JP2017127897A - Au-Ge based solder alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Au-Ge based solder alloy for high temperature excellent in various properties usable as the sealing and joining uses of electronic components required for high reliability.SOLUTION: An Au-Ge based solder alloy contains 13.0 mass% or more and 23.0 mass% or less of Ge, further one or more kinds among Bi, In, Sb, Mg, Ni, Si and Cu and the balance Au except inevitable elements. In respective contents based on mass,: Bi is 1 ppm or more and 1,000 ppm or less when contained; In is 1 ppm or more and 1,000 ppm or less when contained; Sb is 1 ppm or more and less than 100 ppm when contained; Mg is 1 ppm or more and less than 100 ppm when contained; Ni is 1 ppm or more and less than 100 ppm when contained; Si is 1 ppm or more and less than 1,000 ppm when contained; and Cu is 1 ppm or more and less than 100 ppm when contained.SELECTED DRAWING: None

Description

  The present invention relates to a high-temperature Pb-free solder alloy mainly composed of Au and Ge, and particularly for sealing and joining electronic components that require extremely high reliability such as crystal devices, SAW filters, and MEMS. The present invention relates to an inexpensive high-temperature Au-Ge solder alloy that can be used.

  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 to a substrate. Lead (Pb) has long been used as a main component in solder materials, but lead has already been 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 bonding electronic components to a substrate are roughly classified into high temperature (about 260 to 400 ° C.) and medium and low temperature (about 140 to 230 ° C.) depending on the use limit temperature. Regarding solder for solder, lead-free solder has been put into practical use with Sn as a main component. For example, in Patent Document 1, Sn is the main component, Ag is 1.0 to 4.0% by weight, Cu is 2.0% by weight or less, Ni is 0.5% by weight or less, and P is 0.2% by weight. The following lead-free solder alloy composition is described. Patent Document 2 contains 0.5 to 3.5% by weight of Ag, 0.5 to 2.0% by weight 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 high-temperature Pb-free solder. 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 additive 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.

  Among the high-temperature Pb-free solder materials, Au—Sn alloys and Au—Ge alloys are already used in crystal devices, SAW filters, MEMS (microelectromechanical systems) and the like as expensive Au-based solder alloys. For example, in Patent Document 5, a low-melting point Au alloy brazing material made of Au—Ge alloy, Au—Sb alloy or Au—Si alloy is preheated, and then sequentially sent to a press die provided with a heat insulation section. The press working method of the plate-like low melting point Au alloy brazing material is characterized in that the press working is performed in a temperature range of 100 to 350 ° C.

  Patent Document 6 discloses a brazing material used for brazing external leads of electronic components, and Ag is 10 to 35 wt%, and at least one of In, Ge, and Ga is 3 to 15 wt% in total. An Au alloy is disclosed which contains and the balance is Au. It is described that the brazing material can be improved in electromigration resistance by containing Au as a main component, and therefore the time until short-circuiting in the electromigration test can be 1.5 hours or more. Further, the addition of 10 to 35 wt% of Ag as an additive element is for obtaining brazing strength, and the addition of 3 to 15 wt% of at least one of In, Ge and Ga in total is for lowering the melting point. Have been described.

  Further, Patent Document 7 discloses a ternary alloy brazing material including an Au—Ge alloy, where 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 a temperature of 50 ° C. And according to this patent document 7, it does not melt at the reflow temperature while realizing lead-free, and the temperature for bonding is not too high, so that the adhesive and the component itself are not damaged. It is described that it is possible to provide a brazing material suitable for bonding of the above.

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 Pb-free solder materials for high temperatures, various reports and proposals have been made in addition to the above-mentioned patent documents, but in reality, no low-cost and versatile solder materials have yet been found. That is, since electronic parts and substrates generally use materials having a relatively low heat resistance such as thermoplastic resins and thermosetting resins, the working temperature during bonding is less than 400 ° C., preferably 370 ° C. or less. It is desirable to make it. 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.

  Moreover, although Au—Sn solder and Au—Ge solder have been put to practical use as expensive Au solder, since Au solder uses a large amount of extremely expensive Au, general-purpose Pb solder and Sn solder are used. It is very expensive compared to solder. For this reason, it is only used for soldering in places that require particularly high reliability, 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, and the rolling roll must be made of a special material that does not easily wrinkle. Therefore, extra costs are incurred. Further, even during press molding, the Au-based solder is hard and brittle, so that cracks and burrs are likely to occur, and the yield is much lower than other solders. When processing into a wire shape, there is a similar serious problem. Even if an extruder with very high pressure is used, the extrusion speed cannot be increased due to its hardness, and the productivity is about one hundredth of Pb solder. There is only.

  Patent Documents 5 and 6 propose techniques for dealing with the various problems of Au-based solder as described above. However, Patent Documents 5 and 6 have the following problems. In other words, a plate-like (sheet-like) low melting point Au alloy brazing material made of Au—Ge alloy, Au—Sb alloy, Au—Si alloy, etc. exhibits brittleness like a glass plate at room temperature, and has a direction toward material properties. Therefore, in general, there is a drawback that in the longitudinal direction, even a slight bending is easy to break and the propagation of cracks is easy to proceed.

  Therefore, conventionally, so-called compound molds are used for press working, and in order to cope with the problems of mold accuracy and mold life that this compound mold technology has, heating is performed as described above in Patent Document 5. The materials are sequentially sent to a press die provided with a heat retaining part, and warm pressing is performed in a temperature range of 100 to 350 ° C. However, since the oxidation of the solder alloy proceeds in warm press processing, even if the solder contains a large amount of Au, other elements such as Ge, Sb, Sn, etc. Oxidation cannot be prevented, and when pressed at a temperature higher than room temperature, the surface is oxidized and wettability is greatly reduced. In addition, since solder expands at high temperatures compared to room temperature, even if it is devised, the accuracy of the shape is difficult to obtain compared to the press at room temperature, and the softened solder is more likely to stick to the mold and the solder bends. Since the pressing is performed in a state of being distorted or distorted, burrs and chips are likely to occur.

  On the other hand, the Au alloy described in Patent Document 6 can prevent the occurrence of electromigration and obtain 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. Therefore, the content of Ag is relatively high, the melting point is lowered, and it is easy to become a solder material that is difficult to use, and the strength and the electromigration prevention effect are sufficient as compared with a conventional Au-based alloy such as an Au-Ge alloy. I can't say that.

  The ternary alloy brazing material containing Au-Ge described in Patent Document 7 includes a very wide composition range because the difference between the liquidus temperature and the solidus temperature is allowed to about 50 ° C. It is unlikely that a brazing material having the same effects and characteristics can be obtained in a wide composition range. As an easy-to-understand example, when 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 are compared, The characteristics are clearly different.

  Specifically, since Ge is a metalloid, the Au-12.5 mass% Ge alloy is clearly inferior to the Au-20 mass% Sn alloy. Due to the generation, Au-12.5 mass% Ge has a lower yield. Naturally, even if a small amount of the third element is contained in each of them, there is a composition range in which the original characteristics do not change greatly due to the solid solution of the third element. For example, Au-12.5 mass% Ge-Sn The properties of the alloy and the Au-20 mass% Sn-Ge alloy are greatly different. Further, when considering the Ge—Sn alloy, since the solidus temperature is 231 ° C., the melting point is too low as a high-temperature solder. 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 Patent Document 7 is less than 50 ° C. Is still too low.

  The present invention has been made in view of the various problems of the above-described Au-based solder, and is used for sealing and joining electronic components that require extremely high reliability such as crystal devices, SAW filters, and MEMS. It is an object of the present invention to provide a high-temperature Au—Ge solder alloy excellent in various properties that can be used as a low-cost product.

  In order to achieve the above object, the Au—Ge based solder alloy provided by the present invention contains 13.0% by mass to 23.0% by mass of Ge, Bi, In, Sb, Mg, Ni, Si, and In the case where it further contains at least one element selected from the group consisting of Cu and the remainder is an Au—Ge solder alloy made of Au except for elements inevitably included in production, and contains Bi on a mass basis When the content is 1 ppm or more and 1000 ppm or less, In is contained, the content is 1 ppm or more and 1000 ppm or less, when Sb is contained, the content is 1 ppm or more and less than 100 ppm, and when Mg is contained, the content is 1 ppm. More than 100 ppm, when Ni is contained, the content is 1 ppm or more and less than 100 ppm, and when Si is contained, the content is 1 ppm or more and 100 Less than ppm, when containing Cu is characterized by its content of less than 100ppm than 1 ppm.

  According to the present invention, it is possible to provide a lower cost Au—Ge solder alloy while ensuring the same or better wet spreadability, bondability, bonding reliability, and the like compared to conventional Au solder.

It is a typical longitudinal cross-sectional view which shows the joined body by which the solder alloy was joined on Cu board | substrate which has Ni plating layer. It is a top view which shows typically the solder alloy which spreads wet on the Ni plating layer of the joined body of FIG. It is a typical longitudinal section of a joined body formed by soldering a Cu substrate having a Ni plating layer and a Si chip with a solder alloy sample.

  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 mainly of two of Au and Ge, and contains 13.0% by mass to 23.0% by mass of Ge. And it further contains one or more members selected from the group consisting of Bi, In, Sb, Mg, Ni, Si, and Cu, and the balance is made of Au except for elements that are inevitably included in production.

  The Au—Ge solder alloy having the above composition can provide the same or better wetting spreadability and bonding reliability as compared with the conventional Au solder alloy, and can reduce the Au content. Can be realized. Therefore, conventional Au-based solder alloys for joining and sealing electronic devices that require extremely high reliability, such as electronic devices having crystal devices, SAW filters, MEMS, etc., and electronic devices in which the electronic devices are mounted are used. It can be provided at a lower cost than solder.

  Specifically, since Au is very difficult to oxidize, it is most suitable as a solder for electronic components that require high reliability in terms of characteristics typified by wettability. For this reason, Au-based solder is frequently used for joining or sealing electronic components such as crystal devices and SAW filters that require high reliability. However, in such electronic components that require high reliability, the solder and the joint surface of the joint part to be joined together are joined in a state in which a homogeneous intermetallic compound is generated for the joint reliability. Is desirable. Therefore, it is a desirable condition at the time of solder joining that the solder first uniformly spreads on the joint surface and then generates a uniform intermetallic compound. In addition, Au-based solder is very expensive because it contains Au as a main component, and there is a constant demand for cost reduction. However, it is technically very difficult to simultaneously realize the above-described good wettability, bondability, and cost reduction, and it has been difficult to achieve with conventional solder alloys.

  The present invention has been made in response to such market demands, and a group consisting of Bi, In, Sb, Mg, Ni, Si, and Cu is added to an Au—Ge solder alloy having a predetermined amount of Ge. In addition to the above-described excellent wettability and bondability, the workability and flexibility of the solder material can be remarkably improved. Since the Au content can be reduced by increasing the Ge content from the composition of the eutectic point of −12.5 mass% Ge, cost reduction can be realized. Since the Au-Ge solder alloy of the present invention has the Au content reduced from the eutectic point composition to improve the workability described above, the Ge content is 13 on the Ge rich side from the eutectic point composition. It is 0.0 mass% or more and 23.0 mass% or less.

  The solder alloy of the present invention has a composition relatively close to the eutectic point of the Au—Ge alloy while reducing the Au content by reducing the amount of additive elements such as Bi described above. The reason for this is that the solidus temperature becomes 356 ° C. in the range where the Ge content is moderately increased from the eutectic point of the Au—Ge alloy. For example, from the Au-12.5% by weight Ge solder alloy to the solder alloy of this composition. Even if it is replaced, it is not necessary to greatly change the handling conditions such as the joining conditions, so it can be said that the alloy is very easy to use.

  As the Ge content is increased, the liquidus temperature naturally increases. However, Au—Ge alloys are also used in a range richer in Ge than the composition of eutectic points. In this case, the problem that occurs when Ge is more than about 12.5% by mass of the composition of the eutectic point is not a problem that occurs at the time of bonding or after bonding, but it is fragile and difficult to process when processed into a desired shape. Is. The present invention solves the problem of workability caused by increasing the Ge content above the eutectic point by adding a small amount of the above-described additive elements, and adding a small amount of the above Bi or the like. By doing so, the workability and flexibility are greatly improved and the cost is reduced with almost no change in the solidus temperature.

  In the present invention, the element contained in the Au—Ge alloy is selected from Bi, In, Sb, Mg, Ni, Si, and Cu. The role of these elements is to improve the workability and flexibility and to reduce the material cost by reducing the Au content. However, the mechanisms for improving the workability and flexibility are different. It can be divided into two categories.

<Bi, In, Mg, Sb>
Bi, In, Mg, and Sb are the first class of additive elements added to the Au—Ge alloy of the present invention, and the effects obtained by including one or more of these four elements are processed. The principle of the effect is to suppress dislocation movement by distorting the lattice like solid solution strengthening.

  Specifically, Bi is only slightly dissolved in both Au and Ge. For this reason, when a very small amount is contained in the Au—Ge alloy, the strength is improved by solid solution strengthening, and the workability and the like are also improved. The Bi content is 1 ppm or more and 1000 ppm or less on a mass basis. If the Bi content is less than 1 ppm, the content is too small and the effect of inclusion is not substantially exhibited. On the other hand, if the content exceeds 1000 ppm, the lattice distortion becomes too large, and the solder alloy becomes too hard and too brittle. The Bi content is preferably not less than 10 ppm and not more than 800 ppm because the effect of inclusion is further enhanced.

  In is solid-dissolved in Au at about 4% by mass, and is hardly dissolved in Ge. The effect of improving workability can be obtained when In is contained in a small amount as well as Bi. However, if it is added excessively, the solid solubility limit is large, so that it hardens more than necessary and conversely leads to a decrease in workability. The content of In is 1 ppm or more and 1000 ppm or less on a mass basis. If it is less than 1 ppm, the content is too small and the effect of inclusion is not substantially exhibited. On the other hand, if it exceeds 1000 ppm, processability and flexibility are extremely lowered. It is preferable that the content of In is 10 ppm or more and 800 ppm or less because the effect of inclusion is further exhibited.

Mg forms a solid solution of several mass% in Au, and hardly forms a solid solution in Ge to form a GeMg ₂ intermetallic compound. Mg improves workability and the like by solid solution strengthening as well as Bi. The Mg content is 1 ppm or more and less than 100 ppm on a mass basis. If it is less than 1 ppm, the content is too small and the effect of inclusion is not substantially exhibited. Even if Mg is contained in a very small amount in the solder alloy, a very hard intermetallic compound is generated. Therefore, Mg should not be contained in an amount of 100 ppm or more. The Mg content is preferably not less than 10 ppm and not more than 80 ppm because the effect of inclusion is further enhanced.

  Sb is slightly dissolved in Au and hardly dissolved in Ge. Sb has properties similar to Bi, and exhibits almost the same behavior when incorporated in an Au-Ge alloy. The Sb content is 1 ppm or more and less than 100 ppm by mass. If it is less than 1 ppm, the content is too small and the effect of inclusion is not substantially exhibited. On the other hand, if the content is 100 ppm or more, the strain of the lattice becomes too large, and the solder alloy becomes too hard and too brittle. The Sb content is preferably not less than 10 ppm and not more than 80 ppm because the effect of inclusion is further enhanced.

<Ni, Si>
Ni and Si are a second class of additive elements added to the Au-Ge alloy of the present invention, and the effect obtained by containing at least one of these two elements is workability and flexibility. The principle of the improvement and its effect is due to the refinement of the crystal. Specifically, Ni has a melting point of 1455 ° C. and Si has a melting point of 1414 ° C., both of which are very high. For this reason, when solidifying after melting at the time of soldering, first, Ni or Si having a high melting point is solidified and becomes a nucleus to generate crystals. In this way, Ni and Si are dispersed in the solder and become nuclei, so that the crystal becomes finer. The refined solder alloy is less prone to crack generation and progress even when thermal stress is applied, thereby improving workability and flexibility. Thus, the solder alloy with improved workability and the like can be easily processed into a desired shape even if it deviates to some extent from the composition of the eutectic point.

  The Ni content is 1 ppm or more and less than 100 ppm on a mass basis. If it is less than 1 ppm, the content is too small and the effect of inclusion is not substantially exhibited. On the other hand, if it is contained in an amount of 100 ppm or more, the number of nuclei is excessive and the crystal is coarsened, or the solder alloy is too hard and brittle. The Ni content is preferably not less than 10 ppm and not more than 80 ppm because the effect of inclusion is further enhanced.

  On the other hand, the Si content is 1 ppm or more and less than 1000 ppm on a mass basis. If it is less than 1 ppm, the content is too small and the effect of inclusion is not substantially exhibited. On the other hand, if it is contained in an amount of 1000 ppm or more, Si is segregated and workability is lowered, or a melting phenomenon occurs at the time of joining, which is not preferable. The content of Ni is preferably 10 ppm or more and 800 ppm or less because the effect of inclusion is further exhibited.

<Cu>
Cu is the third class of additive elements added to the Au-Ge alloy of the present invention, and the effect obtained by containing this element is to improve workability and flexibility, and the effect is generated. This principle is due to alloying with the joint surface. Specifically, Cu, like Ni and Si, improves workability and the like by nucleation, and is easy to be alloyed at the joint surface of the joint portion and enables strong joining. That is, in general, the uppermost surface of the joint when soldering is abundant with Au or Ag, but Ni or Cu is present underneath. Therefore, when a small amount of Cu is contained in the Au—Ge solder, good bonding with the underlying Ni or Cu becomes possible.

  Content of Cu which exhibits such an effect is 1 ppm or more and less than 100 ppm on a mass basis. If it is less than 1 ppm, the content is too small and the effect of inclusion is not substantially exhibited. On the other hand, if it is contained in an amount of 100 ppm or more, the compound layer at the joint interface becomes too thick or too hard and the joint reliability is lowered. The Cu content is preferably not less than 10 ppm and not more than 80 ppm since the effect of inclusion is further enhanced.

  Au, Ge, Bi, In, Sb, Mg, Ni, Si, and Cu, 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 materials was placed in 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 materials 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 started 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 a mold, a flat solder mother alloy was prepared using a mold having a width of 45 mm, a thickness of 5 mm, and a length of 250 mm in order to produce a punched product. In this manner, Au—Ge solder mother alloys of Samples 1 to 45 in which the mixing ratios of the respective raw materials were changed were produced. The composition of each of the obtained solder mother alloys of Samples 1 to 45 was subjected to composition analysis using an ICP emission spectroscopic analyzer (SHIMAZU S-8100). The obtained composition analysis results are shown in Tables 1 and 2 below.

<Ribbon shape processing and workability evaluation 1>
Next, it rolled until it formed into the ribbon shape of thickness 50 micrometers using the rolling machine with respect to the said plate-shaped solder mother alloy (plate-shaped ingot of thickness 5mm) for punching goods manufacture of the samples 1-45. At the time of rolling, attention was paid to the following points. First, rolling was performed while applying an appropriate amount of lubricating oil as required so that the sample did not stick to the roll. Thus, by making an oil film between a roll, a ribbon, and a ribbon, a ribbon, it can suppress that a roll, a ribbon, or ribbons adhere.

  In addition, it is necessary to consider the feeding speed of the sample. If the feeding speed is too high, the ribbons are easily stuck together, or the tension is too high and the ribbon is cut off. On the other hand, if the feeding speed is too slow, bending may occur and winding may be lost, or a ribbon having a uniform thickness may not be obtained. Thus, when each plate-like solder mother alloy is processed into a ribbon shape, “X” indicates that five or more cracks or scratches per 10 m of the ribbon occur, and “△” indicates that one to four cracks occur. The case where there was no evaluation was evaluated as “◯”, and the evaluation was made as workability evaluation 1.

<Manufacture of disk-shaped and rectangular punched products and evaluation of workability 2, 3>
Each ribbon obtained was processed into a punched product using a press. Specifically, after the ribbon is set in a press machine, while supplying lubricating oil, a disc shape having a diameter of 10.0 mm (hereinafter also referred to as a φ10 mm product) and a square shape having a size of 8.0 mm × 8.0 mm (hereinafter, referred to as “φ10 mm”). □ 8mm product). The punched product obtained was collected in a container containing an organic solvent and washed with the organic solvent. Then, it dried for 2 hours, drawing a vacuum with a vacuum dryer, and obtained the sample for evaluation.

  As described above, a φ10 mm product and a □ 8 mm product were punched in 1000 samples, and a punched product that did not cause chipping or cracking and was punched cleanly was judged as a good product, and a yield rate was calculated. Then, the yield rate of φ10 mm product was defined as processability evaluation 2, and the □ 8 mm product yield rate was defined as processability evaluation 3. Further, a φ10 mm product was used for wettability evaluation, and a □ 8 mm product was used for bondability evaluation, storage property evaluation, and reliability evaluation.

<Evaluation of wettability (measurement of aspect ratio)>
In order to evaluate the wetting and spreading property, a disc-shaped sample was used to make a joined body with the substrate, and the aspect ratio of the solder that spread out when the joining surface was seen from the vertical direction was measured. Specifically, first, a wettability tester (device name: atmosphere control type wettability tester) is started, a double cover is applied to the heater part to be heated, and nitrogen gas is supplied from four locations around the heater part to 12 L / L. While flowing at a flow rate of minutes, the heater was heated to a set temperature of 50 ° C. higher than the melting point of each sample.

  After the heater has stabilized at the set temperature, a Cu substrate (thickness: 0.3 mm) with a Ni plating layer (film thickness: 3.0 μm) on the upper surface is set in the heater section and heated for 25 seconds, then φ10 mm product The solder sample was placed on a Cu substrate and heated for 25 seconds. After the heating of the solder sample was completed, the Cu substrate was picked up from the heater part, placed in a place where the nitrogen atmosphere next to the Cu substrate was kept, allowed to cool sufficiently, and then taken out into the atmosphere.

  The aspect ratio of the solder alloy sample 3 that spreads wet with respect to the joined body in which the solder alloy sample 3 was joined to the Ni plating layer 2 of the Cu substrate 1 as shown in FIG. 1 was determined. Specifically, as shown in FIG. 2, the major axis (X1) which is the maximum solder wetting spread length and the minor axis (X2) which is the minimum solder wetting spreading length are measured, and the following formula 1 is used. The aspect ratio was calculated.

[Calculation Formula 1]
Aspect ratio = major axis / minor axis

  As this aspect ratio is closer to 1, it is understood that the wetting and spreading property is better because the wetting and spreading is more circular on the Cu substrate 1. On the other hand, as the aspect ratio becomes larger than 1, the wetting and spreading shape deviates from a perfect circle, the movement distance of the molten solder in the joining surface direction varies, the reaction becomes uneven, and the thickness of the alloy layer varies. Or the components vary, and uniform and good bonding cannot be performed. Furthermore, since a large amount of solder flows so as to flow only in a certain direction on the joint surface, there are places where the amount of solder is excessive and insufficient, and there are poor joints and, in some cases, parts that cannot be joined.

<Evaluation of bondability (measurement of void fraction)>
In order to evaluate the bondability, a bonded body in which the Si chip and the substrate were bonded with a □ 8 mm solder sample was produced, and the void ratio was measured. Specifically, first, a die bonder (made by West Bond, MODEL: 7327C) is started, the heater part to be heated is covered and nitrogen is allowed to flow from the periphery of the heater part (nitrogen flow rate: 8 L / min in total). Heating was performed at a preset temperature that was 50 ° C. higher than the melting point of each sample.

  After the heater has stabilized at the set temperature, a Cu substrate (plate thickness: 0.3 mm) having a Ni plating layer (film thickness: 3.0 μm) on the upper surface is set in the heater section and heated for 25 seconds, and then □ 8 mm A sample solder alloy sample was placed on a Cu substrate and heated for 25 seconds, and a Si chip was placed on it, scrubbed for 2 seconds, and left for 10 seconds. After 10 seconds, the Cu substrate was picked up from the heater part, placed in a place where the nitrogen atmosphere next to the Cu substrate was kept, allowed to cool sufficiently, and then taken out into the atmosphere.

  In order to confirm the bondability of the bonded body as shown in FIG. 3 thus obtained, the void ratio of the bonded body was measured using an X-ray transmission device (TOSMICRON-6125 manufactured by Toshiba Corporation). Specifically, X-rays are transmitted perpendicularly from the Si chip 4 side to the joint surface of the joined body in which the Cu substrate 1 having the Ni plating layer 2 and the Si chip 4 are joined by the solder alloy sample 3, and Using the calculation formula 2, the void ratio (%) was calculated.

[Calculation Formula 2]
Void ratio (%) = void area / (void area + joint area of solder and Cu substrate) × 100

<Evaluation of storage>
When the solder sample is stored for a long period of time, if the surface of the solder changes due to corrosion or oxidation, the wettability and bondability may decrease, and good bonding may not be possible. Furthermore, when the solder surface changes with time, the joining state may vary. Therefore, it is preferable for obtaining a good joint that the solder surface does not change depending on the environment. In order to evaluate this storability, each □ 8 mm product is placed in a constant temperature and humidity chamber (manufactured by Yamato Scientific Co., Ltd., model: IW242) and tested for 1000 hours under a high temperature and humidity condition of 85 ° C. and 85% humidity. Went.

  Then, assuming that the film thickness of the oxide film before the constant temperature and humidity test of sample 1 is 100, the film thickness of the oxide film after 100 hours and 1000 hours after the start of the constant temperature and humidity test of each sample is relative. evaluated. Here, the thickness of the oxide film is the solder when the oxygen concentration is reduced to 50% when the oxygen concentration is measured in the depth direction from the solder surface with the maximum oxidation concentration near the solder alloy surface being 100%. It was defined as the depth (distance) from the surface. The oxygen concentration of the solder alloy was measured with a field emission Auger electron spectrometer (manufactured by ULVAC-PHI, model: SAM-4300).

<Reliability evaluation (heat cycle test)>
A heat cycle test was conducted to evaluate the reliability of solder joints. In this test, two samples of a Cu substrate / Si chip assembly prepared using a solder alloy sample were prepared in the same manner as in the evaluation of the bondability described above, and one of them was prepared at −40 A heat cycle with one cycle of cooling at 0 ° C. and heating at + 150 ° C. was repeated up to 500 cycles for intermediate confirmation, and the same heat cycle was repeated up to 1000 cycles for the other.

  Thereafter, the samples subjected to 500 cycles and 1000 cycles of heat cycle were embedded in the resin, subjected to cross-sectional polishing, and the bonded surface was observed by SEM (device name: HITACHI S-4800). As a result of this observation, the case where the joint surface peeled or the solder 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 indicated as “◯”. . These reliability evaluation results are shown in the following Tables 3 and 4 together with the above-described workability evaluations 1 to 3, wettability evaluation, bondability evaluation, and storability evaluation.

  As can be seen from Tables 3 and 4 above, all of the Au-Ge solder alloy samples 1 to 29 satisfying the requirements of the present invention are workability, wettability, bondability, storability, and reliability. In all the evaluation items, good characteristics are shown. That is, in the evaluation of workability, no cracks or the like occurred in the ribbons in all the samples, and the yield rate of punched products was 100% for both φ10 mm products and □ 8 mm products. In the evaluation of wettability, the aspect ratio is 1.02 or less, and in the bondability evaluation, the void ratio is 0.2% or less, and it has uniform wetness spread and very good bondability. I understood that. Furthermore, in the evaluation of the storage property, it was found that the oxide film thickness on the surface of the solder alloy hardly changed before and after the test, and the storage property was excellent. In the reliability evaluation, no defect occurred even after 1000 heat cycles were repeated. The reason why such an excellent result was obtained is considered that the solder alloy composition is within the range of the requirements of the present invention.

  On the other hand, since the solder alloys of Samples 30 to 45, which are comparative examples of the present invention, do not satisfy the requirements of the present invention, unfavorable results were obtained in at least one of the evaluation items. That is, in the evaluation of workability, cracks and the like were generated except for the sample 44, and the yield rate of the punched product was about 97% at the highest. Furthermore, in the wettability evaluation, the aspect ratio is about 1.3 to 1.5 excluding samples 30, 31, 44, and 45, and in the evaluation of bondability, the void ratio is excluding samples 30, 31, 44, and 45. It was 10% or more. In the evaluation of storability, the film thickness of the oxide film before the test was 104% or more of the sample 1 by relative comparison, and most of the samples were about 110 to 150%. Furthermore, after the test, all of them were thicker than 115%. In the reliability evaluation, all samples except samples 30, 31, 44, and 45 were defective by 500 cycles.

1 Cu substrate 2 Ni plating layer 3 Solder alloy sample 4 Si chip

Claims (6)

  It contains 13.0% by mass or more and 23.0% by mass or less of Ge, further contains one or more members selected from the group consisting of Bi, In, Sb, Mg, Ni, Si, and Cu, and the remainder is inevitable in production. An Au—Ge solder alloy composed of Au excluding the elements contained in the composition, on a mass basis, when Bi is contained, its content is 1 ppm or more and 1000 ppm or less, and when it contains In, its content is 1 ppm. 1000 ppm or less, when Sb is contained, the content is 1 ppm or more and less than 100 ppm, when Mg is contained, the content is 1 ppm or more and less than 100 ppm, and when Ni is contained, the content is 1 ppm or more and less than 100 ppm, Si When the content is 1 ppm or more and less than 1000 ppm, when Cu is contained, the content is 1 ppm or more and 100 p. Au-Ge-based solder alloy and less than m.   When Ge is contained, the content is 10 ppm or more and 800 ppm or less when Bi is contained, and when In is contained, the content is 10 ppm or more and 800 ppm or less. When containing Sb, the content is 10 ppm or more and 80 ppm or less, when containing Mg, the content is 10 ppm or more and 80 ppm or less, and when containing Ni, the content is 10 ppm or more and 80 ppm or less and contains Si 2. The Au—Ge solder alloy according to claim 1, wherein the content is 10 ppm or more and 800 ppm or less when Cu is contained, and the content thereof is 10 ppm or more and 80 ppm or less when Cu is contained.   A quartz crystal device sealed with the Au—Ge solder alloy according to claim 1.   A SAW filter sealed with the Au—Ge solder alloy according to claim 1.   An electronic device comprising an electronic component joined using the Au—Ge solder alloy according to claim 1.   A semiconductor device comprising the electronic device according to claim 5.

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