KR101141089B1 - Au-Sn ALLOY POWDER FOR SOLDER PASTE - Google Patents

Abstract

assignment

Provided are Au-Sn alloy powders used for producing a low void Au-Sn alloy solder paste.

Solution

For solder paste containing 20.5-23.5 mass% of Sn, the remainder being a composition consisting of Au and an unavoidable impurity, and the structure which the fine Sn-rich superphase of particle size: 3 micrometers or less is crystallized 0.5-30 area% in the base material Au-Sn alloy powder.

Description

Au-Sn alloy powder for solder paste {Au-Sn ALLOY POWDER FOR SOLDER PASTE}

The present invention relates to an Au-Sn alloy powder for producing a low void Au-Sn alloy solder paste, and in particular to the production of Au-Sn alloy solder paste that does not generate large voids of more than 25 ㎛ diameter The present invention relates to an Au-Sn alloy powder, and to an Au-Sn alloy solder paste containing the Au-Sn alloy powder, which is particularly effective for soldering Au-plated substrates.

In general, Au-Sn alloy solder paste is used to bond semiconductor substrates such as GaAs optical devices, GaAs high frequency devices, thermoelectric devices, and substrates, and to seal packages such as SAW filters and crystal oscillators that require fine and high density. It is known that there is. The Au-Sn alloy powder contained in this Au-Sn alloy solder paste is known to be Au-Sn eutectic alloy powder which contains 20 mass% of Sn and has the composition which consists of Au and an unavoidable impurity. In general, it is also known to be obtained by gas atomization.

In recent years, miniaturization of the package size is progressing rapidly, and the size of the package sealed is reduced to dimensions of 1.6 mm in length and 1.0 mm in width. The edge width of the lid joint portion provided in the package having a length of 1.6 mm and a width of 1.0 mm is narrow at 100 to 250 μm, and the Au-Sn alloy solder paste is applied to the narrow edge of the package. The lid is mounted thereon and heated to seal the package. However, as the size of the package is reduced, the width of the package becomes narrower. In the case of sealing a package such as a SAW filter, a crystal oscillator, or the like requiring high tightness by soldering to a narrow edge, if a large number of voids are generated in the solder joint, the airtight performance is deteriorated due to the generation of voids. The reliability of the is lowered. In particular, the generation of large voids exceeding 25 µm is one of the biggest causes of lowering the airtight performance of the small package.

In order to improve these, Sn: 7-25 mass% is contained in the surface of the Au-Sn alloy powder which contains 15-25 mass% of Sn, and whose remainder consists of Au and an unavoidable impurity, and the remainder is Au and There is provided an Au-Sn alloy solder paste using an Au-Sn alloy powder in which Au-rich superphase having a composition composed of unavoidable impurities is crystallized by 10 area% or more. The Au-Sn alloy powder in which the Au-rich superphase is crystallized by 10 area% or more is used for the Au-Sn alloy molten metal in which the temperature of the Au-Sn alloy molten metal is kept at a lower temperature (below 300 to 600 ° C). It is used, the melt pressure and injection pressure is lower than the usual melt pressure pressure: 20 ~ 300kPa, injection pressure: 500 ~ 5000kPa, and the nozzle diameter is smaller than normal (diameter: less than 0.3 ~ 2mm) gas The Au-Sn alloy powder obtained by atomization and thus obtained has more Au-rich superfine crystals crystallized on the surface of the Au-Sn alloy powder than the composition of the Au-Sn alloy powder. Since much of this is crystallized, the ratio of the surface oxidation decreases, the oxidation does not proceed even if stored for a long time in the air, and the surface is not damaged well when it is sifted and classified, and thus a classification powder having a smaller oxide film is obtained. Is, the paste containing the Au-Sn alloy powder with a Au-rich second top is crystallized on the surface is that the voids can be obtained with less good bonding (see Japanese Laid-Open Patent Publication No. 2003-105462).

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

However, when soldering using the paste containing Au-Sn alloy powder described in Japanese Unexamined Patent Publication No. 2003-105461, the number of voids is surely reduced, but large voids exceeding 25 µm are found in the soldering portion. The generation of such large voids cannot reliably seal a small package as described above. Therefore, there has been a demand for a paste containing Au-Sn alloy powder having no large voids exceeding 25 µm and having fewer voids.

Means to solve the problem

Thus, the present inventors have conducted studies to obtain Au-Sn alloy pastes having fewer void generations and no large void generation exceeding 25 µm. As a result, (A) Au: 20.5-23.5 mass% of Sn, Au having the composition which consists of Au and an unavoidable impurity, and the structure which crystallized the fine Sn-rich superphase whose particle diameter was 3 micrometers or less in the base material. Solder paste obtained by mixing -Sn alloy powder with flux, when soldered using the solder paste, does not generate large voids exceeding 25 µm in the soldering portion, and the conventional Au-Sn alloy hand paste The number of void occurrences becomes smaller than

(B) However, even in the case of Au-Sn alloy powder in which a fine Sn-rich superphase having a particle size of 3 µm or less is crystallized, the crystallization amount is in a range of 0.5 to 30 area% and no Au-rich superphase is crystallized. It is necessary to be Au-Sn alloy powder having a, the research results were obtained.

The present invention has been made based on the results of these studies,

(1) Solder paste Au containing 20.5-23.5 mass% of Sn, the remainder consisting of Au and an unavoidable impurity, and 0.5-30 area% of fine Sn-rich ultrafine phase of 3 micrometers or less in crystal | crystallization in a base material. -Sn alloy powder,

(2) The solder paste formed by the flux which consists of Au-Sn alloy powder of the said (1) description, and rosin, an activator, a solvent, and a thickener, is characterized by the above-mentioned.

Particle diameter of the present invention: Au-Sn alloy powder for solder paste in which a fine Sn-rich ultrafine phase of 3 µm or less is crystallized at 0.5 to 30 area% contains Sn: 20.5 to 23.5 mass%, and the remainder is Au and unavoidable impurities. The molten metal obtained by dissolving the Au-Sn alloy having a composition consisting of was maintained at a temperature of 600 ° C to 1000 ° C, and mechanically stirred or mechanically stirred, and then the stirred molten metal was pressurized at a pressure of 300 to 800 kPa and a spray pressure of 5000. It is manufactured by injecting an inert gas at a nozzle gap of 0.3 mm or less from a small diameter nozzle having a diameter of 1 to 2 mm at a pressure of 8000 kPa. It is preferable that the said stirring is mechanical stirring, and propeller stirring is more preferable also in mechanical stirring. Electrical stirring, such as electromagnetic stirring, may be used together with the mechanical stirring, and the present invention also includes using electronic stirring together with mechanical stirring. Although the rotational speed of mechanical stirring is not specifically limited, It is preferable to carry out propeller stirring at 60-100 r.p.m for 3 to 10 minutes.

In the manufacturing method of the Au-Sn alloy powder for solder pastes of this invention, when Au-Sn alloy molten metal is mechanically stirred, Sn-rich superphase does not grow and becomes large and Au-Sn which does not have Au-rich supernormal cluster By melting the Au-Sn alloy molten metal obtained by agitation, the alloy molten metal was obtained, and the fine Sn-rich ultrafine phase having a particle diameter of 3 µm or less was crystallized in 0.5 to 30% by area, and the Au-rich Au-free Au-free phase was not found. When Sn alloy powder is obtained and soldered using a solder paste formed from such an Au-Sn alloy powder and a flux consisting of a rosin, an activator, a solvent, and a thickener, the number of voids generated in the solder portion is reduced, in particular, 25 µm. The occurrence of large voids in excess of will not be observed.

Conventionally, a method of producing Au-Sn alloy powder by inert gas atomizing molten metal obtained by dissolving Au-Sn alloy containing 20.5-23.5 mass% of Sn and having a composition consisting of Au and unavoidable impurities is known. However, the Au-Sn alloy powder obtained by gas atomizing the Au-Sn alloy molten metal containing 20.5-23.5 mass% of Sn and the remainder which consists of Au and an unavoidable impurity as it is, without mechanical agitation, has a particle diameter of 3 micrometers. Even if the following fine Sn-rich superphase is crystallized, the quantity does not exceed 0.4 area%, and in most cases, the coarse Sn-rich ultrafine phase with a particle size exceeding 3 micrometers is crystallized, and the Sn whose particle size exceeds 3 micrometers When the rich ultranormal is crystallized, the number of voids is generated, and large voids exceeding 25 µm are generated.

The said particle diameter: The Au-Sn alloy powder for solder pastes of this invention which has a structure which is 0.5-30 area% crystallized with the fine Sn-rich ultrafine phase of 3 micrometers or less, and has no Au rich ultrafine phase, is Sn: 20.5-23.5 mass It can manufacture by stirring Au-Sn alloy molten metal of the composition which contains%, and remainder consists of Au and an unavoidable impurity, and atomizes this stirred Au-Sn alloy molten metal.

The content of Sn contained in the Au-Sn alloy powder for solder paste of the present invention is limited to 20.5 to 23.5% by mass, and this type of solder paste is conventionally used to solder on an Au plated coated substrate. With this method of use, when the Sn content in the Au-Sn alloy powder is less than 20.5% by mass, Au in the Au-plated coating dissolves the Au-Sn alloy in the brazing metal and the Au concentration increases. The Au-rich superphase is crystallized at the joining interface of the molten Au-Sn alloy, the melting point becomes high, the melt viscosity becomes high, and gas generated during paste melting is trapped in the vicinity of the substrate, and Sn content is 23.5 mass. When it exceeds%, even if the molten metal is mechanically agitated, the coarse Sn-rich superphase having a particle size of more than 3 μm is crystallized, and the Sn-rich ultrafine phase is more than 30 area% in the total. It is not desirable.

The Sn-rich supercrystalline phase crystallized in the cross section of the Au-Sn alloy powder for solder paste of the present invention contains 37 to 39 mass% of Sn and has a component composition composed of Au and inevitable impurities. This is because the Sn-rich superphase crystallized from the molten metal containing 20.5-23.5 mass% of Sn, and the remainder consisting of Au and an unavoidable impurity has a composition containing 37-39 mass% of Sn.

Particle diameter crystallized in the Au-Sn alloy powder of the present invention: The fine Sn-rich ultrafine phase of 3 µm or less is limited to 0.5-30 area%, and the particle diameter crystallized in the cross section of the Au-Sn alloy powder: 3 µm or less. When the amount of the fine Sn-rich superfine phase is less than 0.5 area%, Au of the Au-coated substrate usually dissolves the Au-Sn alloy when the paste is used. Therefore, the Au-rich superfine phase at the substrate and the Au-Sn alloy interface is used. This Au-rich phase has a higher melting point than other process structure portions, and therefore, has a high melt viscosity at the same temperature and is not preferable because the gas generated during paste melting is trapped near the substrate, while the Au-Sn alloy powder When the fine Sn-rich superphase of 3 µm or less is crystallized in excess of 30 area%, the melting point of the powder is shifted to a high temperature, and the ratio of the Sn-rich superphase is high, resulting in a process point. By standing a shift increases the melting point, since the viscosity of the melt and the fluidity it is lowered, not preferable because the gas tends to trap generated during the paste melted. The more preferable range of the crystallization amount of the Sn-rich supercrystalline phase crystallized in the cross section of the Au-Sn alloy powder of this invention is 10-20 area%.

Effects of the Invention

Since the solder paste containing the Au-Sn alloy powder of the present invention does not generate large voids exceeding 25 µm in diameter, it provides a solder paste that is more reliable than the solder paste containing the conventional Au-Sn alloy powder. As a result, the incidence rate of defective products in semiconductor devices can be reduced, thereby reducing the cost, resulting in an excellent industrial effect.

Best Mode for Carrying Out the Invention

While melting the Au-Sn alloy having the component composition shown in Table 1 by the high frequency melting furnace, while maintaining the obtained molten metal at the temperature shown in Table 1, the time propeller shown in Table 1 is rotated at the rotational speed shown in Table 1, and the molten metal is machined. After stirring or mechanical stirring, the pressure shown in Table 1 was applied to the molten metal to drop the molten metal from the nozzle provided at the bottom of the high frequency melting furnace, and at the same time, the diameter shown in Table 1 provided so that the nozzle gap was around 0.2 mm. The gas atomized powder was produced by injecting Ar gas at the injection pressure shown in Table 1 to the molten metal falling from the gas nozzle, and sifting this gas atomized powder to a sieve of the present invention Au-Sn having an average particle diameter of 20 µm. Alloy powders 1 to 5 and comparative Au-Sn alloy powders 1 to 5 and conventional Au-Sn alloy powders 1 to 2 were prepared.

The Au-Sn alloy powders 1 to 5 of the present invention, comparative Au-Sn alloy powders 1 to 5, and conventional Au-Sn alloy powders 1 to 2 are embedded in resin and polished in cross section, the cross section is photographed in EPMA, and in this EPMA image, Powder cross-sectional diameter: 15 µm randomly selected 10 samples, using the image processing software to find the particle size of the Sn-rich ultra-normal phase and the area% occupied by the Sn-rich super-phase of the particle diameter to the powder cross-sectional area and the result Table 2 shows.

A solder paste was prepared by mixing a common RMA flux with a flux ratio of 7% by mass to these Au-Sn alloy powders 1 to 5, comparative Au-Sn alloy powders 1 to 5, and conventional Au-Sn alloy powders 1 to 2, respectively. .

Next, the following measurement was performed using these solder pastes.

First, a plate made of a Fe-Ni-based alloy (Ni: 42%, an alloy composed of remaining Fe and inevitable impurities) having dimensions of 10 mm in length, 10 mm in width, and 1 mm in thickness was prepared. Ni plating with a thickness of 2.5 μm was performed on the surface of the alloy plate and then Au plated with a thickness of 0.03 μm, and this plated plate was prepared as a substrate.

The solder paste was printed on the substrate using a mask having a diameter of 6.5 mu m and a thickness of 1.2 mm, followed by a reflow treatment (preheat 150 deg. C / 60 seconds + main heat 320 deg. C / 60 seconds). The number of voids obtained by using the transmission X-ray apparatus and image processing software for the voids of various sizes shown in the generated Table 2 was shown in Table 2.

From the results shown in Tables 1 and 2, the solder paste containing the Au-Sn alloy powders 1 to 5 of the present invention has a smaller number of voids than the solder paste containing Au-Sn alloy powders 1 and 2, and is conventionally used. Solder pastes containing Au-Sn alloy powders 1 to 2 generate large voids exceeding 25 µm, whereas solder pastes containing Au-Sn alloy powders 1 to 5 of the present invention generate voids exceeding 25 µm. I can see that it does not.

However, it turns out that the comparative Au-Sn alloy powders 1-5 which deviate from the conditions of this invention are unpreferable since the number of generation of a void increases.

Claims (4)

Sn: 20.5-23.5% by mass, the remainder of which is composed of Au and inevitable impurities, and in the substrate, a fine Sn-rich ultrafine phase having a particle size of 3 µm or less is crystallized from 0.5 to 30 area%, and further Au-rich An Au-Sn alloy powder for solder paste, which has a structure in which ultra-normal phases are not crystallized. The solder paste formed from the flux which consists of Au-Sn alloy powder of Claim 1, rosin, an active agent, a solvent, and a thickener. Claim 1 characterized by dissolving Au-Sn alloy containing 20.5-23.5 mass% of Sn, and having the composition which consists of Au and an unavoidable impurity, and the molten metal obtained is mechanically stirred or mechanically stirred. The manufacturing method of the Au-Sn alloy powder for solder pastes of Claim. The method of claim 3, wherein The mechanical agitation is a method for producing an Au-Sn alloy powder for solder paste, characterized in that the propeller agitation.