JP6459472B2 - Pb-free Au-Ge solder alloy with controlled energy absorption and electronic component sealed or bonded using the same - Google Patents

Description

  The present invention relates to a Pb-free solder alloy containing Au as a main component, and more particularly to a Pb-free Au—Ge solder alloy whose energy absorption is controlled and an electronic component sealed or bonded using the same.

  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 also referred to as Pb-free solder or lead-free solder) has been actively conducted.

  Solder used when bonding a semiconductor element to a substrate is 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, as a lead-free solder material for medium and low temperatures, Patent Document 1 has Sn as a main component, Ag is 1.0 to 4.0 mass%, Cu is 2.0 mass% or less, and Ni is 1.0 mass%. Hereinafter, a lead-free solder alloy composition containing 0.2 mass% or less of P is disclosed, and Patent Document 2 discloses 0.5 to 3.5 mass% of Ag and 0.5 to 2.0 mass% of Cu. There is disclosed a lead-free solder having an alloy composition containing Sn and the balance being Sn.

  On the other hand, research and development is also underway at various institutions for high-temperature Pb-free solder. For example, Patent Document 3 discloses Bi / Ag brazing material containing 30 to 80 at% Bi and having a melting temperature of 350 to 500 ° C. Is disclosed. Patent Document 4 discloses a solder alloy in which a binary Kyochang alloy is added to a Bi-containing 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.

  Further, as an expensive high-temperature Pb-free solder material mainly composed of Au, an Au—Sn alloy, an Au—Ge alloy, or the like has electronic components such as a crystal device, a SAW filter, and a MEMS (microelectromechanical system). Used in electronic equipment. For example, in Patent Document 5, Au—Ge, Au—Sb, or Au—Si plate-like low melting point Au alloy solder is preheated, and then the material is sequentially sent to a press die provided with a heat insulation section. It describes a press working method for a plate-like low melting point Au alloy solder, characterized in that the press working is carried out in a temperature range of from 0 to 350 ° C.

  In Patent Document 6, as a brazing material used for brazing external leads of a semiconductor package, Ag is 10 to 35 wt%, at least one of In, Ge, and Ga is 3 to 15 wt% in total, and the balance An electromigration-preventing brazing material characterized in that the time until short-circuiting in an electromigration test is 1.5 hours or more. This brazing material can prevent electromigration by containing Au as a main component. As an effect of the additive element, the brazing strength can be obtained by adding 10 to 35 wt% of Ag. At least one of In, Ge, and Ga can be obtained. It is described that the melting point can be lowered by adding 3 to 15 wt% of the total types.

  Further, in Patent Document 7, in a brazing material of a ternary alloy containing Au—Ge, Tl−Ts <50 degrees when Ts is a temperature at which a liquid phase starts to be generated and Tl is a temperature at which a liquid phase is completely formed. It describes a brazing material characterized by the following. And according to this patent document 7, while realizing Pb-free, it does not melt at the reflow temperature, and does not damage the adhesive or the component itself by suppressing the temperature for bonding. 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

  Regarding lead-free solder materials for high temperatures, various reports and proposals have been made in addition to the cited references described above, but no low-cost and versatile solder materials have been found yet. That is, 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 during bonding is less than 400 ° C., preferably 370 ° C. or less. It is requested to be. 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 400 to 700 ° C. or more, and joining is performed. It will exceed the heat resistance temperature of electronic parts and substrates.

  In addition, in the case of Au-Sn solder or Au-Ge solder, a very large amount of Au is used, so it is very expensive compared to general-purpose Pb solder or Sn solder, and has been put to practical use. However, its application is limited to soldering where particularly high reliability is required, such as quartz devices, SAW filters, and 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, or a roll of a special material that is difficult to wrinkle must be used. Cost. In addition, since the Au-based solder is hard and brittle at the time of press molding, cracks and burrs are likely to occur, and the yield is significantly lower than other solders. There is a similar serious problem when processing into a wire shape, and even if a very high pressure extruder is used, the extrusion speed is slow because it is hard, and the productivity is about one hundredth of that of Pb solder. There is only.

  In order to deal with various problems of the Au-based 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. In other words, the material characteristics of Au-Ge, Au-Sb, Au-Si and other plate-like (sheet-like) low-melting point Au alloy solders are brittle like glass plates at room temperature and generally have a directionality. The surface parallel to the longitudinal direction has a problem that it is easy to break even with a slight bending, and the propagation of cracks easily proceeds. As a countermeasure against this, press working using a compound mold has been conventionally performed. However, even in this compound mold technology, there are problems of mold accuracy and mold life.

  In Patent Document 5, it is shown that a technique is adopted in which a material is 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 in such warm press working. That is, in the warm press, the oxidation of the solder alloy proceeds. Therefore, even if the solder contains a large amount of Au, Au-based solder containing other metals such as Ge, Sb, or Sn cannot prevent the progress of oxidation of these elements and is higher than room temperature. When pressed at a temperature, the surface is oxidized and the wettability is greatly reduced. Furthermore, since the processing is performed at a high temperature, the solder expands as compared with the normal temperature, and even if it is devised, the accuracy of the shape cannot be obtained as compared with the press at the normal temperature. In addition, since the solder that has become relatively soft is likely to stick to the mold and is pressed in a state where the solder is bent or distorted, burrs and chips are likely to occur. In addition, the warm press has a problem that the equipment cost is higher than that of a normal press.

  The Au alloy described in Patent Document 6 can prevent the occurrence of electromigration in comparison with an Ag-based brazing material of Ag-28 wt% Cu or Ag-15 wt% Cu, and can provide a strong and stable brazing strength. It was developed as a material. For this reason, although the brazing strength after being left in a 1% NaCl solution has been evaluated, the bonding state including wetting and spreading has not been confirmed. In the reliability evaluation, it is necessary to perform a temperature cycle test for confirming stress relaxation including the bonded state, etc., but the technique of Patent Document 6 has not been carried out, and whether high reliability can be obtained. Is not confirmed.

  Since the ternary alloy brazing material containing Au—Ge described in Patent Document 7 includes a very wide composition range in which the difference between the liquidus temperature and the solidus temperature is less than 50 ° C., It is not possible to obtain only a brazing material exhibiting similar effects and characteristics over a wide composition range. When comparing Au-12.5 mass% Ge alloy (eutectic point composition) and Au-20 mass% Sn alloy (eutectic point composition) belonging to the above composition range, their characteristics are clearly different. Yes.

  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. Even when a small amount of a third element is contained in each of these, there is a composition range in which the characteristics do not change greatly by dissolving the third element, so that, for example, Au-12 with a small amount of Sn added. The 5 mass% Ge—Sn alloy and the Au-20 mass% Sn—Ge alloy added with a small amount of Ge belong to the composition range of Patent Document 7, but the characteristics of the two types of ternary alloy brazing materials 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 this Ge—Sn alloy, there is a region where the difference between the liquidus temperature and the solidus temperature defined in the claims of Patent Document 7 is less than 50 ° C. However, the melting point is still too low for high-temperature solder.

  The present invention has been made in view of the above-described conventional circumstances, and is excellent in wet spreadability, bondability, and bond strength, and is an electronic device that requires extremely high reliability such as a crystal device and a SAW filter. An object of the present invention is to provide a high-temperature Pb-free Au—Ge solder alloy that can be suitably used as a joining or sealing solder.

In order to achieve the above object, the Au—Ge based solder alloy provided by the present invention contains Ge in an amount of 7.0% by mass or more and 17.0% by mass or less, and the balance is for laser soldering composed of Au and inevitable impurities. and a ball-shaped Au-Ge-based solder alloy, L * is 50.0 or more 64.0 or less in the L * a * b * display system color conforming to JIS Z8781-4 of its surface, a * is -1.0 to 4.0, b * is Ri der 10.0 or 23.0 or less, the maximum major axis smallest among all cross-section through the center of the ball-shaped Au-Ge-based solder alloy length ratio divided by the short diameter is characterized by der Rukoto 1.00 to 1.20.

  According to the present invention, it is possible to provide an Au—Ge solder alloy which does not contain lead and has better wettability, bondability, and bonding strength than conventional Au solder. Productivity can be increased by using this Au-Ge solder alloy for bonding or sealing of electronic devices that require high reliability such as quartz devices, SAW filters, and MEMS. Equipment costs can be reduced.

It is a typical longitudinal cross-sectional view which shows the joined body by which the solder alloy was joined to Cu board | substrate plated with Ni. It is a typical top view which shows the major axis (X1) and minor axis (X2) of the solder alloy sample which spreads on the Cu substrate. It is a typical longitudinal cross-sectional view which shows the state by which the container for sealing was sealed with the ball-shaped solder alloy. It is a schematic diagram which shows the length ratio of the ball-shaped solder alloy or the solder alloy which crushed this into the disk-shaped body.

  First, the Au—Ge solder alloy according to the first embodiment of the present invention will be described. The Au—Ge solder alloy according to the first embodiment of the present invention is composed of two components of Au and Ge, and the Ge content is 7.0 mass% or more and 17.0 mass% or less. The remainder is made of Au except for elements inevitably included in production. The surface of the solder alloy has an L * of 47.0 or more and 67.0 or less, an a * of −2.0 or more and 5.0 or less, b * in the L * a * b * display system according to JIS Z8781-4. Is 7.0 or more and 27.0 or less.

  In order to increase the bonding reliability of the solder alloy, it is desirable that the solder alloy and the bonding surface be bonded in a state where a homogeneous intermetallic compound is generated. For this reason, first, it is desirable that the solder uniformly spreads on the joint surface to generate a uniform intermetallic compound. Uniform wetting and spreading can be defined by suppressing the aspect ratio of the solder seen from above to a predetermined value or less when the ball-shaped solder alloy is melted. In order to satisfy this, the solder alloy of the present invention limits the color of the solder surface as described above. Further, in order to produce an intermetallic compound uniformly, the composition of the solder alloy contains 7.0 mass% or more and 17.0 mass% of Ge, and the balance is Au except for inevitable impurities.

  That is, the Au—Ge solder alloy of the first embodiment of the present invention is based on the composition of the eutectic point of Au and Ge, and the color of the solder surface of the solder alloy having the composition near the eutectic point is L * A * b * Display system. As a result, when performing melt bonding with a laser or the like, variations in energy absorption amount, molten state, and the like are suppressed, and bonding excellent in various characteristics such as wet spreadability and bondability becomes possible. This reduces the incidence of bonding failure and improves yield, so when used for bonding and sealing of electronic devices that require very high reliability, such as expensive quartz devices, SAW filters, MEMS, Since high productivity can be maintained, an electronic device can be manufactured at low cost as a result.

  Next, the Au—Ge solder alloy of the second embodiment of the present invention will be described. The Au—Ge solder alloy according to the second embodiment of the present invention contains 7.0 mass% or more and 17.0 mass% or less of Ge, and contains Ag, Al, Cu, Mg, Ni, Sb, Sn, Zn, and In the case of containing one or more of P and containing Ag, 0.01 mass% to 30.0 mass%, and in the case of containing Al, 0.01 mass% to 1.5 mass%, Cu 0.01 mass% or more and 1.0 mass% or less when Mg is contained, 0.01 mass% or more and 0.8 mass% or less when Mg is contained, 0.01 mass% or more and 1 mass% when Ni is contained 0.0 mass% or less, when containing Sb, 0.01 mass% or more and 0.8 mass% or less, when containing Sn, 0.01 mass% or more and 15.0 mass% or less, when containing Zn When it contains 0.01 mass% or more and 3.0 mass% or less and P is contained, it contains 0.5500 mass% or less, respectively. The surface of the solder alloy has an L * of 47.0 or more and 67.0 or less in the L * a * b * display system based on JIS Z8781-4, as in the first embodiment of the present invention. Is −2.0 to 5.0 and b * is 7.0 to 27.0.

  The Au—Ge solder alloy according to the second embodiment of the present invention has the effects of the various additive elements described above in addition to the effects obtained by the Au—Ge solder alloy according to the first embodiment. This makes it possible to provide a better solder alloy. The essential elements contained in the Au—Ge solder alloys of the first and second embodiments of the present invention, the elements added as necessary, and the L * a * b * display system will be described below.

<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 is most suitable in terms of characteristics as a solder for joining and sealing of electronic parts that require high reliability. Therefore, Au-based solder is frequently used for joining and sealing of quartz devices and SAW filters, and the solder alloy of the present invention is based on Au, thereby providing a solder suitable for use in the above technical fields. can do.

  However, since Au is a very expensive metal, it is required to keep the cost as low as possible. Therefore, from the viewpoint of manufacturing, improving the manufacturing yield of electronic components is one of the most important matters. Therefore, in the present invention, the surface state of the solder alloy is managed and controlled by color, thereby realizing uniform and good bonding at the time of bonding, thereby improving the reliability. Furthermore, when considered from the composition aspect, the addition of these elements by adding one or more of Ag, Al, Cu, Mg, Ni, Sb, Sn, Zn, and P to the Au—Ge based alloy as necessary. It is possible to reduce the content of expensive Au.

<Ge>
Ge is an essential element in the solder alloy of the present invention. Ge forms a eutectic alloy with Au, and the solidus temperature can be lowered to 361 ° C. The Ge content is 7.0% by mass or more and 17.0% by mass or less in order to make the Au—Ge-based alloy of the present invention a solder alloy having extremely excellent wettability and bonding reliability. If the Ge content deviates from this range, the liquidus temperature becomes too high and the separation phenomenon occurs, so that the substrate or chip and the solder may not be alloyed uniformly, resulting in poor bonding. . If the Ge content is 10.0% by mass or more and 14.0% by mass or less, the composition becomes closer to the composition of the eutectic point, so that it is possible to achieve further excellent bonding, which is preferable.

<Ag>
Ag is an element to be contained as necessary in the solder alloy of the present invention, and the main effect obtained by containing Ag is to improve wettability and bondability. Ag has good reactivity with Cu and Ni used on the uppermost surface of the substrate and the like, and can improve wettability. Of course, it is needless to say that it is excellent in reactivity with Ag or Au metallized layer often used for the bonding surface of the semiconductor element. The content of Ag having such an effect is 0.01% by mass or more and 30.0% by mass or less. If the amount is less than 0.01% by mass, the content is too small and the effect of adding Ag does not appear substantially. If the amount exceeds 30.0% by mass, the composition of the eutectic point is greatly deviated, resulting in coarse crystals. And the difference between the liquidus temperature and the solidus temperature becomes too large, causing a phenomenon of melting and separating, which is not preferable.

<Sn>
Sn is an element added as necessary in the solder alloy of the present invention. Sn forms a eutectic alloy with Au and has been conventionally used for applications requiring reliability as Au-20 mass% Sn solder, which is a typical Au-based solder. One of the reasons why it is used for applications requiring reliability in this way is that Sn is highly reactive with Cu, which is the main component of the substrate. That is, since Sn can be firmly bonded to a substrate or the like, high bonding reliability can be obtained. The reason why Sn is contained in the Au—Ge solder alloy of the present invention is such a high reactivity of Sn. That is, by containing Sn, strong bonding is possible, and high bonding reliability is obtained. Furthermore, it can adjust to desired melting | fusing point by adjusting content of Sn suitably.

  In this way, the Sn content may be adjusted and contained in accordance with the purpose of improving the bondability and adjusting the melting point. The content of Sn that exhibits the excellent effect of Sn as described above is 0.01% by mass or more and 15.0% by mass or less. If the Sn content is less than 0.01% by mass, the content is too small and the effect of inclusion is not exhibited. On the other hand, if the Sn content exceeds 15.0% by mass, the content will increase too much, and the proportion of intermetallic compounds will exceed the allowable range and become too hard or too brittle.

<Al, Mg>
Al and Mg are elements added as necessary to improve or adjust various properties in the present invention, and the main effects obtained by containing these elements are almost the same. That is, since Al and Mg are more easily oxidized than Au and Ge, by including at least one of them in the Au—Ge solder alloy, it is preferentially oxidized and deposited on the solder surface, and a thin oxide layer is formed. It generates. As a result, the oxidation of the elements constituting the parent phase is suppressed, making it difficult for oxygen atoms to penetrate into the solder, resulting in improved wettability.

  That is, Al is dissolved in Au by several mass%. Since Al dissolved in this manner is overwhelmingly bonded to oxygen more than Au or Ge when the solder alloy is heated and joined, it precipitates on the solder surface and forms a dense oxide layer. In this way, when Al oxidizes itself, oxidation of Ge or the like is suppressed, and Ge or the like is not oxidized by the dense oxide layer, and the oxide layer is kept thin. And since this oxide layer is thin, an oxide layer is easily destroyed at the time of joining, and it becomes easy for a board | substrate or a semiconductor element and a molten solder alloy to contact metal directly, and wettability and joining property are improved.

  However, if too much Al is contained, the thickness of the oxide layer of Al becomes too thick, which may reduce wettability. 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 obtained, and if it is 0.7 mass% or less, the effect of containing Al further appears and it is preferable. On the other hand, the lower limit of the Al content is 0.01% by mass. If the amount is less than 0.01% by mass, the content is too small to substantially obtain the above-described effects.

  Similar to Al, Mg is an element that is included as necessary in order to improve or adjust various properties in the present invention, and the main expected effect is to improve wettability. Since Mg is more reducible than Al, it is easily oxidized and is more effective than Al when it exhibits the effect of improving wettability. Therefore, it is effective in a small amount. However, a large amount of Mg cannot be contained. In other words, Mg is easier to bond with oxygen than Al, so it forms a strong oxide layer, and even if it is a relatively thin oxide film, the oxide layer is not sufficiently destroyed at the time of bonding, which causes a decrease in wettability. It may become. 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 is obtained, and when the content is 0.3% by mass or less, the above-described effect is more remarkable, which is 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.

  The melting points of Al and Mg are 660 ° C. for Al and 650 ° C. for Mg. Accordingly, when adjusting the melting point such as the liquidus temperature of the solder alloy, the melting point of these Al and Mg may be included with reference to the melting point. As described above, almost the same effect can be obtained by adding Al and Mg, but considering the properties and melting points of solid solutions and intermetallic compounds produced when these elements are added. The content may be determined as appropriate so as to adjust to the intended characteristics.

<Cu, Ni, Sb>
Cu, Ni and Sb are elements added as necessary to improve or adjust various properties in the present invention, and the main effects obtained by containing these elements are almost the same, and workability And to improve stress relaxation. That is, Cu, Ni, and Sb are first precipitated when the solder alloy is solidified after being melted, and fine crystals grow using it as a nucleus. Therefore, the structure becomes a fine crystal structure, and as a result, the progress of cracks is easily stopped at the grain boundary. This makes it difficult for cracks to progress even when various stresses such as thermal stress are applied to the solder alloy, and it is possible to process without breaking by suppressing the occurrence of defects such as cracks when processing into sheet shape etc. And the joint reliability is greatly improved.

  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. That is, if the content of these elements is too large, the density of the nuclei increases, and 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% by 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 these composition ranges, it can be set as the solder alloy which has a favorable characteristic.

<Zn>
Zn is an element added as necessary to improve or adjust various properties in the present invention, and 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 forms a solid solution 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 the content of Zn including the production method, and the upper limit is substantially 3.0% by mass. If this value is exceeded, the thickness of the oxide layer becomes too thick even under manufacturing 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 the content is less than 0.01% by mass, the content is too small to obtain substantially the effect.

<P>
P is an element contained as necessary in the solder alloy of the present invention, and its effect is in improving wettability. The mechanism by which P improves wettability is that P is highly reducible, so that it oxidizes itself, thereby suppressing oxidation of the solder alloy surface and reducing the substrate surface to improve wettability. In general, Au-based solder is difficult to be oxidized and is excellent in wettability, but 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. 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. There is.

<L *, a *, b *>
In the Au-Ge series solder alloy of the present invention, the L * of the brightness of the solder surface in the L * a * b * display system conforming to JIS Z8781-4 is 47.0 or more and 67.0 or less, and the hue and saturation are a * is from -2.0 to 5.0, and b * is from 7.0 to 27.0. Generally, when a solder alloy is melted with a laser or the like, the amount of energy absorbed varies depending on the surface state of the solder alloy.

  As a result, if the numerical value in the L * a * b * display system is different, the time from when energy is applied to the solder until the start of melting, the completion time of melting, wetting and spreading after melting, generated by reacting with the substrate, etc. Very large differences can occur in the alloy phases, metal structures, etc. It is necessary to control the surface state in order to stably maintain the same state when the solder alloy is melted and after joining. Therefore, the Au—Ge solder alloy of the present invention has a surface color within the above-mentioned range in the L * a * b * display system, so that the amount of energy absorbed when the solder alloy is melted with a laser or the like. Variation, and thus stable meltability and wettability can be obtained. As a result, excellent bondability can be obtained, and an electronic device having high bonding reliability can be provided.

  L * indicating the brightness of the solder surface color is 47.0 or more and 67.0 or less, a * indicating the hue and saturation is -2.0 or more and 5.0 or less, and b * is 7.0 or more and 27.0 or less. The reason is because of the experimental results. In the experimental results, if L *, a *, and b * deviate from this range, even if the laser energy or focus is adjusted, it does not melt sufficiently, but only partially melts or conversely melts rapidly. The wet spread was uneven. In the experiment, when the solder shape is a ball shape, L * should be 50.0 or more and 64.0 or less, a * should be -1.0 or more and 4.0 or less, and b * should be 10.0 or more and 23.0 or less. As a result, the material melted more uniformly and the wetting spread became uniform, and a better joint was obtained.

  The shape of the Au—Ge solder alloy of the present invention is not particularly limited, but when the solder alloy is ball-shaped, sphericity may be required as a shape characteristic. The reason for this is that if the sphericity is poor, the direction of movement will not be determined during transport, it will not spread in a perfect circle when melted, and it will short-circuit with adjacent electrodes or wiring, or if the chip is bonded, the entire bonded surface This is because there is a risk of contact with the solder. Therefore, in the case of a ball-shaped Au—Ge solder alloy, as shown in the plan view of FIG. 4A, the smallest major axis L2 is divided by the smallest minor axis L1 in every cross section passing through the center. It is preferable that the long / short ratio (L2 / L1) shown in the following calculation formula 1 is 1.00 or more and 1.20 or less. When the length / short ratio is 1.20 or less, the solder can easily approach the true sphere due to surface tension when the solder is melted, and can be spread uniformly on the joint surface. If this length ratio exceeds 1.20, it will be difficult to spread evenly on the joint surface even if surface tension is applied during melting of the solder.

[Calculation Formula 1]
Long / Short Ratio = Long Diameter L2 / Long Diameter L1

  Alternatively, as shown in the perspective view of FIG. 4B, the ball-shaped solder alloy is crushed from one direction to form a disc-like body 10 having flat portions 10a and 10b parallel to each other on the front and back surfaces, and the flat portion 10a. 10b, when placed on the horizontal plane 11, the thickness of the flat portion 10a, 10b of the disc-like body 10 in the crushed direction (vertical direction) is Z1, and the disc-like body 10 is from above. When the diameter of the circumscribed circle circumscribing the projection when projected onto the horizontal plane 11 is Z2, the length-to-short ratio (Z2 / Z1) shown in the following calculation formula 2 is more than 1.00 and less than 1.50. Preferably there is.

[Calculation Formula 2]
Long / Short Ratio = Minimum circumscribed circle diameter Z2 / vertical thickness Z1

  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 solder placed on the joint surface is viewed from directly above, the solder is circular. When the solder is melted in this state, the solder spreads in a circular shape. However, if the above-mentioned length-to-short ratio of the Au—Ge solder alloy crushed from one direction exceeds 1.50, the relatively hard Au—Ge alloy may crack and may not spread in a circular shape. May break the solder.

  By controlling the shape of the Au—Ge solder alloy in this way, when the solder alloy is melted on the joint surface, the solder alloy is wet-spread in a state close to a perfect circle when viewed from the direction perpendicular to the joint surface. Can do. As a result, better bonding and sealing are possible, the defect occurrence rate of bonded and sealed electronic devices can be reduced, and electrons bonded or sealed using an extremely expensive Au-based solder alloy It becomes possible to significantly reduce the cost of a device and a semiconductor device on which the electronic device is mounted. In addition, since the bonding property is excellent, the bonding reliability is naturally improved.

  On the other hand, for example, when the solder alloy is greatly deviated from the spherical shape and the length-to-short ratio exceeds 1.5, for example, when the above balls are crushed, the solder does not spread circularly on the joint surface when the solder melts. There is a possibility that a portion that is not sufficiently alloyed may be generated due to partial protrusion from the portion to be joined or a portion that cannot be joined due to insufficient solder amount for good solder joining. Furthermore, the thickness of the solder becomes non-uniform, causing problems such as chip tilt.

[Example 1]
First, Au, Ge, Ag, Al, Cu, Mg, Ni, Sb, Sn, Zn, and P each having a purity of 99.99% by mass or more were prepared as raw materials. Large flakes and bulk-shaped raw materials were reduced to a size of 3 mm or less by cutting and crushing while paying attention to ensure that the alloy after melting did not vary in composition depending on the sampling location. Next, a predetermined amount of these raw materials was weighed and put 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 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 raw material began to melt, it was thoroughly stirred 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 taken out, and the molten metal in the crucible was poured into the mold of the solder mother alloy.

  As the mold, one having a width of 30 mm × thickness of 5 mm for rolling and a cylinder having a diameter of 24 mm for submerged atomization were used in accordance with the purpose. Thus, the solder mother alloys of Samples 1 to 89 were produced by changing the mixing ratio of the raw materials. About each solder mother alloy of these samples 1-89, the composition analysis was performed using the ICP emission-spectral-analyzer (SHIMAZU S-8100). The obtained analysis results are shown in Tables 1 to 4 below.

  Next, the solder mother alloys of Samples 1 to 34 and 59 to 78 were each rolled using a warm rolling mill and processed into a sheet shape, and then processed into a disk-shaped punched product using a press. On the other hand, the solder mother alloys of Samples 35 to 58 and 79 to 89 were each processed into a ball shape using a submerged atomizer. Hereinafter, these manufacturing methods will be described.

<Punched product manufacturing method>
Each of samples 1 to 34 and 59 to 78 made of a plate-like mother alloy having a width of 30 mm, a thickness of 5 mm and a length of 15 cm was rolled with a warm rolling mill. The rolling conditions were the same for all samples. That is, the number of rolling was 5 times, the rolling speed was 15 to 30 cm / second, the roll temperature was 250 ° C., and rolling was performed to 50.0 ± 1.2 μm by 5 times rolling. Each sample processed into a sheet in this way was punched with a press to produce a punched product. The shape was a disk shape with a diameter of 0.8 mm.

<Ball manufacturing method>
Samples 35 to 58 and 79 to 89 made of a cylindrical mother alloy having a diameter of 24 mm are placed in a nozzle of a submerged atomizer, and the nozzle is heated at 300 ° C. above the quartz tube containing oil (high-frequency dissolution). Set in the coil). The mother alloy in the nozzle was heated to 650 ° C. by high frequency and held for 5 minutes, and then 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. Each of the obtained sample balls was washed with ethanol three times and then dried for 3 hours in a vacuum at 40 ° C. in a vacuum dryer. Then, using the biaxial classifier, the balls obtained by the above method were classified in a range of 0.30 ± 0.015 mm in diameter.

<Surface condition adjustment>
Next, samples 1 to 89 described above were heat-treated at 80 to 250 ° C. for 0.1 to 5.0 hours in a hydrogen reducing atmosphere to adjust the degree of oxidation and the metal structure of the solder alloy surface. * And b * were adjusted. L *, a *, and b * are measured for each of the solder alloys of Samples 1 to 89 whose surface conditions are adjusted in this way, and after each sample is bonded to the substrate, the aspect ratio of the solder after bonding is determined. The wettability was evaluated by measuring, and the bondability was evaluated by measuring the void ratio.

  As a test for evaluating the sealing performance, the sealing container was sealed with each solder alloy sample in a vacuum, and the leakage state was examined. Furthermore, the reliability evaluation by a heat cycle test was performed using the sealing body obtained by the said sealing test. Hereinafter, L *, a *, b * measurement method, aspect ratio measurement method (wetting spreadability evaluation), void ratio measurement method (bondability evaluation), leak state confirmation method (sealing property evaluation), and heat The cycle test method (reliability evaluation) is described.

<Measurement of L *, a *, b *>
L *, a *, and b * were measured for each of the above samples 1 to 89 using a spectrocolorimeter (manufactured by Konica Minolta Optics, model: CM-5). First, the apparatus was calibrated with a standard light source. Thereafter, each sample was placed on a measurement table, the lid was closed, and measurement was automatically performed.

<Evaluation of wettability (measurement of aspect ratio of joined body)>
A laser soldering apparatus (YAG laser, wavelength 1064 nm) was started, and nitrogen gas was allowed to flow at a flow rate of 50 L / min. Then, the Cu substrate 1 (plate thickness: 0.3 mm) having the Ni plating layer 2 (film thickness: 3.0 μm) is automatically conveyed to the laser irradiation unit, and then a disk-shaped or ball-shaped sample is supplied to It is placed on a Ni-plated Cu substrate 1 and heated and melted by a laser for 0.3 seconds, and then the Cu substrate 1 is automatically conveyed from the laser irradiation unit and cooled by a conveyance unit in which a nitrogen atmosphere is maintained. After sufficiently cooling, it was taken out into the atmosphere.

  The aspect ratio of the solder alloy spread by wetting was obtained for the joined body in which the solder alloy sample 3 was joined on the surface of the Ni plating layer 2 of the Cu substrate 1 as shown in FIG. Specifically, as shown in FIG. 2, the maximum solder wetting spread length (major axis: X1) and the minimum solder wetting spread length (minor axis: X2) are measured, and the aspect ratio is calculated by the following calculation formula 3. Was calculated.

[Calculation Formula 3]
Aspect ratio = X1 ÷ X2

  It can be judged that the closer the aspect ratio of the calculation formula 3 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 non-uniform, and the thickness of the alloy layer and the component variation increase, resulting in uniform and good bonding Will not be able to. Furthermore, it spreads so that a lot of solder flows in a certain direction, and there are places where the amount of solder is excessive and where there is no or little solder.

<Evaluation of bondability (measurement of void fraction)>
With respect to the joined body shown in FIG. 1 obtained in the same manner as the evaluation of the wettability, the void ratio of the Cu substrate to which the solder alloy is joined is measured with an X-ray transmission device (TOSMICRON-6125, manufactured by Toshiba Corporation). And measured. Specifically, X-rays were transmitted vertically through the joint surface between the solder alloy and the Cu substrate from above, and the void ratio (%) was calculated using the following calculation formula 4.

[Calculation Formula 4]
Void ratio = void area / (void area + solder alloy / Cu substrate bonding area) × 100

<Evaluation of sealing performance (confirmation of leak condition)>
In order to confirm the sealing performance by the solder alloy, the sealing container 4 having the shape shown in FIG. 3 was sealed with each solder alloy sample 3. For sealing, a laser soldering apparatus (YAG laser, wavelength 1064 nm) was used, nitrogen gas was flowed at a flow rate of 50 L / min, and the laser was heated and melted for 0.3 seconds to perform sealing. Then, the sealing body was automatically conveyed from the laser irradiation part, cooled by the conveyance part by which nitrogen atmosphere was maintained, and after taking out enough, it took out in air | atmosphere. Each sealing body prepared in this way was immersed in water for 2 hours, and then the sealing body was taken out from the water and disassembled to confirm a leak state. And when water was contained in the disassembled sealing body, it was judged that there was a leak, and “×” was evaluated as the sealing performance. The case where such a leak did not occur was evaluated as “◯”.

<Reliability evaluation (heat cycle test)>
The sealing body in which leakage did not occur in the evaluation of the sealing performance described above was repeated for a predetermined number of cycles, with -40 ° C. cooling and 250 ° C. heating as one cycle. Thereafter, the joined body was embedded in a resin, subjected to cross-sectional polishing, and the joined 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 evaluated as “X”, and the case where there was no such defect and the same joint surface as in the initial state was evaluated as “◯”. . The evaluation results are shown in Tables 5 to 8 below together with the measurement results of L *, a *, and b *, the evaluation results of sealing properties, the evaluation of bondability, and the measurement results of the aspect ratio of the joined body.

  As can be seen from Tables 5 to 8, all of the solder alloys of Samples 1 to 58 that satisfy the requirements of the present invention exhibit good characteristics in all the evaluation items. That is, the aspect ratio, which is an evaluation of wettability, is 1.01 or less, and the void ratio, which is an evaluation of bondability, is 0.0%, and no voids are generated. Furthermore, no leakage was observed for all samples in the leak state, which is an evaluation of sealing performance, and no defects appeared in the heat cycle test, which is an evaluation of reliability. The reason why such a good result was obtained was that the composition of the present invention and the requirements of L *, a *, b * were satisfied in any solder alloy sample, so that the laser energy was made uniform and stable. Thus, it is considered that excellent meltability, wettability, bondability and the like were obtained.

  On the other hand, the solder alloys of Samples 59 to 89 that did not satisfy the requirements of the present invention resulted in undesirable results in any of the evaluation items. In other words, the aspect ratio is 1.1 or more, the substrate does not spread evenly on the substrate, the void ratio is 5% or more, and the leak condition is confirmed except for the samples 60 and 70. A leak occurred, and in the heat cycle test, defects occurred in these samples 60 and 70 up to 500 times.

[Example 2]
In Example 1 above, it was confirmed that a good bonded state could be obtained if the solder alloy satisfies the composition and surface color, which are requirements of the solder alloy of the present invention. However, when the solder alloy is used in the form of a ball, its shape may be limited particularly from the viewpoint of conveyance and wetting and spreading. Therefore, in Example 2, evaluation was performed with respect to limited requirements that can be obtained when the solder alloy has a ball shape.

  First, in the same manner as in Example 1, solder mother alloys of Samples 90 to 130 were produced. The composition analysis was performed on each solder mother alloy of these samples 90 to 130 using an ICP emission spectroscopic analyzer (SHIMAZU S-8100) in the same manner as in Example 1. The measurement results are shown in Table 9 below.

  Next, each solder mother alloy of the samples 90 to 130 is processed into a ball shape by a submerged atomizing apparatus in the same manner as in the first embodiment, and the surface state is prepared in the same manner as in the first embodiment. And L *, a *, and b * were measured using a spectrocolorimeter (manufactured by Konica Minolta Optics, Inc., model: CM-5). Further, among these ball-shaped samples, samples 120 to 124 and 128 to 130 were crushed by applying pressure from one direction to form a substantially disc-like shape having front and back surfaces. Specifically, using a warm press, crush the sample ball 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 then fill the nitrogen-filled side box The product was taken out after being cooled to room temperature. The degree of crushing was adjusted so as to obtain a predetermined crushing amount by controlling the gap between the molds.

  On the other hand, with respect to the samples 90 to 119 and 125 to 127, the diameters are measured at arbitrary 50 locations with a three-dimensional measuring machine, and the maximum length (major axis L2) among them is calculated as in the above-described calculation formula 1. Was divided by the minimum length (minor axis L1) to obtain the long / short ratio (L2 / L1). On the other hand, for samples 120 to 124 and 128 to 130 formed by crushing the ball into a disk-shaped body, the width (thickness) in the direction of crushing is arbitrarily measured at 10 points as in the above-described calculation formula 2. Then, the minimum thickness (corresponding to Z1 in FIG. 4B) is obtained, and the length in the direction perpendicular to the crushed direction is arbitrarily measured at 10 points to determine the maximum thickness (FIG. 4). (B) corresponds to the diameter Z2 of the smallest circle among the circumscribed circles in the projection when the disk-like body 10 is projected onto the horizontal plane 11 from directly above. The maximum length (Z2) was divided by the minimum thickness (Z1) to obtain a length / short ratio (Z2 / Z1).

  The evaluation of the wettability of the solder alloy of the ball-shaped body or disk-shaped body obtained as described above (measurement of the aspect ratio when the joined body is viewed from directly above) was performed in the same manner as in Example 1 above. . In addition, evaluation of bondability (measurement of non-bonding rate) was performed on a bonded body obtained in the same manner as in the evaluation of wettability. Specifically, the X-ray transmission device (TOSMICRON-6125 manufactured by Toshiba Corporation) is used to transmit X-rays from directly above the joined body to the joint surface of the joined body, and the non-attachment shown in the following calculation formula 5 from the measurement result. The rate (%) was calculated.

[Calculation Formula 5]
Non-bonding rate = (area where solder alloy does not exist in equivalent circle + area of void in equivalent circle) / area of equivalent circle × 100

  Here, the equivalent circle is a circle centered on the central portion on the substrate of the solder alloy sample before melting, and the wet spread area when the solder alloy sample melts and spreads on the substrate. Is a circle having an area equal to. This evaluation based on the non-bonding rate includes not only defective bonding due to void generation but also the case where the molten solder alloy does not spread out in a perfect circle and the solder alloy does not reach the desired surface to be bonded, resulting in poor bonding. Bondability can be evaluated. The evaluation results are shown in Table 10 below together with the above-described crushing step presence / absence, length / short ratio, and color measurement results.

  As can be seen from Table 10 above, each of the solder alloys of Samples 90 to 124 shows good characteristics in each evaluation item. That is, the aspect ratio when the joined body, which is an evaluation of the wetting and spreading property of the solder alloy balls, is viewed from directly above is 1.02 or less, and the wetting and spreading is almost circular. It can be seen that better wettability is obtained compared to the alloy. In addition, it can be seen that the non-bonding rates of the solder alloys of the samples 90 to 124 are all 0%, which is better than the solder alloys of the samples 125 to 130.

  The reason why good results were obtained in each of the solder alloys of Samples 90 to 124 in this way is that it has a suitable composition and surface color, and has a ball shape that is closer to a true sphere. In addition, it is considered that this is because it has been formed into a disk shape that is closer to a perfect circle in a plan view, and therefore, excellent wet spreadability and the like have been obtained. In other words, in the case of ball-shaped solder, by limiting its roundness or roundness viewed from one direction when it is crushed from one direction, it can be used in special applications that require strict wetting and spreading properties. It can be seen that soldering can be performed well.

DESCRIPTION OF SYMBOLS 1 Cu board | substrate 2 Ni plating layer 3 Solder alloy sample 4 Container for sealing 10 Solder alloy of a disk-shaped body 11 Horizontal surface

Claims (7)

  This is a ball-like Au—Ge solder alloy for laser soldering containing 7.0 mass% or more and 17.0 mass% or less of Ge, the balance being Au and inevitable impurities, and the surface color is JIS In the L * a * b * display system compliant with Z8771-4, L * is 50.0 or more and 64.0 or less, a * is -1.0 or more and 4.0 or less, and b * is 10.0 or more and 23.0. The long / short ratio obtained by dividing the largest major axis by the smallest minor axis among all cross sections passing through the center of the ball-shaped Au—Ge solder alloy is 1.00 or more and 1.20 or less. A ball-shaped Au—Ge solder alloy for laser soldering. It contains 7.0 mass% or more and 17.0 mass% or less of Ge, contains one or more of Ag, Al, Cu, Mg, Ni, Sb, Sn, Zn and P, and the balance is Au and inevitable impurities A ball-shaped Au—Ge solder alloy consisting of the following: 0.01% by mass to 30.0% by mass when Ag is contained, and 0.01% by mass when Al is contained % To 1.5% by mass, Cu containing 0.01% to 1.0% by mass, Mg containing 0.01% to 0.8% by mass, Ni In the case of containing Sb, 0.01% to 0.8% by weight, and in the case of containing Sn, 0.01% to 15.0% by weight. % By mass or less, and when Zn is contained, 0.01% by mass to 3.0% by mass and P is contained. In the case of 0.5% by mass or less, the surface color of the solder alloy is L * a * b * in the L * a * b * display system according to JIS Z8781-4, 50.0 or more and 64.0 or less, and a * -1.0 or more and 4.0 or less, b * is 10.0 or more and 23.0 or less, and the largest major axis is the smallest minor in all cross sections passing through the center of the ball-shaped Au-Ge solder alloy. divided by long and short ratio is 1.00 to 1.20 in Au-Ge-based solder alloy and shaped ball in laser soldering, characterized in that the radial. It is an Au-Ge series solder alloy for laser soldering containing 7.0 mass% or more and 17.0 mass% or less of Ge and the balance being Au and inevitable impurities, and the surface color is JIS Z8781-4 L * in the compliant L * a * b * display system is 50.0 or more and 64.0 or less, a * is -1.0 or more and 4.0 or less, b * is 10.0 or more and 23.0 or less , It has a shape the ball Lumpur shape of the Au-Ge-based solder alloy discoid member having parallel flat portions to each other on the front and back surfaces crushing from one direction, one of the flat portion in a horizontal plane facing downward The length-to-short ratio obtained by dividing the diameter of the minimum circumscribed circle in the figure in which the disk-shaped body is projected from directly above and divided by the thickness of the flat surface portion of the disk-shaped body in the crushed direction exceeds 1.00 a u-Ge-based solder alloys for laser soldering, characterized in that it is 1.50 or less. It contains 7.0 mass% or more and 17.0 mass% or less of Ge, contains one or more of Ag, Al, Cu, Mg, Ni, Sb, Sn, Zn and P, and the balance is Au and inevitable impurities An Au-Ge-based solder alloy for laser soldering comprising 0.01 mass% or more and 30.0 mass% or less when Ag is contained, and 0.01 mass% or more and 1.1 mass% when containing Al. 5 mass% or less, 0.01 mass% or more and 1.0 mass% or less when Cu is contained, 0.01 mass% or more and 0.8 mass% or less when Mg is contained, 0 when Ni is contained 0.01% by mass or more and 1.0% by mass or less, 0.01% by mass or more and 0.8% by mass or less when containing Sb, 0.01% by mass or more and 15.0% by mass or less when containing Sn, When Zn is contained, 0.01 mass% or more and 3.0 mass% or less, and when P is contained, 0.50% Less than 5% by mass, and the color of the surface of the solder alloy is 5 * or more and 64.0 or less in L * a * b * display system in accordance with JIS Z8781-4, and is -1.0 or more in a * 4.0 or less, b * in Ri der 10.0 or 23.0 or less, the disc having parallel plane portion with each other on the front and back surfaces smashed ball Lumpur shape of the Au-Ge-based solder alloy from one direction has a shape in Jo body, the diameter of the smallest circumscribed circle of a diagram obtained by projecting the circular plate-shaped body from directly above one of the flat portion placed on a horizontal surface facing downward, the plane of the circular plate-like body laser soldering a u-Ge-based solder alloy, characterized in that short and long ratio divided by thickness direction crushed in section is 1.50 or less than 1.00. A quartz crystal device sealed by using the Au-Ge solder alloy for laser soldering according to any one of claims 1 to 4. A SAW filter, which is sealed using the Au-Ge solder alloy for laser soldering according to any one of claims 1 to 4. An electronic device comprising an electronic component joined using the Au-Ge solder alloy for laser soldering according to any one of claims 1 to 4.

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