TWI673372B - Au-sn alloy solder paste, method for manufacturing au-sn alloy solder layer and au-sn alloy solder layer - Google Patents

Abstract

The Au-Sn alloy solder paste of the present invention is made of Au-Sn atomized powder containing Sn: 38% by mass or more and 54% by mass or less, and the residue is Au and unavoidable impurities, and Au-Sn atomized For powder mixed flux, the oxygen concentration contained in the Au-Sn atomized powder is set to 50 ppm or more and 1500 ppm or less.

Description

Method for manufacturing Au-Sn alloy solder paste, Au-Sn alloy solder layer, and Au-Sn alloy solder layer

The present invention relates to a method for manufacturing an Au-Sn alloy solder paste, an Au-Sn alloy solder layer, and an Au-Sn alloy solder layer.

This case claims priority from Japanese Patent Application No. 2014-234795 filed by Japan on November 19, 2014, and incorporates its contents here.

The prior art of Patent Document 1 discloses that, as Au-Sn alloy welding, Au-20 mass% Sn alloy solder paste containing Au-20 mass% Sn having a melting point of 278 ° C, or Au-90 solder paste having a melting point of 217 ° C is included. Au-90 mass% Sn alloy solder paste with mass% Sn.

Among the above solder pastes, Au-20 mass% Sn alloy solder pastes having a high melting point are used, for example, in a high temperature environment.

[Prior technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2011-167761

However, in recent years, Au-Sn alloy welding, which is used as an electronic part used in a high-temperature environment, is expected to be used in a high-temperature environment of 300 ° C or higher. For example, in power semiconductors for electric power control used in electric vehicles and the like, a large amount of heat is generated due to the application of a large current, and since it is used in a high temperature environment such as a machine room, it is expected that the solder can be used in a high temperature environment such as the above .

However, since the melting point of the Au-20 mass% Sn alloy welding of the conventional high melting point welding is 278 ° C, it is difficult to use it in a high temperature environment of 300 ° C or higher.

In addition, the Au-20 mass% Sn alloy solder paste used for forming Au-20 mass% Sn alloy solder has a problem that the cost is increased because the Au ratio is as high as 80 mass%.

Therefore, the present invention is to provide an Au-Sn alloy solder paste, a method for manufacturing Au-Sn alloy solder paste, and an Au-Sn alloy solder layer which can be used in a high temperature environment of 300 ° C and can reduce cost. A method and an Au-Sn alloy solder layer are used for the purpose.

In order to solve the above problems, according to an aspect of the present invention, Provided is an Au-Sn alloy solder paste, which is characterized by Au-Sn atomized powder containing Sn: 38% by mass or more and 54% by mass or less, and Au and unavoidable impurities remaining, and the aforementioned Au-Sn mist For the flux mixed with the powder, the oxygen concentration contained in the aforementioned Au-Sn atomized powder is 50 ppm or more and 1500 ppm or less.

According to the aforementioned Au-Sn alloy solder paste, since Au-Sn atomized powder composed of Sn: 38% by mass or more and 54% by mass or less, remaining as Au and unavoidable impurities, can be used to weld Au-Sn alloy The melting point becomes higher than 300 ° C.

Accordingly, the Au-Sn alloy solder layer formed using the Au-Sn alloy solder paste can be used in a high temperature environment of 300 ° C or higher.

In addition, compared with the Au ratio of Au-20 mass% Sn alloy welding, which is a conventional high melting point welding, it is possible to reduce the ratio of high-priced Au to 46 mass% or more and 62 mass% or less. As a result, compared with Au-20 mass% Sn alloy solder paste, the cost of Au-Sn alloy solder paste can be reduced.

However, when the Au-Sn atomized powder is produced, when the Sn concentration in the Au-Sn atomized powder is increased, the powders tend to agglomerate with each other, and the yield of the classified Au-Sn atomized powder may be reduced.

In the state where the metal surface is not oxidized, since the surface activity is very high and becomes unstable, the powders are agglomerated with each other to become a stable state.

Therefore, as described above, since the concentration of oxygen contained in the Au-Sn atomized powder becomes 50 ppm or more, the aggregation of the Au-Sn atomized powder is suppressed, and the yield of the classified Au-Sn atomized powder can be improved. Also, since 1500 ppm or less, when mixed with a flux, does not adversely affect melting properties.

In the Au-Sn alloy solder paste, the average particle diameter of the Au-Sn atomized powder may be in a range of 1 to 30 μm.

The average particle diameter of the Au-Sn atomized powder is smaller than 1 μm. When the Au-Sn alloy solder paste is reflowed after printing, the Au-Sn atomized powder may be difficult to melt.

On the other hand, when the average particle diameter of the Au-Sn atomized powder is larger than 30 μm, the printability of the Au-Sn alloy solder paste may deteriorate, and the flux and the Au-Sn atomized powder may be separated at the same time.

According to this, by setting the average particle diameter of the Au-Sn atomized powder in the range of 1 to 30 μm, the separation of the flux and the Au-Sn atomized powder can be suppressed, and the printing of the Au-Sn alloy solder paste can be suppressed at the same time. The decrease in suitability can further make the Au-Sn atomized powder more easily melted during the reflow process.

In the Au-Sn alloy solder paste, the content of the flux may be 5% by mass or more and 40% by mass or less of the entire paste.

When the content of the flux (the content of the flux when the total amount of Au-Sn alloy solder paste is set to 100% by mass) is less than 5% by mass, the viscosity of the Au-Sn alloy solder paste is excessively increased, and the printing method is used Printing Au-Sn alloy solder paste may become difficult.

On the other hand, when the content of the flux exceeds 40% by mass, there is a possibility that print sags may occur during printing of the Au-Sn alloy solder paste, and at the same time, insufficient aggregation of the Au-Sn atomized powder may occur during reflow processing.

Based on this, the content of mixed powder and flux is determined as Within the above numerical range, in addition to suppressing the occurrence of printing sags and the occurrence of insufficient agglomeration of the Au-Sn atomized powder, the Au-Sn alloy solder paste can be easily printed.

In order to solve the above-mentioned problems, according to another aspect of the present invention, a method for manufacturing an Au-Sn alloy solder layer is provided, which is characterized in that the Au-Sn alloy solder paste is used to form an Au-Sn alloy solder paste. The temperature between the solidus and liquidus lines melts.

According to the aforementioned method for manufacturing an Au-Sn alloy solder layer, the Au-Sn alloy solder paste is melted at a temperature between the solid-phase and liquid-phase lines of the Au-Sn alloy constituting the Au-Sn alloy solder paste. The -Sn alloy solder layer melts at a temperature of 309 ° C or higher, so it can be used in a high temperature environment of 300 ° C or higher.

In addition, compared with the Au ratio of Au-20 mass% Sn alloy welding, which is a conventional high melting point welding, it is possible to reduce the ratio of high-priced Au to 46 mass% or more and 62 mass% or less. As a result, compared with Au-20 mass% Sn alloy solder paste, the cost of Au-Sn alloy solder paste can be reduced.

In order to solve the above problems, according to another aspect of the present invention, an Au-Sn alloy solder layer is provided, which is obtained by the aforementioned method for manufacturing an Au-Sn alloy solder layer.

According to the present invention, since the Au-Sn alloy solder layer is melted at a temperature of 309 ° C or higher, the Au-Sn alloy solder layer can be used in a high temperature environment of 300 ° C or higher.

According to the present invention, an Au-Sn alloy solder layer that can be used in a high temperature environment of 300 ° C. or higher can be obtained, and the cost of the Au-Sn alloy solder layer can be reduced.

[Fig. 1] State diagram of Au-Sn alloy.

Hereinafter, an embodiment to which the present invention is applied will be described in detail with reference to the drawings.

<Au-Sn alloy solder paste>

The Au-Sn alloy solder paste of this embodiment contains Au-Sn atomized powder composed of Sn: 38% by mass or more and 54% by mass or less, and Au and unavoidable impurities remaining, and Au-Sn atomized powder. The mixed flux, Au-Sn atomized powder contains an oxygen concentration of 50 ppm or more and 1500 ppm or less. The content of the Sn is preferably 45% by mass or more and 53% by mass or less, and the oxygen concentration contained in the Au-Sn atomized powder is preferably 100 ppm or more and 500 ppm or less, but is not limited thereto.

The average particle diameter of the Au-Sn atomized powder can be set, for example, in a range of 1 to 30 μm.

The content of the flux can be, for example, 5 mass% or more and 45 mass% or less of the entire paste.

As the flux, for example, a general flux (for example, a flux including rosin, an active agent, a solvent, and a tackifier) can be used. As the flux, from the viewpoint of wettability of Au-Sn alloy solder paste, for example, a weakly active (RMA) type flux or an active (RA) type flux may be used. The average particle diameter of the Au-Sn atomized powder is preferably 5 to 20 μm, and the content of the flux is preferably 7 mass% or more and 25 mass% or less of the entire paste, but it is not limited thereto.

<Manufacturing method of Au-Sn alloy solder paste>

Next, the manufacturing method of Au-Sn alloy solder paste will be explained briefly.

First, an Au-Sn alloy made of Sn: 38% by mass or more and 54% by mass or less and remaining as Au and unavoidable impurities is prepared, and a melt is prepared by dissolving the Au-Sn alloy.

Second, the temperature of the melt is maintained at a specific temperature (for example, 600-1000 ° C), and the melt is mechanically stirred.

The Au-Sn atomized powder can be formed by, for example, a gas atomization method. Specifically, for example, a molten solution obtained by melting an Au-Sn alloy having a specific composition (Sn: 38% by mass or more and 54% by mass or less and remaining as a specific composition in a range of Au and unavoidable impurities) is maintained at a specific temperature. (For example 550 ~ 1000 ℃). Next, the melt is stirred (for example, mechanically stirred), or after stirring, the melt is pressurized (for example, a pressure of 300 to 800 kPa) and sprayed with an inert gas from a small-diameter nozzle (diameter 1 to 2 mm). form.

As a condition of the above spraying, for example, the spraying pressure can be set to 5000 ~ 8000kPa, nozzle gap is set to 0.3 or less.

Next, by classifying the Au-Sn atomized powder so as to have the above average particle size, Au-Sn atomization made of Sn: 38% by mass or more and 54% by mass or less, with Au and unavoidable impurities remaining powder.

As the mechanical stirring, for example, propeller stirring is preferred. In addition, mechanical stirring and electric stirring such as electromagnetic stirring can be used together.

When a propeller is used as mechanical stirring, the rotation speed of the propeller can be, for example, 60 to 100 rpm. The stirring time in this case can be appropriately selected, for example, in a range of 3 minutes to 10 minutes.

In the step of preparing the above-mentioned Au-Sn atomized powder, for example, an Au-Sn atomized powder having the above composition and average particle diameter may be produced by using a gas added with oxygen to the above inert gas.

Regarding the mixing ratio of the inert gas and oxygen during gas atomization, the oxygen concentration of the obtained powder was adjusted in a manner not exceeding 1500 ppm. The concentration of oxygen contained in a gas made of an inert gas and oxygen can be, for example, 10 to 100 ppm. When the concentration of oxygen in the gas is less than 10 ppm, since it is difficult to sufficiently obtain the effect of oxidizing Sn constituting the Au-Sn atomized powder, the oxygen in the Au-Sn atomized powder becomes less than 50 ppm, and Au is sufficiently suppressed -The effect of agglomeration of the Sn atomized powder becomes difficult.

On the other hand, when the concentration of oxygen contained in the gas is more than 100 ppm, the oxygen in the powder exceeds 1500 ppm, which may reduce the melting property.

However, when a gas with the same oxygen concentration is used, when the powder with a large particle size is produced, the specific surface area of the powder is small, so the oxygen concentration in the powder is necessarily reduced. degree. On the other hand, when a powder having a small particle diameter is produced, the specific surface area is increased, so that the oxygen concentration is increased. Therefore, it is necessary to adjust the oxygen concentration in the gas in accordance with the particle size and oxygen concentration of the target powder.

Next, an Au-Sn alloy solder paste was prepared by mixing the Au-Sn atomized powder having the above-mentioned average particle size and composition with a flux. As a mixing method at this time, for example, a star-stirring method can be used.

<Au-Sn alloy solder layer>

Fig. 1 is a state diagram of an Au-Sn alloy.

The Au-Sn alloy solder layer is formed by printing between the solid phase line and the liquidus line of the Au-Sn alloy solder paste after printing the Au-Sn alloy solder paste described above. An Au-Sn alloy solder layer made of Sn: 38% by mass or more and 54% by mass or less, and the residue is Au and unavoidable impurities. Although the reflow (melting) temperature of the aforementioned Au-Sn alloy is preferably 310 to 440 ° C, it is not limited thereto.

Referring to FIG. 1, when the Sn contained in the Au-Sn alloy is more than 20% by mass and less than 38% by mass, the solidus temperature becomes 278 ° C. When the Sn contained in the Au-Sn alloy is more than 54% by mass and less than 70% by mass, the solidus temperature becomes 252 ° C. When the Sn contained in the Au-Sn alloy is 38% by mass or more and 54% by mass or less, the solidus temperature becomes 309 ° C higher than 278 ° C.

That is, by setting the composition of the Au-Sn alloy solder layer to Sn: 38% by mass or more and 54% by mass or less, and the remaining is Au and unavoidable impurities, the temperature of the solidus line of the molten Au-Sn alloy solder layer can be adjusted. Set to 300 ℃ on.

In the above Au-Sn alloy solder paste, when the content of flux (the ratio of the flux when the total amount of Au-Sn alloy solder paste is set to 100% by mass) is less than 5% by mass, the Au-Sn alloy The viscosity of the solder paste is too high, and it may become difficult to print the Au-Sn alloy solder paste by printing.

On the other hand, when the content of the flux exceeds 40% by mass, there is a possibility that print sags may occur during printing of the Au-Sn alloy solder paste, and at the same time, insufficient aggregation of the Au-Sn atomized powder may occur.

According to this, by setting the content of the Au-Sn atomized powder and the flux within the above-mentioned numerical range, in addition to suppressing the occurrence of printing sag and the occurrence of insufficient aggregation of the Au-Sn atomized powder, Au can be easily printed. -Sn alloy solder paste.

In the above Au-Sn alloy solder paste, the average particle diameter of the Au-Sn atomized powder is smaller than 0.1 μm. When the Au-Sn alloy solder paste is reflowed (melted) after printing, it becomes difficult to melt Au. -Sn atomized powder.

On the other hand, when the average particle diameter of the Au-Sn atomized powder is larger than 30 μm, the printability of the Au-Sn alloy solder paste may deteriorate, and the flux and the Au-Sn atomized powder may be separated at the same time.

According to this, by setting the average particle diameter of the Au-Sn atomized powder in the range of 0.1 to 30 μm, the separation of the flux and the Au-Sn atomized powder can be suppressed, and the printing of the Au-Sn alloy solder paste can be suppressed at the same time. The decrease in suitability can further make the Au-Sn atomized powder melt during the reflow process.

Au-Sn alloy solder paste, Au-Sn according to this embodiment Manufacturing method of alloy solder layer, and Au-Sn alloy solder layer, Au-Sn alloy solder paste includes Au-Sn made of Sn: 38% by mass or more and 54% by mass or less, and the residue is Au and unavoidable impurities The atomized powder makes it possible to weld the Au-Sn alloy to a higher temperature than 300 ° C.

Accordingly, the Au-Sn alloy solder layer formed using the Au-Sn alloy solder paste can be used in a high temperature environment of 300 ° C or higher.

In addition, compared with the Au ratio of Au-20 mass% Sn alloy welding, which is a conventional high melting point welding, it is possible to reduce the ratio of high-priced Au to 46 mass% or more and 62 mass% or less. As a result, compared with Au-20 mass% Sn alloy solder paste, the cost of Au-Sn alloy solder paste can be reduced.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to those specific embodiments, and various modifications can be made within the scope of the gist of the present invention described in the scope of the patent application. Change is possible.

For example, in this embodiment, as an example of a method for applying an Au-Sn alloy solder paste, the printing method is described as an example, but instead of the printing method, a dispense method or a needle transfer method may be used.

In addition, in this embodiment, as an example, a case where the reflow process is performed in a normal inert gas environment will be described as an example. In this case, when the reflow temperature is too high, there is a possibility that the cleaning performance of the flux may deteriorate in the cleaning step of the flux performed after the reflow treatment.

In the case of reflow treatment under a normal inert gas environment When the reflow temperature is lower than the solidus temperature, it becomes difficult to melt the Au-Sn atomized powder.

For these reasons, in this embodiment, a case where the reflow temperature is 309 ° C or higher will be exemplified.

However, when a vacuum reflow device such as a vacuum reflow device that can be reflowed in a vacuum has a furnace capable of supporting high temperatures, it can be used at a temperature 20-20 ° C higher than the liquidus temperature of a common Au-Sn alloy composition. Perform reflow processing.

[Example]

Hereinafter, although Examples and Comparative Examples are described, the present invention is not limited to the following Examples.

<Production of Au-Sn alloy solder paste>

Under the conditions shown in Table 1, the Au-Sn alloy solder pastes P1 to P12 of Examples 1 to 12 and the Au-Sn alloy solder pastes Q1 to Q4 of Comparative Examples 1 to 4 were produced by the methods described above.

Specifically, Au-Sn alloy solder pastes P1 to P12 and Q1 to Q4 were produced using the following method.

First, an Au-Sn alloy having the composition shown in Table 1 was prepared, and the Au-Sn alloy was dissolved to prepare a melt. The melt was mechanically stirred while the temperature of the melt was maintained at 800 ° C.

Next, the molten liquid in the state of mechanical stirring is pressurized at 500 kPa, and the molten liquid is led out from a small-diameter nozzle having a diameter of 1.5 mm under the condition that the ejection pressure is 6000 kPa. Moreover, for the derived melt, a gas made of argon and oxygen was sprayed to produce Au-Sn atomized powder. At this time, the nozzle gap was 0.2 mm.

Then, the Au-Sn atomized powder was classified by wind to produce an average particle diameter and composition shown in Table 1, and the remaining was an Au-Sn atomized powder made of Au and unavoidable impurities.

Next, the Au-Sn atomized powder having the above-mentioned average particle diameter and composition was mixed with the RA-type flux so as to have the flux ratio shown in Table 1 to prepare an Au-Sn alloy solder paste P1. ~ P12, Q1 ~ Q4. As a mixing method at this time, a star-stirring method is used.

<Assessment of oxygen concentration>

The oxygen concentration in the obtained Au-Sn atomized powder was measured by the inert gas melting-infrared absorption method. Specifically, the sample was dissolved with a power of 5000 W, and the amount of gas generated at that time was analyzed.

<Yield Evaluation after Classification>

The yield after the classification is calculated based on the ratio of the amount of the Au-Sn atomized powder to the amount of the Au-Sn atomized powder obtained after the classification.

<Evaluation of average particle size>

The average particle diameter of the obtained Au-Sn atomized powder was measured by a laser diffraction method.

<Melting onset temperature>

The DSC (differential scanning calorimeter) was used to measure the external start temperature, and this temperature was set as the melting start temperature.

<Evaluation test of printability>

First, a substrate for evaluation was formed by electrolytic plating on a surface of a Kovar alloy plate (length 30 mm × width 20 mm) in a nickel plating layer having a thickness of 5 μm and a gold plating layer having a thickness of 0.1 μm.

Next, in order to form an Au-Sn alloy welding frame with a package size of 1610 (length: 1.6 mm × width: 1.0 mm), 100 through-grooves with a width of 60 μm were set, and a stencil mask for printing with a thickness of 15 μm was prepared mask).

Next, an Au-Sn alloy paste was printed on a substrate for evaluation using a mask for printing. Next, the stencil mask for printing was removed from the evaluation substrate.

Then, using an optical microscope, 100 frame-shaped Au-Sn alloy solder pastes (hereinafter referred to as "frame-shaped solders") formed on the substrate for evaluation were observed. paste"). A case where the number of the frame-shaped solder pastes having the same shape as the frame-shaped through grooves of the printing template mask was 90 or more was determined as A, and a case where the number was 80 or more and less than 90 was determined as B.

The frame-shaped solder paste having the same shape as the frame-shaped through groove refers to a frame-shaped solder paste in which the frame of the frame-shaped solder paste is not interrupted and the frame of the frame-shaped solder paste is not defective.

<Evaluation Test of Meltability>

The evaluation substrate used in the evaluation test for printability (specifically, the evaluation substrate with the mask for printing removed and 100 frame-shaped solder pastes formed) was performed by the following method.

First, under a nitrogen environment, 100 substrates for evaluation of the frame-shaped solder paste were formed by heating, and the frame-shaped solder paste was reflow-treated to prepare a solder layer.

At this time, the peak temperature was set to 320 ° C, and the reflow processing time was set to 3 minutes.

Then, using the above-mentioned optical microscope, to observe 100 frame-shaped solder pastes subjected to reflow treatment, if the number of frame-shaped solder pastes with melting residues is 2 or less, it is judged as A, and those with frame-shaped solder pastes with melting residues. When the number is 3 or more and 5 or less, it is judged as B, and when the number of frame-shaped solder pastes with residual melting is more than 5, it is judged as C. At this time, if there is unagglomerated powder, it is determined that there is melting residue.

<Summary of evaluation test results>

Referring to Table 1, it was confirmed that in order to reduce the melting temperature of the frame solder paste to Above 300 ° C, the atomized powder must contain more Sn than 37% and less than 55%.

In addition, in Examples 1 to 13, it was confirmed that the evaluation results of both printability and meltability were B or A.

When the oxygen concentration in the atomized powder is in the range of 50 to 1500 ppm, it can be confirmed that the melting property is B or A. When it exceeds 1500 ppm, the melting property is deteriorated (the evaluation becomes C) (Comparative Example 4).

When the oxygen concentration in the atomized powder was 47 ppm, it was confirmed that the yield of the classified atomized powder became lower than 80% (Comparative Example 3). In Examples 1 to 12, good results of the classified atomized powder yield of 80% were obtained.

The average particle diameter of the atomized powder was smaller than 1 μm, and it was confirmed that the meltability was slightly reduced as compared with the case where the average particle diameter was 1 μm or more (Example 4). When the average particle diameter exceeds 30 μm, the printability is reduced (Example 7). When the ratio of the flux was less than 5 wt%, it was confirmed that the evaluation result of printability and meltability was B (Example 8). In addition, even when the ratio of the flux was more than 40 wt%, it was confirmed that the evaluation results of printability and meltability were B (Examples 11 and 12).

[Industrial availability]

According to the Au-Sn alloy solder paste of the present invention, an Au-Sn alloy solder layer that can be used in a high temperature environment of 300 ° C. or higher can be obtained, and the cost of the Au-Sn alloy solder layer can be reduced. Therefore, the aforementioned Au-Sn alloy Solder paste can be used in high temperature environments such as power semiconductors for power regulation used in electric vehicles, or machine rooms.

Claims (7)

An Au-Sn alloy solder paste containing Au: Sn atomized powder composed of Sn: 38% by mass or more and 54% by mass or less, remaining as Au and unavoidable impurities, and the aforementioned Au-Sn atomized powder For the mixed flux, the above-mentioned Au-Sn atomized powder contains an oxygen concentration of 506 ppm or more and 1500 ppm or less. The Au-Sn alloy solder paste according to claim 1, wherein the average particle diameter of the aforementioned Au-Sn atomized powder is in the range of 1 to 30 μm. For example, the Au-Sn alloy solder paste of claim 1 or claim 2, wherein the content of the flux is 5 mass% or more and 40 mass% or less of the entire paste. A method for manufacturing an Au-Sn alloy solder layer is to use the Au-Sn alloy solder paste as claimed in claim 1 or claim 2 to constitute the solid phase line and liquid of the Au-Sn alloy of the Au-Sn alloy solder paste. The temperature between the phase lines causes it to melt. An Au-Sn alloy solder layer is obtained by a method for manufacturing an Au-Sn alloy solder layer as claimed in claim 4. A method for manufacturing an Au-Sn alloy solder layer is to form an Au-Sn alloy solder paste as claimed in claim 3 to constitute a solid-phase line and a liquidus line of the Au-Sn alloy solder paste of the Au-Sn alloy solder paste The temperature makes it melt. An Au-Sn alloy solder layer is obtained by a method for manufacturing an Au-Sn alloy solder layer as claimed in claim 6.