JP7189214B2 - composite material - Google Patents

Description

The present disclosure relates to composite members. This application claims priority from Japanese Patent Application No. 2018-132580 filed on July 12, 2018. All the contents described in the Japanese patent application are incorporated herein by reference.

Patent Documents 1 and 2 disclose a composite material as a heat dissipation member for a semiconductor device, which is obtained by dispersing diamond particles in a metal matrix such as Ag or Cu. Patent Documents 1 and 2 disclose forming a metal layer on the surface of a composite material by plating, vacuum deposition, or the like.

JP-A-2004-197153 WO2016/035795

A composite member according to one aspect of the present disclosure includes:
a composite material comprising a plurality of diamond particles and a metal matrix bonding the diamond particles;
A metal plating layer covering at least part of the surface of the composite material,
A modified layer formed of an amorphous layer or a graphite layer is provided on the surface of the diamond particles that is in contact with the metal plating layer.

1 is a schematic partial cross-sectional view schematically showing a composite member according to an embodiment; FIG. FIG. 4 is a diagram showing an example of a CK edge XAFS spectrum of the surface of diamond particles present in the surface layer of the composite material provided for the composite member according to the embodiment. FIG. 4 is a diagram showing an example of a CK edge XAFS spectrum of the surface of diamond particles present in the surface layer of the composite material provided for the composite member according to the embodiment.

[Problems to be Solved by the Present Disclosure]
Generally, a semiconductor element and a heat dissipation member are joined by soldering. When the heat dissipating member is made of a composite material of diamond particles and a metal matrix, the diamond particles may be exposed on the surface layer of the composite material. Diamond has poor wettability with solder. Therefore, when a composite material is used for a heat dissipation member, it is necessary to form a metal layer as a base layer for solder on the surface of the composite material.

One method of forming a metal layer on the surface of a composite material is to plate the surface of the composite material to form a metal plating layer. However, if the diamond particles are exposed on the surface layer of the composite material, the adhesion between the diamond particles and the plating is low. Therefore, blistering may occur at the interface between the diamond particles and the plating during soldering or heat resistance testing. Therefore, it is desired to improve the adhesion between the composite material and the metal plating layer.

As one method for improving the adhesion between the composite material and the plating, the surface of the composite material is subjected to silane coupling treatment to modify the surface of the diamond particles in the surface layer of the composite material, thereby improving the adhesion between the diamond particles and the plating. It is conceivable to improve adhesion. However, in this case, it is necessary to oxidize the surface of the diamond particles as a pretreatment for silane coupling. The metal matrix is damaged under the influence of the acid used in this oxidation treatment. As a result, the surface layer of the composite material may become rough, and the adhesion between the metal matrix and the plating may deteriorate.

Accordingly, one object of the present disclosure is to provide a composite member having excellent adhesion between the composite material and the metal plating layer.

[Effect of the present disclosure]
The composite member of the present disclosure has excellent adhesion between the composite material and the metal plating layer.

[Description of Embodiments of the Present Disclosure]
The present inventors have made various studies on techniques for forming a highly adhesive metal plating layer on the surface of a composite material of diamond particles and a metal matrix, and have obtained the following findings. The surface of the composite material is ion-etched to make the surface of the diamond particles in the surface layer of the composite material amorphous, or the surface of the composite material is subjected to electrical discharge machining to graphitize the surface of the diamond particles in the surface layer of the composite material. The present inventors have found that this can improve the adhesion between the diamond particles and the plating, thereby improving the adhesion of the metal plating layer. In addition, the metal matrix on the surface of the composite material is hardly damaged by ion etching or electric discharge machining. I got the knowledge that it was not effective. First, the contents of the embodiments of the present disclosure will be listed and described.

(1) A composite member according to one aspect of the present disclosure,
a composite material comprising a plurality of diamond particles and a metal matrix bonding the diamond particles;
A metal plating layer covering at least part of the surface of the composite material,
A modified layer formed of an amorphous layer or a graphite layer is provided on the surface of the diamond particles that is in contact with the metal plating layer.

The composite member has a modified layer formed of an amorphous layer obtained by amorphizing diamond or a graphite layer obtained by graphitizing diamond on the surface of the diamond particles that is in contact with the metal plating layer. By having the modified layer on the surface of the diamond particles in contact with the metal plating layer, the adhesion between the diamond particles and the metal plating layer can be improved, and the adhesion between the composite material and the metal plating layer is improved. Therefore, since the composite member has excellent adhesion between the composite material and the metal plating layer, the metal plating layer does not blister or peel off during soldering or heat resistance tests. can be reduced.

(2) As an example of the above composite member,
For example, the modified layer has a thickness of 5 nm or more.

When the modified layer has a thickness of 5 nm or more, the adhesion between the diamond particles and the metal plating layer can be effectively improved.

(3) As an example of the above composite member,
The metal forming the metal matrix may be Ag or Ag alloy.

Metals constituting the metal matrix include metals having high thermal conductivity (e.g., 120 W/mK or higher, particularly 200 W/mK or higher), such as Ag, Cu, Al, Mg, or alloys thereof. mentioned. Among them, Ag or Ag alloy is suitable because it has a high thermal conductivity and can improve the thermal conductivity of the composite material.

(4) As an example of the above composite member,
The surface roughness of the metal plating layer is less than 2.0 μm in terms of arithmetic mean roughness Ra.

When the arithmetic mean roughness Ra of the surface of the metal plating layer is less than 2.0 μm, it is possible to minimize the thickness of the solder when soldering a semiconductor element or the like to the surface of the metal plating layer. Therefore, it is easy to form a thin and uniform solder, and an increase in thermal resistance due to locally thick solder can be suppressed. When the composite member is used as a heat dissipation member for a semiconductor element, it becomes easier to efficiently transfer the heat of the semiconductor element to the composite member.

(5) As an example of the composite member, the metal forming the metal plating layer is Ni or a Ni alloy.

Since diamond is non-conductive, electroless plating can be used to form the metal plating layer. The metal forming the metal plating layer can be appropriately selected, and examples thereof include Ni, Cu, Au, Ag, and alloys thereof. Among them, a metal plating layer made of Ni or a Ni alloy can be formed at low cost by electroless plating.

[Details of the embodiment of the present disclosure]
Hereinafter, specific examples of composite members according to embodiments of the present disclosure will be described with reference to the drawings as appropriate. The present invention is not limited to these exemplifications, but is indicated by the scope of the claims, and is intended to include all modifications within the meaning and scope of equivalents to the scope of the claims.

<Composite material>
FIG. 1 is a partial cross section schematically showing the vicinity of the surface layer of the composite material 10 in a cross section obtained by cutting the composite member 1 in the thickness direction (the lamination direction of the composite material 10 and the metal plating layer 40; vertical direction in FIG. 1). It is a diagram. In FIG. 1, the diamond particles 20 are schematically shown in an exaggerated manner for convenience of explanation. A composite member 1 of an embodiment will be described with reference to FIG.

As shown in FIG. 1, the composite member 1 of the embodiment includes a composite material 10 including a plurality of diamond particles 20 and a metal matrix 30 that bonds the diamond particles 20 together, and at least a portion of the surface of the composite material 10. and a metal plating layer 40 . One of the features of the composite member 1 of the embodiment is that the surface of the diamond particles 20 in contact with the metal plating layer 40 has a modified layer 21 formed of an amorphous layer or a graphite layer. Each element will be described in detail below.

(composite material)
The composite material 10 is mainly composed of diamond particles 20 and a metal matrix 30, and is a composite of diamond and metal. A known material can be used for the composite material 10, and the composite material 10 can be manufactured by a known manufacturing method such as an infiltration method or a sintering method. As for the shape of the composite material 10, an appropriate shape such as a plate shape or a block shape can be selected according to the application of the composite member 1. FIG. For example, when the composite member 1 is used as a heat dissipation member for a semiconductor element, the composite material 10 may be flat and plate-shaped with a surface having an area capable of mounting a component such as a semiconductor element. In such applications, the thinner the composite member 1 is, the more easily the heat of the semiconductor element is transmitted to the installation target such as a cooling device. mentioned. The surface roughness of the composite material 10 is, for example, an arithmetic mean roughness Ra of less than 2.0 μm, more preferably less than 1.0 μm. The surface roughness of the composite material 10 can be reduced to some extent by polishing the surface of the composite material 10 before forming the metal plating layer 40 .

(diamond particles)
Since diamond has high thermal conductivity (typically 1500 W/m·K or more), composite member 1 comprising composite material 10 containing diamond particles 20 can be suitably used as a heat dissipation member. The plurality of diamond particles 20 are dispersed in the metal matrix 30 and exist on the surface layer of the composite material 10 with some of the diamond particles 20 exposed from the metal matrix 30 . In other words, the surface of the composite material 10 is mainly composed of the surface of the diamond particles 20 and the surface of the metal matrix 30 existing in the surface layer of the composite material 10 . The surface of the diamond particles 20 located in the surface layer of the composite material 10 is in contact with the metal plating layer 40 and has a modified layer 21 on the contact surface with the metal plating layer 40 . The modified layer 21 on the surface of the diamond grain 20 will be described later.

Specifications such as the shape, particle size and content of the diamond particles 20 can be appropriately selected. Since the above specifications typically substantially maintain the specifications of the diamond powder used as the raw material, it is preferable to select the specifications of the raw material diamond powder so as to achieve the desired specifications.

The shape of the diamond particles 20 is not particularly limited. Although the cross-sectional shape of the diamond particles 20 is polygonal in FIG. 1, the diamond particles 20 may have various cross-sectional shapes.

The average particle diameter of the diamond particles 20 is, for example, 10 μm or more and 100 μm or less. If the content of the diamond particles 20 is the same, the number of diamond particles 20 per unit volume of the composite material 10 is smaller than the case where the diamond particles 20 have a larger particle size, and the interface of the diamond particles 20 becomes smaller. decrease in the abundance of Therefore, the interfacial thermal resistance of the diamond particles 20 is reduced, and the thermal conductivity of the composite material 10 is improved. The smaller the diameter of the diamond particles 20, the smaller the irregularities due to the diamond particles 20 exposed on the surface of the composite material 10, and the easier it is to smooth the surface of the composite material 10. Therefore, the surface roughness of the composite material 10 can be reduced. From such a point of view, the average particle size of the diamond particles 20 may be, for example, 15 μm or more and 90 μm or less, and more preferably 20 μm or more and 50 μm or less. In addition, when the diamond particles 20 include relatively fine particles and relatively coarse particles, the composite material 10 can be easily densified during the manufacturing process of the composite material 10, and the thermal conductivity of the composite material 10 can be improved. is possible.

In the measurement of the average particle diameter of the diamond particles 20, the cross section of the composite material 10 is observed with a scanning electron microscope (SEM) or the like, and exists within a predetermined measurement field (eg, 0.3 mm × 0.2 mm). The diamond grains are extracted, and the diameter of the equivalent area circle of each grain is taken as the grain size. For example, the average value of 20 or more particle sizes can be used as the average particle size.

The content of the diamond particles 20 in the composite material 10 is, for example, 40% by volume or more and 85% by volume or less. The higher the content of diamond particles 20, the easier it is to obtain a composite material 10 with high thermal conductivity and a small coefficient of linear expansion. If the content of the diamond particles 20 is 85% by volume or less, the inclusion of the metal matrix 30 to some extent can reliably bond the diamond particles 20 together and prevent the coefficient of linear expansion from becoming excessively small. From this point of view, the content of the diamond particles 20 is, for example, 45% by volume or more and 80% by volume or less, and further 50% by volume or more and 75% by volume or less.

The diamond particles 20 in the metal matrix 30 may be coated particles having a coating film (not shown) made of metal carbide formed on their surfaces. Examples of the metal carbide forming the coating film include carbides of one or more metals selected from Ti, Hf, and Zr. The coating film contributes to increasing the wettability between the diamond particles 20 and the molten metal that finally becomes the metal matrix 30 in the manufacturing process of the composite material 10 . By having the coating film on the surface of the diamond particles 20, the adhesion between the diamond particles 20 and the metal matrix 30 can be improved. In particular, when the carbon component forming the carbide is derived from the diamond particles 20, the adhesion between the diamond particles 20 and the coating film is high. The dense composite material 10 with few pores can be obtained by the diamond particles 20 adhering to the metal matrix 30 via the coating film. Such a composite material 10 is excellent in thermal conductivity with less reduction in thermal conductivity due to pores. In addition, even if such a composite material 10 is subjected to a thermal cycle, the state of the interface between two of the above three (the diamond particles 20, the coating film, and the metal matrix 30) is unlikely to change, so the thermal cycle characteristics Also excellent. The coating film is preferably thin within the range where the effect of improving the wettability with the metal matrix can be obtained. This is because the carbide has a lower thermal conductivity than the metal forming the diamond particles 20 and the metal matrix 30, and is inferior in thermal conductivity.

(metal matrix)
Examples of the metal forming the metal matrix 30 include one or more pure metals selected from silver (Ag), copper (Cu), aluminum (Al), and magnesium (Mg), or alloys thereof. Among them, Ag or Ag alloy has high thermal conductivity, and when the metal matrix 30 is Ag or Ag alloy, the thermal conductivity of the composite material 10 can be increased, so it is suitable.

(metal plating layer)
The metal plating layer 40 covers at least a portion of the surface of the composite material 10 and is formed on the diamond particles 20 and the metal matrix 30 existing on the surface layer of the composite material 10 . Since the metal plating layer 40 is made of a metal having high wettability with solder, it functions as a base layer for solder when a semiconductor element or the like is soldered to the composite member 1 . In addition, the metal plating layer 40 can protect the composite material 10 from the external environment, mechanically protect it, and improve its appearance. For example, the metal plating layer 40 is provided in the solder forming range of the composite member 1 . By appropriately masking the surface of the composite material 10 when forming the metal plating layer 40 , the metal plating layer 40 can be formed in a desired area of the composite material 10 .

The metal plating layer 40 may be formed by electroless plating. The metal forming the metal plating layer 40 includes, for example, one or more pure metals selected from nickel (Ni), copper (Cu), gold (Au), and silver (Ag), or alloys thereof. . Above all, when the metal plating layer 40 is a Ni plating layer made of Ni or a Ni alloy, it can be formed at low cost by electroless plating. Ni alloys forming the Ni plating layer include, for example, Ni alloys containing phosphorus (P) (Ni—P alloys) and Ni alloys containing boron (B) (Ni—B alloys).

The surface roughness of the metal plating layer 40 is, for example, an arithmetic mean roughness Ra of less than 2.0 μm. The smaller the surface roughness (Ra) of the metal plating layer 40, the smoother the surface, and the thinner the solder can be when soldering a semiconductor element or the like to the surface of the metal plating layer 40. . Therefore, it is easy to form a thin and uniform solder, and an increase in thermal resistance due to locally thick solder can be suppressed. When the composite member 1 is used as a heat radiating member for a semiconductor element, the heat of the semiconductor element can be efficiently transferred to the composite member 1 easily. The surface roughness (Ra) of the metal plating layer 40 is, for example, 1.8 μm or less, preferably 1.5 μm or less, and more preferably 1.0 μm or less.

The thickness of the metal plating layer 40 can be appropriately selected, and is, for example, 1 μm or more and 20 μm or less, and further 10 μm or less. When the thickness of the metal plating layer 40 is 1 μm or more, the wettability with solder can be sufficiently secured, and the metal plating layer 40 functions sufficiently as a base layer for solder. The thinner the metal plating layer 40 is, the more easily the heat of the semiconductor element is transferred to the composite material 10, and the more easily the thermal conductivity of the composite member 1 as a whole is improved.

The thickness of the metal plating layer 40 is determined by observing a cross section of the composite member 1 cut in the thickness direction using an SEM or the like. Then, the thickness of the metal plating layer 40 is measured at 10 or more locations, and the average value thereof is used as the thickness of the metal plating layer 40 .

(Modified layer)
A modified layer 21 is provided on the surface of the diamond particles 20 located in the surface layer of the composite material 10 and in contact with the metal plating layer 40 . The modified layer 21 is provided on the surface of the diamond grain 20 that contacts the metal plating layer 40, and is formed of an amorphous layer or a graphite layer. The amorphous layer is formed by partially amorphizing the surface of the diamond grains 20 . The graphite layer is formed by partially graphitizing the surface of the diamond particles 20 . The modified layer 21 improves adhesion between the diamond particles 20 and the metal plating layer 40 and improves adhesion between the composite material 10 and the metal plating layer 40 . When the modified layer 21 is an amorphous layer, for example, the surface of the composite material 10 is ion-etched, and the surface of the diamond particles 20 on the surface of the composite material 10 is made amorphous by ion etching. On the other hand, in the case of the graphite layer, for example, the surface of the composite material 10 is subjected to electrical discharge machining, and the surface of the diamond particles 20 on the surface of the composite material 10 is graphitized by electrical discharge machining.

The presence or absence of modified layer 21 on the surface of diamond grain 20 can be examined by analyzing the state of carbon (C) on the surface of diamond grain 20 . A specific analysis method includes X-ray absorption spectroscopy (XAFS). XAFS is suitable because it is relatively easy to determine whether it is amorphous or graphitized compared to other analysis methods such as X-ray photoelectron spectroscopy (XPS). The analysis of the surface of the diamond particles 20 can be performed by observing the surface layer of the composite material 10 with the metal plating layer 40 removed from the composite member 1 . The metal plating layer 40 can be removed by dissolving or peeling off the metal plating layer 40 .

2A and 2B show an example of the CK edge XAFS spectrum of the diamond grain surface in this embodiment. FIG. 2A shows the K absorption edge spectrum of C near the surface (depth of 1 nm or more and less than 5 nm) measured by the total electron yield method (TEY), and FIG. 2B shows a relatively deep position measured by the partial fluorescence yield method (PFY) 2 shows a K absorption edge spectrum of C (with a depth of 10 nm or more and less than 20 nm). In each of FIGS. 2A and 2B, the solid line is the XAFS spectrum when the surface of the diamond particles is modified (amorphized) by argon (Ar) ion etching (sample A), and the surface of the diamond particles is modified by electrical discharge machining. The XAFS spectrum of (graphitization) (Sample B) is indicated by a dashed line. As a reference, in each figure, the thick line indicates the XAFS spectrum of the case where the surface of the diamond particles is not modified (Sample C). In the XAFS spectrum shown in each figure, the vertical axis is intensity (arbitrary unit) and the horizontal axis is absorption edge energy (eV).

From the XAFS spectrum shown in FIG. 2A, sample C has a concave peak characteristic of a diamond structure near 303 eV, indicating that it has a diamond structure in the range of 1 nm to 5 nm from the surface. Samples A and B have no concave peak near 303 eV and a peak corresponding to the sp2 component near about 285 eV, and have an amorphous or graphite structure mainly composed of the sp2 component in the range of 1 nm to 5 nm from the surface. is found to have Therefore, in the case of samples A and B, it is considered that an amorphous layer or a graphite layer is formed on the surface of the diamond particles.

In addition, as shown in FIG. 2B, sample A has an XAFS spectrum similar to that of sample C in the range of 10 nm to 20 nm from the surface, and has a diamond structure. Therefore, in the case of sample A, it is considered that the amorphous layer is formed only near the surface of the diamond grains. On the other hand, sample B has a graphite structure because there is no concave peak near 303 eV and a peak corresponding to the sp2 component is observed even in the range of 10 nm to 20 nm from the surface. Therefore, in the case of sample B, it is considered that the graphite layer is formed from the surface of the diamond grain to a relatively deep position.

Although the thickness of the modified layer 21 is not particularly limited, it may be 5 nm or more for both the amorphous layer and the graphite layer. When the thickness of the modified layer 21 is 5 nm or more, the adhesion between the diamond particles 20 and the metal plating layer 40 can be effectively improved. Moreover, the upper limit of the thickness of the modified layer 21 is 1.5 μm or less for both the amorphous layer and the graphite layer. This is because if the modified layer 21 becomes too thick, the thermal conductivity of the diamond grains 20 will decrease.

A method for measuring the thickness of the modified layer 21 will be described. If the thickness of the modified layer 21 is less than 20 nm, the CK edge XAFS spectrum of the surface of the diamond particle 20 is measured with TEY and PFY, and from each XAFS spectrum, the presence or absence of a concave peak near 303 eV to decide. That is, when a concave peak is observed in the vicinity of 303 eV in TEY, the thickness of the modified layer 21 is made less than 5 nm. When a concave peak near 303 eV is not observed with TEY but is observed with PFY, the thickness of the modified layer 21 is 5 nm or more and less than 20 nm, and here the thickness is 5 nm. When no concave peak is observed near 303 eV in both TEY and PFY, the thickness of the modified layer 21 is 20 nm or more. When the modified layer 21 has a thickness of 20 nm or more, cross-sectional observation is performed with a scanning transmission electron microscope (STEM), and line analysis is performed from the surface of the diamond particle 20 in the depth direction by electron energy loss spectroscopy (EELS). When analyzed by EELS, a concave peak is observed in the vicinity of 303 eV in the CK edge ELNES spectrum for the diamond structure, similar to XAFS. According to line analysis, the thickness of the modified layer 21 is defined as the depth just before a concave peak appears near 303 eV.

<Manufacturing method of composite member>
An example of a method for manufacturing the composite member 1 of the embodiment described above will be described. The composite member 1 includes a step of preparing the composite material 10 (hereinafter referred to as a preparation step), a step of performing ion etching or electrical discharge machining on the surface of the composite material 10 (hereinafter referred to as a modification step), and It can be manufactured by a manufacturing method including a step of forming the metal plating layer 40 (hereinafter referred to as a plating step). Each step will be described in detail below.

(Preparation process)
The preparation step is a step of preparing a composite material 10 having a plurality of diamond particles 20 and a metal matrix 30 bonding the diamond particles 20 together.

The composite material 10 is produced by a known manufacturing method such as an infiltration method as described in Patent Documents 1 and 2, using diamond powder and metal powder, metal pieces, metal lumps, etc. forming the metal matrix 30 as raw materials. can be manufactured. When the coated particles are formed by forming a coating film made of the metal carbide on the surface of the diamond particle 20, it is preferable to use a compound powder as described in Patent Documents 1 and 2 as a raw material for the coating film. .

(Reforming process)
The modification step is a step of subjecting the surface of the composite material 10 to Ar ion etching or electric discharge machining to modify the surface of the diamond particles 20 . As a result, a modified layer 21 made of an amorphous layer or a graphite layer is formed on the surface of the diamond particles 20 present in the surface layer of the composite material 10 .

By subjecting the surface of the composite material 10 to Ar ion etching or electric discharge machining, the surface of the diamond particles 20 on the surface of the composite material 10 is made amorphous or graphitized, and the modified layer 21 consisting of an amorphous layer or a graphite layer is formed on the surface of the diamond particles 20. can be formed. A commercially available ion milling device or electrical discharge machine can be used for Ar ion etching or electrical discharge machining.

The thickness of the modified layer 21 can be controlled by changing various conditions of Ar ion etching and electrical discharge machining. In the case of Ar ion etching, for example, conditions such as processing time and acceleration voltage are changed. The longer the processing time of Ar ion etching or the higher the accelerating voltage, the more amorphous the surface of the diamond particles 20 progresses, and the amorphous layer forming the modified layer 21 tends to become thicker. For example, the processing time of Ar ion etching is 60 seconds or more and 600 seconds or less, and the acceleration voltage is 0.3 kV or more and 10.0 kV or less. In the case of electric discharge machining, changing the conditions such as the machining current can be mentioned. Graphitization of the surface of the diamond particles 20 progresses as the machining current of electric discharge machining increases, and the graphite layer forming the modified layer 21 tends to become thicker. For example, the peak current of electric discharge machining is set to more than 0A and 100A or less.

(Plating process)
The plating step is a step of performing electroless plating on the surface of the composite material 10 to form the metal plating layer 40 on at least part of the surface of the composite material 10 after the modification step.

In the modification step, the surface of the diamond particles 20 on the surface of the composite material 10 is modified to form a modified layer 21 consisting of an amorphous layer or a graphite layer on the surface of the diamond particles 20 in contact with the metal plating layer 40 . Therefore, the adhesion between the diamond particles 20 and the metal plating layer 40 is high. Known electroless plating can be used to form the metal plating layer 40 . As the metal plating layer 40, for example, a Ni plating layer made of a Ni alloy can be formed by electroless Ni alloy plating. Further, the thickness of the metal plating layer 40 can be adjusted by changing conditions such as the processing time of the electroless plating and the temperature of the plating solution. A commercially available plating solution can be used for electroless plating.

In addition, pretreatment for electroless plating includes desmutting (surface conditioning), addition of a catalyst such as Pd, and catalyst activation (accelerator). Commercial products can be used as the chemicals used for these treatments. In addition, degreasing, pre-dipping, or the like may be performed.

(Other processes)
A step of polishing the surface of the composite material 10 (hereinafter referred to as a polishing step) and a step of etching the surface of the composite material 10 (hereinafter referred to as an etching step) can be provided before the plating step. By polishing the surface of the composite material 10 by the polishing process, the surface can be easily flattened and the surface roughness of the composite material 10 can be reduced. The surface polishing of the composite material 10 can be performed using an appropriate whetstone or the like. In the etching step, the surface of the metal matrix 30 on the surface layer of the composite material 10 is etched with an acid or alkali that does not substantially react with diamond and can remove only the metal matrix 30 . If the etching depth in the etching step is too large, the surface roughness of the composite material 10 is deteriorated. The polishing step and the etching step may be performed before the modifying step.

In the modification step, when the surface of the composite material 10 is subjected to electrical discharge machining, the surface of the metal matrix 30 on the surface of the composite material 10 may be oxidized. When the above-described polishing process and etching process are provided, the oxide film on the surface of the metal matrix 30 generated by electrical discharge machining can be removed by polishing or etching.

<Main effects of the embodiment>
Since the composite member 1 of the embodiment includes the composite material 10 containing the diamond particles 20 having high thermal conductivity, it has excellent thermal conductivity. From this point, the composite member 1 can be suitably used for various heat radiating members. In particular, the coefficient of linear expansion of the composite material 10 is close to the coefficient of linear expansion of the semiconductor element and its peripheral parts due to the combination of the diamond particles 20 and the metal matrix 30 . In addition, since the composite member 1 has the metal plating layer 40 on the surface of the composite material 10, it has good wettability with solder, and the semiconductor element can be satisfactorily bonded to the composite material 10 (metal plating layer 40) by soldering. can. From these points, the composite member 1 can be suitably used as a heat dissipation member for a semiconductor device.

In particular, the composite member 1 of the embodiment has a modified layer 21 formed of an amorphous layer or a graphite layer on the surface of the diamond particles 20 that contacts the metal plating layer 40 . By having the modified layer 21 on the surface of the diamond particles 20 in contact with the metal plating layer 40, the adhesion between the diamond particles 20 and the metal plating layer 40 can be improved, and the adhesion between the composite material 10 and the metal plating layer 40 can be improved. improves. Therefore, in the composite member 1, the adhesion between the composite material 10 and the metal plating layer 40 is excellent. can be reduced.

[Test Example 1]
Electroless plating was performed on the surface of a composite material having diamond particles and a metal matrix of Ag to prepare a sample of a composite member comprising the composite material and a metal plating layer (Ni plating layer), and the adhesion of the metal plating layer was measured. evaluated.

A composite material prepared based on the manufacturing method described in Patent Document 2 was prepared. The prepared composite material is a square flat plate material with a side length of 50 mm and a thickness of 1.4 mm, with a diamond particle content of 60% by volume and an Ag metal matrix content of about 40% by volume. and the average particle size of the diamond particles is 20 μm. Here, the surface of the composite material was polished.

After polishing, the surface of the composite material was etched with Ar ions to amorphize the surface of the diamond grains present in the surface layer of the composite material to prepare a modified sample. Here, samples were prepared by changing the conditions of Ar ion etching. 1, No. 2. In addition, a sample was prepared by subjecting the surface of the composite material to electric discharge machining to graphitize the surface of the diamond particles present in the surface layer of the composite material. This sample is referred to as sample no. 3. Ar ion etching was performed with a batch-type ion milling apparatus (IML-580-LL) manufactured by Hitachi High-Tech Solutions Co., Ltd. The electric discharge machining was performed with a die-sinker electric discharge machine (AG40L) manufactured by Sodick Co., Ltd.

Sample no. The conditions for Ar ion etching of No. 1 are shown below.
Holder tilt: -30°
Processing time: 1 minute Acceleration voltage: 500 V, acceleration current: 1600 A, deceleration voltage: -200 V
Bias voltage: 20V
Microwave incident power: 600W
Process gas flow rate: 30 sccm
Milling pressure: 3 × 10 ^-2 Pa (3E-2 Pa)
Holder rotation speed: 3 rpm
Sample no. The conditions for the Ar ion etching of No. 2 are shown below.

Holder tilt: -30°
Processing time: 1 minute Acceleration voltage: 700 V, acceleration current: 1600 A, deceleration voltage: -200 V
Bias voltage: 20V
Microwave incident power: 600W
Process gas flow rate: 30 sccm
Milling pressure: 3 × 10 ^-2 Pa (3E-2 Pa)
Holder rotation speed: 3 rpm
Sample no. The electrical discharge machining conditions of No. 3 are shown below.

Working fluid: VITOL-2
Liquid treatment: injection Liquid pressure: 0.03 MPa
Setting depth: 0.20mm
Peak current: 7.0A
After modification of the diamond particle surface by Ar ion etching or electrical discharge machining, the surface of the composite material of each sample was etched. Here, a cyan-based etchant was used to etch the surface of the Ag metal matrix present in the surface layer of the composite material. The etching conditions were as follows: composition of etchant: concentration of potassium cyanide: 50 g/L, temperature: 30° C., processing time: 1 minute, and the etching depth was adjusted to 1 μm to 3 μm.

After etching, the surface of the composite material of each sample was subjected to electroless plating to form a metal plating layer, thereby producing a composite member. Here, a Ni plating layer made of a Ni--P alloy was formed by electroless Ni--P alloy plating after a catalyst application treatment as a pretreatment. A Pd—Sn colloidal solution was used as the catalyst application treatment liquid. Electroless plating conditions are as follows: composition of plating solution: nickel sulfate 20 g/L, sodium hypophosphite 24 g/L, lactic acid 27 g/L, propionic acid 2.0 g/L, temperature: 85° C., treatment time: 30 minutes and the thickness of the Ni plating layer was adjusted to 5.5 μm.

As described above, sample no. 1 to No. 3 composite members were fabricated. Table 1 shows the specifications of the composite member of each sample.

For comparison, sample no. 1 to No. Sample no. Ten composite members were made. In addition, sample no. In 10, no etching was performed prior to electroless plating.

The surface roughness of the metal plating layer (Ni plating layer) was measured for the composite member of each sample. Table 1 shows the results. Here, the arithmetic average roughness Ra (μm) was measured using a laser microscope VK-X100 manufactured by KEYENCE CORPORATION with a 50-fold objective lens.

(Evaluation of adhesion of metal plating layer)
Adhesion between the composite material and the metal plating layer (Ni plating layer) was evaluated for the composite member of each sample. Adhesion was evaluated by fabricating a plurality of composite members of each sample, conducting a heat resistance test, and evaluating the blistering occurrence rate of the Ni plating layer. It means that the lower the swelling occurrence rate of the Ni plating layer, the higher the adhesion of the Ni plating layer. The swelling occurrence rate of the Ni plating layer is obtained by visually observing the Ni plating layer after the heat resistance test, observing the presence or absence of swelling of the Ni plating layer, and obtaining the number of composite members in which swelling has occurred in the Ni plating layer out of 100 pieces. Calculated by Further, the heat resistance test was conducted at 400° C. and 780° C. for 40 minutes each, and the blistering occurrence rate at each temperature was investigated. Table 1 shows the results.

(Peeling of metal plating layer)
For the composite member of each sample, the metal plating layer formed on the surface of the composite material was peeled off with a peeling solution. For the stripping solution, Ni plating stripping agents “Top Lip F-85” and “Top Lip PF-X” manufactured by Okuno Chemical Industry Co., Ltd. were dissolved in pure water at concentrations of 80 g/L and 200 mL/L, respectively. A mixed solution was used. Then, the composite member of each sample was immersed in a stripping solution at 85° C. for 1 hour, and then ultrasonically cleaned with pure water. After washing, the surface of each sample was observed with an SEM to confirm that no Ni remained on the surface of the composite material.

After peeling off the metal plating layer, the surface of the composite material of each sample was subjected to XAFS measurement with TEY and PFY to obtain the CK edge XAFS spectrum of the surface of diamond grains present in the surface layer of each composite material. From the analysis results of the obtained CK end XAFS spectra, sample No. 1, No. In No. 2, an amorphous layer was confirmed on the surface of the diamond particles by Ar ion etching. Sample no. In No. 3, a graphite layer formed by electric discharge machining was confirmed on the surface of the diamond particles. Also, for each sample, the thickness of the modified layer formed of an amorphous layer or a graphite layer was obtained. Table 1 shows the results. Sample no. 1, no concave peak was observed near 303 eV in the CK edge XAFS spectrum measured by TEY, and a concave peak was observed near 303 eV in the CK edge XAFS spectrum measured by PFY. Therefore, sample no. In 1, it was confirmed that the surface of the diamond particles was amorphized to a depth of at least 5 nm. Sample no. 2, No. For 3, a cross section of the composite material cut in the thickness direction was observed by STEM, and line analysis was performed in the depth direction from the surface of the diamond particles by EELS. From the acquired CK edge ELNES spectrum, sample No. In 2, it was confirmed that the surface of the diamond particles was amorphized to a depth of 50 nm. Sample no. In 3, it was confirmed that the surface of the diamond particles was graphitized to a depth of 300 nm.

XAFS measurements were performed at BL17 (soft X-ray) at Kyushu Synchrotron Light Research Center, Saga Prefecture, and R3000 manufactured by VG Sienta Co., Ltd. was used as the photoelectron spectrometer. The measurement conditions were incident energy: 350 eV, 600 eV, incident angle: 45°, detection angle: 45°.

Sample No. which does not have a modified layer on the surface of the diamond particles in contact with the metal plating layer (Ni plating layer). In No. 10, the blistering occurrence rate after the heat resistance test was 100%. On the other hand, sample No. having a modified layer formed of an amorphous layer or a graphite layer on the surface of the diamond particles in contact with the metal plating layer (Ni plating layer). 1 to No. 3, sample no. Compared to No. 10, it can be seen that the swelling occurrence rate after the heat resistance test can be reduced. Therefore, sample no. 1 to No. 3 shows that the adhesion between the composite material and the metal plating layer is improved.

REFERENCE SIGNS LIST 1 composite member 10 composite material 20 diamond particles 21 modified layer 30 metal matrix 40 metal plating layer

Claims (5)

a composite material comprising a plurality of diamond particles and a metal matrix bonding the diamond particles;
A metal plating layer covering at least part of the surface of the composite material,
Of the diamond particles constituting the surface of the composite material, only the regions exposed from the metal matrix have a modified layer,
The modified layer is in contact with the metal plating layer and is composed of an amorphous layer or a graphite layer ,
Composite member. The composite member according to claim 1, wherein the modified layer has a thickness of 5 nm or more. 3. The composite member according to claim 1, wherein the metal forming said metal matrix is Ag or an Ag alloy. The composite member according to any one of claims 1 to 3, wherein the surface roughness of the metal plating layer is less than 2.0 µm in terms of arithmetic mean roughness Ra. The composite member according to any one of claims 1 to 4, wherein the metal forming the metal plating layer is Ni or a Ni alloy.

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