TW201701985A - Au-Sn-Ag solder paste and electronic components bonded or sealed using the Au-Sn-Ag solder paste - Google Patents

Abstract

An object of the present invention is to provide a solidus temperature of about 300 ° C or less suitable for use in assembly of an electronic component, etc., which is excellent in oxidation resistance and wettability, and excellent in workability, stress relaxation, and reliability, and does not contain Pb. Further, compared with the Au-based solder alloy such as the Au-Sn-based flux alloy, the high-temperature solder paste composed of the Au-Sn-Ag alloy is significantly lower in price. The solution of the present invention is a Pb-free Au-Sn-Ag solder paste which is a solder paste obtained by mixing a flux alloy powder and a flux, characterized in that the flux alloy powder is set to be a total of When it is 100% by mass, Sn is contained in an amount of 27.5% by mass or more and less than 33.0% by mass, and Ag is contained in an amount of 8.0% by mass or more and 14.5% by mass or less. The remainder is composed of Au in addition to elements which are inevitably contained in the production.

Description

Au-Sn-Ag solder paste and electronic components bonded or sealed using the Au-Sn-Ag solder paste

The present invention relates to a Pb-free solder paste for high temperature use. In particular, an Au-Sn-Ag solder paste obtained by mixing an Au-Sn-Ag flux alloy containing Au as a main component and a flux, and an electronic component bonded or sealed using the solder paste .

In recent years, the regulation of chemical substances that are harmful to the environment has become more and more stringent. This control is not limited to the flux material used for the purpose of bonding electronic parts or the like to the substrate. In the flux material, lead has been used as a main component since ancient times, but it has become a substance to be controlled in the Rohs directive. Therefore, development of a lead (Pb)-free solder material (hereinafter referred to as a lead-free solder material or a lead-free solder material) is prevalent.

The flux material used when bonding an electronic component to a substrate is roughly classified into a high temperature (about 260 ° C to 400 ° C) and a medium low temperature (about 140 ° C to 230 ° C) depending on the use limit temperature. Among the high-temperature use and the medium-low temperature, the lead-free material for the medium and low temperature is practically used for the lead-free use of Sn as a main component.

For example, Patent Document 1 describes "a lead-free solder alloy composition containing Sn as a main component and containing Ag to 1.0 to 4.0% by weight, Cu to 2.0% by weight or less, and Ni to 1.0% by weight or less, P. It is 0.2% by weight or less."

Further, Patent Document 2 describes "a lead-free solder containing an alloy of 0.5 to 3.5% by weight of Ag and 0.5 to 2.0% by weight of Cu and having the remainder consisting of Sn".

On the other hand, various developments have been made regarding the Pb-free flux material for high temperature. For example, Patent Document 3 discloses "a Bi/Ag brazing material having a melting temperature of 350 to 500 ° C containing 30 to 80 at% of Bi".

Further, Patent Document 4 discloses "a flux alloy in which a ternary eutectic alloy is added to a eutectic alloy containing Bi, and an element is further added". Although the flux alloy is a multi-component flux alloy of a quaternary system or more, it shows a reduction in the liquidus temperature and a variation in the variation.

As a Pb-free flux material for high-priced high-temperature, Au-Sn alloy or Au-Ge alloy has been used in crystal devices, SAW filters, and MEMS.

Au-20% by mass Sn (meaning that 80% by mass of Au and 20% by mass of Sn are formed, the same applies hereinafter) is a composition of a eutectic point, and its melting point is 280 °C. On the other hand, the composition of the Au-12.5 mass% Ge eutectic point has a melting point of 356 °C.

The Au-Sn alloy is distinguished from the use of the Au-Ge alloy by the difference in melting point. That is, although it is used at high temperatures, it is used at lower temperatures. In the case of bonding of the parts, an Au-Sn alloy is used. Also, an Au-Ge alloy is used at a higher temperature. Further, the Au-based flux alloy is very hard compared to the Pb-based flux alloy or the Sn-based flux alloy. In particular, since the Au-Ge alloy is a metal-like metal, it is very difficult to process it into a sheet shape or the like. Therefore, productivity or yield is poor, which is a cause of rising costs.

The Au-Sn alloy is also difficult to process even if it does not reach the level of the Au-Ge alloy, and is inferior in productivity or yield for processing of a preform material or the like. That is to say, although Au-20% by mass Sn is a composition of a eutectic point, it is composed of an intermetallic compound. Therefore, dislocations are difficult to migrate and are difficult to be deformed, and if they are rolled or perforated by pressurization, cracks or burrs are likely to occur.

Of course, in the case of the Au-based flux alloy, the material cost is higher than that of other flux materials. The Au-Sn alloy is used for melting or processing properties, and is often used as a sealing device for crystal devices requiring high reliability. Further, in order to use the Au-Sn alloy at a low cost and more easily, for example, an Au-based flux alloy as described below has been developed.

Patent Document 5 discloses "a brazing material characterized in that a composition ratio (Au (wt%), Ag (wt%), Sn (wt%)) is a ternary composition of Au, Ag, and Sn. In the figure, it is located at point A1 (41.8, 7.6, 50.5), point A2 (62.6, 3.4, 34.0), point A3 (75.7, 3.2, 21.1), The area surrounded by points A4 (53.6, 22.1, 24.3) and points A5 (30.3, 33.2, 36.6).

This document aims to "provide a low-melting point and easy operation, excellent strength and adhesion, and a low-cost brazing material and a piezoelectric device".

Patent Document 6 discloses "a high-temperature lead-free solder alloy for melt sealing, which is characterized in that it is composed of Ag 2 to 12% by mass, Au 40 to 55% by mass, and the balance being Sn."

In this document, "the purpose is to provide a lead-free high-temperature solder having a lower addition amount of Au than the conventional Au-Sn eutectic alloy and having a solidus temperature of 270 ° C or higher." In addition, the purpose of "providing a joint in which the joint portion between the container main body and the lid member is excellent in heat-resistant cycle or mechanical strength" is intended.

Further, Patent Document 7 discloses "a hard solder joint lead frame characterized in that, at the tip end of the pin of the lead frame, Au 20-50 wt% and Ge 10-20 wt% or Sn 20~ are added to Ag. 40% by weight of brazing material."

This document "provides a hard soldering of a brazing material which has a low melting point, does not embrittle the lead frame of the Fe-Ni alloy, stabilizes the bonding strength with a moderate solder flow, and does not reduce the corrosion resistance of the lead frame. The lead frame is for the purpose.

Further, Patent Document 8 discloses "an Au-Sn alloy solder paste characterized in that (A) contains 55 to 77 parts by mass of Sn in 100 parts by mass of the total of Au and Sn. The Au-Sn mixed powder and the (B) flux, the component (A) contains (A1) an Au-Sn alloy solder powder containing 18 to 23.5 parts by mass of Sn in 100 parts by mass of the total of Au and Sn, and (A2) The Au-Sn alloy solder powder containing 88 to 92 parts by mass of Sn in total of 100 parts by mass of Au and Sn.

This document is "providing an Au-Sn solder paste capable of bonding at a low temperature of 280 ° C or lower, and the Au-Sn alloy solder formed by the paste is subjected to secondary reflow by Sn-Ag-based lead-free solder. (second reflow) does not melt; it can be easily bonded to an LED element, and it is not melted at the time of secondary reflow, and an Au-Sn alloy solder paste having a reduced material cost can be obtained by low Au.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 11-77366

[Patent Document 2] Japanese Patent Laid-Open No. Hei 8-215880

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2002-160089

[Patent Document 4] Japanese Laid-Open Patent Publication No. 2006-167790

[Patent Document 5] Japanese Patent Laid-Open Publication No. 2008-155221

[Patent Document 6] Japanese Patent No. 4305511

[Patent Document 7] Japanese Patent No. 2670098

[Patent Document 8] Japanese Laid-Open Patent Publication No. 2011-167761

Although the Pb-free flux material for high temperature has been developed in various organs in addition to the above-mentioned patent documents, a low-cost and versatile flux material has not yet been found. In other words, in general, a material having a low heat resistance temperature such as a thermoplastic resin or a thermosetting resin is often used for an electronic component or a substrate. Therefore, it is necessary to set the working temperature to less than 400 ° C, preferably 370 ° C or less. However, in the case of using, for example, a Bi/Ag alloy disclosed in Patent Document 3 as a brazing material, the liquidus temperature is as high as 400 to 700 °C. Therefore, the working temperature at the time of bonding also becomes 400 to 700 ° C or more, and exceeds the heat resistant temperature of the joined electronic component or substrate.

The Au-Sn-based flux material or the Au-Ge-based flux material which is put into practical use is used for welding of a crystal device, a SAW filter, and a MEMS, etc., which are particularly required to have high reliability. However, since the Au-based flux material is used in a large amount of Au, it is very expensive compared to the commonly used Pb-based flux material or Sn-based flux material, and it cannot be said that it is widely used. In addition, the Au-based flux alloy is very hard and difficult to process. Therefore, for example, it is necessary to take time to roll into a sheet shape, or to use a special material which is less likely to cause flaws on the roll, and it is costly. Further, at the time of press molding, cracks or burrs are likely to occur due to the hard and brittle nature of the Au-based flux alloy. Thus, the yield is significantly lower compared to other flux alloys. In the case of processing into a line shape, there are similar serious problems. Even if an extruder having a very high pressure is used, the extrusion speed is slow due to hardness, so that only about one-hundredth of the Pb-based flux alloy is productive. .

In addition to the above problems, the Au-based flux material has various problems depending on the use, the shape at the time of use, and the like. In order to solve such a problem, a technique such as that shown in Patent Document 5 has been disclosed. That is, Patent Document 5 describes a brazing material and a piezoelectric device which are provided with a low melting point and which are easy to handle, excellent in strength and adhesion, and low in cost. Further, it is also stated that by limiting the composition range of each of Au, Sn, and Ag, the Au content is more reduced than in the past, and equivalent characteristics as a sealing material can be obtained.

However, the reason for improving the strength or adhesion of the Au-Sn alloy by adding Ag is not described. Further, the reason why the same characteristics as the sealing material (which can be interpreted as equivalent to the Au-Ge alloy) can be obtained is not described. That is, the reason why the same characteristics as those of the Au-Ge eutectic alloy or the Au-Sn eutectic alloy can be obtained, for example, the reliability is not described at all, and the technical basis of the invention is not known. In addition, for the reasons stated below, it is presumed that reliability, etc., is superior to Au-Ge eutectic alloy or Au-Sn eutectic alloy, and even as disclosed in Patent Document 5 The same characteristics as those of the Au-Ge eutectic alloy or the Au-Sn eutectic alloy are not obtained in all regions of the composition range. Therefore, it is presumed that the technique of Patent Document 5 cannot be implemented.

Hereinafter, the reason why the technique of Patent Document 5 is considered impossible is explained. Patent Document 5 sets the composition ratio (Au (wt%), Ag (wt%), and Sn (wt%)) in the ternary composition diagram of Au, Ag, and Sn, and is located at point A1 (41.8, 7.6, 50.5). ), The composition of the area surrounded by points A2 (62.6, 3.4, 34.0), points A3 (75.7, 3.2, 21.1), points A4 (53.6, 22.1, 24.3), and points A5 (30.3, 33.2, 36.6). However, this area is too broad, and it is theoretically impossible to obtain the same purpose in all areas of such a wide range of composition. For example, the difference in the content of the point A3 from the point A5 is 45.4% by mass. In this way, it is clear that there is a large difference in the Au content, but the similar characteristics at point A3 and point A5 are simply unimaginable. As long as the composition ratios of Au, Sn, and Ag are different, the intermetallic compounds formed are different, and the liquidus temperature or the solidus temperature is also greatly different. If the difference in Au content which is most difficult to oxidize reaches 45.4% by mass, of course, the wettability also largely changes. The type or amount of the intermetallic compound formed at the time of joining is also greatly different, and it is not possible to achieve excellent characteristics similar to workability and stress relaxation property in a wide range as shown in Patent Document 5.

In the brazing material described in Patent Document 6, since Ag is 2 to 12% by mass and Au is 40 to 55% by mass, the remaining portion of Sn is 33 to 58% by mass. However, if the content of Sn is large as described above, oxidation may occur and the wettability or the like may not be sufficiently obtained. Since Au-20 mass% Sn can be used practically without problems, if Sn is 30 mass%, there is a possibility that wettability is ensured. On the other hand, it is estimated that if Sn exceeds 40% by mass, it is difficult to ensure the wettability. Moreover, since there is no eutectic alloy in the composition range, the crystal grains are coarse, or the difference between the liquidus temperature and the solidus temperature is large, and the melting separation occurs at the time of joining. For example, it is difficult to obtain sufficient joint reliability.

Further, the content of the brazing material Au in Patent Document 7 is at most 50% by mass, and the effect of reducing the Au raw material is extremely large. Since the content of Sn is also 40% by mass or less (or less than 40% by mass), there is a possibility that a certain degree of wettability can be secured. However, the object of the invention is to avoid embrittlement of the lead frame made of Fe-Ni alloy, or to stabilize the joint strength with a moderate brazing flow, and to avoid a decrease in corrosion resistance of the lead frame. It is difficult to imagine that the brazing material shown in Patent Document 7 which is invented by such a viewpoint satisfies the characteristics required for joining of semiconductor elements, for example, stress relaxation by expansion and contraction due to heat. Further, since there is no eutectic alloy in this composition range, the crystal grains are coarse, or the difference between the liquidus temperature and the solidus temperature is large, and melting and separation occur at the time of joining, and it can be said that it is difficult to obtain sufficient bonding. reliability. Further, it is also difficult to imagine that an alloy suitable for a metallization layer of a semiconductor element or a bonding substrate of Cu or the like is formed as a brazing material for use in an Fe-Ni alloy. In view of such a viewpoint, it is understood that the brazing material is not suitable for bonding with a crystal device or the like.

Patent Document 8 describes a low Au and low cost Au-Sn solder paste. In this way, low cost is an important issue in the Au-based flux materials, and it is very important for the market demand to be technologically advanced. However, the technique described in Patent Document 8 can be said to have a very large problem.

That is, the flux alloy powder is used by combining the Au-Sn alloy composed of two kinds of compositions, but the flux alloy powder is simply mixed. The combination does not change the melting point of the alloy powder of the individual composition. Therefore, the low melting point phase of (A2) (Sn = about 90%) exists, and it is difficult to use it as a solder paste for high temperature.

Patent Document 8 describes that the Au-Sn alloy solder paste containing the component (A1) and the component (A2) of the present invention is a mechanism for bonding a semiconductor element such as an LED to a substrate, but it is not clear. By heating at 260 to 280 ° C, first, the component (A2) is melted, and the adherend such as a semiconductor element such as an LED or a substrate is wetted, and then the component (A2) and the component after melting ( The diffusion between A1) forms the Au-Sn alloy flux mixed with the component (A2) and the component (A1); according to this mechanism, bonding to the LED element can be easily achieved by heating at 280 ° C or lower, and An Au-Sn alloy solder paste of an Au-Sn alloy flux having a solidus temperature of 250 ° C or higher can be formed after bonding.

However, it is assumed that in the case where the Sn-rich (A2) component is melted and diffused and bonded to the component (A1) close to the Au-Sn eutectic point, the Au-Sn alloy of the joint portion largely deviates from the eutectic point. composition. In this case, it is presumed that the structure is not a layered structure but a very hard and brittle phase, and there is no stress relaxation property, and the joint reliability is also extremely low. Further, there is no guarantee that the diffusion will occur uniformly, and the possibility of uniformly melting and diffusing during the mixing of the fine flux alloy powder and the flux can be said to be infinitely close to zero. Therefore, it is understood that the Au content is lowered to reduce the cost of the solder paste, but it is not a practical technique for the above reasons.

Au-based flux materials include solder paste and have the above There are various issues that should be improved. The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a high-temperature Au-character which is excellent in various characteristics which can be sufficiently used in joining, such as a crystal device, a SAW filter, or a MEMS. The Sn-Ag-based solder paste is particularly a Pb-free solder paste which is excellent in processability, stress relaxation property, and bonding reliability, and has excellent wettability at low cost.

In order to achieve the above object, the Pb-free Au-Sn-Ag solder paste of the present invention is obtained by mixing a flux alloy powder and a flux, and the flux alloy powder is set to 100% by mass in total. The content of Sn is 27.5% by mass or more and less than 33.0% by mass, and the content of Ag is 8.0% by mass or more and 14.5% by mass or less. The remainder is composed of Au in addition to elements which are inevitably contained in the production.

Further, in the Pb-free Au-Sn-Ag solder paste of the present invention, the flux contains rosin.

Further, the Pb-free Au-Sn-Ag solder paste of the present invention contains Sn in an amount of 29.0% by mass to 32.0% by mass, and Ag in an amount of 10.0% by mass or more and 14.0% by mass or less, and the remainder is inevitably contained in addition to production. In addition to the elements, it consists of Au.

Further, in the Pb-free Au-Sn-Ag solder paste of the present invention, at least a part of the metal structure of the flux alloy powder is a layered structure.

Further, in the Pb-free Au-Sn-Ag solder paste of the present invention, the metal structure of the flux alloy powder is a layered structure, and the ratio thereof is 90. More than 5% by volume.

Moreover, the present invention provides a Si semiconductor element bonded body which is bonded by using the above-mentioned Pb-free Au-Sn-Ag solder paste.

Further, the present invention provides a crystal vibrating sub-sealing element which is sealed by using the above-mentioned Pb-free Au-Sn-Ag solder paste.

According to the present invention, it is possible to provide a flux material which is used at a site requiring a very high reliability such as a crystal device, a SAW filter, and a MEMS, at a lower cost than the conventional Au-based flux material.

Further, since the flux alloy powder of the present invention is based on a eutectic metal, it can provide a layered structure having a fine metal structure, and has excellent flexibility, excellent stress relaxation property, and excellent joint reliability, and is mixed with a flux. An Au-based solder paste which is excellent in wettability and bondability by forming a solder paste. Therefore, the industrial contribution is extremely high.

1‧‧‧Cu substrate

2‧‧‧Ni layer

3‧‧‧Solder alloy (solder paste)

4‧‧‧Si chip

5‧‧‧Crystal Vibrators

6‧‧‧ Conductive adhesive

7‧‧‧ Terminal

8‧‧‧ Sealing cover

9‧‧‧Seal container

[Fig. 1] is a state diagram of the Au-Sn-Ag ternary system.

[Fig. 2] A photograph showing the metal structure of the Au-based flux alloy.

[Fig. 3] is a cross-sectional view schematically showing an embodiment of a wettability test in which a flux material is welded to a Cu substrate having a Ni layer.

[Fig. 4] is a side view schematically showing the aspect ratio measurement state of the wettability test in Fig. 3.

[Fig. 5] is a cross-sectional view schematically showing a bonded body in which a Si wafer is bonded to a Cu substrate having a Ni layer using a flux material.

[Fig. 6] is a cross-sectional view schematically showing a crystal vibrating sub-package.

As a result of repeated efforts by the present inventors, it has been found that in the solder paste obtained by mixing Au-Sn-Ag flux alloy powder and flux in the vicinity of the composition of the ternary eutectic point of Au and Sn and Ag. If the specific flux alloy composition range is satisfied, the following characteristics or effects are obtained, and thus the present invention has been completed. First, it is softer than the Au-Sn alloy, and it is excellent in workability and stress relaxation property, and a part of expensive Au is replaced by Sn and Ag, whereby an Au-based alloy powder in which the Au content is greatly reduced and the cost of the flux alloy is lowered can be obtained. . Further, by soldering with a flux to form a solder paste, the bonding material having excellent shape freedom, wettability, bonding reliability, and the like is obtained.

Hereinafter, the flux alloy powder and the flux in the Au-Sn-Ag-based solder paste of the present invention will be described in detail. First, the composition of the Au-Sn-Ag-based flux alloy of the present invention is characterized in that it contains Sn of 27.5% by mass or more and less than 33.0% by mass, and contains Ag of 8.0% by mass or more and 14.5% by mass or less, and the remainder is manufactured. In addition to the elements that are inevitably included, it consists of Au.

The flux alloy of the present invention is a very high cost Au-based welding The cost of the alloy is reduced, and the composition of the ternary eutectic is formed by containing a soft metal Ag in order to hold excellent workability or stress relaxation, thereby making the crystal finer (see 1 picture). That is, the composition of the Au-Sn-Ag ternary eutectic point is Au=57.2% by mass, Sn=30.8% by mass, and Ag=12.0% by mass (in terms of at%, the system Au=43.9 at%, Sn=39.3). At%, Ag = 16.8 at%) as a basic composition. As a result, the crystal structure can be made into a layered structure, and workability, stress relaxation, and the like are remarkably improved, and Sn and Ag are contained in a large amount, so that the Au content can be reduced, and a large cost reduction effect can be obtained. Further, by containing a large amount of Ag which is highly reactive and difficult to oxidize, good wettability and bondability can be obtained. Hereinafter, the elements necessary for the flux alloy used in the present invention will be described in further detail.

<Au>

Au is used as a main component of the flux alloy of the present invention, and is of course an essential element. Since the Au system is very difficult to oxidize, it is most suitable as a component of a flux material for bonding or sealing of electronic parts requiring high reliability on the characteristic surface. Therefore, an Au-based flux material is often used as a seal for a crystal device or a SAW filter. The flux alloy used in the present invention also uses Au as a basis to provide a flux material belonging to the technical field requiring such high reliability. However, since Au is a very expensive metal, it is preferable to be as low as possible for the user. Therefore, it is hardly used in electronic parts requiring a high level of reliability. Characteristics of wettability or jointability of the flux alloy used in the present invention The surface was equal to or higher than the Au-20% by mass Sn alloy or the Au-12.5% by mass of the Ge solder alloy. In addition, in order to improve the flexibility and the workability, in addition to reducing the Au content and reducing the cost, it is an alloy in the vicinity of the composition of the ternary eutectic point of the Au-Sn-Ag system.

<Sn>

Sn is an essential element used in the flux alloy of the present invention and is an element constituting the base. The Au-Sn solder alloy is usually used in the vicinity of the eutectic point, that is, the composition in the vicinity of Au-20% by mass. Thereby, the solidus temperature is 280 ° C, and the crystal is refined to obtain a softer one. However, although it is a eutectic alloy, the Au-20% by mass Sn alloy is hard and brittle because it is composed of an Au ₁ Sn ₁ intermetallic compound and an Au ₅ Sn ₁ intermetallic compound. Therefore, it is difficult to process, for example, when it is processed into a sheet by calendering, it can be thinned only a little. Therefore, the productivity is poor, or a plurality of cracks are generated at a time delay, and the yield is poor, but the hard and brittle nature of the intermetallic compound generally cannot be changed. Although it is such a hard and brittle material, it is used in applications requiring high reliability because it is not easily oxidized and has excellent wettability and reliability.

The flux alloy used in the present invention is composed of an Au ₁ Sn ₁ intermetallic compound and a ruthenium phase (ξ phase Au-Sn-Ag intermetallic compound, the ratio of which is expressed in at% as Au:Sn:Ag=30.1: 16.1:53.8; Reference: Ternary Alloys, AComprehensive Compendium of Evaluated Constitutional Data and Phase Diagrams, Edited by G. Petzow and Effenberg, VCH), and based on the composition near the eutectic point. Since the ruthenium phase is more flexible and forms a layered structure as a basic component in the vicinity of the eutectic point, the flux alloy used in the present invention is excellent in workability and stress relaxation property. Further, the melting point can also be lowered, and the eutectic point temperature of 370 ° C which does not greatly differ from the eutectic point temperature of the Au-Ge alloy. It is also one of the advantages of the flux alloy used in the present invention to have an appropriate melting point as such a high-temperature flux alloy.

The content of Sn is not less than 33.0% by mass of 27.5 mass% or more. When it is less than 27.5% by mass, the crystal grains become large, and the effects of flexibility, workability, and the like cannot be sufficiently exhibited. Further, the difference between the liquidus temperature and the solidus temperature is excessively large to cause a melt separation phenomenon or the like. Furthermore, since the Au content is also likely to increase, the cost reduction effect is also limited. On the other hand, when the content of Sn is 33.0% by mass or more, the composition of the eutectic point is too deviated, and the crystal grain is coarsened, and the difference between the liquidus temperature and the solidus temperature is increased. In addition, if the content of Sn is too large, the Au-Sn-Ag alloy becomes easily oxidized, and the wettability of the characteristics of the Au-based flux material is lost, and thus it is difficult to obtain high joint reliability.

When the Sn content is 29.0% by mass or more and 32.0% by mass or less, the composition of the eutectic point is closer to the eutectic point, and the effect of refining the crystal grains is obtained, and the phenomenon of melting and separation is less likely to occur, which is preferable.

<Ag>

Ag is an essential element in the flux alloy used in the present invention, It is an indispensable element of the alloy of ternary eutectic. By forming a composition in the vicinity of the ternary eutectic point of Au-Sn-Ag, first, excellent flexibility, workability, stress relaxation property, suitable melting point, and the like can be obtained. Further, since the Au content can be greatly reduced, a substantial cost reduction can be achieved. The addition of Ag also has the effect of improving the wettability. In other words, by adding Ag, the reactivity of the Au-Sn-Ag alloy with Cu, Ni, or the like which is used for the uppermost surface of the substrate or the like is improved, and the wettability can be improved. Of course, it is self-evident that the reactivity with the Ag or Au metallization layer which is often used for the bonding surface of the semiconductor element is excellent.

In this manner, the content of Ag exhibiting an excellent effect is 8.0% by mass or more and 14.5% by mass or less. When the content of Ag is less than 8.0% by mass, the composition of the eutectic point is excessively deviated, and the liquidus temperature becomes too high, or the crystal grains are coarsened, and it becomes difficult to obtain good bonding. On the other hand, when the content of Ag exceeds 14.5% by mass, the liquidus temperature also becomes high, causing a phenomenon of melting separation or a problem of coarsening of crystal grains.

When the content of Ag is from 10.0% by mass to 14.0% by mass, the composition of the eutectic point is approached, and the effect of containing Ag is further exhibited, which is preferable.

<Metal composition>

In the present invention, at least a part of the metal structure of the Au-Sn-Ag-based flux alloy is a layered structure, and the ratio thereof is 90% by volume or more. The layered structure refers to the stripe-like tissue with a spacing of 0.1 μm. Metal structure of 2.0 μm or less. For example, the portion surrounded by the square in Fig. 2 is a layered structure as defined in the present invention. In this manner, by forming the flux alloy structure after bonding into a fine layered structure, cracks are less likely to occur and are less likely to progress, so that higher joint reliability can be obtained.

<flux>

The type of the flux used in the solder paste of the present invention is not particularly limited, and for example, a resin system, an inorganic chloride system, an organic halide system or the like can be used. Here, the most common flux, that is, the use of rosin as a base material and in which an active agent and a solvent are added thereto will be described.

In the case where the total amount of the flux is 100% by mass, the rosin of the base material is preferably 20 to 30% by mass, the active agent is 0.2 to 1% by mass, and the solvent is 70 to 80. Blending is carried out in a manner of about % by mass. Thereby, a solder paste having good wettability and bonding property can be obtained. Moreover, it is possible to use a solder paste which is easier to use by containing a thixotropic agent and adjusting thixotropy. As the rosin as a base material, for example, natural undenatured rosin such as wood resin rosin, gum rosin, tall oil rosin, or rosin ester, hydrogenated rosin, rosin denatured resin, or the like may be used. Denatured rosin such as polymerized rosin.

The solvent may be acetone, pentylbenzene, n-amine alcohol, benzene, carbon tetrachloride, methanol, ethanol, isopropanol, n-butanol, isobutanol, methyl ethyl ketone, toluene, turpentine, two Toluene, cyclohexane, ethylene glycol monophenyl ether, ethylene glycol monobutyl ether, carbon tetrachloride, trichloroethane, alkane diol, Alkylene glycol, butanediol, triethylene glycol, tetraethylene glycol, tetradecane, and the like.

As the active agent, phosphoric acid, sodium chloride, ammonium chloride, zinc chloride, stannous chloride, aniline hydrochloride, hydrazine hydrochloride, cetylpyridinium bromide, phenylhydrazine hydrochloride, tetrachlorochloride can be used. Naphthalene, methylhydrazine hydrochloride, methylamine hydrochloride, ethylamine hydrochloride, diethylamine hydrochloride, butylamine hydrochloride, benzoic acid, stearic acid, lactic acid, citric acid, Oxalic acid, succinic acid, adipic acid, sebacic acid, triethanolamine, diphenylguanidine, diphenylguanidine HBr, erythritol, xylitol, sorbitol, ribitol, and the like.

Moreover, it is possible to use a solder paste which is easier to use by containing a thixotropic agent and adjusting thixotropy. As the thixotropic agent, for example, decylamine stearate, decyl oleate, guanyl erucamide can be used.

Among these solvents and active agents, a suitable flux is obtained by selecting a substance which meets the purpose and appropriately adjusting the amount of the additives. For example, when the oxide film on the joint surface of the flux alloy or the substrate is strong, it is preferable to add a rosin or an active agent in a large amount, and adjust the viscosity or fluidity with a solvent.

The solder paste obtained by mixing the flux alloy and the flux has excellent wettability due to the action of the flux. Further, the flux alloy can be used in a powder form which can be easily processed without being processed into a sheet shape or the like which is difficult to process.

Then, by using the high-temperature Pb-free solder paste of the present invention for bonding the electronic component to the substrate, it is possible to provide durability reliability even under severe conditions such as use in a thermal cycle environment. high Substrate for electronic parts. Therefore, the electronic component substrate is mounted on a power semiconductor device such as a thyristor or an inverter, and is used in various control devices such as automobiles and solar cells, which are used under severe conditions. The reliability of these various devices can be further improved. Moreover, the solder paste of the present invention which is excellent in the above is very suitable for sealing a crystal vibrator, and can be used for sealing a crystal vibrator package as shown in Fig. 6, for example.

[Examples]

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

First, as the raw material, Au, Sn, and Ag having a purity of 99.99% by mass or more, and Ge for the Au-Ge alloy for comparison are prepared. In the case of a large-sized sheet or a bulk material, the alloy is cut and pulverized to a size of 3 mm square or less in order to prevent the composition from being uneven due to the composition of the sampled place. Next, a specific amount is taken from these raw materials and placed in a graphite crucible for a high-frequency dissolving furnace.

The crucible after the raw material is charged is placed in a high-frequency dissolving furnace, and in order to suppress oxidation, nitrogen is supplied at a flow rate of 0.7 L/min or more per 1 kg of the raw material. In this state, the power source of the dissolution furnace is turned on to heat and melt the raw material. If the metal begins to melt, it is thoroughly stirred by a mixing rod to uniformly mix to avoid localized structural variations. After confirming that it was sufficiently melted, the high-frequency power source was turned off, and it was quickly taken out from the crucible, and the molten liquid in the crucible was poured into the mold of the flux master alloy. In the mold, a cylinder with an inner diameter of 140 mm is used. The shape is used for atomization in the gas phase for producing a powder.

In this manner, the flux master alloys of the samples 1 to 16 were prepared in the same manner as described above except that the mixing ratio of the raw materials was changed. For each of the flux master alloys of the samples 1 to 16, the composition analysis was carried out using an ICP emission spectroscopic analyzer (SHIMAZU S-8100). The analysis results obtained are shown in Table 1 below.

<Method for Producing Flux Alloy Powder>

The method for producing the alloy powder for solder paste is not particularly limited, but is generally produced by an atomization method. The atomization method is in the gas phase or in the liquid phase. In the middle, it is sufficient to select the particle size or particle size distribution of the target flux alloy powder. In the present embodiment, a flux alloy powder is produced by a gas phase atomization method which is high in productivity and capable of producing a fine powder.

Specifically, atomization in the gas phase is performed by a high-frequency dissolution method using a gas phase atomization device (manufactured by Nisshin Technik Co., Ltd.). First, the flux master alloys of the above samples 1 to 16 were processed into powders in batches. Specifically, the sample of the master alloy is placed in a high-frequency dissolving crucible, and the upper lid is sealed, and then nitrogen is refluxed to be substantially oxygen-free. The sample discharge port or the recovery container portion is also subjected to nitrogen reflux to be in an anaerobic state.

In this state, the switch of the high-frequency power source is turned on, and the flux master alloy is heated to 450 ° C or higher, and the molten flux master alloy is pressurized with nitrogen to be atomized while the alloy is sufficiently melted. The flux alloy powder produced in this manner is recovered in a container, and is sufficiently cooled in the container and taken out into the atmosphere. The reason why it is sufficiently cooled and taken out is that if it is taken out at a high temperature, it may cause a fire, or the flux alloy powder may be oxidized, and the effect of wettability or the like may be lowered.

Each of the powders produced in this manner was classified by a sieve having a pore size of 20 μm and 50 μm, respectively, to obtain an alloy powder sample having a diameter of 20 to 50 μm.

<Calculation of the proportion of the layered structure of the flux alloy powder>

The proportion of the layered structure of the flux alloy powder was measured for the alloy powder of the samples 1 to 10 of the examples of the present invention. Determination of the proportion of layered tissue The flux alloy powder is embedded in a resin, and the cross section of the flux alloy powder is exposed by polishing, and the ratio of the cross-sectional area of the layered structure in the range of 10 μm × 10 μm is measured at any ten places, and the average value of 10 points is used. The value calculated by the 3/2th power is taken as the volume %. The results are shown in Table 1.

<Method of manufacturing solder paste>

Next, the flux alloy powders respectively prepared from the flux master alloy samples were mixed with the flux to prepare a solder paste. In the present invention, the flux is not particularly limited, but in the present embodiment, the flux is polymerized rosin as a base material, and diethylamine hydrochloride ((C ₂ H ₅ ) ₂ NH‧HCl) is used as the flux. The active agent and ethanol are used as solvents. The respective contents were such that the flux was 100% by mass, the polymerized rosin was 23% by mass, the diethylamine hydrochloride was 0.3% by mass, and the remainder was made into ethanol. The flux and the flux alloy powder were blended at a ratio of 9.2% by mass of the flux and 98.8% by mass of the flux alloy powder, and mixed by a small mixer to prepare a solder paste.

In this manner, solder pastes of Samples 1 to 16 were prepared from the flux master alloys of Samples 1 to 16 shown in Table 1 above. Next, the evaluations shown below were performed for each of the solder pastes of the samples 1 to 16. That is, the melting residue of the flux alloy powder was confirmed as the wetness evaluation 1, and the aspect ratio was measured as the wettability evaluation 2, and the measurement of the void ratio was performed as the evaluation of the bonding property 1, and the shear strength was measured. Evaluation of bondability 2, thermal cycle test was performed as an evaluation of reliability.

<Evaluation of wetness 1 (confirmation of melting residue of flux alloy powder)>

As evaluation of the wettability 1, as shown in FIG. 3, a mask is used on the Cu substrate 1 (thickness: about 0.70 mm) having a Ni layer 2 (layer thickness: about 2.5 μm) on the surface, and the solder paste 3 is used. It was printed in a shape having a diameter of 2.0 mm and a thickness of 150 μm. Then, the substrate on which the solder paste 3 was printed was heated and joined as follows to form a bonded body, and it was confirmed by an optical microscope whether or not the molten alloy powder was not melted.

First, the wetness tester (device name: environmentally controlled wetness tester) was started, and the heated heater was partially covered with a two-layer lid, and nitrogen was allowed to flow from the four parts around the heater section (nitrogen flow rate: 12 L/s each) Minute). Thereafter, the heater set temperature was set to be 50 ° C higher than the melting point of each sample to perform heating. After the heater temperature was stabilized at the set temperature, the Cu substrate coated with the solder paste was placed in the heater portion and heated for 25 seconds. Then, the Cu substrate is picked up from the heater portion, and temporarily moved to a place where the nitrogen atmosphere is maintained on the side thereof to be cooled. After sufficient cooling, it was taken out in the atmosphere. In order to confirm the melting residue of the flux alloy powder, the cleaning of the joined body is not performed at all.

Each of the joined bodies produced in this manner was confirmed by optical microscopy from the direction perpendicular to the surface on which the flux alloy 3 was bonded, and from the side of the surface on which the flux alloy 3 was bonded, to the absence of melting of the flux alloy powder. The case where the flux alloy powder remains is referred to as "x", and the case where the flux alloy powder remains and the flux alloy powder is melted and the flux alloy having a perfect metallic luster is infiltrated into the substrate is referred to as "○".

<Evaluation of wettability 2 (measurement of aspect ratio)>

As the evaluation of the wettability 2, a joined body which is the same as the bonded body produced at the time of confirming the melting residue of the flux alloy powder is prepared, the bonded body is washed with alcohol, and then vacuum dried, and the wetting is measured. The aspect ratio of the solder alloy of the substrate. With respect to the obtained bonded body, that is, as shown in FIG. 3, the bonded body of the solder alloy 3 was bonded to the Ni layer 2 of the Cu substrate 1, and the aspect ratio of the wetted solder alloy 3 was determined.

Specifically, the aspect ratio X1 of the largest solder wett length shown in FIG. 4 and the short diameter X2 of the minimum solder wettance length were measured, and the aspect ratio was calculated by the following calculation formula 1. The closer the aspect ratio of Equation 1 is to 1, the more the substrate will be infiltrated into a circular shape, and the wettability can be judged to be good. As it becomes larger than 1, the infiltrated shape gradually deviates from the circular shape, and a difference occurs in the moving distance of the molten solder alloy, the reaction becomes uneven, and the thickness or composition of the alloy layer becomes large, resulting in inhomogeneous and good bonding. . When a large number of flux alloys are expanded in a certain direction, a portion where the amount of the flux alloy is excessive and a portion having no amount of the flux alloy may be generated, and the joint may be defective or may not be joined due to the situation. The measurement results of the aspect ratio of the joined body are shown in Table 2.

[Calculation 1] Aspect ratio = long diameter ÷ short diameter

<Evaluation of bonding 1 (measurement of void ratio)>

As the evaluation 1 of the bonding property, a bonded body which is the same as the bonded body produced at the time of confirming the melting residue of the flux alloy powder was produced, and the bonded body was produced. The mixture was washed with an alcohol, and then vacuum-dried, and the void ratio was measured as follows in the bonding system in which the flux alloy was wetted.

The void ratio of the Cu substrate 1 to which the flux alloy 3 was bonded via the Ni layer 2 was measured using an X-ray transmission device (manufactured by Toshiba Co., Ltd., TOSMICRON-6125) for the bonded body shown in Fig. 3 . Specifically, X-rays are perpendicularly transmitted from the surface side to which the flux alloy 3 is bonded to the bonding surface of the solder alloy 3 and the Cu substrate 1, and the following calculation formula 2 is used in accordance with each area obtained from the obtained X-ray image. Calculate the void ratio. The measurement results of the void ratio of the joined body are shown in Table 2.

[Calculation formula 2] void ratio (%) = void area ÷ (void area + joint area of flux alloy and Cu substrate) × 100

<Evaluation of Bondability 2 (Measurement of Shear Strength)>

In order to confirm the bondability of the flux alloy, the Si wafer 4 was bonded to the Ni layer 2 (layer thickness: 2.5 μm) of the Cu substrate 1 (thickness: 0.7 mm) as shown in Fig. 5 using a solder paste sample. The joint body was measured for shear strength. That is, a mask is used on the Ni layer 2 of the Cu substrate 1, and the solder paste 3 is printed into a shape of 2.0 mm × 2.0 mm and a thickness of 100 μm. After the substrate is heated, a solder paste 3 is placed on the solder paste 3 at 2.0 mm × 2.0. The Si wafer 4 of mm was heated and bonded as follows to prepare a Si wafer bonded body, and the shear strength was measured.

The production of the joined body was carried out using a die bonder (manufactured by Westbond, model: 3727C). First, it circulates in the heater unit of the device. Nitrogen gas is at a temperature 40 ° C higher than the melting point of the solder paste sample to be used. Thereafter, a Cu substrate is placed in the heater portion, and the solder paste is applied and then heated for 35 seconds to deposit Si on the molten solder alloy. The wafer 4 was washed for 5 seconds to form an Si wafer bonded body. After the completion of the washing, the joined body was quickly moved to a cooling portion through which nitrogen gas flowed, and after cooling to room temperature, it was taken out in the air. The same treatment was performed using each solder paste, and the shear strength was measured using the shear strength test on the produced Si wafer bonded body. Specifically, the bonded body is fixed to the device, and the shear strength is measured by pressing the Si wafer 4 from the lateral direction by the jig. The measurement results are shown in Table 2.

<Assessment of Reliability (Heat Cycling Test)>

A thermal cycle test was conducted in order to evaluate the reliability of the solder joint. In addition, this test was performed using the bonded body in which the substrate prepared by the evaluation of the bonding property 2 and the Si wafer were solder-bonded. First, the bonded body was cooled to -40 ° C, heated to 250 ° C, and then cooled again to -40 ° C as a cycle, which was repeated for a specific cycle. Thereafter, the Cu substrate to which the flux alloy was bonded was embedded in a resin, and subjected to cross-section polishing, and the joint surface was observed by SEM (S-4800, manufactured by Hitachi, Ltd.). In the case where the joint surface is peeled off or the flux alloy is cracked, it is "x", and the joint surface which is the same as the initial state without such a defect is referred to as "○". The measurement results are shown in Table 2.

As is apparent from the above Table 2, the flux alloys of the samples 1 to 10 of the present invention showed good characteristics in each evaluation item. That is, in the evaluation of wettability 1, there was no melt residue of the powder. In the evaluation of wettability 2, the aspect ratio was 1.03 or less and uniformly infiltrated into a circular shape. In the evaluation 1 of the bondability, the void ratio was 0.8% or less and was a very low value. In the evaluation of the wettability 2, as a result of the shear strength test, the strength of the flux alloy was high and all the wafers were broken, and there was no fracture in the flux alloy. In the evaluation of the reliability, no heat failure occurred until 500 cycles.

The reason why such a good result is obtained in this way is because the flux alloy of the present invention is within an appropriate composition range, and the solder paste is produced under appropriate conditions. In addition, the sample 3, 8 series of flux alloy powder gold The genus tissue is 90% by volume or more of layered tissue, and the results of each evaluation are very good results. When the ratio of the fine layered structure is 90% by volume or more, the flux alloy is uniformly melted, and the respective portions can be uniformly joined, so that high joint reliability and the like are obtained. result.

Further, the samples 15 and 16 of the comparative example of the conventional product having a large amount of Au were found to give good results in the same manner as in the examples.

On the other hand, each of the flux alloys of the samples 11 to 14 of the comparative example obtained poor results in at least one of the properties. That is, in the samples 11 to 14, the flux alloy powder was melted and left, and the aspect ratio was 1.04 or more. Furthermore, the shear strength is as low as 39 to 54 MPa, and the void ratio is about 10 to 22%, and the voids occur in a considerable ratio. Further, in the thermal cycle test for evaluating the reliability, all the samples were defective in the period up to 300 cycles.

Further, it is known that the flux alloy of the present invention has an Au content of as much as 61%, and an Au content is remarkable as compared with the currently practical 80% by mass of the Au-20% by mass alloy or the 88% by mass of the Au-12% by mass Ge alloy. It is low and therefore low cost.

In addition, since the crystal vibrator package causes the oscillation frequency of the crystal vibrator to be uneven or unstable when a leak occurs, it is necessary to use a bonding material (flux material) having high bonding reliability. For example, if the flux material is uneven or flows out during sealing, sufficient bonding property or short circuit may not be obtained. The occurrence of voids can also be a cause of micro-leakage (small leakage), which increases the defect rate and is therefore not good. By using The solder paste of the present invention is a flux material which can be supplied to the sealed container with a precision along the sealing shape, and the sealed container and the sealing cover can be accurately joined. Since the flux alloy after bonding is excellent in stress relaxation property compared with the conventional Au-based flux alloy, it is excellent in bonding property, reliability, and the like. Moreover, since the amount of Au used can be reduced, it is suitable as a flux material for sealing a crystal vibrating sub-package which is low in cost and requires very high reliability.

Claims (7)

A Pb-free Au-Sn-Ag-based solder paste is a solder paste obtained by mixing a flux alloy powder and a flux, and the flux alloy powder is contained in a total of 100% by mass. Sn is 27.5% by mass or more and less than 33.0% by mass, and Ag is contained in an amount of 8.0% by mass or more and 14.5% by mass or less. The remainder is composed of Au in addition to elements which are inevitably contained in the production. The Pb-free Au-Sn-Ag solder paste of claim 1, wherein the flux comprises rosin. The Pb-free Au-Sn-Ag solder paste of claim 1 or 2 contains Sn of 29.0% by mass or more and 32.0% by mass or less, and Ag contains 10.0% by mass or more and 14.0% by mass or less, and the remainder is manufactured. In addition to the elements that are inevitably included, it consists of Au. The Pb-free Au-Sn-Ag solder paste according to any one of claims 1 to 3, wherein at least a part of the metal structure of the flux alloy powder is a layered structure. The Pb-free Au-Sn-Ag solder paste according to any one of claims 1 to 4, wherein the metal structure of the flux alloy powder is a layered structure, and the ratio thereof is 90% by volume or more. A Si semiconductor element bonded body characterized by being bonded using the Pb-free Au-Sn-Ag solder paste according to any one of claims 1 to 5. A crystal vibrator sealing element characterized by being sealed with a Pb-free Au-Sn-Ag solder paste according to any one of claims 1 to 5.