CN102803574B - Copper alloy for electronic material and preparation method thereof - Google Patents

Abstract

The invention provides a copper alloy for electronic materials with excellent uniformity of plating film. The copper alloy for electronic materials is characterized in that when a cross section parallel to the rolling direction is observed through a SIM, the area ratio of the amorphous structure and the crystal grains with the grain diameter of less than 0.1 mu m is less than 1% within the range of the depth of 0.5 mu m from the surface layer, and the number ratio of the crystal grains with the grain diameter of more than 0.1 mu m and less than 0.2 mu m to the total crystal grains with the grain diameter of more than 0.1 mu m is more than 47.5% within the range of the depth of 0.2-0.5 mu m from the surface layer.

Description

Copper alloy for electronic material and preparation method thereof

technical field

The present invention relates to a copper alloy suitable as an electronic material requiring excellent platability and a method for producing the same.

Background technique

Copper alloys used in electronic devices are subjected to bonding plating for wire bonding or printed circuit board mounting, in addition to functional material plating utilizing the physical properties of the plating film itself, such as electrical and magnetic properties. For example, for conductive spring materials such as terminals, connectors, switches, and relays, Ni plating, Cu plating, and Sn plating are implemented for the purpose of improving contact resistance, solderability, and pluggability. Ag and Cu plating for wire bonding, flux plating for substrate mounting, etc.

In several types of copper alloys, such as corson alloy or phosphor bronze, when plating is applied to the surface, the plating film tends to form unevenly (Figure 2). If the surface of this type of coating is observed through a high-power microscope, island-shaped depressions (hereinafter referred to as "island coating") can be seen in the thin parts of the coating (Figure 3). If the plating film is not uniform, in addition to the appearance problem, there will be a problem that various functions provided by the plating cannot be fully exhibited.

However, generally, in a copper alloy prepared by appropriately combining heat treatment, hot rolling, cold rolling, and polishing after casting, a layer different from the inner layer called a work-induced layer exists on the surface layer. The process-altered layer consists of the outermost beilby layer, which is an amorphous structure, and the microcrystalline layer, which is located inside it. As it goes deeper into the interior, the grains gradually increase, and finally reach the same size as the parent phase grains.

Conventionally, it has been known that a process-deteriorated layer adversely affects platability, and therefore, an operation of removing the process-deteriorated layer is performed before plating.

For example, in Japanese Patent Laid-Open Publication No. 11-29894 (Patent Document 1), it is described that since the work-affected layer inhibits the adhesion between the coating film and the base material, it should be removed by electrolytic etching in an alkaline aqueous solution such as caustic soda aqueous solution. Nickel plating is carried out after the surface has been processed and deteriorated (thickness of about 30~40μm).

Japanese Unexamined Patent Application Publication No. 2006-2233 (Patent Document 2) describes that for the purpose of providing an object to be plated that does not cause cracks in the coating layer during bending, etc., and has excellent formability, the content of the process-deteriorated layer is removed. The methods of layering include dissolution methods using acids such as sulfuric acid, nitric acid, hydrochloric acid, hydrogen peroxide, and hydrofluoric acid, electrolytic dissolution methods in electrolyte solutions, sputtering methods, etching methods, and the like.

Japanese Patent Application Laid-Open No. 2007-39804 (Patent Document 3) describes that for the purpose of providing a copper alloy for electronic devices that does not cause abnormal deposition of plating or lowers the adhesion of the oxide film, and has excellent plating properties, the processing of the surface layer is modified. Copper alloys for electronic devices whose layer (amorphous to crystal grain size less than 0.2 μm) has a thickness of 0.2 μm or less. The thickness of the altered layer here is the average value of the measured values at five observed locations, the thickness of the thickest portion of the altered layer measured within the magnified observation field of view. This document records that the process-altered layer can be removed by physical treatment such as chemical dissolution treatment or electrochemical dissolution treatment, spraying, etc., and it is described in its examples by immersion in a mixed acid of sulfuric acid and hydrogen peroxide, and in a hydrogen reducing atmosphere. Heat treatment in a heating furnace, electrolytic dissolution in an aqueous solution containing phosphoric acid removes and processes the contents of the altered layer.

prior art literature

patent documents

Patent Document 1: Japanese Patent Application Laid-Open No. 11-29894

Patent Document 2: Japanese Unexamined Patent Publication No. 2006-2233

Patent Document 3: Japanese Patent Laid-Open No. 2007-39804.

Contents of the invention

The problem to be solved by the invention

Although it is described in prior art documents that the process-degraded layer is removed for the purpose of suppressing the adhesion between the plating film and the base material or the abnormal deposition of plating, there is still room for improvement in terms of the uniformity of the plating film. Therefore, it is an object of the present invention to provide a copper alloy for electronic materials excellent in the uniformity of the plated film. In addition, another subject of the present invention is to provide a method for preparing such a copper alloy for electronic materials.

means of solving problems

The inventors of the present invention have found during intensive studies to solve the above problems that removing only the Beyer layer within the altered layer and leaving a microcrystalline layer with a predetermined thickness can improve the uniformity of the coating film compared to completely removing the altered layer. Specifically, it was found that since crystal grains having a particle size of 0.1 μm or more and less than 0.2 μm contribute to the improvement of the uniformity of the coating film, only a predetermined thickness remains in the layer containing more than a certain proportion of crystal grains having a particle size in this range. is important.

One aspect of the present invention made on the basis of the above knowledge is a copper alloy for electronic materials in which, when a cross-section in a direction parallel to the rolling direction is observed by SIM, within a range where the depth from the surface layer is 0.5 μm or less, The area ratio of amorphous structure and crystal grains with a particle size of less than 0.1 μm is 1% or less, and within the depth of 0.2 to 0.5 μm from the surface, the crystal grains with a particle size of 0.1 μm or more and less than 0.2 μm are relatively The number ratio of all crystal grains with a grain size of 0.1 μm or more was 47.5% or more.

In one embodiment of the copper alloy for electronic materials according to the present invention, when the cross-section in the direction parallel to the rolling direction is observed by SIM, the particle size is 0.1 μm or more in the range where the depth from the surface layer is less than 0.2 μm Furthermore, the number ratio of crystal grains of less than 0.2 μm to all crystal grains having a particle size of 0.1 μm or more was 57.5% or more.

In another embodiment of the copper alloy for electronic materials according to the present invention, the copper alloy is phosphor bronze, titanium copper or Corson alloy.

Another aspect of the present invention is a method for preparing a copper alloy for electronic materials. The preparation method includes the following process 1 and process 2: the process 1 is relative to the surface of the copper alloy substrate, using #600~8000 Grinding the abrasive material of the label of , and forming a process-altered layer of sufficient thickness, so that when the cross-section parallel to the rolling direction is observed by SIM after process 2, within the depth of 0.2-0.5 μm from the surface layer, the grains Grains with a diameter of more than 0.1 μm and less than 0.2 μm account for more than 47.5% of all crystal grains with a diameter of more than 0.1 μm; the second step is to use a grain size of 0.01 to 0.5 μm ( The abrasive material of d50) is ground to remove the amorphous structure and the microcrystalline grains with a particle size of less than 0.1 μm from the processed deteriorated layer, so that when the cross section parallel to the rolling direction is observed by SIM, the depth from the surface layer is In the range of 0.5 μm or less, the area ratio of amorphous structure and crystal grains with a particle size of less than 0.1 μm is 1% or less, and in the range of 0.2 to 0.5 μm in depth from the surface, the particle size is 0.1 μm or more Furthermore, the ratio of crystal grains with a particle size of less than 0.2 μm to all crystal grains with a particle size of 0.1 μm or more accounted for 47.5% or more.

In one embodiment of the method for preparing a copper alloy for electronic materials according to the present invention, the abrasive used in step 1 is made of silicon carbide, and the abrasive used in step 2 is made of alumina or colloidal silica. of abrasive materials.

In one embodiment of the method for producing a copper alloy for electronic materials according to the present invention, the polishing in step 1 and step 2 is performed by polishing.

Still another aspect of the present invention is an object to be plated in which a plating film is provided on the surface of the copper alloy according to the present invention.

In one embodiment of the object to be plated according to the present invention, the plated film contains any one or more of Ni, Sn, and Ag.

The effect of the invention

According to the present invention, the uniformity of the plating film applied on the surface of the copper alloy is improved, and island plating is reduced.

Description of drawings

[FIG. 1] An example of a SEM photo of a uniform coating film applied on the surface of the copper alloy of the present invention.

[Fig. 2] Example of SEM photo of uneven coating applied on copper alloy surface.

[Fig. 3] An enlarged SEM photograph of a part of the island-shaped plating in Fig. 1.

[Fig. 4] The schematic diagram of the copper alloy cross section of the present invention (from: "Metal Surface Technology Handbook", Metal Surface Technology Association edits and revises the new edition).

Detailed ways

<1. Composition of Copper Alloy>

The present invention can be applied to copper alloys having various compositions without particular limitation, and can be suitably applied to phosphor bronze, Corson alloy, brass, nickel nickel and titanium copper where island plating tends to be a problem.

In the present invention, phosphor bronze refers to a copper alloy containing copper as a main component and containing Sn and P in a smaller mass than Sn. As an example, phosphor bronze has a composition containing 3.5 to 11% by mass of Sn, 0.03 to 0.35% by mass of P, and the balance is composed of copper and unavoidable impurities.

In the present invention, Corson alloy refers to a copper alloy to which an element forming a compound with Si (for example, any one or more of Ni, Co, and Cr) is added and precipitated as second-phase particles in the matrix phase. As an example, a Corson alloy has a composition containing 1.0 to 4.0% by mass of Ni, 0.2 to 1.3% by mass of Si, and the balance being copper and unavoidable impurities. As another example, a Corson alloy has a composition containing 1.0 to 4.0% by mass of Ni, 0.2 to 1.3% by mass of Si, and 0.03 to 0.5% by mass of Cr, with the remainder being copper and unavoidable impurities. As yet another example, a Corson alloy has a composition containing 1.0 to 4.0% by mass of Ni, 0.2 to 1.3% by mass of Si, 0.5 to 2.5% by mass of Co, and the balance is copper and unavoidable impurities. As yet another example, a Corson alloy contains 1.0 to 4.0% by mass of Ni, 0.2 to 1.3% by mass of Si, 0.5 to 2.5% by mass of Co, and 0.03 to 0.5% by mass of Cr, with the balance consisting of copper and unavoidable Composition of impurities. As yet another example, a Corson alloy has a composition containing 0.2 to 1.3% by mass of Si, 0.5 to 2.5% by mass of Co, and the balance is composed of copper and unavoidable impurities.

Other elements (such as Mg, Sn, B, Ti, Mn, Ag, P, Zn, As, Sb, Be, Zr, Al, and Fe) can also be optionally added to the Corson alloy. These other elements are usually added up to about 2.0% by mass in total. For example, as yet another example, the Corson alloy contains 1.0 to 4.0% by mass of Ni, 0.2 to 1.3% by mass of Si, 0.01 to 2.0% by mass of Sn, and 0.01 to 2.0% by mass of Zn, with the remainder consisting of copper and Avoid impurities that make up the composition.

In the present invention, brass refers to an alloy of copper and zinc, and particularly refers to a copper alloy containing 20% by mass or more of zinc.

In the present invention, zinc white copper refers to a copper alloy containing copper as a main component, 60% to 75% by mass of copper, 8.5% to 19.5% by mass of nickel, and 10% to 30% by mass of zinc.

In the present invention, titanium copper refers to a copper alloy containing copper as a main component and 1.0% by mass to 4.0% by mass of Ti. As an example, titanium copper has a composition containing 1.0 to 4.0% by mass of Ti, and the balance is composed of copper and unavoidable impurities. As another example, titanium copper has a composition containing 1.0 to 4.0% by mass of Ti, 0.01 to 1.0% by mass of Fe, and the balance is copper and unavoidable impurities.

<2. Section structure>

When the cross section of the copper alloy of the present invention in a direction parallel to the rolling direction is observed by SIM, it has the following characteristic microstructure.

First, the amorphous structure and fine crystal grains with a grain size of less than 0.1 μm should be removed. The reason for this is that such a structure is "island-like plating", which adversely affects the uniformity of the plating film.

Specifically, within the range of a depth from the surface layer of 0.5 μm or less, the area ratio of the amorphous structure and crystal grains with a particle size of less than 0.1 μm is 1% or less, preferably 0.5% or less, more preferably 0% %. The reason for specifying the depth from the surface layer to 0.5 μm is that the influence on the uniformity of the plating film is less in the deeper portion. This area ratio is measured by the following method. Specifically, a measurement area of 0.5 μm in the depth direction and 15 μm in the width direction is set from the surface layer, and the crystal grains with a grain size of 0.1 μm or more are marked, and the marked crystal grains and other The structure (that is, an amorphous structure and crystal grains with a particle size of less than 0.1 μm) is binarized and distinguished by image processing. From this, the area ratio of the amorphous structure and crystal grains of less than 0.1 μm to the total area of the measurement field of view was calculated. The average value of 5 fields of view was taken as the measured value.

On the other hand, since crystal grains having a particle size of 0.1 μm or more and less than 0.2 μm contribute to the improvement of the uniformity of the plating film, they should be positively left. The particle diameters in this range have been considered to be removed because they belong to the crystal grains constituting the microcrystalline layer. However, according to the study of the present inventors, it is desirable to actively form them in order to improve the uniformity of the plating film. In addition, if even the crystal grains of this size are removed, the remaining crystal grains are of a larger size, and such large-sized crystal grains hardly contribute to the uniformity of the coating film.

Therefore, in one embodiment of the copper alloy according to the present invention, within the range of 0.2 to 0.5 μm in depth from the surface layer, crystal grains having a particle size of 0.1 μm or more and less than 0.2 μm are 0.1 μm in relation to the particle size. The number ratio of all the above crystal grains is more than 50%, and it is desirable that the number ratio is higher, for example, it can be set as 50-90%. However, if the remaining ratio of crystal grains in this particle size range is increased, the ratio of amorphous structure and fine crystal grains with a particle size of less than 0.1 μm will gradually increase, and the effect of improving the uniformity of the coating film will be weakened. Therefore, the preferred number ratio is 80% or less, more preferably 70% or less.

In addition, in another embodiment of the copper alloy according to the present invention, the crystals having a particle diameter of 0.1 μm or more and less than 0.2 μm are 0.1 μm or more with respect to the particle diameter within the range of a depth from the surface layer of less than 0.2 μm. The number ratio of all crystal grains is more than 60%, and it is desirable that the number ratio is higher, for example, it can be set to 60-90%. However, for the same reason as above, if it is too high, the effect of improving the uniformity of the plating film will be weakened, so the number ratio is preferably 90% or less, more preferably 80% or less.

In the present invention, the number ratio of crystals with a particle size of 0.1 μm or more to less than 0.2 μm to all crystal grains with a particle size of 0.1 μm or more in each depth range is measured by the following method. First, the cross section of the copper alloy to be measured is cut in a direction parallel to the rolling direction by FIB to expose the cross section, and then the magnification is set to 8000 to 15000 times, and the cross section is observed by SIM. Next, it is divided into a depth range of less than 0.2 μm from the surface layer and a depth range of 0.2 to 0.5 μm from the surface layer, and the particle diameters of all crystal grains existing in the field of view are measured one by one, and the grain size of the crystal grains with a particle diameter of 0.1 μm or more and less than 0.2 μm is calculated. The ratio of the number of crystals to all crystal grains with a particle size of 0.1 μm or more. A total of five visual fields were measured. Particles that cross the field of view and thus are only partially visible are not counted. The average value of 5 fields of view was taken as the measured value.

In the present invention, the individual grain diameters of crystal grains are defined as the average value of the longest line segment in the depth direction that can traverse the inside of the crystal grain and the longest line segment in the direction perpendicular to the depth direction.

In addition, in the present invention, the above-mentioned number ratio is expressed in 5% intervals (divisions) by mantissa-processing the obtained measured values. For example, when the measured value is 47.5% or more and less than 52.5%, it is expressed as 50%. Therefore, when the lower limit is set at 50%, the measured values are 48.2%, 50.0%, and 51.2%, all of which are within the scope of the present invention.

<3. Preparation method>

The copper alloy according to the present invention can be produced by preparing a copper alloy base material having a desired composition by combining conventional means such as heat treatment after casting, hot rolling, and cold rolling, and then performing a predetermined surface treatment.

Before surface treatment, it is desirable to perform degreasing and pickling in order to remove and clean greasy dirt adhering to the surface of the raw material. The degreasing method is not particularly limited, and examples thereof include alkali degreasing, solvent degreasing, and electrolytic degreasing. The method of pickling is not particularly limited, and it can be soaked in a pickling tank containing sulfuric acid for a certain period of time.

The surface treatment includes the following steps: a step 1 of grinding the surface of the copper alloy substrate with an abrasive of #600-8000, and a step 2 of grinding with an abrasive having a particle size of 0.01-0.2 μm.

The purpose of step 1 is to form a work-altered layer. Although the work-deteriorated layer can be formed to some extent during the production of the copper alloy by conventional means, it is desirable to form a sufficiently thick work-deteriorated layer in step 1. The reason for this is to make crystal grains with a particle diameter of 0.1 μm or more and less than 0.2 μm exist in a sufficiently deep range. The label of the abrasive material effective for forming a process-altered layer is in the range of #600 to #8000 specified in JIS6001 (1998), preferably in the range of #1200 to #4000, more preferably in the range of #1500 to #3000. The material of the abrasive material used in step 1 is not limited, and examples thereof include silicon carbide, alumina, diamond, and the like, and there is no particular limitation as long as they are within the above reference numerals.

The purpose of step 2 is to remove the outermost Beyer layer (corresponding to an amorphous structure and microcrystalline grains with a grain size of less than 0.1 μm in the present invention) from the work-affected layer produced in step 1 . The particle size of the abrasive material effective for the selective removal of the Beyer layer from the process-altered layer is, as measured by the laser diffraction scattering method, d50 being in the range of 0.01 to 0.5 μm, preferably in the range of 0.05 to 0.4 μm, more preferably 0.1 ~0.3 μm range. If the particle size is greater than 0.1 μm, even crystal grains having a particle size of not less than 0.1 μm and less than 0.2 μm can be easily removed. The material of the abrasive used in step 2 is not limited, but alumina or colloidal silica is preferable because it has a small particle size.

The polishing in Step 1 and Step 2 is preferably performed by polishing. In the present invention, polishing refers to the grinding by making the abrasive material into a paste or suspension (slurry) and infiltrating it into the abrasive cloth, although it is all right with or without the rotation of the polishing wheel (buff). In order to improve the grinding accuracy and make the distribution of crystal grains with a particle size of 0.1 μm or more and less than 0.2 μm uniform, it is desirable to press the polishing wheel against the copper alloy substrate with a certain pressure while rotating the polishing wheel at high speed.

Between step 1 and step 2, pickling may be performed to facilitate removal of only the Bailby layer in the second polishing. However, it is desirable to use sulfuric acid for pickling at this time, preferably sulfuric acid with a concentration of 10 to 200 g/L. This is because even crystal grains having a particle diameter of 0.1 μm or more and less than 0.2 μm can be easily removed in the case of a mixed acid of sulfuric acid and hydrogen peroxide.

<4. Types of plating>

Various types of plating can be applied to the copper alloy involved in the present invention, and the type is not particularly limited. For example, plating of Ni, Sn, Ag, etc. can be applied. Among them, Ni is particularly suitable for use in the present invention because it is easy to form island-like plating. Therefore, in one embodiment of the present invention, the plated film contains any one or more of Ni, Sn, and Ag.

The plating method is not particularly limited, and can be obtained by, for example, wet plating such as electroplating or electroless plating, or dry plating such as CVD or PVD. From the viewpoint of productivity and cost, electroplating is preferable.

<5. Purpose>

The copper alloy involved in the present invention can be processed into various forms of wrought copper products (such as plates, strips, tubes, rods and wires), and can be suitable for use in lead frames, connectors, plugs (pins), terminals, relays Electronic components such as switches, foil materials for secondary batteries, etc.

Example

Examples of the present invention are shown below together with comparative examples, but these examples are provided for better understanding of the present invention and its advantages, and are not intended to limit the invention.

After casting, the copper alloy having the composition shown in Table 1 was appropriately subjected to repeated heat treatment, hot rolling, and cold rolling to prepare copper alloy sheets each having a thickness of 0.1 mm. These copper alloy sheets were degreased by alkali degreasing, pickled by immersion in a pickling tank containing 100 g/L of sulfuric acid, and then surface treated in the order described in Table 1. In Table 1, silicon carbide was used as the abrasive material in "Polishing (1)". "Sulfuric acid" in "pickling" refers to the treatment of immersing the test panel in sulfuric acid with a concentration of 100g/L for 10 seconds, and "mixed acid" refers to the treatment of immersing the test panel in sulfuric acid containing 100g/L and peroxide of 10g/L. A treatment of immersion in an aqueous solution of hydrogen for 10 seconds. "#3000" of "Polishing (2)" uses silicon carbide as the abrasive material. The particle size (d50) of the abrasive used in the polishing (2) was measured using a laser diffraction particle size distribution analyzer SALD-2100 manufactured by Shimadzu Corporation.

For the copper alloy plate after surface treatment, according to the above method, obtain

A) The area ratio of amorphous structure and crystal grains with a grain size of less than 0.1 μm within a depth of 0.5 μm or less from the surface layer,

B) In the range of 0.2 ~ 0.5 μm from the surface, the proportion of the number of grains with a particle size of 0.1 μm or more and less than 0.2 μm relative to the total number of grains with a particle size of 0.1 μm or more, and

C) Within the depth of less than 0.2 μm from the surface, the ratio of the number of crystal grains with a particle size of 0.1 μm or more to less than 0.2 μm to all crystal grains with a particle size of 0.1 μm or more.

In the table, regarding the values of B and C, the measured values are subjected to mantissa processing, and the values are described at intervals of 5%. For example, more than 62.5% and less than 67.5% are recorded as 65%.

Then, carry out Ni plating according to the following conditions:

<Ni plating conditions>

Bath composition: NiSO ₄ -6H ₂ O 280g/L

Plating conditions: Current density: 5A/dm ²

Plating time: 15s.

Then, an optical microscope photograph (magnification: ×100, field area: 0.15 mm ² ) of each plated surface was taken, and the area ratio of observed island-shaped plating was measured. The evaluation is as follows.

S: No island plating

A: The area ratio of island plating is 10% or less

B: The area ratio of island plating exceeds 10% and is 20% or less

C: The area ratio of island-shaped plating exceeds 20% and is 50% or less

D: The area ratio of the island-shaped plating exceeds 50%

The sound portion and the island-shaped plated portion were binarized by an image analysis device, and the area ratio of the island-shaped plated portion was calculated.

The results are described in Table 1. Fig. 1 is an SEM photograph of the plated surface of No. 14.

[Table 1-1]

[Table 1-2]

As can be seen from Table 1, in the copper alloy Nos. 1 to 27 according to the present invention, island-like plating was reduced and the uniform plating property was excellent.

On the other hand, in Comparative Example Nos. 28, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, and 53, since polishing was not performed, the work-affected layer itself was not formed. Therefore, excellent platability cannot be obtained.

In Comparative Example Nos. 29, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52 and 54, although a processing-deteriorated layer was formed by polishing for the first time, it was not Removed, so the residual Bilby layer. As a result, excellent platability cannot be obtained.

In Comparative Example No. 30, since the process-affected layer formed in the first polishing was removed by strong pickling, not only the Bairby layer was removed, but also the crystal grains with a particle size of 0.1 μm or more and less than 0.2 μm were excessively removed. remove. As a result, the plating property was inferior to the invention example.

In Comparative Example No. 31, after the process-deteriorated layer formed in the first polishing was removed by strong pickling, the second polishing was performed, so not only the Bairby layer was removed, but also the particle size was 0.1 μm or more. Moreover, crystal grains less than 0.2 μm were also completely removed. As a result, the plating property was inferior to the invention example.

Comparative Example No. 32 removes the processing-affected layer formed in the first polishing by strong pickling, and carries out the same polishing as the first time again. As a result, it had the same characteristics as Comparative Example 29.

Claims (8)

1. copper alloy for electronic material, wherein, when observing the cross section with rolling direction parallel direction by SIM, being in the scope of less than 0.5 μm apart from the degree of depth on top layer, amorphous tissue and the area occupation ratio of particle diameter shared by the crystal grain less than 0.1 μm are less than 1%, being in the scope of 0.2 ~ 0.5 μm apart from the degree of depth on top layer, the crystal grain of particle diameter for more than 0.1 μm and less than 0.2 μm is more than 47.5% relative to the number ratio of particle diameter shared by whole crystal grain of more than 0.1 μm.

2. the copper alloy for electronic material of claim 1, wherein, when observing the cross section with rolling direction parallel direction by SIM, being in the scope less than 0.2 μm apart from the degree of depth on top layer, the crystal grain of particle diameter for more than 0.1 μm and less than 0.2 μm is more than 57.5% relative to the number ratio of particle diameter shared by whole crystal grain of more than 0.1 μm.

3. the copper alloy for electronic material of claim 1 or 2, wherein, copper alloy is phosphor bronze, titanium copper or Corson alloy.

4. the preparation method of copper alloy for electronic material, described preparation method comprises following operation 1 and operation 2: described operation 1 is the surface relative to copper alloy substrate, grinding is implemented with the abrasive substance of the label with #600 ~ 8000, form the affected layer of adequate thickness, make when observing the cross section with rolling direction parallel direction by SIM after operation 2, being in the scope of 0.2 ~ 0.5 μm apart from the degree of depth on top layer, the crystal grain of particle diameter for more than 0.1 μm and less than 0.2 μm reaches more than 47.5% relative to the number ratio of particle diameter shared by whole crystal grain of more than 0.1 μm, described operation 2 is then use the abrasive substance with the granularity (d50) of 0.01 ~ 0.5 μm to implement grinding, from affected layer, remove amorphous tissue and particle diameter is microcrystallite less than 0.1 μm, make when observing the cross section with rolling direction parallel direction by SIM, being in the scope of less than 0.5 μm apart from the degree of depth on top layer, amorphous tissue and the area occupation ratio of particle diameter shared by the crystal grain less than 0.1 μm are less than 1%, being in the scope of 0.2 ~ 0.5 μm apart from the degree of depth on top layer, the crystal grain of particle diameter for more than 0.1 μm and less than 0.2 μm reaches more than 47.5% relative to the number ratio of particle diameter shared by whole crystal grain of more than 0.1 μm.

5. the preparation method of claim 4, wherein, the abrasive substance used in operation 1 is silicon carbide abrasive substance, and the abrasive substance used in operation 2 is aluminum oxide or colloided silica abrasive substance.

6. the preparation method of claim 4 or 5, described preparation method implements the grinding of operation 1 and operation 2 by polishing.

7. the copper alloy surface any one of claim 1 ~ 3 is provided with the plated body of plated film.

8. the plated body of claim 7, wherein, plated film contains more than any one in Ni, Sn and Ag.