JP2015020189A - Pb-FREE Au-Ge-Sn-BASED SOLDER ALLOY MAINLY CONTAINING Au - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Pb-free solder alloy for high temperature which is excellent in various properties such as processability and the like, which can be sufficiently used even at a joint required for high reliability and which is inexpensive while Au is a main component.SOLUTION: In a solder alloy where the content of Ge is 0.01 mass% or more and 10.0 mass% or less, the content of Sn is 32.0 mass% or more and 40.0 mass% or less, one or more kinds among Al, Cu, Mg, Ni, Sb and Zn is contained and the balance is composed of Au and inevitable impurities, the content of Al when being contained is 0.01 mass% or more and 1.5 mass% or less, the content of Cu when being contained is 0.01 mass% or more and 1.0 mass% or less, the content of Mg when being contained is 0.01 mass% or more and 0.8 mass% or less, the content of Ni when being contained is 0.01 mass% or more and 1.0 mass% or less, the content of Sb when being contained is 0.01 mass% or more and 0.8 mass% or less and the content of Zn when being contained is 0.01 mass% or more and 3.0 mass% or less.

Description

  The present invention relates to an Au—Ge—Sn based solder alloy that does not contain Pb and contains Au as a main component.

  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 (Pb) has been used as a main component for solder materials for a long time, but lead has already become a regulated substance under the RoHS directive and the like. For this reason, development of solder containing no lead (hereinafter referred to as lead-free solder or lead-free solder) has been actively conducted.

  Solders used when joining electronic components to a substrate are roughly classified into high temperature (about 260 ° C. to 400 ° C.) and medium to low temperature (about 140 ° C. to 230 ° C.) depending on the use limit temperature. As for the solder for medium and low temperature, lead-free solder is put into practical use, which contains Sn as a main component. For example, in Patent Document 1, Sn is the main component, Ag is 1.0 to 4.0 mass%, Cu is 2.0 mass% or less, Ni is 0.5 mass% or less, and P is 0.2 mass%. The following lead-free solder alloy composition is described, and Patent Document 2 contains 0.5 to 3.5% by mass of Ag, 0.5 to 2.0% by mass of Cu, and the balance is Sn. A lead-free solder of composition is described.

  On the other hand, research and development is being conducted in various organizations for lead-free solder for high temperatures. For example, Patent Document 3 discloses a Bi / Ag brazing material containing 30 to 80% by mass of Bi and having a melting temperature of 350 to 500 ° C. Patent Document 4 discloses a solder alloy in which a binary eutectic alloy is added to a eutectic alloy containing Bi and an additional element is further added. This solder alloy is a multi-component solder of a quaternary system or higher. However, it has been shown that the liquidus temperature can be adjusted and variations can be reduced.

  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 a quartz device, a SAW (surface acoustic wave) filter, a MEMS (microelectromechanical system), or the like. For example, in Patent Document 5, Au—Ge, Au—Sb, or Au—Si plate-like low melting point Au alloy brazing is preheated, and then the material is sequentially sent to a press die provided with a heat insulation section. It describes a pressing method for a plate-shaped low melting point Au alloy brazing, characterized in that pressing is performed in a temperature range of from 0C to 350C.

  Patent Document 6 describes a brazing material used for brazing external leads of electronic components such as semiconductor packages, which contains 10 to 35 wt% of Ag, and includes at least one of In, Ge, and Ga in total. An Au alloy containing 3 to 15 wt% with the balance being Au is described. This Au alloy has a time to short-circuit in the electromigration test of 1.5 hours or more, and is shown to be a brazing material having excellent electromigration prevention properties.

  Further, Patent Document 7 describes a brazing material of a ternary alloy containing Au / Ge / Sn, where Ts is a temperature at which a liquid phase starts to be generated and Tl is a temperature at which the liquid phase becomes completely liquid. It describes a brazing material characterized by being <50 ° C. And according to this patent document 7, while realizing lead-free, it does not melt at the reflow temperature, and the temperature for joining is too high so that the adhesive and the component itself are not damaged. It is said that a brazing material suitable for joining of the above can be provided.

Japanese Patent Application Laid-Open No. 11-077366 JP-A-8-215880 JP 2002-160089 A JP 2008-161913 Japanese Patent Laid-Open No. 03-204191 Japanese Patent Laid-Open No. 03-138096 JP 2007-160340 A

  Although various reports and proposals have been made on the high-temperature lead-free solder material in addition to the above-described patent documents, a low-cost and versatile solder material has not yet been found. That is, since electronic materials such as semiconductor devices and substrates are generally made of materials with relatively low heat resistance such as thermoplastic resins and thermosetting resins, the working temperature during bonding is less than 400 ° C., Desirably, the temperature is 370 ° C. or lower. 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., it is estimated that the working temperature at the time of joining is also 400 to 700 ° C. or more and is joined. It will exceed the heat resistance temperature of electronic parts and substrates.

  In addition, Au—Sn solder and Au—Ge solder have been put to practical use as Au solder, but since these Au solders use a large amount of extremely expensive Au, general-purpose Pb solder or Sn solder. It is very expensive compared to such as. Therefore, it is mainly used only for soldering a portion requiring particularly high reliability, such as a crystal device, a SAW filter, and a MEMS.

  In addition, since Au-based solder is very hard and difficult to process, for example, it takes time when rolling into a sheet shape, and a special material that does not easily wrinkle the roll must be used. There will be a cost. In addition, since the Au-based solder is hard and brittle, cracks and burrs are likely to occur during press molding, and the yield is significantly lower than other solders. When processing into a wire shape, there is a similar serious problem, and even if an extruder with a very high pressure is used, the extrusion speed cannot be increased because it is hard, and it is about 1 / 100th of Pb solder. There is only productivity.

  In order to deal with various problems of Au solder including the above problems, the techniques described in Patent Documents 5 to 7 have been proposed. However, the technique of Patent Document 5 has the following problems. That is, the material characteristics of a plate-like (sheet-like) low melting point Au alloy brazing material such as Au—Ge, Au—Sb, and Au—Si are brittle like a glass plate at room temperature and generally have a directionality. The plane parallel to the longitudinal direction is liable to break even with a slight bending, and has a drawback that the propagation of cracks easily proceeds.

  In such a case, press working may be performed using a so-called compound mold, but this compound mold technique also has a problem of mold accuracy and a problem of mold life. Therefore, Patent Document 5 proposes a technique in which materials are sequentially sent to a press die provided with a heating and heat retaining unit and pressed in a temperature range of 100 to 350 ° C. However, there are many problems even in such warm press working.

  That is, in the warm press, the oxidation of the solder alloy proceeds. Therefore, even Au-based solder containing a large amount of Au cannot prevent the progress of oxidation of other metals contained therein, such as Ge, Sb, or Sn, and is pressed at a temperature higher than room temperature. Sometimes the surface is oxidized and the wettability is greatly reduced. Furthermore, since the temperature is high, the solder expands compared to the normal temperature, and even if it is devised, the accuracy of the shape cannot be obtained compared to the press at the normal temperature. In addition, the softened solder tends to stick to the mold and is pressed in a state where the solder is bent or distorted, so that burrs and chips are likely to occur.

  In addition, as described above, Patent Document 6 discloses an electromigration of an Au alloy containing 10 to 35 wt% of Ag, including 3 to 15 wt% in total of at least one of In, Ge and Ga, and the balance being Au. A preventive brazing material is described. Electromigration can be prevented by using Au as a main component, brazing strength can be obtained by adding 10 to 35 wt% of Ag as an additive element, and at least one of In, Ge, and Ga is 3 in total. It is described that the melting point can be lowered by adding ˜15 wt%.

  However, the Au alloy described in Patent Document 6 can prevent the occurrence of electromigration and has a strong and stable brazing strength in comparison with an Ag-based brazing material of Ag-28 wt% Cu or Ag-15 wt% Cu. It was developed as a brazing material to be obtained. For this reason, the Ag content is relatively high, the melting point is lowered, and the solder material is easy to use, and the strength and the electromigration preventing effect are sufficient as compared with conventional Au-based alloys such as Au-Ge alloys. Absent.

  Further, in Patent Document 7, a brazing material of a ternary alloy containing Au / Ge / Sn, where Ts is a temperature at which the liquid phase starts to be generated and Tl is a temperature at which the liquid phase is completely formed is Tl. -Ts <50 degrees, which describes a brazing material, which achieves lead-free, does not melt at the reflow temperature and is too hot for bonding, for example adhesives In addition, it has been shown that a brazing material suitable for joining electrical / electronic components that does not damage the components themselves can be provided.

  However, the ternary alloy brazing material containing Au / Ge / Sn described in Patent Document 7 has a very wide composition range in which the difference between the liquidus temperature and the solidus temperature is less than 50 ° C. In such a wide composition range, only a brazing material having the same effects and characteristics cannot be obtained. As an easy-to-understand example, when comparing an Au-12.5 mass% Ge alloy (eutectic point composition) and an Au-20 mass% Sn alloy (eutectic point composition) belonging to the above composition range, the characteristics are as follows: Obviously different.

  That is, since Ge is a metalloid, the Au-12.5 mass% Ge alloy is clearly inferior in workability compared to the Au-20 mass% Sn alloy. For example, when rolling, the yield of Au-12.5 mass% Ge is lower due to the occurrence of cracks and the like. Naturally, when a small amount of the third element is added to these, there is a composition range in which the third element is dissolved and the characteristics do not greatly change. For example, Au-12.5 mass% Ge-Sn alloy and Au-20 The characteristics of the mass% Sn—Ge alloy are greatly different.

  Furthermore, when considering the Ge—Sn alloy, the solidus temperature is 231 ° C., and the melting point is too low as a high-temperature solder. Naturally, even when a small amount of Au is dissolved in the Ge—Sn alloy, there is a region where the difference between the liquidus temperature and the solidus temperature defined in the claims of the above Patent Document 7 is less than 50 ° C., As a high-temperature solder, the melting point is still too low.

  The present invention has been made in view of the above-described conventional circumstances, and is excellent in various characteristics such as wettability, workability, stress relaxation, and bonding properties, and extremely high in crystal devices, SAW filters, MEMS, and the like. An object of the present invention is to provide a lead-free high-temperature Au—Ge—Sn based solder alloy solder that can be used sufficiently even in a joint that requires reliability and that is inexpensive and contains Au as a main component.

  In order to achieve the above object, the Au—Ge—Sn solder alloy provided by the present invention contains Ge in an amount of 0.01 mass% to 10.0 mass% and Sn in an amount of 32.0 mass% to 40.0 mass%. An Au-Ge-Sn based solder alloy containing not more than mass%, containing at least one of Al, Cu, Mg, Ni, Sb, and Zn, the balance being Au and inevitable impurities, When it contains, the content is 0.01 mass% or more and 1.5 mass% or less, When it contains Cu, the content is 0.01 mass% or more and 1.0 mass% or less, When it contains Mg The content is 0.01 mass% or more and 0.8 mass% or less. When Ni is contained, the content is 0.01 mass% or more and 1.0 mass% or less. When Sb is contained, the content is 0.01 mass% or more and 0.8 mass% or less, and when containing Zn, the content is It is characterized in that a 0.01 wt% to 3.0 wt% or less.

  The Au—Ge—Sn solder alloy of the present invention may further contain P in an amount of 0.500% by mass or less. Moreover, this invention provides the quartz crystal device or SAW filter sealed using the above-mentioned Au-Ge-Sn type solder alloy of this invention.

  According to the present invention, it does not contain lead, has wettability equivalent to that of conventional Au-based solder, is excellent in various properties such as workability, stress relaxation property, and bondability, and has Au as a main component. However, it is possible to provide a high-temperature Au—Ge—Sn solder alloy that is inexpensive and can be used in places where extremely high reliability is required, such as crystal devices, SAW filters, and MEMS. . Since the Au—Ge—Sn based solder alloy of the present invention is particularly excellent in workability, productivity can be improved, and further cost reduction can be realized.

It is an Au-Sn-Ge system phase diagram. It is sectional drawing which shows typically embodiment of the wettability test which soldered the solder alloy on Cu substrate which has Ni layer. It is a side view which shows typically the aspect-ratio measurement state in the wettability test of FIG. It is a top view which shows typically the aspect-ratio measurement state in the wettability test of FIG.

  The composition of the Au—Ge—Sn solder alloy of the present invention contains Ge in an amount of 0.01% to 10.0% by mass, Sn in an amount of 32.0% to 40.0% by mass, Al An Au—Ge—Sn solder alloy containing at least one of Cu, Mg, Ni, Sb, and Zn, the balance being Au except for inevitable impurities and P added as necessary. In the case where Al is contained, the content is 0.01 mass% or more and 1.5 mass% or less, and in the case where Cu is contained, the content is 0.01 mass% or more and 1.0 mass% or less, and Mg is contained. When it contains, the content is 0.01 mass% or more and 0.8 mass% or less, When it contains Ni, the content is 0.01 mass% or more and 1.0 mass% or less, and when it contains Sb The content is 0.01 mass% or more and 0.8 mass% or less, and when Zn is contained, the content is The amount was 0.01 mass% or more 3.0 wt% or less, if containing P is the content of 0.500 mass% or less.

  The Au—Ge—Sn solder alloy of the present invention is a main component in order to reduce the cost of Au—Ge solder and Au—Sn solder, which are very expensive, and to have excellent workability. Sn and Ge are added to Au. In other words, in a ternary alloy of Au, Sn, and Ge, the composition near the eutectic point is basically used to achieve excellent workability and stress relaxation, and thus high bonding reliability, and Sn. Since the contents of Ge and Ge are large, the Au content can be lowered and the cost is reduced.

  Furthermore, the Au—Ge—Sn solder alloy of the present invention is required for a solder alloy by making it an essential requirement to contain at least one of Al, Cu, Mg, Ni, Sb and Zn. Various characteristics can be adjusted, and it can be used for a wide range of applications. In addition, since the Au content can be further reduced, a lower-cost solder material is realized. Hereinafter, the essential elements contained in the Au—Ge—Sn solder alloy of the present invention and the elements contained as necessary will be described in more detail.

<Au>
Au is a main component of the solder alloy of the present invention and is an essential element. Since Au is very difficult to oxidize, it has the most suitable characteristics as a solder for joining and sealing of electronic parts that require high reliability. Therefore, Au-based solder is frequently used for sealing quartz devices and SAW filters. Also in the solder alloy of the present invention, Au is a basic component, and a solder suitable for use in the technical field as described above is provided.

  However, since Au is a very expensive metal, it is desirable not to use it as much as possible from the viewpoint of cost. Therefore, it is rarely used for general-purpose products. On the other hand, in the solder alloy of the present invention, as will be described later, by adding both Sn and Ge to Au, Au-20 mass% Sn and Au-12 are obtained in terms of characteristics such as bondability and reliability. While securing the same level as that of a 0.5 mass% Ge solder alloy, the content of Au is reduced to enable low cost.

  Furthermore, it is an essential requirement to contain at least one of Al, Cu, Mg, Ni, Sb, and Zn. By adopting such an alloy composition, it is possible to adjust various properties required for solder alloys and to be used in a wide range of applications, and further, the Au content can be further reduced. Realizes low-cost solder materials.

<Ge>
Ge is an essential element in the solder alloy of the present invention. Since Ge makes a eutectic alloy with Au and the solidus temperature can be lowered to 361 ° C., it has been practically used as Au-12.5 mass% Ge solder. However, Au-12.5 mass% Ge solder is very expensive because it contains nearly 90 mass% of Au. In order to reduce the Au content, the solder alloy of the present invention has a composition in the vicinity of the eutectic point in the ternary Au—Ge—Sn alloy.

  In the Au—Ge—Sn ternary system, the composition of eutectic points is around Au = 47 atomic%, Ge = 6 atomic%, and Sn = 47 atomic%. That is, when the unit is represented by mass%, Au = 60.6 mass%, Ge = 2.8 mass%, and Sn = 36.5 mass%. FIG. 1 shows an Au—Ge—Sn phase diagram. By setting the composition in the vicinity of the eutectic point, a solder alloy having excellent properties such as workability and stress relaxation can be obtained. In addition, the melting point of the solder alloy can be lowered to about 410 ° C. from the melting point of each element, which makes it very easy to use as a solder.

  The specific Ge content is 0.01 mass% or more and 10.0 mass% or less. If the Ge content is less than 0.01% by mass, the effect of containing Ge is not substantially exhibited because the Ge content is too small. On the other hand, if it exceeds 10.0 mass%, the liquidus temperature becomes too high and it becomes difficult to melt. On the other hand, if the Ge content exceeds 10.0% by mass, the solder alloy is likely to be oxidized, and good bonding with high reliability, which is a characteristic of Au solder, cannot be achieved. The particularly preferable Ge content is 2.0% by mass or more and 3.5% by mass or less, and if it is in this range, it becomes close to the composition of the eutectic point, so that it has excellent workability and flexibility. Even better bonding is possible.

<Sn>
Sn is an essential element in the solder alloy of the present invention, and is an indispensable element because it has a composition near the ternary eutectic point. The above-described Au-12.5 mass% Ge solder and Au-20 mass% Sn solder, which are representative solders of Au-Ge alloy and Au-Sn alloy, have a composition of eutectic points, and thus the crystal is refined. It is relatively flexible. However, even in the case of an eutectic alloy, Ge is a semimetal in the case of Au-12.5 mass% Ge, and is composed of an intermetallic compound in the case of Au-20 mass% Sn. Compared to Sn solder and Sn solder, it is quite hard and brittle.

  For this reason, it is difficult to process. For example, when processing into a sheet by rolling, the thickness can only be reduced little by little, so that productivity is poor, and a large number of cracks are likely to occur, and the yield tends to decrease. In the case of processing into a ball shape, for example, when the ball is formed by the atomizing method, the noise tip is easily clogged, the particle size distribution of the ball is widened, and the yield is low. In particular, in the case of atomizing in oil, the temperature during atomization cannot be raised to a temperature sufficiently higher than the solidus temperature (361 ° C.) of the Au—Ge alloy in order to prevent oil ignition and deterioration. The alloy is easily segregated, and the nozzle is easily clogged, resulting in a decrease in yield.

  Therefore, by adding Sn to Au together with Ge, problems such as workability, productivity, and reliability can be solved. That is, by including both Sn and Ge, it becomes possible to obtain a eutectic composition of Au—Sn intermetallic compound and Ge solid solution, and the crystal becomes finer, and the workability, productivity, stress relaxation, Becomes a solder material with excellent reliability. Naturally, the content of expensive Au can be reduced by adding about 30 to 50% by mass of Sn and Ge, so that it is much larger than Au-12.5% by mass and Au-20% by mass Sn. Cost can be reduced.

  The Sn content is 32.0 mass% or more and 40.0 mass% or less. When the Sn content is less than 32.0% by mass, effects such as improvement in flexibility are not sufficiently exhibited, and the difference between the liquidus temperature and the solidus temperature becomes large, causing a phenomenon of separation. On the other hand, if the Sn content exceeds 40.0% by mass, the melting phenomenon is likely to occur in the same manner, and the Sn content that is easily oxidized as compared with Au is excessively increased, resulting in a decrease in wettability. There is a high possibility of being. The particularly preferable Sn content is 34.0% by mass or more and 39.0% by mass or less, and if it is within this range, the composition of the eutectic point is close and the above-described effect of Sn is sufficiently exhibited.

<Al, Mg>
Al and Mg are added under the condition that at least one selected from the group consisting of Cu and Zn described later is contained in order to improve or adjust various properties of the solder alloy of the present invention. The main effects obtained by adding any of Al and Mg are almost the same. That is, Al and Mg are more easily oxidized than Au, Ge, and Sn, and are preferentially oxidized by adding these elements to the Au—Ge—Sn solder alloy, and precipitate on the solder surface to form a thin oxide. Create a physical layer. Oxidation of the elements constituting the parent phase is suppressed by the oxidation of Al or Mg, and further, the formation of the thin oxide layer makes it difficult for oxygen atoms to penetrate into the solder. The wettability is improved.

  More specifically, Al is a solid solution of several mass% in Au. Since Al dissolved in this manner is overwhelmingly bonded to oxygen more than Au, Ge, or Sn when the solder alloy is heated and joined, it precipitates on the solder surface and forms an oxide layer. Thus, when Al is oxidized by itself, oxidation of Au, Ge, and Sn is suppressed, and an oxide layer is formed thinly. The formation of this thin oxide layer facilitates direct contact between the substrate or semiconductor element and the molten solder alloy as a metal during bonding. As a result, wettability and bondability are improved.

  However, if too much Al is contained, the thickness of the oxide layer due to Al becomes thick, and the wettability may be reduced instead. For this reason, the upper limit of the optimal content of Al is 1.5 mass%. If it is 1.5 mass% or less, favorable wettability and bondability will be acquired, and if it is 0.7 mass% or less, the effect of containing Al will appear further and it is preferable. On the other hand, the lower limit of the Al content is 0.01% by mass. If it is less than 0.01% by mass, the content is too small, and the effect does not substantially appear.

  On the other hand, Mg, like Al, is an element that is added as appropriate in order to improve or adjust various properties in the present invention, and the main expected effect is to improve wettability. Mg is more easily oxidized than Al, and is more effective than Al when exerting an effect of improving wettability. Therefore, it is effective in a small amount. However, Mg cannot be contained so much. The reason is that Mg is easier to bond with oxygen than Al, so that it is easy to form a strong oxide layer, and even a relatively thin oxide film can cause a decrease in wettability. Therefore, the upper limit of the Mg content is 0.8% by mass. When the content is 0.8% by mass or less, good wettability can be obtained, and when the content is 0.3% by mass or less, the effect is more remarkable and preferable. On the other hand, the lower limit of the Mg content is 0.01% by mass. If it is less than 0.01% by mass, the effect is not substantially exhibited because the amount is too small.

  As described above, Al and Mg have an effect common to each other, but may be contained in the solder alloy in consideration of the characteristics of each element. For example, the melting points of Al and Mg are 660 ° C. for Al and 650 ° C. for Mg, respectively. Therefore, when adjusting the melting point such as the liquidus temperature of the solder alloy, the melting points of Al and Mg may be included as a reference. As for the wettability, the reducing property is strong in the order of Mg and Al, and therefore the wettability improving effect is large in this order. Furthermore, in consideration of the properties of the solid solution and intermetallic compound produced when these elements are contained, the elements and the contents may be determined so as to adjust appropriately to the intended characteristics.

<Cu, Ni, Sb>
The condition that Cu, Ni, and Sb contain at least one selected from the group consisting of Al, Mg, and Zn described later in order to improve or adjust various properties of the solder alloy of the present invention. The main effects obtained by adding any of these elements of Cu, Ni, and Sb are almost the same, and the workability and stress relaxation are improved.

  That is, Cu, Ni, and Sb are first precipitated when the solder alloy is melted and solidified, and fine crystals grow using it as a nucleus, so that the structure becomes a fine crystal structure. It becomes easy to stop at the grain boundary. This makes it difficult for cracks to develop even when various stresses such as thermal stress are applied to the solder alloy, and even when processed into sheet materials, cracks and other defects are suppressed, and joint reliability is dramatically improved. To do.

  Since the effect of improving workability is exhibited by the above-described mechanism, it is not preferable to increase the contents of Cu, Ni, and Sb. This is because if the content of these elements is too large, the density of the nuclei increases, the crystal grains are coarsened instead of being refined, and the effect of addition is halved. Therefore, the upper limit when Cu is contained is 1.0 mass%. Further, the lower limit is 0.01% by mass, and if this value is not reached, the precipitation of nuclei is too small and the effect of improving workability cannot be obtained substantially. For the same reason, the Ni content is 0.01% by mass or more and 1.0% by mass or less, and the Sb content is 0.01% by mass or more and 0.80% by mass or less. By setting it as such a composition range, it can become a solder alloy which has a favorable characteristic.

<Zn>
Zn is an element added under the condition that at least one of the group consisting of Al, Cu and the like described above is contained in order to improve or adjust various properties of the solder alloy of the present invention. The main effect obtained by containing this element is to improve workability and stress relaxation. However, it is different from Cu, Ni and Sb in the mechanism for improving workability and the like.

  That is, Zn dissolves in Au and forms a eutectic alloy with Ge. This eutectic alloying improves workability. However, Zn is an element that is easily oxidized, and therefore, oxidation proceeds excessively depending on conditions at the time of manufacturing the solder alloy. For this reason, it is necessary to consider Zn content including a manufacturing method, and the upper limit is 3.0 mass% substantially. If the amount exceeds this value, the oxide layer becomes thick even under the production conditions in which oxidation is suppressed as much as possible, and good bonding cannot be obtained. On the other hand, the lower limit of the Zn content is 0.01% by mass. If it is less than 0.01% by mass, the content is too small and the effect does not substantially appear.

<P>
P is an arbitrary element added as necessary in the solder alloy of the present invention, and its effect is in improving wettability. Explaining the mechanism by which P improves wettability. P is strongly reducible, and P itself is oxidized, thereby suppressing the oxidation of the solder alloy surface and reducing the substrate surface, resulting in improved wettability. Let

  In general, an Au-based solder is excellent in wettability because it is difficult to oxidize, but the oxide on the joint surface cannot be removed. On the other hand, 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 both the oxide film on the solder surface and the oxide film on the bonding 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 P is contained in the solder alloy of the present invention, the P content 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. Containment may cause a large amount of P or P oxide gas to increase the void ratio, or P may segregate by forming a fragile phase, embrittle the solder joint and reduce reliability. Because 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, Ge, Sn, Al, Cu, Mg, Sb, Zn, and P each having a purity of 99.9% 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 made fine to 3 mm or less. A predetermined amount of these raw materials was weighed and placed in a graphite crucible for a high-frequency melting furnace. In addition, when making P contain, it melt | dissolved using the Sn-P alloy as a raw material. If it does in this way, since P which is easy to vaporize is alloyed from the beginning, it becomes easy to make it contain in solder.

  Next, the graphite crucible containing the raw material was put into a high-frequency melting furnace, and nitrogen was flowed at a flow rate of 0.7 liter / min or more per 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 for atomizing in liquid was used.

  In this way, the solder mother alloy of Sample 1 was produced. Moreover, the solder mother alloys of Samples 2 to 45 were produced in the same manner as Sample 1 except that the mixing ratio of the raw materials was changed. About each solder mother alloy of these samples 1-45, the composition analysis was performed using the ICP emission-spectral-analyzer (SHIMAZU S-8100). The obtained analysis results are shown in Table 1 below.

  Each solder mother alloy of Samples 1 to 45 was processed into a ball shape using a submerged atomizer by the following method. As the liquid at that time, oil having a large effect of suppressing the oxidation of solder was used. The ball of each sample obtained was classified into a predetermined particle size by the following method, the yield was examined, and the workability was evaluated.

<Ball manufacturing method>
Put each master alloy (diameter 24mm) of prepared samples 1-45 into the nozzle of submerged atomizer, and set this nozzle on the top of quartz tube containing oil heated to 390 ° C (in high frequency melting coil) did. After heating the mother alloy in the nozzle to 650 ° C. by high frequency and holding it for 5 minutes, pressure was applied to the nozzle with an inert gas and atomization was performed to produce a ball-shaped solder alloy. The ball diameter was set to 0.30 mm, and the nozzle tip diameter was adjusted in advance.

<Evaluation of workability (ball yield)>
In order to evaluate the workability of the solder alloy, the balls obtained by the above manufacturing method using a two-stage classifier composed of two types of sieves having different opening diameters are within a range of 0.30 ± 0.015 mm in diameter. Classified. Specifically, a high-precision circular through hole is drilled by laser processing on a stainless steel plate having a thickness of 0.1 mm to obtain a sieve having an opening diameter of 0.315 mm for the upper stage and an opening diameter of the lower stage of 0 mm. A .285 mm sieve was prepared, and these were set, and in a single classification, defective products that were less than the lower limit of the standard value and defective products that exceeded the upper limit of the standard value were selected and removed. The yield of the balls thus obtained was calculated according to the following calculation formula 1.

[Calculation Formula 1]
Ball yield (%) = ball weight of diameter 0.30 ± 0.015 mm ÷ classified ball weight × 100

  Next, a bonding test with the substrate was performed using each of the ball-shaped solder alloys prepared from the mother alloys of Samples 1 to 45 described above, and the aspect ratio and The void ratio was measured, and the results were regarded as wettability evaluation and bondability evaluation, respectively. Furthermore, the heat cycle test was done with the following method with respect to the board | substrate and solder joined body obtained by the said joining test, and it was set as reliability evaluation.

<Evaluation of wettability (measurement of aspect ratio)>
Start up a wettability tester (device name: atmosphere control type wettability tester), cover the heater part to be heated with a double cover, and let nitrogen gas flow at a flow rate of 12 liters / minute from around the heater part. did. Thereafter, the heater was set to a temperature higher than the melting point by 50 ° C. and heated.

  After the heater temperature is 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 section and heated for 25 seconds, and then each ball-shaped solder The 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.

  The bonded body of the Cu substrate and the solder alloy thus obtained is in a state in which the solder alloy 3 is bonded to the Ni layer 2 of the Cu substrate 1 as shown in FIG. The ratio was determined. Specifically, the maximum solder height Y shown in FIG. 3 and the maximum solder wetting spread length X1 and the minimum solder wetting spread length X2 shown in FIG. 4 were measured, and the aspect ratio was calculated by the following calculation formula 2. . It can be determined that the higher the aspect ratio, the thinner the joined solder and the wider the area, and the better the wettability.

[Calculation Formula 2]
Aspect ratio = [(X1 + X2) ÷ 2] ÷ Y

<Evaluation of bondability (measurement of void fraction)>
With respect to the joined body shown in FIG. 2 obtained in the same manner as in the evaluation of the wettability, the void ratio of the Cu substrate 1 to which the solder alloy is joined is determined by an X-ray transmission device (TOSMICRON-6125, manufactured by Toshiba Corporation). It measured using. Specifically, X-rays were transmitted vertically through the joint surface of the solder alloy 3 and the Cu substrate 1 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

<Reliability evaluation (heat cycle test)>
The joined body shown in FIG. 2 obtained in the same manner as in the evaluation of the wettability was repeated for a predetermined number of cycles, with -40 ° C. cooling and 250 ° C. heating as one cycle. Thereafter, the Cu substrate to which the solder alloy was bonded was embedded in the resin, cross-section polishing was performed, and the bonding surface was observed with SEM (S-4800, manufactured by Hitachi, Ltd.). The case where the joint surface was peeled off or the solder alloy was cracked was indicated as “X”, and the case where there was no such defect and the same joint surface as in the initial state was maintained as “◯”. The results of this heat cycle test (reliability evaluation) are shown in Table 2 below together with the above-described ball yield (workability evaluation), aspect ratio (wetting evaluation), and void ratio (bondability evaluation).

  As can be seen from Table 2 above, each of the solder alloys of Samples 1 to 26 that satisfy the requirements of the present invention exhibits good characteristics in each evaluation item. That is, the ball yield, which is an evaluation of workability, is as high as 47% at the minimum, and Au-12.5 mass% Ge (46%) of the sample 44 which is a comparative example, Au-20 mass% Sn (46 of the sample 45) %) Is not inferior. Further, all of the aspect ratios were 6 or more, the solder was thin and spread widely and had good wettability. The highest void ratio was 0.3%, indicating good bondability. And in the heat cycle test which is a test regarding reliability, no defect appeared even after 500 cycles, and good results were obtained.

  On the other hand, each of the solder alloys of Samples 27 to 45, which are comparative examples, resulted in an undesirable result in at least any of the characteristics. That is, even if the ball yield was high, it was 46%, which was lower than that of any sample of the present invention, and the void ratio was 0.7 to 8.0%, which was clearly worse than that of any sample of the present invention. The aspect ratio is 4 or less except for samples 27, 29, 37, 40, 44, and 45. In the heat cycle test, all samples are defective up to 500 times except for samples 40, 44, and 45. There has occurred.

  In addition, the solder alloys of Samples 1 to 26 in the above examples are not only good results in the evaluation of the above characteristics, and the Au content is as low as 64.8% by mass at the maximum. This Au content is less than Au-12.5 mass% Ge of sample 44 and Au-20 mass% Sn of sample 45, which are the most common eutectic compositions in Au-Ge solder alloys. It can be seen that the Au—Ge—Sn based solder alloy of the present invention is low cost.

1 Cu substrate 2 Ni layer 3 Solder alloy

Claims (4)

  Ge is contained in an amount of 0.01% to 10.0% by mass, Sn is contained in an amount of 32.0% to 40.0% by mass, and at least of Al, Cu, Mg, Ni, Sb, and Zn. In the case of containing an Al-containing Au-Ge-Sn solder alloy containing one type and the balance being Au and inevitable impurities, the content is 0.01 mass% or more and 1.5 mass% or less, Cu In the case of containing Ni, the content is 0.01 mass% or more and 1.0 mass% or less, and in the case of containing Mg, the content is 0.01 mass% or more and 0.8 mass% or less, and Ni is contained Has a content of 0.01 mass% to 1.0 mass%, and when it contains Sb, its content is 0.01 mass% to 0.8 mass%, and when it contains Zn, its content The Au—Ge—Sn system characterized in that the content is 0.01 mass% or more and 3.0 mass% or less. Alloy.   The Au-Ge-Sn solder alloy according to claim 1, further comprising P in an amount of 0.500 mass% or less.   A quartz crystal device sealed with the Au—Ge—Sn solder alloy according to claim 1.   A SAW filter sealed with the Au—Ge—Sn solder alloy according to claim 1.

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