JP2010168666A - HEAT-RESISTANT TINNED STRIP OF Cu-Zn ALLOY IN WHICH WHISKER IS SUPPRESSED - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Cu/Ni two layered substrate reflow tinned strip of a Cu-Zn alloy in which whisker occurrence is suppressed. <P>SOLUTION: In the tinned strip in which a copper alloy containing 15-40 mass% in an average concentration of Zn is used for a base material and a plated film is formed by each layer of a Sn phase, Sn-Cu alloy phase, and Ni phase, from a surface to the base material, a Zn concentration of a surface layer of the Sn phase is adjusted to 0.1-5.0 mass%. The base material may further contain an optional ingredient selected from Sn, Ag, Pb, Fe, Ni, Mn, Si, Al, and Ti within a range of 0.005-3.0 mass% in total. Moreover, the base material contains 15-40 mass% Zn, 8-20 mass% Ni, 0-0.5 mass% Mn, and the balance may be a copper-based alloy including Cu and unavoidable impurities, and further may contain 0.005-10 mass% the optional ingredient in total. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heat-resistant Sn plating strip of a Cu—Zn alloy in which the generation of whiskers is suppressed.

  Cu-Zn alloys are widely used as electrical contact materials for connectors, terminals, relays, switches and the like because they are less expensive than phosphor bronze, beryllium copper, and Corson alloys, although they are less expensive. A typical Cu—Zn alloy is brass, and alloys such as C2600 and C2680 are defined in JIS H3100. When a Cu—Zn alloy is used as an electrical contact material, Sn plating is often applied in order to stably obtain a low contact resistance. And the Sn-plated strip of Cu-Zn alloy utilizes the excellent solder wettability, corrosion resistance, and electrical connectivity of Sn, and is used for terminals of automobile electrical wiring harnesses, terminals of printed circuit boards (PCBs), and connectors for consumer use. It is used in large quantities for electrical and electronic parts such as contacts.

The Sn-plated strip of the Cu-Zn alloy is degreased and pickled, and then a base plating layer is formed by an electroplating method, then an Sn plating layer is formed by an electroplating method, and finally a reflow treatment is performed. Manufactured in the process of melting the plating layer.
In Sn plating of a Cu—Zn alloy, base plating is usually performed prior to Sn plating. This is because when the base plating is not performed, Zn in the base material forms a Zn-concentrated layer on the Sn plating surface during the reflow process, and solder wettability decreases. That is, the base plating is performed in order to obtain a base layer that suppresses the diffusion of Zn as a base material to the Sn plating surface.
When heat resistance of Sn plating is required, Cu / Ni two-layer base plating is applied as the base plating of the Cu—Zn alloy. The Cu / Ni two-layer undercoating is a plating obtained by performing an electroplating in the order of Ni undercoating, Cu undercoating, and Sn plating, followed by a reflow treatment. The structure of the plated film layer after reflowing is Sn from the surface. Phase, Cu-Sn phase, Ni phase, and base material. Details of this technique are disclosed in Patent Documents 1 to 3 and the like.

  It is known that when a Sn plating material is left at room temperature, a single crystal of Sn grows from the surface of the Sn plating. This single crystal of Sn is called a whisker and may cause a short circuit of an electronic component. Whisker is generated due to the internal stress of the Sn plating film generated during electrodeposition. Therefore, melting Sn by reflow treatment to remove the internal stress of the coating is effective as a means for suppressing the occurrence of whiskers. Cu / Ni bilayer base heat-resistant Sn plating of Cu-Zn alloy has been considered to have good whisker resistance because reflow is performed in the manufacturing process.

JP-A-6-196349 JP 2003-293187 A JP 2004-68026 A

However, since extremely large internal stress is locally applied to the electrical contact portion such as a terminal, even if the reflow Sn plating strip has been considered to have good whisker resistance, fine whiskers may occur. In recent years, the distance between terminals has been narrowed due to the increase in the number of connectors, etc., and there has been a risk of causing a short circuit even with a small whisker that has not been a problem in the past. As a result, further improvement in whisker resistance has been demanded for Cu / Ni bilayer base heat-resistant Sn plating of Cu—Zn alloy, which has been considered to have good whisker resistance.
An object of the present invention is to provide a Cu / Ni bilayer base reflow Sn plating strip of a Cu-Zn alloy in which whisker generation is suppressed.

  The present inventors have earnestly studied measures for suppressing the generation of whiskers for Cu / Ni bilayer underlayer reflow Sn plating strips of Cu-Zn alloy, and whisker is suppressed when Zn is concentrated on the Sn plating surface. I found out. However, as described above, when Zn is concentrated on the Sn plating surface, the solder wettability is lowered. Therefore, the present inventor has searched for and found a Zn enriched state in which whisker suppression and good solder wettability are compatible. At the same time, it is possible to clarify the conditions of the base material surface, the Cu base plating thickness, the Ni base plating thickness, the Sn plating thickness, and the heating conditions in the reflow process as the manufacturing conditions for obtaining this appropriate Zn enriched state. It was.

The present invention has been made based on this discovery and is as follows.
(1) Using a copper alloy containing Zn at an average concentration of 15 to 40% by mass as a base material, a plating film is composed of Sn phase, Sn—Cu alloy phase, and Ni phase layers from the surface to the base material. A Cu-Zn alloy Sn plating strip in which whisker generation is suppressed, wherein a Zn concentration of a surface layer of the phase is 0.1 to 5.0 mass%.
(2) The Cu—Zn alloy Sn-plated strip according to (1), wherein the base material is a copper-based alloy containing 15 to 40% by mass of Zn and the balance being made of Cu and inevitable impurities.
(3) The base material further contains at least one element selected from the group consisting of Sn, Ag, Pb, Fe, Ni, Mn, Si, Al and Ti in a total amount of 0.005 to 10% by mass. (2) Cu-Zn alloy Sn plating strip.
(4) 15 to 40% by mass of Zn, 8 to 20% by mass of Ni, and 0 to 0.5% by mass of Mn, with the remainder being a copper base alloy composed of Cu and inevitable impurities (1) Cu-Zn alloy Sn-plated strip.
(5) The base material further contains 0.005 to 10% by mass in total of at least one element selected from the group consisting of Sn, Ag, Pb, Fe, Si, Al and Ti (4) Cu-Zn alloy Sn plating strip.
(6) A method for producing an Sn-plated strip in which whisker generation is suppressed, characterized in that the following steps are sequentially performed on a copper alloy containing 15 to 40% by mass of Zn at an average concentration:
a. A step of adjusting the Zn concentration at a position of 0.1 μm from the surface layer of the base material to a range of 10 to 40% by mass by surface polishing;
b. Step of applying Cu plating with a thickness of 0.1 μm or more after applying Ni plating with a thickness of 0.1 μm or more (however, the sum of the thickness of the Ni plating and the thickness of the Cu plating is 0.3 to 1.0 μm) ,
c. Applying Sn plating with a thickness of 0.3 to 1.0 μm; and d. A step of performing a reflow treatment at a heating time t (second) and a heating temperature T (° C.) defined by the following three formulas.
5 ≦ t ≦ 23,
350 ≦ T ≦ 600, and 500 ≦ (T + 14t) ≦ 670
Note that Sn plating of a Cu—Zn alloy may be performed before pressing a part (pre-plating) or after pressing (post-plating). In both cases, the effect of the present invention is obtained. It is done.

  ADVANTAGE OF THE INVENTION According to this invention, the Cu / Ni bilayer base reflow Sn plating strip of a Cu-Zn alloy with which whisker generation was suppressed can be provided.

It is a figure showing the reflow processing conditions (temperature and time) of this invention. 6 is a chart showing Zn concentration in a surface layer of a base material of Invention Example 3 and Comparative Example 30. It is a chart which shows Zn density | concentration of Sn plating surface layer of the example 8 of an invention, and the comparative example 33.

The present invention will be described in detail below.
(1) Ingredients of base material The present invention is intended for copper alloys containing 15 to 40% by mass of Zn, and the effects of the invention do not appear for copper alloys whose Zn is out of this range. .
There is brass as a copper alloy containing 15 to 40% by mass of Zn. JIS-H3100 defines brass such as C2600, C2680, and C2720. An alloy that exhibits the effects of the present invention is brass.
There is a white as a copper alloy other than brass containing 15 to 40% by mass of Zn. Western white contains Ni in addition to Zn, and also contains a small amount of Mn. In JIS-H3110 and JIS-H3130, whites such as C7521, C7541 and C7701 are defined. Examples of alloys exhibiting the effects of the present invention include white.
Furthermore, the copper alloy base material containing no Ni and Mn according to the present invention is intended to improve the strength, heat resistance, stress relaxation resistance, etc. of the alloy, and further Sn, Ag, Pb, Fe, Ni, Mn, Si. In addition, 0.005 to 10% by mass in total of at least one element selected from the group consisting of Al and Ti can be contained. Similarly, in the copper alloy base material containing Ni and Mn of the present invention, at least one element selected from the group consisting of Sn, Ag, Pb, Fe, Si, Al and Ti is added in a total amount of 0.005 to 10. Can be contained by mass%. The effect of the present invention can be obtained within the above concentration range. On the other hand, when the amount is less than 0.005% by mass, the effect of the additive element is not exhibited. Preferably it is 0.05-5 mass%.

(2) Plating structure The basic structure of the Sn plating of the present invention is the same as in the conventional Cu / Ni double-layer underlayer reflow Sn plating, each layer of Sn phase, Sn-Cu alloy phase and Ni phase from the surface to the base material. Consists of. A feature of the present invention is that Zn having an appropriate concentration is concentrated on the surface layer of the Sn phase.
When local stress is applied to the Sn plating layer, whiskers are generated on the plating surface. Zn on the surface of the Sn plating has the effect of suppressing this whisker. This is presumably because Zn moves to a place where stress is locally high in the Sn plating layer and aggregates, thereby relieving the stress.

Concentration of Zn on the surface of the Sn plating layer is caused by diffusion of Zn contained in the base material during heating in the reflow process. In the case of a Cu / Ni two-layer base, when the Zn concentration of the Sn plating surface layer was 0.1% by mass or more, the effect of suppressing the generation of whiskers was exhibited. Here, the Zn concentration of the Sn plating surface layer is defined as the Zn concentration at a position of 0.01 μm in the depth direction from the surface, analyzed by GDS (glow discharge emission analysis). The critical Zn concentration of 0.1% by mass is 3% by mass (Japanese Patent Application No. 2004-358897) which is a critical Zn concentration confirmed in Cu underplating of a copper alloy containing 20 to 40% by mass of Zn. In comparison, it was quite low.
Cu / Ni two-layer base reflow Sn plating is often used in a high temperature environment due to its good heat resistance. Therefore, it is required not only to exhibit good solder wettability in a reflow-up state, but also to prevent solder wettability from deteriorating even if kept in a high temperature environment for a long time after reflow (hereinafter referred to as heat resistant solder wettability). . When the Zn concentration of the Sn plating surface layer exceeded 5.0 mass%, the heat-resistant solder wettability deteriorated.
As mentioned above, Zn density | concentration of Sn plating surface layer shall be 0.1-5.0 mass%. A more preferable Zn concentration of the Sn plating surface layer is 0.3 to 3.0% by mass, and a whisker suppressing effect and good heat-resistant solder wettability can be obtained more stably.
In addition, since the effect of this invention will be exhibited if Zn on the surface of Sn phase is concentrated in the said range, the thickness of Sn phase after reflow, Sn-Cu alloy phase, and Ni phase is not specifically limited.

(3) Manufacturing Method The plating structure can be obtained by adjusting the Zn concentration of the plating base material surface layer, the thickness of the Ni undercoat, the thickness of the Cu undercoat, the thickness of the Sn plating, and the reflow conditions within an appropriate range. .
a. Zn concentration in surface layer of plating base material In a material plated with Sn using a Cu-Zn alloy as a plating base material, Zn in the plating base material diffuses into the Sn plating layer by heating. When heated under reflow conditions to be described later, if the Zn concentration of the plating base material surface layer is less than 10% by mass, it becomes difficult to adjust the Zn concentration of the Sn plating surface layer to 0.1% by mass or more. If the Zn concentration exceeds 40% by mass, it is difficult to adjust the Zn concentration of the Sn plating surface layer to 5% by mass or less. Therefore, the Zn concentration of the surface layer of the Cu—Zn alloy used for the plating base material is adjusted to 10 to 40% by mass, preferably 15 to 30% by mass. Here, the Zn concentration of the plating base material surface layer is defined as the Zn concentration at a position of 0.1 μm from the surface layer analyzed by GDS.
On the other hand, a Cu—Zn alloy, which is a plating base material, is hot rolled as necessary to an ingot manufactured by melting and casting, and then processed into a strip by repeatedly performing cold rolling and annealing. It is known that the removal of Zn occurs when annealing Cu—Zn alloys. The Zn removal phenomenon is a phenomenon in which when a Cu—Zn alloy is heated to a high temperature during annealing, Zn is oxidized and escapes into the gas phase, and the Zn concentration on the surface of the Cu—Zn alloy decreases. Therefore, in order to adjust the Zn concentration on the surface of the Cu—Zn-based alloy to the above range, it is necessary to remove the Zn-free layer generated by annealing. As this removal method, there are mechanical polishing using a rotary buff, chemical polishing using a corrosive liquid, and the like.

  In the present invention, it is important to adjust the Zn concentration on the surface of the Cu—Zn-based alloy immediately before being subjected to Sn plating to the above range, and means and process order for that purpose are not particularly limited. For example, a Cu—Zn-based alloy for connectors is often used for Sn plating in a tempered state after cold rolling after annealing. In this case, polishing for removing the Zn-free layer is performed before cold rolling. It may be performed (immediately after annealing) or after cold rolling (immediately before plating).

b. Ni undercoat thickness and Cu undercoat thickness The reflowed plating layer of the present invention is composed of Sn phase, Sn-Cu alloy phase, and Ni phase layers from the surface side. The Ni phase suppresses diffusion of base material components (Cu, Zn and alloy elements) into the Sn—Cu alloy phase. The Sn—Cu alloy phase suppresses diffusion of Ni into the Sn phase. Due to the action of the Ni phase and Sn—Cu alloy phase as the diffusion barrier, the Cu / Ni two-layer base material exhibits better heat resistance than the Cu base material and the Ni base material.
In order to obtain desired heat resistance, the thickness of Ni plating during electrodeposition is set to 0.1 μm or more. When the Ni plating is less than 0.1 μm, diffusion of the base material component into the Cu—Sn alloy phase cannot be suppressed. Moreover, the thickness of Cu plating at the time of electrodeposition shall be 0.1 micrometer or more. If the Cu plating is less than 0.1 μm, a sufficiently thick Sn—Cu alloy phase is not formed, and the diffusion of Ni into Sn cannot be suppressed. In addition, the upper limit of the thickness of Ni plating or Cu plating at the time of electrodeposition is prescribed | regulated by the sum total of the thickness of Cu plating at the time of the following electrodeposition, and the thickness of Ni plating at the time of electrodeposition.
Next, in order to adjust the Zn concentration of the Sn plating surface layer after reflowing to 0.1 to 5.0% by mass, the sum of the thickness of Cu plating during electrodeposition and the thickness of Ni plating during electrodeposition (hereinafter referred to as the following) The total thickness is defined as 0.3 to 1.0 μm. When the total thickness is less than 0.3 μm, when heated under reflow conditions described later, the base material Zn excessively diffuses into the Sn phase, and the Zn concentration of the Sn plating surface layer exceeds 5.0 mass%. When the total thickness exceeds 1.0 μm, Zn in the base material does not sufficiently diffuse into the Sn phase when heated under reflow conditions described later, and the Zn concentration of the Sn plating surface layer becomes less than 0.1 mass%. .
More preferable thicknesses include a Cu plating thickness of 0.2 μm or more, a Ni plating of 0.2 μm or more, and a total thickness of 0.4 to 0.7 μm. Zn concentration can be obtained more stably.

c. Sn plating thickness When the thickness of the Sn plating is less than 0.3 μm, the Zn concentration of the Sn plating surface layer exceeds 5.0 mass% when heated under reflow conditions described later. When the thickness of the Sn plating exceeds 1.0 μm, the Zn concentration of the Sn plating surface layer is less than 0.1% by mass when heated under reflow conditions described later. Therefore, the thickness of Sn plating shall be 0.3-1.0 micrometer. A more preferable thickness of Sn plating is 0.6 to 0.8 μm.

d. Reflow conditions The reflow conditions under which the Zn concentration of the Sn plating surface layer falls within the scope of the present invention are shown below. When the heating time is less than 5 seconds, the diffusion of Zn into the Sn plating layer is not sufficient, and the Zn concentration on the Sn plating surface is less than 0.1% by mass. When the heating time exceeds 23 seconds, the diffusion of Zn becomes remarkable, so that the Zn concentration on the Sn plating surface exceeds 5.0% by mass. Therefore, the heating time in the reflow process is 5 to 23 seconds (5 ≦ t ≦ 23, where t represents the heating time and the unit is seconds). Preferably the heating time is 5 to 15 seconds.
Moreover, if heating temperature is less than 350 degreeC, the spreading | diffusion of Zn from a base material to Sn plating layer is not enough, and Zn density | concentration of Sn plating surface layer is less than 0.1 mass%. When the heating temperature exceeds 600 ° C., the diffusion of Zn becomes remarkable, so that not only the Zn concentration of the Sn plating surface layer exceeds 5.0% by mass, but also the plating base material is recrystallized and softens. As a result, the required mechanical strength cannot be obtained. Therefore, the heating temperature in the reflow process is set to 350 to 600 ° C. (350 ≦ T ≦ 600, where T represents the heating temperature and the unit is ° C.). The heating temperature is preferably 400 to 550 ° C.
Furthermore, the diffusion of Zn into the Sn plating layer is determined by the relationship between both temperature and time factors. Therefore, this relationship is defined by the following equation.
500 ≦ (T + 14t) ≦ 670
When (T + 14t) is less than 500, the Zn concentration of the Sn plating surface layer is less than 0.1% by mass, and whiskers are generated. On the other hand, if it exceeds 670, the Zn concentration of the Sn plating surface layer exceeds 5.0% by mass and the heat-resistant solder wettability deteriorates. (T + 14t) is preferably 550 to 650.

In FIG. 1 showing the reflow processing conditions (temperature and time) of the present invention, the reflow processing conditions are indicated by hatching. Here, T represents the heating temperature (° C.), and t represents the heating time (seconds).
As an example of GDS analysis data on the surface of the base material, FIG. 2 shows a GDS chart of the surface of the base material used in Invention Example 3 and Comparative Example 30 described later. The evaluation point is a depth of 0.1 μm from the surface. The analysis conditions are as follows.
Sample pretreatment: ultrasonic degreasing in acetone.
・ Equipment: JOBIN YBON JY5000RF-PSS type.
・ Current Method Program: CNBinteel-12aa-0.
・ Mode: Constant Electric Power = 40W.
・ Ar-Presser: 775Pa.
・ Current Value: 40mA (700V).
・ Flush Time: 20sec.
・ Preburn Time: 2sec.
-Determination Time: Analysis Time = 30sec, Sampling Time = 0.020sec / point.

A Cu—Zn alloy (thickness 0.2 mm) shown in Table 1 was used as a sample. Table 1 shows the average Zn concentration of the base material as the composition of the base material. Further, the Zn concentration (mass%) at a position of 0.1 μm in the depth direction from the surface analyzed by GDS (glow discharge optical emission spectrometer) is shown as the Zn concentration of the base material surface layer.
The surface layer Zn concentration is adjusted by annealing conditions and polishing conditions. Table 2 shows the manufacturing conditions of Comparative Example 30, Invention Examples 1, 2, 3, 23 and Comparative Example 31 of Table 1. After recrystallization annealing under various conditions at a thickness of 0.25 mm, the surface is chemically polished with a 20 mass% H ₂ SO ₄ −1 mass% H ₂ O ₂ aqueous solution, and then cold-cooled to 0.2 mm It is rolling. Table 2 shows the following.
(1) When annealing in combustion gas (weakly oxidizing atmosphere), increasing the CO concentration and decreasing the O ₂ concentration increases the surface Zn concentration. Further, when the polishing amount is increased, the surface layer Zn concentration is increased.
(2) The surface Zn concentration obtained by low-temperature and long-term annealing is higher than the surface Zn concentration obtained by high-temperature and short-time annealing.
(3) When annealing is performed in hydrogen adjusted to a low dew point (strongly reducing atmosphere), Zn oxidation (escape into the gas phase) does not occur, so the surface Zn concentration increases.

Each sample in Table 1 was plated in the following step.
(Step 1) Electrolytic degreasing was carried out in an alkaline aqueous solution using the sample as a cathode under the following conditions.
Current density: 3 A / dm ² . Degreasing agent: Trademark “Pakuna P105” manufactured by Yuken Industry Co., Ltd. Degreasing agent concentration: 40 g / L. Temperature: 50 ° C. Time 30 seconds. Current density: 3 A / dm ² .
(Step 2) Pickling was performed using a 10% by mass sulfuric acid aqueous solution.
(Step 3) Ni base plating was performed under the following conditions.
-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.
・ Ni plating thickness is adjusted by electrodeposition time.
(Step 4) Cu base plating was 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.
・ Cu plating thickness is adjusted by electrodeposition time.
(Step 5) Sn plating was performed under the following conditions.
-Plating bath composition: stannous oxide 41 g / L, phenolsulfonic acid 268 g / L, surfactant 5 g / L.
-Plating bath temperature: 50 ° C.
Current density: 9A / dm ^2.
・ Sn plating thickness is adjusted by electrodeposition time.
(Step 6) As a reflow treatment, the sample was inserted into a heating furnace adjusted to nitrogen (oxygen 1 vol% or less) and heated, and then water-cooled after heating. The temperature of the heating furnace (reflow temperature) and the insertion time into the heating furnace (reflow time) are shown in Table 1.

  About each sample after reflow, the Zn density | concentration of Sn plating surface layer was analyzed on the said conditions using GDS. As an example of the GDS analysis data of the Sn plating surface layer, FIG. 3 shows a chart of Invention Example 8 and Comparative Example 33. The depth of 0.01 μm from the plating surface was taken as the evaluation point, and the Zn concentration at that position was read from the chart and listed in Table 1.

About each sample, the length of a whisker and solder wettability were evaluated by the following method.
(1) Whisker length A spherical indenter (made of stainless steel) having a diameter of 0.7 mm was left on the sample surface with a load of 150 g for 7 days at room temperature to generate whiskers at the indenter contact portion on the plating surface. . The generated whisker was observed with an electron microscope, and the case where the length of the whisker that had grown the longest in each sample was within 10 μm was evaluated as ◯, and the case where it exceeded 10 μm was evaluated as x.
(2) Heat-resistant solder wettability The sample after being held at high temperature was evaluated for wettability with lead-free solder. Specifically, the sample was degreased with acetone and then heated in air at 145 ° C. for 500 hours. After applying 25 mass% rosin-75 mass% ethanol as a flux to the heated sample, it was immersed in a Sn-3.0 mass% Ag-0.5 mass% Cu solder bath at 260 ° C. for 10 seconds. The surface area of the immersion part was 10 mm × 10 mm, and after pulling up from the solder bath, the area ratio of the part where the solder adhered was measured. A case where the adhesion area ratio of the solder was 80% or more was evaluated as ◯, and a case where the adhesion area ratio was less than 80% was evaluated as x.
Table 1 shows the evaluation results of the invention examples and comparative examples.

In each of the inventive examples 1 to 29, since the Zn concentration of the Sn plating surface layer is within the range of the present invention, the whisker length is 10 μm or less, and good heat resistance solder wettability with respect to lead-free solder. Indicated.
In Comparative Example 30, since the Zn concentration on the surface of the base material was less than 10% by mass, the Zn concentration of the Sn plating surface layer decreased to 0.1% by mass with respect to Inventive Examples 1 to 3 having the same base material composition and manufacturing conditions. The whisker exceeding 10 μm was generated. Further, in Comparative Example 31, the Zn concentration on the surface of the base material exceeded 40% by mass, so that the Zn concentration of the Sn plating surface layer increased to 5.0% by mass with respect to Invention Example 23 having the same base material composition and manufacturing conditions. The heat resistance solder wettability deteriorated.

  Inventive Examples 4 to 9 and Comparative Examples 32 to 35 are obtained by changing the thicknesses of the Ni and Cu undercoats for the base materials having the same composition and other manufacturing conditions. When the total thickness of the Ni plating and the Cu plating increases, a tendency that the Zn concentration of the Sn plating surface layer decreases is recognized. In Comparative Example 32 in which the total thickness of Ni plating and Cu plating was less than 0.3 μm, the Zn concentration of the Sn plating surface layer exceeded 5.0 mass%, and the heat resistance solder wettability deteriorated. Moreover, in the comparative example 33 whose total thickness exceeded 1.0 micrometer, Zn density | concentration of Sn plating surface layer became less than 0.1 mass%, and the whisker exceeding 10 micrometers was generated. In Comparative Examples 34 and 35, since Ni and Cu were less than 0.1 μm, respectively, the good heat resistance characteristic of the Cu / Ni two-layer underlayer reflow Sn plating was lost, and the heat resistant solder wettability was deteriorated.

  Inventive Examples 10 to 16 and Comparative Examples 36 to 37 are obtained by changing the Sn plating thickness and other manufacturing conditions for the base material having the same composition. When Sn plating thickness becomes large, the tendency for the Zn density | concentration of Sn plating surface layer to fall is recognized. In Comparative Example 36, in which the Sn plating thickness was less than 0.3 μm, the Zn concentration of the Sn plating surface layer exceeded 5.0 mass%, and the heat resistance solder wettability deteriorated. Further, in Comparative Example 37 in which the Sn plating thickness exceeded 1.0 μm, the Zn concentration of the Sn plating surface layer was less than 0.1 mass%, and whiskers exceeding 10 μm were generated.

  Inventive Examples 17 to 22 and Comparative Examples 38 to 43 are obtained by changing the reflow conditions and combining other manufacturing conditions for the base material having the same composition. In Comparative Examples 38 to 40 where (T + 14t) exceeded 670, the Zn concentration of the Sn plating surface layer exceeded 5.0 mass%, and the heat-resistant solder wettability deteriorated. In Comparative Example 41 in which (T + 14t) was less than 500, the Zn concentration of the Sn plating surface layer was less than 0.1% by mass, and whiskers exceeding 10 μm were generated. In Comparative Example 42 in which the time was less than 5 seconds and Comparative Example 43 in which the temperature was less than 350 ° C., the Zn concentration of the Sn plating surface layer was less than 0.1 mass%, and whiskers exceeding 10 μm were generated.

Claims (5)

  A copper alloy containing 15 to 40% by mass of Zn at an average concentration is used as a base material, and a plating film is composed of each layer of Sn phase, Sn—Cu alloy phase, and Ni phase from the surface to the base material. A Cu-Zn alloy Sn-plated strip in which whisker generation is suppressed, wherein the Zn concentration of the alloy is 0.1 to 5.0% by mass.   2. The Cu—Zn alloy Sn-plated strip according to claim 1, wherein the base material is a copper-based alloy containing 15 to 40% by mass of Zn and the balance of Cu and inevitable impurities.   The base material further contains at least one element selected from the group consisting of Sn, Ag, Pb, Fe, Ni, Mn, Si, Al, and Ti in a total amount of 0.005 to 10% by mass. 2 Cu—Zn alloy Sn plating strip.   The base material is a copper-based alloy containing 15 to 40% by mass of Zn, 8 to 20% by mass of Ni, and 0 to 0.5% by mass of Mn, with the balance being Cu and inevitable impurities. The Cu—Zn alloy Sn plating strip according to claim 1.   The Cu- of claim 4, wherein the base material further contains 0.005 to 10 mass% in total of at least one element selected from the group consisting of Sn, Ag, Pb, Fe, Si, Al and Ti. Zn alloy Sn plating strip.

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