JP2008030093A - Au/Ge ALLOY SOLDER BALL - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Au/Ge alloy solder ball having excellent oxidation resistance and satisfactory wettability compared with the conventional one. <P>SOLUTION: The whole other than a surface layer is composed of an alloy having an Au-Ge eutectic composition or an alloy having a composition near the eutectic composition, and the surface layer is composed of an Au solid solution in which Au and Ge are solid-soluted. The maximum height Ry of the surface roughness is ≤0.5 μm. Regarding its production, a sphere made of an alloy having an Au-Ge eutectic composition or an alloy having a composition near the eutectic composition is charged to a vessel together with pure water admixed with a surfactant, and vibration is applied thereto, thus the Ge content is reduced from the surface layer, so as to modify the surface layer, and thereafter, cleaning is performed, so as to remove the surfactant from the surface. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an Au / Ge alloy solder ball used for joining and sealing electronic components.

  An Au-based alloy called a hard solder is obtained by alloying Au with a metal such as Sn, Ge, or Si. Such an Au-based alloy has good electrical conduction and thermal conduction, and is chemically stable, so that high reliability can be obtained as a solder material. Among Au alloys, the Au / Ge eutectic alloy has a relatively high melting temperature of 356 ° C., so it has better heat resistance than the Au / Sn eutectic alloy that is commonly used as a hard solder. Attention has been focused on as a material for solder balls used for sealing.

  The solder balls used for joining and sealing of electronic components have a small volume and mass, so that when problems such as surface oxidation occur, the influence on joining and sealing is significant. For such problems, measures such as removal of an oxide film and prevention of oxidation are being studied every day.

  For example, in Japanese Patent Application Laid-Open No. 2005-131703, a lead-free type solder ball made of a Sn / Zn-based, Sn / Ag / Cu-based soft solder material is immersed in a fatty acid solution, and vibration and flow A method for producing a solder ball with excellent surface quality by providing at least one of them is described. This method removes the tendrite-like crystals and oxide film formed on the surface of the solder ball, and forms a coating (organic film) with a fatty acid, which is a surface active substance, on the surface of the solder ball. It has improved.

  By the way, Au generally does not oxidize, but in the case of an Au / Ge alloy in which Au is alloyed with Ge, oxidation proceeds from the surface, and as a result, in a solder material using the Au / Ge alloy, wetting defects are caused. Problems may arise. In particular, solder balls have a problem in that surface oxidation is likely to occur due to the manufacturing method, and wet defects are likely to be prominent due to the properties of the solder balls described above.

  In contrast, it is conceivable to deal with this using the method described in Japanese Patent Application Laid-Open No. 2005-131703, but in the case of an Au / Ge alloy solder ball that requires high reliability in bonding and sealing. The organic film may act as an impurity, and its application is difficult.

In view of the above, there is a demand for an Au / Ge alloy solder ball that does not have an organic film on its surface, is excellent in oxidation resistance, and does not cause poor wetting.
JP 2005-131703 A

  An object of the present invention is to provide an Au / Ge alloy solder ball that is superior in oxidation resistance and has better wettability than conventional products.

  The Au / Ge alloy solder ball of the present invention is entirely made of an eutectic of Au and Ge or an alloy near the eutectic except for the surface layer, and the surface layer is an Au solid solution in which Au is a solid solution of Ge. is there. Alternatively, the modified surface layer is formed on the spherical body by removing Ge from the surface layer of the spherical body made of a eutectic of Au and Ge or an alloy near the eutectic.

  Furthermore, the maximum content of Ge in the Au solid solution in which the Au content in the surface layer exceeds the Au content in the eutectic of Au and Ge or an alloy in the vicinity of the eutectic and Au is in solid solution with Ge. It is desirable that the content is not more than the Au content determined by the limit.

  Furthermore, the maximum height Ry of the surface roughness is desirably 0.5 μm or less.

  The method for producing an Au / Ge alloy solder ball according to the present invention improves the surface layer by reducing the Ge content from the surface layer to a spherical body made of an eutectic of Au and Ge or an alloy near the eutectic. Quality.

  Furthermore, it is desirable to modify the surface layer by placing the spherical body in a container and applying vibration. Alternatively, the surface layer is preferably modified by placing the spherical body in a container together with a liquid and applying vibration. Furthermore, it is desirable that the liquid is pure water.

  In a different aspect of the method for producing an Au / Ge alloy solder ball according to the present invention, the spherical body is made together with pure water to which a surfactant is added with respect to a spherical body made of an eutectic of Au and Ge or an alloy near the eutectic. The surfactant is removed from the surface of the spherical body by washing in a container and modifying the surface layer by reducing the Ge content from the surface layer by applying vibration.

  The Au / Ge alloy solder ball of the present invention is suitably used as a soldering material for bonding and sealing that is superior in oxidation resistance and has better wettability than conventional products and requires high reliability.

  As a result of repeated tests and studies in order to solve the conventional problems, the present inventor has found that the surface layer made of a solid solution that is difficult to oxidize and that is mainly made of a solid solution of Au (a solid solution of Ge in Au) is spherical. The present invention was completed by obtaining knowledge that an Au / Ge alloy solder ball having better oxidation resistance than conventional products can be obtained by forming on the surface.

  In the Au solid solution, Au is solid-solved at a concentration within 1.13% by mass, which is the solid solution limit of Ge.

  Usually, since the metal structure of the Au / Ge alloy is a simple binary eutectic, in the case of Au / 12Ge (Ge is 12.0% by mass) having a eutectic composition, Au is a solid solution of Au. Only the eutectic structure phase in which the solid solution and Ge become lamellar is obtained. When the Ge content is less than 12.0% by mass, it becomes hypoeutectic, and has a two-phase structure of an Au solid solution phase crystallized in a dendrite (dendritic) shape as a primary crystal and a lamellar eutectic structure phase. Further, when the Ge content ratio exceeds 12.0% by mass, it becomes hypereutectic and becomes a two-phase structure of a Ge primary crystal phase crystallized into a bulk as an initial crystal and a lamellar eutectic structure phase. In addition, even if it is not strictly a eutectic point, there exists a composition range of binary alloys having industrially usable characteristics. For example, although the melting point is slightly higher than the eutectic point, an industrially usable composition range is determined. By defining such a range including not only the eutectic point but also the eutectic point, the management range of the alloy composition can be widened, and the manufacturing cost can be reduced. In the present invention, this range that can be handled industrially equivalent to the eutectic point is called the vicinity of the eutectic.

  Microscopically, the structure of the Au / Ge alloy is basically composed of an Au solid solution and Ge in any of eutectic, hypoeutectic and hypereutectic. Among these, the Au solid solution hardly oxidizes like Au, so the oxidation of the Au / Ge alloy proceeds through Ge existing in the lamellar structure or the Ge primary crystal. Therefore, by forming the surface of the Au / Ge alloy solder ball with a surface layer mainly made of an Au solid solution, higher oxidation resistance than that of the conventional product can be obtained.

  The thickness of the surface layer must be at least 10 nm. If the thickness of the surface layer is less than 10 nm, the effect of preventing oxidation is insufficient. The surface layer is mainly composed of an Au solid solution, but a small amount of Ge is left, and elements such as S, C, and O are included unavoidably. In order to obtain a sufficient oxidation resistance effect, the Au content in the surface layer exceeds the Au content in the eutectic of Au and Ge or an alloy in the vicinity of the eutectic, and the Au is dissolved in Ge. It is necessary that the Au content is not more than the Au content determined by the maximum solid solubility limit of Ge in the Au solid solution. When the Au content in the surface layer is less than or equal to the Au content in the eutectic of Au and Ge or an alloy near the eutectic, the effect of surface modification cannot be obtained. On the other hand, when the Au content in the surface layer is not less than the Au content determined by the maximum solid solubility limit of Ge in the Au solid solution in which Au is solid-dissolved in Ge, the temperature of the solidus increases and the wettability increases. Adversely affects.

  Further, the surface of the Au / Ge alloy solder ball is mirror-finished to reduce the surface energy, and further improvement can be achieved. Although the maximum height Ry of the surface roughness after the spheronization step is about 0.6 to 0.8 μm, the “surface area / volume” is set by setting the maximum height Ry of the surface roughness to 0.5 μm or less. By reducing the value, that is, by reducing the surface energy, the oxidation resistance of the Au / Ge alloy solder ball can be further improved.

  In joining and sealing with solder, wettability is the most important characteristic, and wettability is strongly influenced by the oxidation of the solder surface. In the Au / Ge alloy solder ball of the present invention, a surface layer mainly composed of an Au solid solution is formed so that the surface is not easily oxidized, so that wettability superior to conventional products can be obtained. In addition, it is sufficient that only the surface of the ball is modified in this way, and if the inside has a eutectic composition, the state of any of the above eutectic, hypoeutectic, and hypereutectic structures. But there is no problem.

  The Au / Ge alloy solder ball according to the present invention can be obtained through the following steps.

  That is, in the method for producing an Au / Ge alloy solder ball according to the present invention, first, an Au / Ge alloy sphere is formed from an Au / Ge alloy having a eutectic composition or a composition in the vicinity of the eutectic composition by a spheronization step. obtain. Note that being in the vicinity of the eutectic composition means that the content of Au is in the range of 8 to 16% by mass.

  As described above, when the obtained Au / Ge alloy sphere is a eutectic (Ge content is equal to 12.0% by mass), the Au solid solution and Ge lamellar eutectic structure phase, hypoeutectic ( In the case where the Ge content is less than 12.0% by mass), two phases of the primary crystal Au solid solution phase, the Au solid solution and the Ge lamellar eutectic structure phase, or hypereutectic (the Ge content is 12). In the case of more than 0.0 mass%), it has a structure of any one of two phases of a primary crystal Ge single phase, an Au solid solution, and a Ge lamellar eutectic structure phase. On the outermost surface of the resulting Au / Ge alloy spheroid, even if an Au / Ge alloy having a eutectic composition is used as a raw material, O, S, and C are caused by organic substances such as Ge oxidation and machine oil used in the manufacturing process. Inevitable elements such as are present on the surface of the spherical body.

  The Au / Ge alloy spherical body is put in a container together with pure water, and vibration is applied by a centrifugal barrel polishing machine, a rotating barrel polishing machine, a vortex barrel polishing machine, or the like. Thus, by putting the Au / Ge alloy spheres in a sealed space and applying vibration, the spheres rub against each other and the surface is polished. This is called co-rubbing. In this way, surface modification is performed.

  The surface of the Au / Ge alloy sphere before surface modification is mainly composed of an Au solid solution and Ge, but the Au solid solution is as soft as pure Au, while Ge is hard. Therefore, the soft Au solid solution on the spherical body surface is plastically deformed by co-rubbing and covers the entire surface of the spherical body. On the other hand, the hard Ge on the surface of the spherical body is also scraped to some extent by co-rubbing to form a scrap and is separated from the spherical body.

  Since this shaving residue may adhere to the surface of the spherical body, the co-rubbing is preferably performed in a liquid in order to prevent adhesion. The liquid used in the co-rubbing step may be pure water, but an aqueous solution to which less than 20% by volume of a surfactant is added is preferable because the effect of the present invention can be remarkably obtained due to its activation effect. When the mixing ratio of the surfactant is 20% by volume or more, it becomes difficult to remove it after the co-rubbing step. Although any surfactant can be adopted, it is preferable to use an alcohol surfactant such as alkyl sulfate, fatty acid amide, alkali metal salt of inorganic acid, polyoxyalkylated higher alcohol, alkylphenol. .

(Example 1)
The Au / Ge alloy (Ge is 12.0% by mass) having the eutectic composition was spheroidized to obtain an Au / Ge alloy solder spheroid having a diameter of 0.4 mm. This corresponds to a conventional Au / Ge alloy solder ball product. When the maximum height Ry of the surface roughness was measured with a Keyence laser microscope, it was about 0.6 μm.

  After immersing the spherical body in an aqueous solution of a surfactant having a concentration of 5%, the container is sealed and subjected to vibration and rotation for 5 minutes with a centrifugal barrel polishing machine (PCF-30SB, manufactured by PG Corporation). Gave. Thereafter, the surfactant remaining on the surface of the spherical body after the surface treatment was removed by washing with an acetone solution to obtain an Au / Ge alloy solder ball having a diameter of 0.4 mm. The maximum height Ry of the surface roughness was about 0.3 μm as measured by a Keyence laser microscope.

  FIG. 1 is a photograph showing the Au / Ge alloy solder ball of the present invention. FIG. 3 is a photograph showing a conventional Au / Ge alloy solder ball. The Au / Ge alloy solder balls of the present invention have a higher reflectance due to scattering compared to the conventional Au / Ge alloy spheres, and due to the co-rubbing effect between the balls and the activation effect due to the surfactant, It is understood that the surface has been modified.

  The Au / Ge alloy solder balls of the present invention and the conventional Au / Ge alloy spheres were subjected to surface analysis using an Auger electron spectroscopic analyzer (SAMVAC 4300, manufactured by ULVAC-PHI). The analysis result of the Au / Ge alloy solder ball of the present invention is shown in FIG. 2, and the analysis result of the conventional Au / Ge alloy sphere is shown in FIG. Table 1 shows the results of analyzing the composition of each surface layer.

  It is understood that the surface of the conventional Au / Ge alloy sphere is mainly an Au / Ge eutectic structure composed of an Au solid solution and Ge. Therefore, there is a high possibility that oxidation will proceed from Ge existing on the surface. On the other hand, it is understood that the surface of the Au / Ge alloy solder ball of the present invention is composed only of an Au solid solution composed of almost Au, and the Ge amount on the surface is significantly lower than the eutectic composition. The Therefore, it can be said that oxidation does not proceed through Ge existing on the surface of the ball.

As for wettability, heating temperature: 370 ° C., Atmosphere: in N _2, it was carried out general wettability test. As a result, the Au / Ge alloy solder ball of the present invention showed better wettability than the conventional spherical Au / Ge alloy.

  Also, when a raw material is an Au / Ge alloy having a hypoeutectic composition with Ge less than 12% by mass, and when an Au / Ge alloy having a hypereutectic composition with Ge exceeding 12% by mass is used as a raw material The surface of the Au / Ge alloy sphere corresponding to the conventional product was confirmed to be composed of the Au solid solution and Ge. On the other hand, it was confirmed that the surface of the Au / Ge alloy solder ball that has undergone the manufacturing process according to the present invention is composed only of an Au solid solution.

  Further, in the case where co-grinding is performed without using a liquid, it is possible to eliminate scraps in place of the liquid by blowing clean dry air onto the alloy solder balls during co-sliding.

It is a photograph which shows one Example of the Au / Ge alloy solder ball of this invention. It is a graph which shows the analysis result of one Example of the Au / Ge alloy solder ball of this invention. It is a photograph which shows the spherical Au / Ge alloy which is a conventional product. It is a graph which shows the analysis result of the spherical Au / Ge alloy which is a conventional product.

Claims (9)

  The Au / Ge alloy solder characterized in that the entire surface layer is made of an eutectic of Au and Ge or an alloy near the eutectic, and the surface layer is made of an Au solid solution in which Au is dissolved in Ge. ball.   An Au / Ge alloy characterized in that a modified surface layer is formed on the spherical body by removing Ge from the surface layer of the spherical body made of an eutectic of Au and Ge or an alloy near the eutectic. Solder ball.   The Au content in the surface layer exceeds the Au content in the eutectic of Au and Ge or an alloy in the vicinity of the eutectic, and the maximum solid solubility limit of Ge in the Au solid solution in which Au is in solid solution with Ge. The Au / Ge alloy solder ball according to claim 1 or 2, wherein the Au content is not more than a predetermined Au content.   The Au / Ge alloy solder ball according to claim 1, wherein the maximum height Ry of the surface roughness is 0.5 μm or less.   A method for producing an Au / Ge alloy solder ball according to any one of claims 1 to 4, wherein the surface layer is made of Ge from a eutectic of Au and Ge or an alloy near the eutectic. A method for producing an Au / Ge alloy solder ball, wherein the surface layer is modified by reducing the content.   6. The method for producing an Au / Ge alloy solder ball according to claim 5, wherein the modification of the surface layer is performed by placing the spherical body in a container and applying vibration.   6. The method for producing an Au / Ge alloy solder ball according to claim 5, wherein the modification of the surface layer is performed by placing the spherical body in a container together with a liquid and applying vibration.   The method for producing an Au / Ge alloy solder ball according to claim 7, wherein the liquid is pure water.   A method for producing an Au / Ge alloy solder ball according to any one of claims 1 to 4, wherein the spherical body is interfaced with a spherical body made of an eutectic of Au and Ge or an alloy near the eutectic. Put in a container with pure water to which an activator has been added, apply vibration, reduce the Ge content from the surface layer, modify the surface layer, and then wash the surface of the spherical body from the interface. A method for producing an Au / Ge alloy solder ball, wherein the activator is removed.