JP5078167B2 - AuGe alloy balls for soldering - Google Patents

Description

  The present invention relates to an AuGe alloy ball for soldering used for sealing and joining electronic components.

AuGe eutectic alloy spheres have a moderate melting point of about 360 ° C. at the eutectic point, are excellent in electrical conductivity and thermal conductivity, and are chemically stable. SAW filters, elastic wave filters, quartz crystals It is used as a solder material for package bonding and sealing of electronic components that require high reliability such as vibrators.
In order to maintain the reliability of electronic component packages, AuGe alloy balls are required to have many characteristics. For example, it is possible to manage the sphere diameter with high accuracy to keep the solder material volume constant, Adopting materials with high sphericity. Insufficient soldering at the time of joining and sealing is an important factor that lowers the reliability of electronic component packages, and research is being carried out every day to further improve the reliability. For example, Japanese Patent Application Laid-Open No. 2008-30093 describes a method for improving a decrease in solderability due to surface oxidation by reducing the Ge content of the surface layer and modifying the surface layer. However, it is not always possible to obtain sufficient solderability only by modifying these surfaces against the decrease in solderability caused by defects in the internal structure of the AuGe alloy sphere. There is a need for alloy balls.

JP 2008-30093 A

  An object of the present invention is to provide an AuGe alloy ball for soldering that has better solderability, in particular wettability and flowability that affects the surroundings than conventional products.

According to the present invention, the following AuGe alloy balls for soldering can be obtained.
(1) Solder characterized in that the total amount of metal elements other than Au and Ge contained in the AuGe alloy is less than 120 ppm by mass, and that Ge fine particles are uniformly and finely dispersed on the surface and cross section of the sphere. AuGe alloy balls for attachment.
(2) The total amount of metal elements other than Au and Ge contained in the AuGe alloy having an Au content of 84.5% by mass or more and 89.0% by mass or less is less than 120 ppm by mass, and the Ge fine particles are spherical. An AuGe alloy sphere for soldering, characterized in that it is uniformly and finely dispersed on the surface and cross section.
(3) The AuGe alloy balls for soldering described above, wherein the average particle diameter of Ge having a cross-sectional eutectic structure is 5 μm or less and uniformly dispersed finely.
(4) The AuGe alloy ball for soldering described above, wherein the Au content in the AuGe alloy is 87.0% by mass or more and 88.0% by mass or less.
(5) The above-mentioned AuGe alloy balls for soldering, wherein the total amount of metal elements other than Au and Ge contained in the AuGe alloy is less than 100 ppm by mass.
(6) The above-mentioned AuGe alloy ball for soldering, wherein the total amount of metal elements other than Au and Ge contained in the AuGe alloy is less than 50 mass ppm.
The metal element here includes a so-called general metal element, a metalloid element, and a non-metal element that is solid at room temperature.

    The AuGe alloy sphere of the present invention has better flowability than conventional products and is suitable as a solder material for joining and sealing electronic components that require high reliability.

FIG. 1 is a diagram showing a cross-sectional structure of an AuGe alloy sphere in a comparative example. FIG. 2 is a diagram showing a surface state of an AuGe alloy sphere in a comparative example. FIG. 3 is a view showing a cross-sectional structure of an AuGe alloy sphere according to an embodiment of the present invention. FIG. 4 is a view showing a surface structure of an AuGe alloy sphere according to an embodiment of the present invention. FIG. 5 is a graph showing the relationship between the Au content and the sphericity of the alloy balls based on the data in Table 2. FIG. 6 is a graph showing the relationship between the content of metal elements other than Au and Ge and the sphericity of the alloy balls based on the data in Table 2. FIG. 7 is a graph showing the relationship between the Au content and the soldering test non-defective rate based on the data in Table 3. FIG. 8 is a graph showing the relationship between the content of metal elements other than Au and Ge and the soldering test non-defective rate based on the data in Table 3.

In joining and sealing of electronic parts that require high reliability, poor soldering has been taken up as a serious problem. In these devices that are highly integrated and highly functional, it is necessary to solder a large number of joints and sealing parts in a lump, and loss due to these soldering defects is particularly serious.
As a result of repeating the soldering test while changing various conditions in order to find the cause of these soldering defects, it was found that the solderability of the AuGe alloy spheres was deteriorated, resulting in poor soldering. .
Therefore, when the surface of these AuGe alloy balls having poor flowability was observed, the generation of Au primary crystals and dendrite structures was observed, and it was found that the structure was uneven. Further, when the cross section of the AuGe alloy sphere was observed, the generation of Au primary crystals and dendrite structures were observed in the same manner as the surface, and it was found that the structure was uneven (see FIGS. 1 and 2).
In such a non-uniform structure, when an Au primary crystal of an AuGe alloy sphere is exposed to heat from a heating source such as a laser beam or a hot plate and when other heat is applied to other parts, the AuGe alloy The temperature at which the sphere melts will be different. As described above, in the AuGe alloy sphere having a non-uniform structure as described above, the melting point is partially different, and the flowability is impaired because melting does not start simultaneously as a whole during soldering.

  An AuGe alloy has a eutectic structure, and the eutectic point Ge content is 12.5% by mass. All the structures become eutectic structures, but the AuGe alloy spheres are spheroidized by surface tension from the molten state. Therefore, it is considered that the Au primary crystal and the dendrite phase are unevenly distributed due to a slight difference in the melting and cooling processes.

Therefore, in order to improve the flowability, the factors that affect the flowability were further searched and the test was repeated. As a result, the presence of impurities in these alloys led to the formation and development of Au primary crystals and dendrite phases. As a result, it was found that the flowability was adversely affected.
In other words, when the flowability is compared under the same conditions using a low-purity AuGe alloy and a high-purity AuGe alloy, the high-purity AuGe alloy sphere has better flowability, and elements other than Au and Ge in the AuGe alloy It has been found that the presence of has an effect on flowability.
In AuGe alloy spheres with a low content of metal elements other than Au and Ge, non-uniform Au primary crystals and dendrite structures disappear not only from the surface of AuGe alloy spheres, but also have a uniform and fine structure in the cross section. (See FIGS. 3 to 4).
Therefore, the spot surface irradiated when the laser beam is irradiated is uniform regardless of the surface of the AuGe alloy sphere.
In addition, when heated by a hot plate, heat is rapidly transferred uniformly from the heating surface to the inside of the AuGe alloy sphere, so that the melting condition is uniform regardless of the location of the AuGe alloy sphere. Due to the difference in the surface of the alloy sphere and the internal structure, it is considered that the high purity AuGe alloy sphere rapidly melts during soldering and exhibits good flowability.

In addition, if the total amount of metal elements other than Au and Ge is suppressed as described above to reduce the impurity content to a certain range or less, it will have a favorable effect on spheroidization in the process of forming AuGe alloy spheres and approach a perfect sphere. I understood that.
Therefore, by reducing the total amount of metal elements other than Au and Ge to a certain level or less, there is an optimum structure state for the AuGe eutectic structure, and fine Ge fine particles are uniformly and finely dispersed on the surface and cross section of the sphere. As a result, it was concluded that more stable solderability can be obtained.
In addition, it was concluded that the total amount of metal elements other than Au and Ge should be reduced in order to improve the product yield in mass production of AuGe alloy balls.

Summarizing these results, the AuGe alloy balls for soldering of the present invention are as follows.
(1) In the AuGe alloy sphere for soldering of the present invention, the total amount of metal elements other than Au and Ge contained in the AuGe alloy is 120 mass ppm or less, and the Ge fine particles are uniformly fine on the surface and cross section of the sphere. Is distributed. When the total amount of metal elements other than Au and Ge is 120 mass ppm or more, preferable solderability cannot be obtained.
(2) The AuGe alloy ball for soldering of the present invention has an Au content of 84.5% by mass to 89.0% by mass, and the total amount of metal elements other than Au and Ge contained in the AuGe alloy Is less than 120 ppm by mass, and Ge fine particles are uniformly and finely dispersed on the surface and cross section of the sphere.
The AuGe alloy sphere targeted by the present invention is based on the Au and Ge eutectic composition, but a uniform fine structure can be obtained from the eutectic composition in the above plus and minus ranges.
When the Au content exceeds 89.0% by mass, the generation of Au primary crystals having a large crystal size and the generation of dendrite phases become excessive, and good soldering is hindered. On the other hand, if the Au content is less than 84.5% by mass, the Ge phase having a large crystal size is excessively generated, and good soldering is hindered.
(3) The average particle diameter of Ge in the eutectic structure in the cross section of the AuGe alloy sphere for soldering of the present invention is 5 μm or less and is uniformly and finely dispersed. When the average particle diameter of Ge exceeds 5 μm, even if the structure is uniform, it cannot be said that the structure is fine, and it is considered that the flowability is lowered and the solderability is impaired.
(4) In the AuGe alloy ball for soldering of the present invention, the Au content in the AuGe alloy is more preferably 87.0% by mass or more and 88.0% by mass or less. If the Au content is 87.0% by mass or more and 88.0% by mass or less, the product yield in mass production of AuGe alloy spheres can be improved, but the product yield is lowered outside this range.
(5) In the AuGe alloy ball for soldering of the present invention, the total amount of metal elements other than Au and Ge contained in the AuGe alloy is more preferably less than 100 mass ppm.
If the content of metal elements other than Au and Ge in the AuGe alloy is less than 100 mass ppm, there is an advantage that it can be displayed as a high-purity material with a purity of 99.99 mass%. Disappears.
(6) Furthermore, in the AuGe alloy ball for soldering of the present invention, the total amount of metal elements other than Au and Ge contained in the AuGe alloy is optimally less than 50 ppm by mass. If the total amount of metal elements other than Au and Ge is less than 50 ppm by mass, the advantage that the product yield in mass production of AuGe alloy balls can be most improved can be exhibited.

[Adjustment of soldering alloy balls]
Example 1. Au having a purity of 99.999% by mass and Ge having a purity of 99.9999% by mass are weighed so as to have a predetermined composition, placed in a carbon crucible, and melted and cast in a vacuum using a high-frequency melting furnace. Got. The ingot was rolled and pressed to obtain an AuGe alloy piece having a diameter of 0.42 mm and t0.10 mm. This AuGe alloy piece was placed on a carbon jig and melted and solidified in a nitrogen / hydrogen mixed atmosphere at 500 ° C. using a conveyor furnace, and then only the spheres having a well-shaped shape were selected to obtain AuGe alloy balls.
Example 2 Similarly, Au having a purity of 99.999% by mass and Ge having a purity of 99.9999% by mass were placed in a dissolution tank, and AuGe alloy balls were obtained using a so-called atomization method.
Furthermore, as a comparative example, Au of 99.9% by mass and Ge of 99.9% by mass were prepared by the same method as described above, and AuGe alloy balls were obtained by the atomizing method.

For the AuGe alloy balls of Examples 1 and 2 of the present invention thus obtained, the cross-sectional structure observed by SEM is shown in FIG. 3, and the surface properties are shown in FIG.
In the AuGe alloy sphere of the present invention, no coarse Au primary crystal and dendrite structure are observed on both the surface and cross section, and it can be seen that the eutectic structure has Ge fine particles uniformly dispersed throughout.
FIG. 3 showing the cross-sectional structure of the example and FIG. 4 showing the surface properties are as follows: Au content with an asterisk in Table 1: 87.5 mass%, content of metal elements other than Au and Ge: 30 mass FIG. 1 and FIG. 2 showing the cross-sectional structure and surface properties of the comparative example are examples of ppm, and the Au content similarly marked with ** in Table 1 is 87.5 mass%, Au, Ge Metal element content other than: An example of 150 mass ppm.

The composition analysis of the AuGe alloy spheres prepared as described above was performed using ICP. The results are shown in Table 1.
The impurities contained in Examples 1 and 2 and Comparative Example were all elements derived from raw materials, and were Ag, Cu, Fe, Mg, Si, Ni, Pb, Pt, Pd, Sn, and Cr.

  According to Table 1, the crystal structure becomes a finely and uniformly dispersed structure of Ge grains in the range of the Au content of the present invention and the metal element content other than Au and Ge, and the Au content and other than Au and Ge Coarse Au primary crystals are generated when the metal element content is outside the range of the present invention, and the dendrite structure is notably developed as shown in FIG. ).

Table 2 shows the results of measuring and evaluating the sphericity of the AuGe alloy spheres thus obtained.
The diameter in the vertical direction and the diameter in the horizontal direction of the AuGe alloy sphere were measured with a tool microscope, and the larger one was A and the smaller one was B, and the sphericity = A / B was determined. A sphericity of 1.00 to 1.02 was judged as good, and a larger sphericity was judged as bad.

FIG. 5 and FIG. 6 show the relationship between the Au content rate and the sphericity yield of the alloy balls, and the relationship between the metal element content other than Au and Ge and the sphericity yield of the alloy balls based on the data in Table 2. This is shown in the graph.
According to FIG. 5 and FIG. 6, with respect to the sphericity yield, there is a correlation between the Au content and the content of metal elements other than Au and Ge. It can be seen that the yield is significantly improved.
According to FIG. 5, the sphericity yield is better in the range of Au content 84.5 to 89.0%, and particularly in the range of Au content 87.0 to 88.0%. The sphericity yield is excellent. These effects are achieved in a low region where the metal element content other than Au and Ge is below a certain level, and when these values are 30 mass ppm or less, the above Au content is almost the entire range. It can be seen that the sphericity of can be achieved, but is limited to a narrow range at a content of 110 mass ppm.
In other words, the lower the content of these metal elements, the better the effect, and almost no effect can be exhibited at about 120 ppm by mass or more, and 150 ppm by mass as in the comparative example, which is extremely inferior. It will be unbearable.
This relationship is clearer when seen in the graph of FIG. 6 showing the relationship between the sphericity yield and the content of metal elements other than Au and Ge, and the content of metal elements other than Au and Ge is less than 120 ppm by mass. When the sphericity yield rate was good (better: 85 to 93%) in the region of (2), and 50 mass ppm or less, the sphericity yield rate was excellent (best: 93% or more).
On the other hand, in the comparative examples in which the Au content is outside the above range and the Au content is 82.0% by mass and 91.0% by mass, even if the metal element content other than Au and Ge satisfies the above range. It can be seen that the sphericity yield is remarkably inferior and cannot be practically used.
[Laser soldering test]

Place a transfer jig on a test gold-plated substrate having 100 recesses with a diameter of 0.5 mm and a depth of 0.3 mm, transfer 100 AuGe alloy balls, remove the transfer jig, and then laser light (output 0.5J) was used for soldering. Whether or not the obtained test base material was properly soldered was determined with a stereomicroscope, and the yield rate of soldering was determined.
These results are shown in Table 3. In addition, it was determined that the AuGe solder material flowed over the entire surface of the concave portion having a diameter of 0.5 mm for each substrate, and it was determined to be defective if any portion that did not flow remained.

7 and 8 show the relationship between the Au content rate and the soldering test non-defective rate based on the data in Table 3, and the relationship between the content rate of metal elements other than Au and Ge and the soldering test non-defective rate.
According to FIG. 7, when the metal element content other than Au and Ge is within the range of the present invention, the soldering test good product rate% good (better) when the Au content rate is 84.5 to 89.0% by mass. ) Achieved almost 90% or more, and when the Au content was in the range of 87.0 to 88.0% by mass, the evaluation of a good product ratio (best) reached around 99%.
On the other hand, when the content of metal elements other than Au and Ge is out of the range of the present invention as in the comparative example, these non-defective products cannot be achieved even if the Au content is within the range of the present invention.

Moreover, according to FIG. 8 showing the soldering test good product rate in relation to the content of metal elements other than Au and Ge, the soldering good product in the region where the content of metal elements other than Au and Ge is less than 120 mass ppm. If the rate is good (good: 85% or more) and 100 mass ppm or less, the soldering non-defective rate is good (better: 90 to 99%), and further, in combination with the optimal condition of the Au content, 50 mass ppm or less Excellent (best: 99% or more) effect was obtained.
On the other hand, it can be seen that even if the content of metal elements other than Au and Ge is within the range of the present invention, the rate of non-defective soldering test is significantly reduced if the content of Au is outside the range of the present invention.
From the above, in the present invention, as the alloy composition applied to the soldering AuGe alloy sphere, the Au content is 84.5 to 89.0 mass%, more preferably 87.0 to 88.0 mass%, Au, Ge When the total content of the metal elements is less than 120 ppm by mass, more preferably less than 100 ppm by mass, and the optimum range is less than 50 ppm by mass, a predetermined effect is exhibited.

    Since the AuGe alloy sphere for soldering of the present invention has a high sphericity and a uniform fine Au and Ge eutectic structure, it melts under uniform conditions regardless of atmospheric heating or spot heating with laser light. It is possible to reliably bond and seal with good flowability, exhibit excellent characteristics as a solder material for bonding and sealing of electronic components that are becoming increasingly fine, It meets the demand for bonding and sealing materials for electronic components that require high definition and high reliability.

Claims (5)

  When the Au content is 84.5 mass% or more and 89.0 mass% or less, and the total amount of metal elements other than Au and Ge contained in the AuGe alloy is less than 120 mass ppm, the Ge fine particles are formed into spheres. AuGe alloy balls for soldering characterized by being uniformly and finely dispersed on the surface and cross section   2. The AuGe alloy ball for soldering according to claim 1, wherein an average particle diameter of Ge having a cross-sectional eutectic structure is 5 μm or less and uniformly finely dispersed.   The AuGe alloy sphere for soldering according to claim 1, wherein the Au content in the AuGe alloy is 87.0 mass% to 88.0 mass%.   3. The AuGe alloy ball for soldering according to claim 1, wherein the total amount of metal elements other than Au and Ge contained in the AuGe alloy is less than 100 mass ppm. 3. The AuGe alloy ball for soldering according to claim 1, wherein the total amount of metal elements other than Au and Ge contained in the AuGe alloy is less than 50 ppm by mass.