JP2016068091A - BALL-SHAPED Au-Sn-Ag SOLDER ALLOY, ELECTRONIC COMPONENT SEALED BY USING THE BALL-SHAPED Au-Sn-Ag SOLDER ALLOY, AND ELECTRONIC COMPONENT MOUNTED DEVICE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-temperature Pb-freed ball-shaped Au-Sn-Ag solder alloy excellent in wet extending property and bondability, excellent in workability and stress relaxation, having a melting point of about 300°C, and far less inexpensive than that of the existing Au-group solder.SOLUTION: A ball-shaped Au-Sn-Ag solder alloy is characterized: in that the shape has an aspect ratio ("the longer diameter divided by the shorter diameter, or the longer side divided by the shorter side", ibid.) of 1.00 to 1.20; in that Sn is contained 42.0 mass % or more and 50.0 mass % or less; in that Ag is contained 2.0 mass % or more and 9.0 mass % or less, and in that the remainder is made of Au excepting an inevitably contained element.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a ball-shaped lead-free solder alloy for high temperature, and relates to a ball-shaped solder alloy mainly composed of Au and Sn, an electronic component sealed using the solder alloy, and the like.

  In recent years, regulations on chemical substances harmful to the environment have become stricter, and this regulation is no exception for solder materials used for the purpose of joining electronic components and the like to substrates. Lead has been used as a main component in solder materials for a long time, but it has already been a regulated substance under the Rohs Directive. For this reason, the development of solder not containing lead (Pb) (hereinafter referred to as lead-free solder or lead-free solder) has been actively conducted.

  Solders used when bonding electronic components to a substrate are roughly classified into high temperature (about 260 ° C. to 400 ° C.) and medium / low temperature (about 140 ° C. to 230 ° C.) depending on the limit temperature of use. As for the solder for medium and low temperature, lead-free solder has been put into practical use, which contains Sn as a main component.

  For example, as a lead-free solder material for medium and low temperatures, Japanese Patent Application Laid-Open No. 11-77366 shown in Patent Document 1 includes Sn as a main component, Ag of 1.0 to 4.0% by weight, and Cu of 2.0. A lead-free solder alloy composition containing no more than wt%, Ni no more than 1.0 wt% and P no more than 0.2 wt% is described. Japanese Patent Laid-Open No. 8-215880 shown as Patent Document 2 has an alloy composition containing 0.5 to 3.5% by weight of Ag, 0.5 to 2.0% by weight of Cu, and the balance being Sn. Lead-free solder is described.

  On the other hand, various organizations have also developed lead-free solder materials for high temperatures. For example, Japanese Patent Laid-Open No. 2002-160089 shown as Patent Document 3 describes a Bi / Ag brazing material having a melting temperature of 350 ° C. to 500 ° C. containing 30 to 80 at% Bi. Japanese Patent Application Laid-Open No. 2008-161913 shown as Patent Document 4 describes a solder alloy in which a binary eutectic alloy is added to a Bi-chang alloy containing Bi and an additional element is further added. Although it is a quaternary or higher multi-component solder, the liquidus temperature can be adjusted and variations can be reduced.

  Further, as an expensive high temperature lead-free solder material, an Au—Sn alloy, an Au—Ge alloy, or the like has already been used in an electronic component mounting apparatus such as a crystal device, a SAW filter, and a MEMS. An Au-20 mass% Sn alloy (meaning composed of 80 mass% Au and 20 mass% Sn, the same applies hereinafter) has a eutectic point composition and a melting point of 280 ° C. On the other hand, Au-12.5 mass% Ge alloy also has a eutectic point composition, and its melting point is 356 ° C.

  The use of the Au—Sn alloy and the Au—Ge alloy depends on the difference in melting point. That is, an Au—Sn alloy having a eutectic temperature of 280 ° C. is used when it is used for bonding at a relatively low temperature even for high temperatures. When the temperature is relatively high, an Au—Ge alloy having a eutectic temperature of 356 ° C. is used.

  Even if an Au alloy is used instead of a Pb solder in consideration of the environment, the Au alloy is much harder than the Pb solder or the Sn solder. In particular, an Au—Ge alloy is very difficult to process because Ge is a metalloid. Moreover, even if the Au—Sn alloy is not as good as the Au—Ge alloy, it is difficult to process, and the productivity and yield at the time of processing are poor. Therefore, Au-based alloys are very hard compared to Pb-based solders and Sn-based solders, and it is difficult to make ball-shaped solder alloys.

Moreover, of course, in the case of Au-20 mass% Sn alloy or Au-12.5 mass% Ge alloy, the material cost is much higher than that of other solder materials.
Therefore, for example, an Au—Sn—Ag solder alloy disclosed in Patent Document 5 has been developed for the purpose of making the Au—Sn alloy inexpensive and easier to use.

Japanese Patent Application Laid-Open No. 2008-155221 shown as Patent Document 5 aims to provide a brazing material and a piezoelectric device that are relatively easy to handle with a low melting point, excellent in strength and adhesion, and inexpensive.
The composition ratio (Au (wt%), Ag (wt%), Sn (wt%))
In the ternary composition diagram of Au, Ag, and Sn,
Point A1 (41.8, 7.6, 50.5),
Point A2 (62.6, 3.4, 34.0),
Point A3 (75.7, 3.2, 21.1),
Point A4 (53.6, 22.1, 24.3),
Point A5 (30.3, 33.2, 36.6)
The brazing material in the area surrounded by is described.

  On the other hand, Japanese Patent Laid-Open No. 2011-198777 shown as Patent Document 6 describes a non-Au-based lead-free solder alloy such as a ball-shaped Sn—Ag—Cu alloy, and Japanese Patent Application Laid-Open No. 2011-235342 shown as Patent Document 7. The publication describes a sheet-like, wire-like, or ball-like non-Au-based lead-free Zn-based solder alloy.

JP-A-11-77366 JP-A-8-215880 JP 2002-160089 A JP 2008-161913 JP 2008-155221 A JP 2011-198777 A JP 2011-235342 A

  Although high-temperature lead-free solder materials have been developed by various organizations other than the above cited references, a low-cost and versatile solder material has not yet been found. In other words, since materials having relatively low heat resistance such as thermoplastic resins and thermosetting resins are generally used for electronic parts and substrates, the working temperature must be less than 400 ° C., preferably 370 ° C. or less. There is. However, for example, in the Bi / Ag brazing material disclosed in Patent Document 3, since the liquidus temperature is as high as 400 to 700 ° C., the working temperature at the time of joining is 400 to 700 ° C. or higher, It will exceed the heat resistance temperature of the substrate.

  In addition, in the case of Au-Sn solder and Au-Ge solder, a large amount of very expensive Au is used, so it is very expensive compared to general-purpose Pb solder and Sn solder, etc. Although being used, the range of use is limited to the use of crystal devices, SAW filters, and soldering where particularly high reliability is required, such as MEMS. In addition, the eutectic temperature of the Au—Sn alloy was 280 ° C., the eutectic temperature of the Au—Ge alloy was 356 ° C., and the only solder having a melting point during this period was Pb-based solder.

  In addition, Au-based solder is very hard and difficult to process. Specifically, it is difficult to process ribbon materials that require a rolling process, punch materials that require pressing, and ball shapes that require high sphericity and surface oxidation suppression. It is very difficult to form a ball-shaped solder alloy that can obtain good wet spreading and adhesion.

  Furthermore, in order to solve such poor workability, a contrivance such as solder paste of Au-based solder has been devised, but it causes new problems such as generation of voids and further cost increase.

  On the other hand, the Au—Sn—Ag solder alloy shown in Patent Document 5 developed for the purpose of solving various problems of Au solder including the above melting point, workability, cost, etc. There is a problem like this.

  Patent Document 5 describes that a brazing material and a piezoelectric device that are relatively easy to handle with a low melting point, excellent in strength and adhesion, and inexpensive are provided. Furthermore, as described above, by limiting the composition range of Au, Sn, and Ag, it is possible to obtain the same characteristics as a sealing material while reducing the Au content as compared with the conventional one. It has been. However, Patent Document 5 does not describe the reason why the strength and adhesiveness are improved. Regarding strength, “a solid solution with Au or Ag may be formed, and a metal element having a bulk melting point of 400 ° C. or higher may be contained in an amount of 0.1 wt% or more and 3% wt or less. , The melting point and the hardness of the brazing material are increased, and a brazing material having excellent heat resistance and mechanical strength is obtained. " It is unclear. Moreover, there is no description about the reason for improving the adhesiveness (which can be interpreted as bonding and wettability), and from this, the adhesiveness of the solder alloy of Patent Document 5 is generally different from that of a solder alloy used. It seems to be the same degree.

  On the other hand, the Au—Sn—Ag solder alloy is optimally formed into a ball shape in order to ensure good wetting and joining properties. Since the lead-free solder alloys shown in Patent Document 6 and Patent Document 7 are non-Au solder alloys, they can be easily processed and easily formed into a ball shape close to a true sphere. However, since the Au—Sn—Ag solder alloy is slightly harder to process than the non-Au solder alloy, the ball may be distorted. In a distorted shape, wetting and spreading properties are not stable, which causes poor bonding. Also, it is not stable during transportation. Furthermore, the amount of laser energy absorption is not stable and the molten state is not stable. Furthermore, it also causes solder scattering.

  The present invention has been made in view of such circumstances, and its object is to join electronic components and electronic component mounting apparatuses that require extremely high reliability, such as crystal devices, SAW filters, and MEMS. Can be used sufficiently, has a melting point of around 300 ° C., and also has excellent wettability and bondability, low cost, high workability, stress relaxation, and high temperature ball shape. It is to provide an Au—Sn—Ag based solder alloy.

  Therefore, in order to achieve the above object, the ball-like Au—Sn—Ag solder alloy according to the present invention is a ball-like Au—Sn—Ag solder alloy having an aspect ratio (“major axis ÷ minor axis”). Or “long side / short side”. The same applies hereinafter) is 1.00 or more and 1.20 or less, Sn is contained in an amount of 42.0% by mass or more and 50.0% by mass or less, and Ag is 2 It is characterized by containing 0.0 mass% or more and 9.0 mass% or less, and the balance is made of Au except for elements inevitably included in production.

  In the present invention, the aspect ratio is 1.00 or more and 1.20 or less, Sn is contained 44.0% by mass or more and 48.0% by mass or less, and Ag is 3.0% by mass or more and 7.0% or less. It is preferable that it is made of Au except for elements which are contained by mass% or less and the remainder is inevitably included in production.

  In the present invention, it further contains at least one of Al, Cu, Ge, In, Mg, Ni, Sb, Zn, and P. When Al is contained, 0.01 mass% or more and 0.8 % By mass or less, 0.01% by mass or more and 1.0% by mass or less when Cu is contained, 0.01% by mass or more and 1.0% by mass or less when Ge is contained, and 0. 01% by mass or more and 1.0% by mass or less, 0.01% by mass or more and 0.5% by mass or less when Mg is contained, 0.01% by mass or more and 0.7% by mass or less when Ni is contained, Sb 0.01 mass% or more and 0.5 mass% or less when containing Zn, 0.01 mass% or more and 5.0 mass% or less when containing Zn, and 0.500 mass% or less when containing P It is preferable to do.

  Moreover, the ball-shaped Au—Sn—Ag solder alloy according to the present invention has the above-mentioned ball-shaped Au—Sn—Ag solder alloy crushed from one direction, and the aspect ratio is more than 1.00 and not more than 1.50. It is characterized by that.

  On the other hand, an electronic component according to the present invention is characterized by being sealed using the above-mentioned ball-shaped Au—Sn—Ag solder alloy.

  An electronic component mounting apparatus according to the present invention is characterized in that an electronic component sealed using the above-described ball-shaped Au—Sn—Ag solder alloy is mounted.

According to the present invention, a high-temperature Au-based solder alloy having a melting point of about 300 ° C. that can be used in places requiring extremely high reliability, such as quartz devices, SAW filters, and MEMS, It can be provided at a much lower price than solder. Furthermore, since the solder alloy of the present invention is based on Ag ₃ Sn intermetallic compound and AuSn ₂ intermetallic compound and has more flexible properties than Au-20 mass% Sn alloy, a ball-like high temperature lead-free solder alloy is used. It can be manufactured with high productivity and further cost reduction can be realized. In addition, by using a ball shape with an appropriate aspect ratio, it has excellent wet spreading properties and high bonding reliability. Accordingly, it is possible to provide a ball-shaped Au-based solder excellent in various characteristics, and the industrial contribution is extremely high.

It is an Au-Sn-Ag system phase diagram. In the figure, AuSn is an Au ₁ Sn ₁ intermetallic compound. It is the schematic diagram explaining the definition of the aspect ratio of the ball-shaped Au-Sn-Ag solder alloy whose ball shape is a football type. It is the schematic diagram explaining the definition of the aspect ratio of the ball-shaped Au-Sn-Ag solder alloy whose ball shape is an ellipse type. It is a schematic diagram of the sample for wettability test evaluation which shows the state which soldered the solder alloy of each sample on Cu board | substrate which has Ni layer (plating). It is the schematic diagram explaining the definition of the aspect ratio regarding the wet spreading property of a ball-shaped Au-Sn-Ag solder alloy, Au-Sn solder alloy, or Au-Ge solder alloy.

Hereinafter, the ball-shaped Au—Sn—Ag solder alloy of the present invention will be described in detail.
The ball-like Au—Sn—Ag solder alloy of the present invention is a ball-like Au—Sn—Ag solder alloy having an aspect ratio of 1.00 to 1.20, and Sn. 42.0% by mass or more and 50.0% by mass or less, Ag is contained by 2.0% by mass or more and 9.0% by mass or less, and the balance is made of Au except for elements inevitably included in production. Yes.

  That is, the ball-shaped Au—Sn—Ag solder alloy of the present invention has an aspect ratio of 1.00 or more and 1.20 or less, so that when the solder alloy melts at the time of joining and spreads wet on the substrate or the like, the solder becomes circular. It can spread evenly. As a result, the solder is uniformly present on the joint surface, and the reaction between the solder and the substrate becomes uniform, thereby obtaining excellent jointability.

  Further, the solder alloy of the present invention contains at least one of Al, Cu, Ge, In, Mg, Ni, Sb, Zn and P as the fourth or more element in order to further improve the characteristics. Well, when Al is contained, 0.01 mass% or more and 0.8 mass% or less, when Cu is contained, 0.01 mass% or more and 1.0 mass% or less, and when Ge is contained, 0.01 mass% % To 1.0% by mass, 0.01% to 1.0% by mass in the case of containing In, 0.01% to 0.5% by mass in the case of containing Mg, Ni When it contains 0.01 mass% or more and 0.7 mass% or less, when it contains Sb, it is 0.01 mass% or more and 0.5 mass% or less, and when it contains Zn, it is 0.01 mass% or more and 5.0 mass% or less. When containing P, it contains 0.500% by mass or less.

The solder alloy of the present invention significantly reduces the cost of Au-based solder such as Au-20 mass% Sn alloy solder, which is very expensive, and uses relatively soft Sn in order to provide excellent workability. It is contained in excess of the composition ratio of the eutectic point of the 20 mass% Sn alloy, and Ag is contained. Furthermore, it may contain any one or more of Al, Cu, Ge, In, Mg, Ni, Sb, Zn and P. First, by using an Au—Sn—Ag ternary alloy, the melting point can be lowered to around 300 ° C., and various characteristics required for a solder alloy can be satisfied. Further, by adding the fourth element and subsequent elements, the characteristics can be further adjusted according to the purpose of use. Since the Au—Sn—Ag solder alloy of the present invention is mainly composed of an intermetallic compound of Ag ₃ Sn or AuSn ₂ , it has excellent workability and sufficient bondability even for extremely high reliability requirements. , Has wettability.

The solder alloy of the present invention contains Sn in an amount of about 46.6% by mass around this, that is, 42% by mass to 50% by mass of Sn. For example, if it is Au-46.6 mass% Sn-5.0 mass% Ag alloy (95 mass% (Au _38.5 Sn _61.5 ) 5 mass% Ag alloy), it shows in the state diagram of FIG. Sn = 61.5 at. % Composition (consisting only of Ag ₃ Sn and AuSn ₂ ). 1 shows that Ag = 5 wt. % (Mass%), Au and Sn are shown as a phase diagram with the atomic ratio (at.%) Changed, and Sn = 61.5 at. % Is converted to Sn = 46.6% by weight. Moreover, Sn = 42 mass% is converted into Sn = 56.8 at. %, Sn = 50 mass% is converted into Sn = 64.8 at. %.

Furthermore, by setting the aspect ratio of the ball shape within a specific range as described above and containing Ag that is highly reactive and difficult to oxidize, particularly excellent wettability and bondability can be obtained.
Hereinafter, the shape and essential elements of the solder alloy of the present invention will be described in more detail.

<Aspect ratio>
In the present invention, it is an essential condition that the aspect ratio of the ball-shaped Au—Sn—Ag solder alloy is 1.00 or more and 1.20 or less. In the present invention, the ball shape is not limited to a true sphere shape, but also includes a football shape and a long oval shape having a linear portion in plan view. In either case, the aspect ratio may be in the above range.
The aspect ratio of the ball-shaped shape of the Au—Sn—Ag solder alloy of the present invention is as defined in the calculation formula 1, FIG. 2 and FIG. The measured value is the major axis or long side, and the measured value at the shortest diameter is the minor axis or short side.
[Calculation Formula 1] Aspect ratio = major axis / minor axis or long side / short side However, FIG. 2 shows an example of a football type, and FIG. 3 shows an example of a long ellipse. In addition, the major axis and the longer side, and the minor axis and the shorter side are not strictly distinguished. 2 and 3 show the aspect ratios outside the range of the aspect ratio of the present invention for easy understanding of the distinction between the long diameter and the long side and the short diameter and the short side.

  By controlling the shape of the ball-shaped Au—Sn—Ag solder alloy in this way, when the solder alloy is melted, it wets and spreads in a state close to a perfect circle in plan view. Even if the solder alloy is in a ball shape to some extent, as the sphericity decreases, the solder does not spread circularly on the joint surface when the solder melts, and the part to be joined partially protrudes or becomes insufficient A portion that cannot be formed occurs, and a portion that is not sufficiently alloyed is formed. Furthermore, the thickness of the solder becomes non-uniform, leading to chip tilt and the like, and sufficient sealing cannot be performed.

  In order to prevent such a problem from occurring, the aspect ratio of the ball-shaped Au—Sn—Ag solder alloy of the present invention is set to 1.00 or more and 1.20 or less. If the aspect ratio is 1.20 or less, the solder spreads in a hemispherical shape due to surface tension when the solder is melted, and the joint surface spreads uniformly in a circular shape. When the aspect ratio exceeds 1.20, in the case of the ball-shaped Au—Sn—Ag solder alloy of the present invention, it becomes difficult to spread evenly on the joint surface even by the surface tension during solder melting. .

  Further, if the aspect ratio is 1.00 or more and 1.10 or less, it is more preferable that the solder spreads in a hemispherical shape due to surface tension when the solder is melted, and the joint surface spreads uniformly in a circular shape.

Further, the ball-shaped Au—Sn—Ag solder alloy of the present invention is crushed from one direction so that the aspect ratio exceeds 1.00 and is equal to or less than 1.50. Basically, it crushes in the direction in which the short diameter (short side) becomes shorter, but the long diameter (long side) side may be crushed. As a result, the aspect ratio should be within the above range. When the solder alloy crushed from one direction is placed on the joint surface, the crushed flat plane comes into contact with the joint surface. For this reason, when the joining surface on which the solder is placed is viewed vertically from the solder side, the solder is substantially circular. When the solder is melted in this state, the solder spreads in a circular shape. However, if the Au—Sn solder alloy or Au—Ge solder alloy is crushed from one direction and the aspect ratio is close to 1.50, it will be hard and will not crack and spread in a circle. May break.
As an advantage of crushing the ball, it is preferable that the ball is spherical when it is joined or sealed with solder, because the ball is easy to roll and the positional stability is poor, and the ball can be stably placed at the target position by crushing.

<Au>
Au is a main component of the solder alloy of the present invention, and is naturally an essential element. Since Au is very difficult to oxidize, it is most suitable in terms of characteristics as a solder for joining and sealing of electronic parts that require high reliability. For this reason, Au-based solder is often used for sealing quartz devices and SAW filters. The solder alloy of the present invention is also based on Au, and provides solder belonging to a technical field that requires such high reliability. To do.

  However, since Au is a very expensive metal, it is better not to use it as much as possible from the viewpoint of cost, and it is desired to reduce the Au content even by 1% by mass. For this reason, it is rarely used for electronic components that require a general level of reliability. The solder alloy of the present invention realizes a reduction in cost by significantly reducing the Au content by containing Ag by increasing the Sn content as compared to the Au-20 mass% Sn solder alloy, In terms of characteristics such as wettability and bondability, it is equivalent to or better than Au-20% by mass Sn solder, and is excellent in flexibility and workability.

<Sn>
Sn is a main component in the solder of the present invention, and is naturally an essential element. The Au—Sn solder alloy is usually used in a composition near the eutectic point, that is, a composition near Au-20% by mass Sn, whereby the solidus temperature becomes 280 ° C. and the crystal becomes finer, It is relatively flexible. However, even if it is called a eutectic alloy, an Au-20 mass% Sn alloy is composed of an Au ₁ Sn ₁ intermetallic compound and an Au ₅ Sn ₁ intermetallic compound, and is hard and brittle. For this reason, it is difficult to process, for example, when it is processed into a sheet shape by rolling, it can only be made thin little by little, the productivity is bad, or many cracks enter during rolling, and the yield is bad. However, the hard and brittle nature of intermetallic compounds cannot generally be changed. Although it is such a hard and brittle material, it is difficult to oxidize and has excellent wettability and reliability, so it is used for highly reliable applications.

However, since Au is a very expensive metal, reducing the cost of Au solder is an important issue to be solved. In order to solve this problem, the solder alloy of the present invention is basically based on the vicinity of the composition composed of Au except for 46.6% by mass of Sn, 5.0% by mass of Ag, and the elements inevitably contained in the balance. Characterize. The reason why such an alloy composition is used is not only the cost reduction of the solder alloy, but also Au-46.6 mass% Sn-5.0 mass% Ag as shown in the Au-Sn-Ag ternary system state of FIG. is composed of an alloy (95 _wt% (Au _{38.5 Sn 61.5)} 5 wt% Ag alloy) is _Ag 3 Sn intermetallic compound and the AuSn ₂ intermetallic compound, the flexible nature than the Au-20 wt% Sn alloy It is for having.

That is, Ag ₃ Sn and AuSn ₂ are intermetallic compounds, but they are more flexible than Au ₁ Sn ₁ intermetallic compounds and Au ₅ Sn ₁ intermetallic compounds constituting Au-20% by mass. Further, when Au-46.6% by mass Sn-5.0% by mass Ag alloy is cooled from a molten state exceeding the liquidus temperature, for example, 330 ° C. or higher, Au ₁ Sn ₁ intermetallic compound is generated _first . When the temperature is further lowered, Ag ₃ Sn and AuSn ₂ are generated simultaneously. As described above, since the crystal formation process follows the process of (1) liquid phase → (2) Au ₁ Sn ₁ + liquid phase → (3) AuSn ₂ + Ag ₃ Sn, AuSn ₂ and Ag ₃ Sn have a fine crystal structure. For this reason, the solder alloy is flexible and has a high bonding reliability in which cracks and the like do not easily develop.

  In addition, the liquidus temperature of this Au-46.6 mass% Sn-5.0 mass% Ag alloy is about 325 degreeC, and a solidus line temperature is about 295 degreeC. This melting point is between the melting points of Au-20 mass% Sn (eutectic temperature: 280 ° C.) and Au-12.5 mass% Ge (eutectic temperature: 356 ° C.) conventionally used as Au-based solder. In addition to being able to replace these Au-based solders, it is possible to meet the conventional strong demand for joining between 280 ° C. and 356 ° C.

The content of Sn in the Au—Sn—Ag solder alloy having such excellent characteristics is 42.0 mass% or more and 50.0 mass% or less. If it is less than 42.0 mass% (for example, Ag = 5 wt.%, 56.8 at.% In FIG. 1), the liquidus temperature becomes too high and good bonding cannot be performed. In addition, the difference between the liquidus temperature and the solidus temperature becomes too large, and a melting phenomenon occurs. Furthermore, since the Au content tends to increase, the cost reduction effect is limited. On the other hand, if the Sn content exceeds 50.0 mass% (for example, Ag = 5 wt.%, 64.8 at.% In FIG. 1), the ratio of AuSn ₄ intermetallic compound is increased to 3 Since various types of intermetallic compounds are mixed, flexibility is lowered, and workability and stress relaxation properties are lowered.

  When the Sn content is 44.0% by mass or more and 48.0% by mass or less, the difference between the liquidus temperature and the solidus temperature is relatively small, and the influence of oxidation is small, so that particularly good bonding is obtained. It is preferable.

<Ag>
Ag is an essential element in the solder of the present invention, and by containing Ag, not only does the content of Au decrease, contributing to lowering the cost of the solder alloy, but also adjusting the melting point of the Au—Sn solder, Further, it is an important element that can improve flexibility and workability, and thus can improve stress relaxation, reliability, productivity, yield, and the like.

The main effects of containing Ag are as follows. By containing Ag, the liquidus temperature and the solidus temperature of the Au—Sn—Ag alloy can be adjusted to about 300 ° C. As a result, the melting point of Au-20% by mass Sn (280 ° C.) or the melting point of Au-12.5% by mass Ge (356 ° C.) can be set. And it becomes possible to make a solder alloy mainly composed of Ag ₃ Sn, AuSn ₂ intermetallic compound, and this intermetallic compound is more flexible than Au ₁ Sn ₁ or Au ₅ Sn ₁ intermetallic compound of Au-20 mass% Sn. Therefore, the Au—Sn—Ag-based alloy of the present invention is more flexible than Au-20% by mass, and thus is excellent in workability, stress relaxation property, reliability, and the like.

  In addition, by containing Ag, the Au content can be reduced, and the cost of the solder alloy can be further reduced. Furthermore, since Ag is a metal that is difficult to oxidize next to Au, the solder surface is difficult to oxidize, and since it has excellent reactivity with various metals, an effect of improving wettability can be expected.

  The content of Ag capable of imparting such excellent characteristics to the solder alloy is 2.0% by mass or more and 9.0% by mass or less. If the content of Ag is within this range, the liquidus temperature and the solidus temperature are within an allowable range in solder joining, and good joining is possible. Furthermore, sufficient wettability, bonding strength, and bonding reliability can be obtained without generating a high melting point intermetallic compound.

  Furthermore, the preferable Ag content is 3.0 mass% or more and 7.0 mass% or less, and if it is in this range, the effect of containing Ag appears more remarkably.

<Al, Ge, Mg>
Al, Ge, and Mg are elements that may be included for improving or adjusting various properties in the present invention, and the main effects obtained by including these elements are the same, which is in improving wettability. .

  Al is dissolved in Au by several mass%, slightly dissolved in Sn, and is dissolved in Ag by several mass%. As described above, Al is in a state of being dissolved in a small amount in an Au—Sn—Ag alloy in a solid state, but Al is more likely to be oxidized than Au, Sn, and Ag in a molten state at the time of joining, so Al is preferential. It is oxidized to form a thin oxide film on the solder surface, and the wettability is improved by suppressing the progress of oxidation of the parent phase. The content of Al having such an effect of improving wettability is 0.01% by mass or more and 0.8% by mass or less. If it is less than 0.01% by mass, the content is too small and the effect of containing Al does not appear substantially, and if it exceeds 0.8% by mass, the oxide film becomes too thick and conversely reduces wettability. . If the content of Al is 0.1% by mass or more and 0.5% by mass or less, the effect of inclusion is more remarkable and preferable.

  Ge forms a eutectic alloy composed of Au and a solid solution, hardly dissolves in Sn, and Ag forms a eutectic alloy composed of a solid solution. It is preferable that Ge is contained so as not to generate an intermetallic compound with Sn so as not to cause embrittlement of the solder alloy. The mechanism by which Ge improves wettability is as follows. Ge has a relatively small specific gravity, and floats on the solder surface to a certain degree in the molten solder and oxidizes to form a thin oxide film, which suppresses the progress of oxidation of the mother phase and improves the wettability. The Ge content having such an effect is 0.01% by mass or more and 1.0% by mass or less. If the Ge content is less than 0.01% by mass, the content is too small and substantially no effect is exhibited. If the Ge content exceeds 1.0% by mass, the content is too much to cause embrittlement of the solder alloy or segregation of Ge. Raises the jointability and reliability.

Mg forms Au and AuMg ₃ intermetallic compound, hardly forms a solid solution in Sn, forms a Mg ₂ Sn intermetallic compound, and forms a solid solution in Ag of about 6% by mass. The main effect of containing Mg is to improve wettability. However, since many intermetallic compounds are produced in this way, there is a tendency to become brittle and many cannot be contained. The mechanism for improving the wettability of Mg is as follows. Since Mg is very easy to oxidize, Mg is oxidized by itself to improve wettability. As described above, a large amount cannot be contained, but the reducibility is very strong, so that even if it is contained in a small amount, the effect is exhibited. The Mg content is 0.01% by mass or more and 0.5% by mass or less. If it is less than 0.01% by mass, the content is too small, and substantially no effect appears. On the other hand, when the Mg content exceeds 0.5 mass%, as described above, brittle AuMg ₃ intermetallic compound and Mg ₂ Sn intermetallic compound are generated, and the reliability and the like are extremely lowered.

<Cu, In, Sb>
Cu, In, and Sb are elements that may be included for improving or adjusting various properties in the present invention, and the main effects obtained by including these elements are the same, and crack propagation in solder is the same. In control.

Cu forms an intermetallic compound of Au and AuCu and dissolves in Sn and Ag. If an intermetallic compound is generated beyond the allowable range or a coarse compound is present, it becomes brittle and tip tilt is generated, so it must be avoided. However, when an appropriate amount of intermetallic compound is generated and finely dispersed in the solder, the tensile strength of the solder is improved and a crack suppressing effect is exhibited. That is, when cracks propagate in the solder due to thermal stress or the like, if the intermetallic compound is dispersed, the tip of the crack collides with the intermetallic compound, and the crack progress is stopped by the hard intermetallic compound. This mechanism is basically the same mechanism as the crack suppression effect of the Ag ₃ Sn intermetallic compound of the Pb—Sn—Ag solder, that is, the reliability improvement effect. The Cu content exhibiting such excellent effects is 0.01% by mass or more and 1.0% by mass or less. If the Cu content is less than 0.01% by mass, the content is too small to exhibit the effect. If the Cu content exceeds 1.0% by mass, an intermetallic compound is generated in excess of the allowable amount, and it becomes hard and brittle. Etc. will be reduced.

  In hardly dissolves in Au, but about 1% by mass in Sn, and 20% by mass in Ag. When In is contained in the solder alloy, the tensile strength of the solder is moderately increased by solid solution strengthening, and cracks are difficult to progress. The content of In having such an effect is 0.01% by mass or more and 1.0% by mass or less. If the In content is less than 0.01% by mass, the content is too small to produce an effect. If the In content exceeds 1.0% by mass, the strength is excessively increased and the stress relaxation effect is reduced. When applied, the solder cannot relieve stress and the chip breaks.

Sb produces a eutectic alloy composed of Au, an Au solid solution, and AuSb ₂ , and is slightly dissolved in Sn and is dissolved in Ag by about 7% by mass. The effect of containing Sb is the suppression of crack propagation in the solder, and the mechanism is the same as that of In. That is, when Sb is contained in the solder alloy, the tensile strength of the solder is moderately increased by solid solution strengthening, and cracks are difficult to progress. Content of Sb which has such an effect is 0.01 mass% or more and 0.5 mass% or less. If the Sb content is less than 0.01% by mass, the content is too small to produce an effect. If the Sb content exceeds 0.5% by mass, the strength increases so much that the solder shrinks during cooling after chip bonding. Otherwise, the chip will break.

<Ni>
Ni is an element that may be contained for improving or adjusting various properties in the present invention, and its effect is in improving the bonding reliability and the like by crystal refinement. Ni dissolves slightly in Sn and Ag. And when Ni is slightly contained in the solder alloy in this way, when the solder is cooled from the molten state and solidifies, Ni of high melting point is first dispersed and formed in the solder, and crystals are formed using the Ni as a nucleus. To do. For this reason, the solder crystal becomes finer. The finely crystallized solder has improved tensile strength, and cracks basically propagate along grain boundaries, making cracks harder to progress, and thus reliability in heat cycle tests, etc. It improves. The content of Ni that exhibits such an effect is 0.01% by mass or more and 0.7% by mass or less. If the Ni content is less than 0.01% by mass, the content is too small to produce an effect. If the Ni content exceeds 0.7% by mass, the crystal grains become coarse and the reliability and the like are lowered.

<Zn>
Zn is an element that may be contained to improve or adjust various properties in the present invention, and its main effect is to improve wettability and bondability. Zn forms a solid solution of about 4% by mass in Au, forms a eutectic alloy of solid solutions with Sn, and forms a solid solution of 20% by mass or more in Ag. Thus, Zn that forms a solid solution in a solder alloy or produces a eutectic alloy does not produce a hard and brittle intermetallic compound beyond the allowable range, and therefore does not significantly affect mechanical properties and the like. And since Zn has good reactivity with Cu etc. which are the main components of a board | substrate, wettability and bondability are improved. That is, Zn in the solder reacts with Cu or the like to form an alloy while being wetted and spread on the substrate to form a strong alloy layer. Content of Zn which has such an effect is 0.01 mass% or more and 5.0 mass% or less. If the Zn content is less than 0.01% by mass, the content is too small and substantially no effect appears. If the Zn content exceeds 5.0% by mass, the alloy layer becomes too thick or the oxide film on the solder surface is easily oxidized. Becomes too thick and causes a decrease in wettability. And when wettability falls, an alloy phase cannot fully produce | generate or a void will increase, and the fall of joining strength etc. will also arise notably.

<P>
P is an element that may be contained to improve or adjust various properties in the present invention, and its effect is in improving wettability. The mechanism by which P improves the wettability is that the reducibility is strong, and by oxidizing itself, the surface of the solder alloy is suppressed and the substrate surface is reduced to improve the wettability. In general, even if Au solder is difficult to oxidize and is excellent in wettability, the oxide on the joint surface cannot be removed. However, P can remove not only the oxide film on the solder surface but also the oxide film on the bonding surface such as the substrate. Due to the effect of removing the oxide film on the solder surface and the joint surface, gaps (voids) formed by the oxide film can also be reduced. This effect of P further improves the bondability and reliability.

  Note that P does not remain on the solder, the substrate, or the like because the solder alloy or the substrate is reduced to become an oxide and is vaporized at the same time and flows into the atmosphere gas. For this reason, there is no possibility that the residue of P adversely affects reliability and the like, and P can be said to be an excellent element from this point. When the solder alloy of the present invention contains P, the content of P is preferably 0.500% by mass or less. Since P is very reducible, the effect of improving the wettability can be obtained if a trace amount is contained, but the effect of improving the wettability does not change so much even if contained in excess of 0.5% by mass. Containing P and P oxide gas in large quantities may increase the void ratio, or P may segregate by forming a brittle phase, making the solder joints brittle and reducing reliability. There is.

Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited to these examples.
First, Au having a purity of 99.999% by mass or more and Sn, Ag, Al, Cu, Ge, In, Mg, Ni, Sb, Zn, and P having a purity of 99.99% by mass or more were prepared as raw materials. Large flakes and bulk-shaped raw materials were cut and pulverized, etc. so as to be uniform with no variation in composition depending on the sampling location in the alloy after melting, and were reduced to a size of 3 mm or less. Next, predetermined amounts corresponding to the samples 1 to 28 in Table 1 and Samples 31 to 91 in Table 2 were weighed out from these raw materials into a graphite crucible for a high frequency melting furnace.

  The crucible containing the raw material was placed in a high-frequency melting furnace, and nitrogen was flowed at a flow rate of 0.7 L / min or more per 1 kg of the raw material in order to suppress oxidation. In this state, the melting furnace was turned on to heat and melt the raw material. When the metal began to melt, it was stirred well with a mixing rod and mixed uniformly so as not to cause local compositional variations. After confirming sufficient melting, the high frequency power supply was turned off, the crucible was quickly removed, and the molten metal in the crucible was poured into the solder mother alloy mold. As the mold, a cylindrical shape having a diameter of 24 mm was used for submerged atomization for producing balls.

  Thus, the solder mother alloys of Samples 1 to 28 and Samples 31 to 91 were produced in the same manner except that the mixing ratio of the raw materials was changed. About each solder mother alloy of these samples 1-28 and samples 31-91, the composition analysis was performed using the ICP emission-spectral-analysis analyzer (SHIMAZU S-8100). The obtained analysis results are shown in Tables 1 and 2 below.

  Next, a method for manufacturing a ball-shaped solder alloy from each solder mother alloy for obtaining the samples 1 to 28 and samples 31 to 91 and a method for measuring the aspect ratio of the solder alloy sample will be described.

<Method for producing ball-shaped solder alloy>
Each master alloy (diameter 24 mm) of the prepared samples 1 to 28 and samples 31 to 91 was put into a nozzle of a submerged atomizer, and this nozzle was heated to 230 ° C. above the quartz tube containing oil (high frequency melting coil) Set inside). After heating the mother alloy in the nozzle to 540 ° C. by high frequency and holding it for 5 minutes, the nozzle was pressurized with an inert gas and atomized to obtain a ball-shaped solder alloy. The ball diameter was set to 0.30 mm, and the nozzle tip diameter was adjusted in advance. The obtained ball-shaped samples were each washed with ethanol three times, and then dried in a vacuum dryer at 40 ° C. for 3 hours. And each sample of the ball-shaped shape dried was selected into what satisfy | fills the aspect ratio of this invention, and the thing which does not satisfy | fill. As a sorting method, an apparatus as disclosed in Japanese Patent Application Laid-Open No. 11-319728 is used, and a sample is dropped on an inclined surface for sorting by applying a vibration that goes straight in a direction perpendicular to the falling direction of the sample. The first stage of selection was performed on the assumption that those falling within a certain range satisfy the aspect ratio, and those falling on other areas did not satisfy the aspect ratio. Thereafter, each sample was finally selected by measuring the aspect ratio described later.

  Further, the samples 16 to 20, 27, 28, 67 to 71, 90, and 91 were crushed into a ball shape to have a flat shape. Specifically, using a warm press, crush the sample with a mold heated to 200 ° C while flowing nitrogen at a flow rate of 5 L / min to suppress oxidation, hold it for 30 seconds, and move to a side box filled with nitrogen And cooled to room temperature and taken out. The amount of crushing was adjusted by controlling the gaps in the mold so that the degree of crushing was the desired aspect ratio.

<Measurement of Aspect Ratio of Solder Alloy Sample>
For samples 1 to 15, 21 to 26, 31 to 66, 72 to 89, the diameter is measured at an arbitrary 50 locations with a three-dimensional measuring machine, the minimum length is the short diameter or short side, and the maximum length is the long diameter. Or the long side.
For the crushed samples 16-20, 27, 28, 67-71, 90, 91, the length (thickness) of the actually crushed portion in the crushed direction is arbitrarily measured at 10 locations to obtain the minimum length. The thickness (thickness) was defined as the short side, and the length was arbitrarily measured at 10 points in the direction perpendicular to the direction in which the short side was measured, and the maximum length was defined as the long side.

  Tables 1 and 2 show the measurement results and analysis results of the aspect ratio of the solder alloy samples. Table 1 shows an example composed of Au, Sn, and Ag, and Table 2 shows an example that further contains one or more of Al, Cu, Ge, In, Mg, Ni, Sn, Zn, and P. It is.

（注）表中の※を付した試料は比較例である。

(Note) Samples marked with * are comparative examples.

（注）表中の※を付した試料は比較例である。

(Note) Samples marked with * are comparative examples.

  Next, each evaluation will be described, and each evaluation result obtained is shown in Tables 3 and 4.

<Evaluation of wettability (measurement of aspect ratio of joined body)>
In order to evaluate the wetting and spreading property, a joined body in which the solder alloy 3 of each sample is soldered to the Ni plating layer 2 of the Cu substrate 1 as shown in the schematic diagram of FIG. The aspect ratio was measured.

  A wettability tester (device name: atmosphere control type wettability tester) was started, a double cover was applied to the heater part to be heated, and nitrogen gas was allowed to flow from four locations around the heater part at a flow rate of 12 L / min. . Thereafter, the heater was set to a temperature higher than the melting point by 50 ° C. and heated. After the heater temperature has stabilized at the set value, a Cu substrate (plate thickness: 0.3 mm) plated with Ni (film thickness: 3.0 μm) is set in the heater and heated for 25 seconds, and then a ball-shaped solder alloy Was placed on a Cu substrate and heated for 25 seconds. After the heating was completed, the Cu substrate was picked up from the heater part, once installed in a place where the nitrogen atmosphere next to it was maintained, cooled, and after sufficiently cooled, taken out into the atmosphere.

For the obtained joined body, that is, a joined body in which the solder alloy 3 is joined to the Ni plating layer 2 of the Cu substrate 1 as shown in FIG. 4, the wet spread length of the wet spread solder alloy is measured to determine the aspect ratio. Asked. Specifically, the maximum solder wetting and spreading length shown in FIG. 5 was taken as the major axis, the minimum solder wetting and spreading length was taken as the minor axis, and the aspect ratio was calculated from the measured values by the following formula 2.
[Calculation Formula 2] Table 3 and Table 4 show the measurement results of the aspect ratio of the aspect ratio = long diameter / short diameter joined body.

  It can be judged that the closer the aspect ratio of the calculation formula 2 is to 1, the more wetting and spreading in a circular shape on the substrate, the better the wetting and spreading property. As it becomes larger than 1, the wetting and spreading shape deviates from the circle, the movement distance of the molten solder varies, the reaction becomes uneven, the thickness of the alloy layer and the component variation increase, and the like is uniform and good It becomes impossible to join. Furthermore, it spreads so that a lot of solder flows in a certain direction, and a portion where the amount of solder is excessive and a portion where there is no solder are formed. Although depending on the components of the solder alloy, the aspect ratio is preferably less than 1.3 at the maximum.

<Evaluation of bondability (measurement of void fraction)>
For the joined body shown in FIG. 4 obtained in the same manner as the evaluation of the wettability, the void ratio of the Cu substrate to which the solder alloy was joined was measured using an X-ray transmission device (TOSMICRON-6125 manufactured by Toshiba Corporation). Measured. Specifically, X-rays were transmitted vertically through the joint surface of the solder alloy and the Cu substrate from above, and the void ratio was calculated using the following calculation formula 3.
[Calculation Formula 3]
Void ratio (%) = void area / (void area + solder alloy / Cu substrate bonding area) × 100
Tables 3 and 4 show the measurement results of the void ratio of the joined body.

<Heat cycle test (reliability evaluation)>
A heat cycle test was conducted to evaluate the reliability of solder joints. This test was performed using the joined body shown in FIG. 4 in which the solder alloy and the Cu substrate obtained in the same manner as the evaluation of the joining property were joined. First, the bonded body was cooled at −40 ° C. and heated at 230 ° C. as one cycle, and this was repeated for a predetermined cycle. Thereafter, the Cu substrate to which the solder alloy was bonded was embedded in the resin, the cross section was polished, and the bonded surface was observed with SEM (S-4800, manufactured by Hitachi, Ltd.). The case where the joint surface was peeled or cracked in the solder was indicated as “×”, and the case where there was no such defect and the same joint surface as in the initial state was maintained as “◯”.
Tables 3 and 4 show the heat cycle test results of the joined bodies.

（注）表中の※を付した試料は比較例である。

(Note) Samples marked with * are comparative examples.

（注）表中の※を付した試料は比較例である。

(Note) Samples marked with * are comparative examples.

  As can be seen from Tables 3 and 4 above, each of the solder alloys of Samples 1 to 20 and 31 to 71 of the present invention shows good characteristics in each evaluation item. That is, in the wetting and spreading property evaluation, all samples are uniformly spread in a circular shape with an aspect ratio of 1.09 or less, and in the joining property evaluation, there is almost no void, and the heat cycle is a reliability evaluation. In the test, no defects occurred in all samples up to 500 cycles. The reason why such a good result was obtained is that the aspect ratio of the solder alloy of the present invention is within the determined range and the alloy composition is within the composition range.

  On the other hand, each of the solder alloys of Samples 21 to 28 and 72 to 91, which are comparative examples, resulted in an undesirable result in at least one of the characteristics. That is, in the evaluation of the wet spreading property, the aspect ratio of all samples was 1.67 or more and spread unevenly. Moreover, in evaluation of joining property, many voids generate | occur | produced with about 10-23%. In the heat cycle test, which is an evaluation of reliability, defects occurred up to 300 cycles for samples other than samples 21, 22, 27, 28, 72, 73, 90, 91, and up to 500 cycles for all samples. There was a defect.

Furthermore, the solder alloy of the present invention has an Au content of 49.5% by mass or less, and currently 80% by mass Au-20% by mass alloy and 87.5% by mass Au-12.5% by mass Ge. The Au content is much lower than that of the alloy, and thus the cost is very low. In addition, since the ball yield is high, the cost is further reduced.
As described above, the solder alloy of the present invention is excellent in various characteristics, low in cost, and has a low melting point as compared with Au-Ge alloy, etc., so that it has the characteristics that it is very easy to use and can be manufactured safely. Yes.

1 Cu substrate 2 Ni plating 3 Solder alloy

Claims (6)

  It is a ball-shaped Au—Sn—Ag solder alloy, and its shape has an aspect ratio (“major axis ÷ minor axis, or long side ÷ short side”, the same applies hereinafter) of 1.00 or more. 20 or less, Sn is contained in an amount of 42.0 mass% or more and 50.0 mass% or less, Ag is contained in an amount of 2.0 mass% or more and 9.0 mass% or less, and the remainder is an element inevitably included in production. An Au—Sn—Ag solder alloy characterized by being made of Au.   The aspect ratio is 1.00 or more and 1.20 or less, Sn is contained in 44.0% by mass or more and 48.0% by mass or less, Ag is contained in 3.0% by mass or more and 7.0% by mass or less, and the balance The ball-shaped Au—Sn—Ag solder alloy according to claim 1, wherein the ball-shaped Au—Sn—Ag solder alloy is made of Au, excluding elements inevitably contained in production.   Furthermore, it contains any one or more of Al, Cu, Ge, In, Mg, Ni, Sb, Zn and P. When Al is contained, 0.01% by mass to 0.8% by mass and Cu is contained. In the case of containing Ge, 0.01% to 1.0% by weight in the case of containing Ge, and 0.01% to 1.0% in the case of containing In. % By mass or less, 0.01% by mass or more and 0.5% by mass or less when Mg is contained, 0.01% by mass or more and 0.7% by mass or less when Ni is contained, and 0. The present invention is characterized by containing from 0.01% by mass to 0.5% by mass, 0.01% by mass to 5.0% by mass in the case of containing Zn, and 0.500% by mass or less in the case of containing P. Item 3. The ball-shaped Au—Sn—Ag solder alloy according to item 1 or 2.   The ball-shaped Au-Sn-Ag solder alloy according to any one of claims 1 to 3 is crushed from one direction and has an aspect ratio of more than 1.00 and not more than 1.50. -Sn-Ag solder alloy.   An electronic component, which is sealed using the ball-shaped Au—Sn—Ag solder alloy according to claim 1.   6. An electronic component mounting apparatus, wherein the electronic component according to claim 5 is mounted.

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