JP2016052662A - Au-Sn SOLDER ALLOY HAVING CONTROLLED METALLOGRAPHIC STRUCTURE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Au-Sn-based solder alloy which has excellent wettability and where a solder volume substantially contributing to solder joint at solder jointing can be almost maintained.SOLUTION: An Au-Sn-based solder alloy includes 18.5 mass% or more and 23.5 mass% or less of Sn, preferably 19.0 mass% or more and 22.8 mass% or less and the balance Au except elements inevitably included in production and 25% or less of the cross sectional area of the solder alloy is occupied by a metallographic structure consisting of a striped lamellar structure and/or a circular or elliptical lamellar structure.SELECTED DRAWING: None

Description

  The present invention relates to a high-temperature Au—Sn solder alloy mainly composed of Au and having a controlled metal structure, and an electronic device sealed or brazed using the solder alloy.

  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. Although lead has been used as a main component for solder materials for a long time, lead has already been a regulated substance under the RoHS Directive. Therefore, development of Pb-free (lead-free) solder materials is being promoted by various organizations, and for high-temperature Pb-free solder materials, expensive Au-Sn alloys and Au-Ge alloys are crystal devices, SAW filters, MEMS, etc. In practical use.

  The Au-Sn alloy has a composition of Au-20% by mass Sn (meaning that it is composed of 80% by mass Au and 20% by mass Sn, and so on), and has a eutectic point. 280 ° C. On the other hand, the Au—Ge alloy has an eutectic point with a composition of Au-12.5 mass% Ge, and its melting point is 356 ° C. These Au-based solder alloys have hard and brittle characteristics. In particular, Au-Sn alloys have no stickiness and can be ruptured cleanly, and can be processed thin and small, so that they can be used as frame shapes. Many. On the other hand, Au—Ge alloys are often used in a ball shape that is relatively easy to process.

  With regard to such an Au-based solder, for example, Patent Document 1 discloses a technique related to improvement of wettability by the surface roughness of an Au—Sn brazing material, and specifically, a surface roughness Ra specified by JISB0601. A technology for providing a gold-tin alloy brazing material excellent in wettability by being in the range of 0.01 to 5 μm is shown. Patent Document 2 discloses a technique relating to control of oxygen concentration in the Au—Sn solder paste and control of wettability by reducing the particle size.

JP 2001-150182 A JP 2003-260588 A

  In recent years, electronic devices such as crystal devices and SAW filters have been required to be small and thin as electronic devices have become smaller and thinner. Therefore, it is desirable that the shape of the solder alloy used in these electronic devices can be controlled with high accuracy when the solder is melted. For example, an Au-Sn alloy that is frequently used for sealing a quartz crystal resonator is often used in a frame shape for sealing at the peripheral edge of the sealing lid, but the bonding surface is Au at the time of melting. -If the Sn alloy is not evenly wetted, there is a risk that problems such as leakage failure may occur.

  In addition, when an Au—Sn alloy is used for bonding of semiconductor elements, sufficient bonding strength cannot be obtained unless the bonding surface is uniformly wetted, or the reliability of bonding is remarkably increased because the semiconductor element that is the object to be bonded is inclined. It may decrease. Furthermore, when wetting becomes uneven and partial wetting spreads or flows out, the volume of solder that substantially contributes to solder bonding is reduced, distortion due to thermal stress, etc. cannot be relieved sufficiently, and cracks occur. This may cause problems such as ease of bonding and reduced bonding reliability. Thus, it can be said that wettability is a particularly important characteristic in an Au—Sn alloy.

  The various problems described above tend to become apparent as the above-described electronic devices are reduced in size and thickness. In other words, as the electronic equipment becomes smaller and thinner, the distance between the solder alloy and the electronic component such as the crystal resonator becomes narrower. The risk of contact with is increasing. In addition, as electronic devices become smaller and thinner, the size and thickness of the solder alloy itself are also limited. Therefore, if the above-mentioned uneven wetting spreads or flows out of the joint surface, the solder volume of the solder joint is reduced. The reduction rate becomes more remarkable, and the problem of impairing the reliability of solder joints is becoming more prominent. In general, the ratio of partial wetting and spreading is preferably suppressed to 25% or less of the total area of the cross section of the solder before joining.

  Under such circumstances, the technique of Patent Document 1 increases the surface area if the surface roughness is rough, and also increases the rate of oxidation of Sn in the component. Therefore, the surface roughness is reduced, that is, the surface area is reduced. Therefore, it is considered that the ratio of oxidation of Sn in the component is suppressed, thereby improving the wettability. However, it is unlikely that the brazing material exhibits the same excellent wettability over a wide range of surface roughness of 0.01 to 5 μm as shown in Patent Document 1. For example, when the surface roughness becomes 500 times rough, the ratio of oxides existing on the surface of the brazing material increases by an order of magnitude, so it can be easily estimated that the wettability is greatly deteriorated.

  In addition, when the surface roughness increases, a space is likely to be generated between the Au—Sn brazing material and the substrate to be brazed. There is a risk that voids will occur in the product and the reliability of the product after brazing will be greatly impaired. On the contrary, when the surface roughness becomes finer, the wettability tends to be improved as described above, but that is not sufficient as a brazing material. That is, the uniformity of the composition and structure of the substrate metal and brazing material is more important than the surface roughness. If the composition and structure are not uniform, the alloys produced during bonding will be locally different, resulting in wetting spread and bondability. Variation will occur.

  Further, as shown in Patent Document 2, when the oxygen concentration of the Au—Sn solder paste itself is increased, the generation of a surface oxide film becomes remarkable at the time of melting of the solder, which affects the wettability. In this case, although excessive wetting and spreading can be suppressed, voids may be generated by the oxide film or airtightness may not be maintained. In addition, there is a risk of incurring quality problems such as inducing cracks.

  Furthermore, if the average particle size is reduced from 50 to 100 μm to 10 to 35 μm, there may be a problem that the amount of the surface oxide film per unit mass of the Sn fine particles increases. That is, generally, if the surface oxide film is not broken, the melted internal molten metal does not flow out. Therefore, even if the fine particles whose surface is once oxidized reach the melting point, the solution does not easily flow out. Further, substantial melting temperature variation and composition variation become large, and the fine particles are difficult to be dissolved uniformly. This may cause sealing failure and bonding failure, thereby reducing the reliability of the product. Therefore, the technique of Patent Document 2 is not suitable for use in sealing a SAW filter or a crystal device that requires high airtightness or bonding to a substrate such as a semiconductor element.

  As described above, high-temperature Pb-free solder materials used in quartz devices, SAW filters, MEMS, etc. that require particularly high reliability can be used stably if there are voids or poor sealing. Therefore, Au-based solder materials used for these are required to have good wettability. Especially in applications that require high airtightness and joint reliability, in addition to having good wettability, the solder volume is maintained during solder joining, that is, the solder alloy used is effectively soldered. In many cases, it is required to contribute to bonding. As described above, a solder used for an electronic apparatus such as a quartz device that requires particularly high reliability is required to have a seemingly contradictory function of appropriate wettability and maintenance of a solder volume during solder joining.

  Under the circumstances described above, the present inventors conducted extensive research on Au-Sn solder alloys for electronic devices such as quartz devices that require particularly high reliability. Although it is affected by various conditions such as bonding temperature, time, atmosphere, etc. at the time of melt bonding, it is greatly affected by the control of the metal structure by heat treatment or the like, more specifically, Au—Sn alloy By controlling the metallographic structure by heat-treating a solder alloy having a composition at or near the eutectic point, the solder volume that contributes substantially to solder joints with good wettability can be maintained almost completely. As a result, it was found that an electronic device having high bonding reliability can be produced, and the present invention has been achieved.

  That is, the Au-Sn solder alloy according to the present invention contains 18.5 mass% or more and 23.5 mass% or less of Sn, and the Au-Sn is composed of Au except for elements that are inevitably included in the production. The solder alloy is characterized in that 25% or less of the cross-sectional area is occupied by a striped lamellar structure and / or a metal structure composed of a circular or elliptical lamellar structure.

  According to the present invention, wettability superior to that of conventional Au-based solder can be obtained, and a solder volume that substantially contributes to solder bonding can be substantially maintained, so that extremely high reliability of crystal devices, SAW filters, MEMS, etc. It is possible to provide an Au-based solder alloy having high bonding reliability suitable for applications such as electronic devices that require high performance. And since the electronic device using this Au system solder alloy has high airtightness, the electronic device carrying this electronic device is very reliable.

It is a metal structure photograph which shows the solder alloy in which the lamella structure and the metal structure of a mottled pattern are mixed. It is a metal structure photograph of a lamella structure. It is a metal structure photograph which shows the solder alloy which a lamella structure occupies 25% or less of a cross section. It is the typical top view which looked at Cu substrate to which the sample of solder alloy was joined from the solder sample side, (a) is a joined body (evaluation "○") with good wetting spread nature, (b) is wet. The joined body (evaluation "x") with bad expansibility is shown. It is a typical longitudinal cross-sectional view which shows the state which sealed the container for sealing and the lid | cover for sealing with the sample of the solder alloy. FIG. 3 is a schematic plan view of a Cu substrate to which a solder alloy sample is bonded as viewed from the solder sample side, and shows a major axis X1 and a minor axis X2 for calculating an aspect ratio indicating wettability of the solder alloy sample. Has been.

  Hereinafter, embodiments of the Au—Sn solder alloy of the present invention having a controlled metal structure will be described in detail. In general, at the eutectic point of a binary solder alloy, a metal structure including a lamellar structure in which two layers of α phase and β phase are alternately laminated at the time of casting is obtained. Such a lamellar structure improves the mechanical properties of the alloy. As a result of earnest research on the ratio of the lamellar structure in the metal structure, the present inventors adjust heat treatment conditions, processing speed, etc. during casting after alloy raw material melting, during warm rolling, or during atomization. It was found that the ratio of the lamellar structure in the metal structure can be controlled by this, and that the solder wettability is greatly affected.

  A solder alloy is generally cast and then rolled, extruded, atomized, pressed, etc. to obtain a product with a predetermined shape. Among these, particularly in casting and warm rolling, the heat treatment conditions and the processing conditions affect the metal structure, but these conditions have been conventionally determined in consideration of the functionality and productivity. For this reason, as shown in FIG. 1, a striped portion in which a plurality of strip-shaped portions showing a lamellar structure are arranged substantially uniformly and a rough mottled pattern portion made up of a plurality of random-shaped island portions are mixed. It was an organizational structure. When the solder alloy having such a structure is remelted at the time of joining, a substantially uniform lamellar structure is melted first, and then a rough mottled metal structure is melted. And since the lamellar structure | tissue which melt | dissolved first spreads on a board | substrate etc., the metal structure of a rough mottled pattern does not melt | dissolve relatively, and it may become the non-uniform wetting spread as a whole.

  On the other hand, the solder alloy according to the embodiment of the present invention contains Sn in the range of 18.5% by mass to 23.5% by mass, preferably 19.0% by mass to 22.8% by mass, with the balance being in the manufacturing process. An Au—Sn solder alloy composed of Au excluding elements inevitably contained, and 25% or less of the cross-sectional area is composed of a striped lamellar structure and / or a circular or elliptical lamellar structure. It is characterized by being occupied by a metal structure.

  Here, the striped lamellar structure is such that when viewed from the direction perpendicular to the laminating surface of the α phase and the β phase, the band portions of the α phase and the band portions of the β phase are alternately arranged in a striped pattern. In this case, the width of each band-shaped portion is a metal structure of 0.01 μm or more and 0.75 μm or less. On the other hand, a lamellar structure having a circular or elliptical shape is similar to the case where the α or β phase forms a circular or elliptical island when viewed from a direction perpendicular to the laminating surface of the α and β phases. In the case of a circular shape, the length of the diameter is 0.01 μm or more and 0.75 μm or less, and in the case of an ellipse, the length of the short diameter is 0.01 μm or more and 0.75 μm or less. Shall.

  For example, FIG. 2 (a) is a metallographic photograph showing a case where an Au-20 mass% Sn solder alloy forms a striped lamellar structure, and FIG. 2 (b) shows that the solder alloy is circular. It is a metal structure photograph which shows the case where the lamella structure is formed. The direction of the cross section in which the ratio of the lamella structure is measured is determined in consideration of the solder processing method. For example, when the solder shape is a plate shape or a frame shape to be described later, the measurement is performed on a cross section parallel to the thickness direction. On the other hand, in the case of a ball shape, any cross section may be measured as long as the cross section passes through the central portion.

  The measurement of the area occupied by the lamellar structure in the cross section of the solder alloy can be calculated by the area calculation function attached to the metal microscope. For example, out of a 0.20 mm x 0.20 mm rectangular frame taken with a micrograph, arbitrarily select five measurement ranges of 20 μm x 20 μm, and the ratio of the area occupied by the lamellar tissue in each of them It can be determined by measuring and arithmetically averaging them. FIGS. 3A and 3B show a case where the lamellar structure occupies 25% or less of the cross section in the Au-20 mass% Sn alloy.

  In this way, by controlling the ratio of the lamellar structure in the cross section of the solder alloy to 25% or less, good wettability can be obtained, and the solder volume that substantially contributes to solder bonding can be maintained almost completely. A solder alloy having high joint reliability can be provided. The ratio of the lamellar structure in the cross section of the solder alloy can be 25% or less by controlling the heat treatment conditions and the processing speed.

  Specifically, by gradually cooling at the time of casting or by increasing the temperature at the time of rolling, each strip portion constituting the stripe is widened, or the size of the circular or elliptical island portion is increased. As a result, it is possible to obtain a metal structure having a small ratio of fine lamella structures that are almost uniform, that is, a rough and mottled pattern. This is because, when cooled rapidly, the crystal becomes finer and a finer lamella structure can be obtained, whereas when cooled slowly, the crystal grain size increases. The preferable range of the structure of the solder alloy is a numerical value obtained experimentally and experimentally in an actual production line. Next, the composition of the solder alloy of the embodiment of the present invention will be described.

<Au>
Au is an essential element constituting the main component of the solder alloy of the present invention. Since Au has a property that 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. In the solder alloy according to the embodiment of the present invention, by using Au as a main component, it is possible to provide a solder that is particularly suitable for applications requiring high reliability, such as for sealing crystal devices and SAW filters. In order to add excellent wettability and the function of maintaining the solder volume at the time of joining to the solder alloy containing Au as a main component, the metal structure is controlled by heat treatment or the like as described above.

<Sn>
Sn is an essential element that forms the basis together with Au in the solder of the present invention. The Au—Sn solder alloy is usually used with a composition in the vicinity of Au-20 mass% Sn, which is the eutectic point, whereby the solidus temperature is stabilized at 280 ° C. and uniform wettability is obtained. The solder alloy according to the embodiment of the present invention is based on Au-20 mass% Sn, so that the Sn content is 18.5 mass% or more and 23.5 mass% or less, preferably 19.0 mass% or more and 22.8 mass%. %, And the balance is Au except for elements inevitably included in the production. If an appropriate production condition is selected in the composition within the above range, a preferable metal structure can be obtained.

  When Sn is less than 18.5% by mass or exceeds Sn23.5% by mass, it becomes hypoeutectic or hypereutectic, so that primary crystals are generated and mixed with lamellar structures, and the production conditions are adjusted. A solder alloy having good wettability cannot be obtained. Naturally, when solidifying after remelting, each alloy produced has a part that is partly fast or slow due to the difference in melting point. For this reason, there are variations in wettability, and there are portions that spread individually and are difficult to wet. For example, when a ring-shaped Au—Sn solder alloy is melted, the Au—Sn solder may spread in a wave shape, and it may be difficult to ensure a certain volume, and reliability as a solder may not be ensured. For this reason, the above composition range is required.

  The solder alloy described above can be formed into a frame shape, a sheet shape, a ribbon shape, a ball shape, or the like by a processing method such as warm rolling, atomizing, or pressing after vacuum melting and casting. . Solder alloys molded into various shapes are used for joining electronic devices such as quartz devices, SAW filters, or MEMS that require airtightness.

  A plurality of Au—Sn solder alloy samples having different lamella structure ratios in the Sn content and the solder cross section were prepared, and their wettability and reliability were evaluated. Specifically, Au and Sn having a purity of 99.999% by mass or more were prepared as raw materials. Large flakes and bulk-shaped raw materials were cut and pulverized, etc. so as to be uniform with no variation in composition depending on the sampling location in the alloy after melting, and were reduced to a size of 3 mm or less. Next, a predetermined amount of these raw materials was weighed into a graphite crucible for a high-frequency melting furnace.

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

  As the mold, one that can obtain a plate-like alloy having a thickness of 3 mm, a width of 40 mm, and a length of 150 mm was used for rolling, and a mold that was used to obtain a columnar alloy having a diameter of 19 mm was used. In addition, a rapid cooling jacket was attached to the rolling mold, and the ratio of the lamella structure was varied by changing the amount of cooling water supplied to the sample in various ways. In this way, solder mother alloys of Samples 1 to 43 having different compositions and metal structures were produced. The solder mother alloys of Samples 1 to 43 were subjected to composition analysis using an ICP emission spectroscopic analyzer (SHIMAZU S-8100).

  Next, with respect to what is processed into a plate shape, the ratio of the lamella structure is varied by changing the drawing speed of the plate material during the rolling process for each sample. On the other hand, in the case of processing into a ball shape by atomization, when annealing is performed in an inert gas, the annealing temperature and annealing time are changed for each sample so that the proportion of the lamella structure is different.

  If it demonstrates concretely, each solder mother alloy of samples 1-9, 19-33, and 40-43 was processed into the ribbon shape using the warm rolling mill. At that time, in addition to the melt casting process, the metal structure was also adjusted in the warm rolling process. Specifically, the prepared plate-shaped mother alloy sample having a thickness of 3 mm, a width of 40 mm, and a length of 150 mm was rolled with a warm rolling mill. The temperature during rolling (roll temperature) was 120 to 260 ° C., the rolling speed was 0.5 to 4 m / min, and the metal structure was adjusted by adjusting the heat and time applied to the sample. Each sample was rolled to a thickness of 30.0 ± 1.5 μm. Thus, the metal structure was adjusted by controlling the temperature and rolling speed during rolling and adjusting the heat and time applied to the sample.

  On the other hand, each mother alloy (cylindrical shape with a diameter of 27 mm) of Samples 10 to 18 and 34 to 39 was put into a nozzle of a submerged atomizer, and this nozzle was heated to 250 ° C. above the quartz tube containing oil (250 ° C.). Set in the high frequency melting coil). The mother alloy in the nozzle was heated to 520 ° C. by high frequency and held for 5 minutes, and then atomized by applying pressure to the nozzle with an inert gas 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 in a vacuum dryer at 45 ° C. for 2 hours. Furthermore, in order to control the metal structure of each solder sample, annealing was performed in nitrogen gas under conditions of an annealing temperature of 40 to 250 ° C. and an annealing time of 3 to 120 minutes.

  The area of the lamellar structure occupying the cross section of the solder alloy samples 1 to 43 thus obtained was determined using a Keyence digital microscope (VHX-900). At that time, the striped lamellar structure is limited to a width of each band-shaped portion constituting the stripe of 0.01 μm or more and 0.75 μm or less, and a circular or elliptical lamellar structure has a long diameter when it is circular. However, in the case of an ellipse, the length of the minor axis was limited to 0.01 μm or more and 0.75 μm or less. Moreover, the direction of the cross section was a cross section parallel to the thickness direction of the ribbon-shaped one, and an arbitrary cross section passing through the center of the ball-shaped one. The analysis results are shown in Table 1 and Table 2 below together with the results of the composition analysis described above.

  Next, among the ribbon-shaped samples, samples 1 to 9, 28 to 33 were punched into a 1.0 mm × 1.0 mm square shape while supplying pressing oil with a press machine, and the preform material (punched) After that, the punched sample was washed with alcohol, dried in a vacuum at 40 ° C. for 2 hours, a punched product was manufactured, and wet spreadability was evaluated. In addition, samples 19 to 27 and 40 to 43 among the ribbon-shaped samples are punched into a frame shape having an outer size of 1.5 mm × 2.0 mm and a frame width of 150 μm with a press machine, thereby producing punched products and sealing properties. And the reliability was evaluated. Further, the roundness of the ball-like sample was evaluated. These evaluation methods will be specifically described below.

<Wet spreadability evaluation 1>
With respect to the rectangular punched product, the wet spreadability evaluation 1 was made based on the evaluation criteria such as whether the substrate and the sample were not partially wet spread. Specifically, 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 / min. Flowed at a flow rate. Thereafter, the heater was set to a temperature higher than the melting point by 50 ° C. and heated.

  After the heater temperature is stabilized at the set value, a Cu substrate (plate thickness: 0.3 mm) plated with Ni (film thickness: 3.0 μm) is set in the heater section and heated for 25 seconds, and then a rectangular solder sample Was placed on a Cu substrate and heated for 25 seconds. After the heating was completed, the Cu substrate was picked up from the heater part, once installed in a place where the nitrogen atmosphere next to it was maintained, cooled, and after sufficiently cooled, taken out into the atmosphere.

  As for the joined body joined in this way, as shown in FIG. 4A, the case where the solder sample 3 and the Cu substrate 1 are properly joined and the square shape is maintained is “◯”, and FIG. ) When the protruding portion 3a is generated by partially spreading out on the Cu substrate 1 without retaining the rectangular shape before bonding, or when the substrate cannot be partially bonded by repelling the solder or can be bonded. The case where there was not was evaluated as "x".

<Joint reliability evaluation 1 (sealing property) of punched product (frame shape)>
In order to confirm the sealing performance by the solder alloy with respect to the frame-shaped punched product, the sealing container 4 and the sealing lid 5 having the shape shown in FIG. 5 were sealed with each solder alloy sample. A simple die bonder (Model: 7327C, manufactured by Westwest Bond) is used for sealing, and is kept in a nitrogen flow (8 L / min) for 30 seconds at a temperature 50 ° C. higher than the melting point. After sufficiently cooling to room temperature, the sealing body was taken out into the 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. When water was contained in the disassembled sealing body, it was determined that there was a leak, and “×” was evaluated as the sealing performance evaluation. The case where there was no such leak was evaluated as “◯”.

<Joint Reliability Evaluation 2 (Heat Cycle Test) for Stamped Products (Frame Shape)>
A heat cycle test was performed on the frame-shaped punched product in order to evaluate the reliability of solder bonding. In addition, this test was done using the sealing body sealed with the solder alloy obtained similarly to the said joint reliability evaluation 1. FIG. First, for each sealing body, cooling at −40 ° C. and heating at 250 ° C. were taken as one cycle, and this was repeated for a predetermined cycle. Then, each sealing body which performed the heat cycle test was immersed in water for 2 hours, then, the sealing body was taken out from the water, disassembled, and the leak state was confirmed. When water was contained in the disassembled sealing body, it was determined that there was a leak, and “×” was evaluated as the sealing performance evaluation. The case where there was no such leak was evaluated as “◯”.

<Evaluation of ball wettability 2 (measurement of aspect ratio of joined body)>
A wettability tester (device name: atmosphere control type wettability tester) was started, a double cover was applied to the heater part to be heated, and nitrogen gas was allowed to flow from four locations around the heater part at a flow rate of 12 L / min. . Thereafter, the heater was set to a temperature higher than the melting point by 50 ° C. and heated. After the heater temperature has stabilized at the set value, a Cu substrate (plate thickness: 0.3 mm) plated with Ni (film thickness: 3.0 μm) is set in the heater and heated for 25 seconds, and then a ball-shaped solder alloy Was placed on a Cu substrate and heated for 25 seconds. After the heating was completed, the Cu substrate was picked up from the heater part, once installed in a place where the nitrogen atmosphere next to it was maintained, cooled, and after sufficiently cooled, taken out into the atmosphere.

  As shown in FIG. 6, the obtained joined body had a form in which the solder alloy sample 3 was wet spread on the surface of the Ni layer 2 of the Cu substrate, and the aspect ratio was obtained. Specifically, the major axis of the maximum solder wetting spread length shown in FIG. 6 was measured as X1 and the minimum solder wetting spread length minor axis X2, and the aspect ratio was calculated by dividing X1 by X2. It can be judged that the closer the aspect ratio is to 1, the more wetting and spreading in a circular shape on the substrate, and 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 a portion where the amount of solder is excessive and a portion where there is no solder are formed. The measurement results of the aspect ratio of the joined body are shown in the following Tables 3 and 4 together with the above-described wettability evaluation 1, joint reliability evaluation 1, and joint reliability evaluation 2.

  As can be seen from Tables 3 and 4 above, the solder mother alloys of Samples 1 to 27 that satisfy the requirements of the present invention show good characteristics in each evaluation item. In other words, all results were satisfactory in Wetting Spreadability Evaluation 1 (extruding and repelling of solder), Wetting Spreadability 2 (aspect ratio), Bonding Reliability Evaluation 1 (sealing property), and Bonding Reliability Evaluation 2 (heat cycle test). It became. The reason why such a good result was obtained is considered to be that the solder alloy sample is within the composition range of the present invention and the ratio of the lamellar structure occupying the predetermined cross section is 25% or less.

  On the other hand, the solder alloys of Samples 28 to 43 of Comparative Examples not satisfying the requirements of the present invention resulted in undesirable results in at least any of the characteristics. In the samples 32, 33, 42, and 43, which are Au-20Sn mass% generally used from the past, the wetting spread compared to the sample satisfying the requirements of the present invention in which the metal structure is controlled within a preferable range. The result was inferior. In addition, the samples 32, 33, 42, and 43 that are Au-20Sn% by mass show the same performance as the conventional Au-Sn solder alloy. These are required to have better properties as the market demand increases.

DESCRIPTION OF SYMBOLS 1 Cu board | substrate 2 Ni layer 3 Solder alloy sample 3a Overhang | projection part 4 Sealing container 5 Sealing lid

Claims (6)

  It is an Au-Sn solder alloy containing 18.5 mass% or more and 23.5 mass% or less of Sn, and the balance is composed of Au except for elements inevitably included in production, and 25% of the cross-sectional area thereof An Au—Sn based solder alloy characterized in that the following is occupied by a striped lamellar structure and / or a metal structure composed of a circular or elliptical lamellar structure.   The width of each band-shaped portion constituting the striped lamellar structure is 0.01 μm or more and 0.75 μm or less. When the circular or elliptical lamellar structure is circular, the length of the diameter is elliptical. 2. The Au—Sn solder alloy according to claim 1, wherein the length of the minor axis is 0.01 μm or more and 0.75 μm or less.   The Au-Sn solder alloy according to claim 1 or 2, wherein the Sn is contained in an amount of 19.0 mass% or more and 22.8 mass% or less.   The Au—Sn solder alloy according to claim 1, wherein the solder alloy has a frame shape, a sheet shape, a ribbon shape, or a ball shape.   An electronic device sealed with the Au—Sn solder alloy according to claim 1.   An electronic apparatus comprising the electronic device according to claim 5.