness was adjusted by the electrodeposition time.
(Cu base plating conditions)
Plating bath composition: copper sulfate 200 g / L, sulfuric acid 60 g / L.
Plating bath temperature: 30 ° C.
Current density: 2.5 A / dm ² .
The Cu plating thickness was adjusted by the electrodeposition time.

(Sn plating conditions)
Plating bath composition: stannous oxide 41 g / L, phenolsulfonic acid 268 g / L, surfactant 5 g / L.
Plating bath temperature: 45 ° C.
Current density: 4 A / dm ² .
The Sn plating thickness was adjusted by the electrodeposition time.
(Zn plating conditions)
Plating bath composition: zinc sulfate 200 g / L, aluminum sulfate 30 g / L, sodium chloride 30 g / L.
Plating bath temperature: 25 ° C.
Current density: 2 A / dm ² .
The Zn plating thickness was adjusted by the electrodeposition time.

(Surface treatment conditions)
Surface treatment solution: 1 ml / L aqueous solution of sulfuric acid to which zinc sulfate is added at a concentration of 4 or 12 g / L (1 ml / L aqueous solution of sulfuric acid containing 0.5, 1.5 or 5.0 g / l of zinc).
Immersion time: 10 seconds Treatment liquid temperature: Room temperature (25 ° C.)
(Reflow processing conditions)
The sample was inserted into a heating furnace adjusted to 400 ° C. and the atmosphere gas to nitrogen (oxygen 1 vol% or less) for 10 seconds and cooled with water.

The following evaluation was performed about the sample produced in this way.
(A) Surface analysis by XPS After the reflowed sample was ultrasonically degreased in acetone, concentration profiles of Sn, Cu, Ni, and Zn in the depth direction were determined by an X-ray photoelectron spectrometer (XPS). The measurement conditions are as follows.
Sample pretreatment: ultrasonic degreasing in acetone.
Apparatus: ULVAC-PHI Co., Ltd. model 5600MC.
Ultimate vacuum: 3.3 × 10 ⁻⁸ Pa
Excitation source: Monochromatic AlKα
Output: 300W
Detection area: 800μmφ
Ion species: Ar
Acceleration voltage: 3 kV
Sputtering rate: 4.5 nm / min (SiO ₂ conversion)
As a result of measurement by the above method, the phase thickness of the Sn plating film sample used in Table 1 below is all Sn phase 1.0 / Ni phase 0.3 μm / base material from the surface to the base material. The phase thickness of the Sn plating film sample used in No. 2 was Sn phase 1.0 μm / Cu phase 0.3 μm / Ni phase 0.3 μm / base material from the surface to the base material.

(B) Heat resistance (change in contact electrical resistance)
For a sample heated at 155 ° C. in the atmosphere for 400 hours, contact electrical resistance was measured by a four-terminal method using a contact simulator (trade name CRS-1) manufactured by Yamazaki Seiki. The measurement conditions are as follows.
Contact load: 50 g.
Current: 200 mA
Sliding speed: 1 mm / min, sliding distance: 1 mm.
In the following table, ◎ represents a contact electric resistance of 10 mΩ or less even after heating at 155 ° C. in an air atmosphere for 400 hours, ◯ represents less than 10 to 20 mΩ, Δ represents 20 to 50 mΩ, and x represents greater than 50 mΩ.

(C) Solderability A strip-shaped test piece having a width of 10 mm and a length of 21 mm was collected and washed in a 10% by mass sulfuric acid aqueous solution. The solder wetting time was measured by a meniscograph method using a solder checker (trade name SAT-5000, manufactured by Reska). The measurement conditions are as follows.
Flux: 25% rosin-ethanol.
Solder composition: Sn-3Ag-0.5Cu, Solder temperature: 250 ° C.
Immersion (drawing) speed: 25 mm / sec for 10 seconds, immersion depth: 2 mm.
In the following table, ◎ represents a wet time of 1 second or less, ◯ represents 1 to 3 seconds, Δ represents 3 to 5 seconds, and x represents 5 seconds or more.
(D) Appearance The surface of the base metal plating was judged visually.
In the following table, ○ indicates no cloudiness, Δ indicates slightly cloudy, and × indicates cloudy.

FIG. 1 shows the measurement results by XPS of the Sn concentration and the Zn concentration with respect to the distance from the surface of the Sn plating strip of Example 2. The Zn content from the outermost surface to 0.025 μm is about 7 mass%, but the Zn content cannot be confirmed at a distance of 0.05 μm or more from the outermost surface.
FIG. 2 shows the measurement results of Comparative Example 6 and FIG. 3 shows the measurement results of Comparative Example 7. In Comparative Example 6, the Zn concentration on the outermost surface is about 9% by mass, but the Zn concentration increases as it becomes deeper, reaches a maximum of about 25% by mass at a depth of about 0.025 μm, and the Zn concentration decreases as the depth further increases. The depth is about 9% by mass at a depth of 0.10 μm. In Comparative Example 7, the Zn concentration on the outermost surface is about 14% by mass, but the Zn concentration increases as the depth becomes deeper, reaches a maximum of about 55% by mass at a depth of 0.025 μm, and the Zn concentration decreases as the depth further increases. Still, it is about 16% by mass at a depth of 0.10 μm.
From the above, it was not possible to produce the Sn plating strip of the present invention even with ultra thin Zn plating of 0.02 μm.
The distance from the surface shown in FIGS. 1 to 3 is a value calculated from the sputtering rate in terms of SiO ₂ based on the sputtering time, and is different from the actual distance.

From Table 1, in the Sn plating strip having the configuration of Sn phase 1.0 μm / Ni phase 0.3 μm / base material, Examples 2 to 4 treated with Zn in the present invention were compared with Comparative Example 1 where Zn treatment was not performed. The contact electrical resistance after high temperature heating was good and the solderability was also good.
Comparative Examples 5 to 7 in which Zn plating was performed on Sn plating were inferior in solder wettability, and were inferior in appearance when the thickness was increased, and the contact electrical resistance increased after high-temperature heating.

From Table 2, in the Sn plating strips having the structure of Sn phase 1.0 μm / Cu phase 0.3 μm / Ni phase 0.3 μm / base material, Examples 9 to 11 treated with Zn in the present invention do not undergo Zn treatment. Compared to Comparative Example 8, both the contact electrical resistance after high-temperature heating and the solderability were very good.
In Comparative Examples 12 and 13 in which Zn plating is performed on Sn plating, the heat resistance and the appearance are inferior when the thickness of the Zn plating is thin (Comparative Example 13). It was not good.
As described above, the Sn plating strip of the present invention maintains a low contact electric resistance for a long time and / or at a high temperature and is solderable, even with a Sn plating film thinner than a conventional material obtained by performing Zn plating on Sn plating. The appearance was excellent.

The measurement result by XPS of Sn density | concentration with respect to the distance from the surface of the Sn plating strip of Example 2 and Zn density | concentration is shown. The measurement result by XPS of the Sn plating strip of the comparative example 6 is shown. The measurement result by XPS of the Sn plating strip of the comparative example 7 is shown.

Claims (8)

It has a Sn plating film on the surface, Zn is present at a concentration of 0.1 to 10% by mass on the outermost surface of the Sn plating film after the reflow treatment, and 0.1 μm (in terms of SiO ₂ ) or more from the outermost surface. A copper or copper alloy Sn plating strip characterized by having a Zn concentration of 0.01 mass% or less at a depth.   2. The Sn plating strip according to claim 1, wherein a thickness of the Sn phase of the Sn plating film is 0.1 to 1.5 μm.   From the surface to the base material, a plating film is constituted by each layer comprising an Sn phase and an Sn—Cu alloy phase, the thickness of the Sn phase is 0.1 to 1.5 μm, and the thickness of the Sn—Cu alloy phase is 0.1. The Sn plating strip according to claim 1, which is ˜1.5 μm.   From the surface to the base material, a plating film is constituted by each layer composed of the Sn phase and the Ni phase, the thickness of the Sn phase is 0.1 to 1.5 μm, and the thickness of the Ni phase is 0.1 to 2.0 μm. The Sn plating strip according to claim 1.   From the surface to the base material, a plating film is constituted by each layer composed of Sn phase, Sn—Cu alloy phase, Cu phase, and Ni phase, and the thickness of the Sn phase is 0.1 to 1.5 μm. The Sn plating strip according to claim 1, wherein the thickness is 0.1 to 1.5 µm, the thickness of the Cu phase is 0 to 1.5 µm, and the thickness of the Ni phase is 0.1 to 2.0 µm.   The method for producing an Sn-plated strip according to any one of claims 1 to 5, wherein after the Sn base is plated with Sn, a surface treatment is performed in which a plating surface is brought into contact with a solution containing zinc ions, and then a reflow treatment is performed.   The said surface treatment is a manufacturing method of Claim 6 performed in the surface treatment tank provided with the solution which added the zinc sulfate.   The manufacturing method according to claim 6 or 7, wherein the zinc concentration of the solution is 0.1 to 10 g / L.

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