JP2016074011A - Au-Ge SOLDER ALLOY HAVING CONTROLLED METALLOGRAPHIC STRUCTURE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Au type solder alloy which has uniform wet spreading property and high bonding reliability and, further, can retain solder volume substantially contributing to bonding and encapsulation.SOLUTION: An Au-Ge type solder alloy comprises 10.0 to 15.0 mass%, preferably 11.5 to 13.5 mass% of Ge and the balance Au with elements inevitably contained upon manufacture. Therein, such a lamella structure that a stripe interval of striped structure is 0.01 to 0.75 μm and/or a metallographic structure made of circular and ellipsoidal structures which respectively have a diameter in the case of a circular shape and a minor axis in the case of an elliptic shape, of 0.01 to 0.75 μm occupies an area of 25% or less with respect to the total cross-section.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a high-temperature Pb-free solder alloy mainly composed of Au, and in particular, a high-temperature Au-Ge solder alloy having a controlled metal structure and an electron sealed or brazed using the solder alloy. Relates to the device.

  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. For this reason, development of Pb-free (lead-free) solder materials is being promoted by various organizations, and for high-temperature Pb-free solder materials, expensive Au-Ge alloys and Au-Sn alloys are crystal devices, SAW filters, MEMS, etc. In practical use.

  The Au-Ge alloy is composed of Au-12.5 mass% Ge (meaning composed of 87.5 mass% Au and 12.5 mass% Ge, and so on). It has a composition of crystal points, and its melting point is 356 ° C. On the other hand, the Au—Sn alloy has a composition of eutectic point of Au-20 mass% Sn, and its melting point is 280 ° C. These Au-based solder alloys have hard and brittle properties, but Au-Sn alloys are often used in a frame shape because they are relatively easy to process. On the other hand, Au—Ge alloys are sticky and difficult to break cleanly. However, Au-Ge alloys can be processed thinly or smallly, and are often used as various connecting solders or package sealing solders as pellet shapes or ball shapes that do not require processing. .

  For example, a ball-shaped Au—Ge alloy is used as a solder ball for sealing a package such as a crystal device or a SAW filter. This package is generally made of ceramics, and after placing a crystal resonator or the like in the space inside the package, the internal space is sealed in a vacuum or in a state filled with an inert gas. The package has a through hole with a step in a part of the lid facing the bottom on which the crystal unit or the like is placed, and a ball-shaped high-temperature solder alloy is placed on the step of the through hole so that the laser can be seen from above. By irradiating light toward the solder alloy, the solder alloy is melted to seal the package. The sealed package is reheated at 240 to 260 ° C. in a reflow process for mounting on a mounting substrate or the like. As described above, since the melting point at the eutectic point is 356 ° C., which is higher than the temperature of the reflow process, the Au—Ge alloy has an advantage that there is less risk of remelting and leaking in the reflow process.

  With respect to such an Au—Ge based solder alloy, for example, in Patent Document 1, in order to solve the problem that the wettability and the like are hindered by oxidation of the surface of a solder ball made of an Au—Ge alloy, Au—Ge A technique for obtaining a solder alloy material having good wettability and oxidation resistance by modifying an oxidized surface layer of a solder ball made of an alloy and then washing it is disclosed.

JP 2008-30093 A

  In recent years, along with the downsizing and thinning of electronic devices, electronic devices such as crystal devices and SAW filters have been required to have a small and thin external shape. 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, as described above, a ball-shaped Au—Ge alloy is used for the solder that seals the through hole of a package that accommodates a crystal unit or the like. At this time, the Au—Ge alloy is used as the bonding surface of the through hole. If it does not spread evenly, there is a risk of problems such as leak failure. In addition, when wet and spread unevenly at the time of melting, there is a possibility that the solder flowing out from the through hole short-circuits the electrode wiring or the like.

  In addition, when using a solder alloy for bonding semiconductor elements, sufficient bonding strength cannot be obtained unless the bonding surface is uniformly wetted, or the bonding reliability of the bonded semiconductor element is significantly reduced due to the inclination of the bonded semiconductor element. There is a risk of 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 Au—Ge alloys.

  The various problems described above tend to become apparent as the above-described electronic devices are reduced in size and thickness. That is, with the downsizing and thinning of electronic equipment, the distance between the through hole and the electrode wiring, the distance between the solder alloy and the electronic component such as the crystal resonator, and the like become narrower. The risk of contact between the crystal unit or the electrode wiring and the solder alloy is increasing due to the flow out. In addition, as electronic devices become smaller and thinner, the size and thickness of the solder alloy itself are also limited. Therefore, under the condition that sealing and joining must be performed with a limited solder volume, the above-described disadvantages are required. When uniform wetting and spreading out of the joint surface occur, the substantial volume of the solder in the solder joint portion is reduced, and the problem that the reliability of the solder joint is impaired becomes more prominent. Of course, from the viewpoint of cost, there is a strong demand to minimize the amount of expensive Au used. In general, the ratio of partial wetting and spreading needs to be suppressed to 25% or less of the total area of the solder cross section before joining.

  As described above, Pb-free solder materials for high temperature used in quartz devices, SAW filters, MEMS, etc. that require particularly high reliability cannot be used as electronic components if there is a sealing failure. And having high reliability. Especially in applications that require high airtightness and reliability, in addition to having good wettability, the solder volume is maintained when joining and sealing with solder, that is, the solder alloy used In many cases, it is required to effectively contribute to bonding and sealing. As described above, a solder used in an electronic apparatus such as a quartz device that requires high reliability is required to have functions that seem to conflict with each other such as appropriate wettability and maintenance of the solder volume.

  Under the circumstances described above, the present inventors conducted extensive research on Au-based solder alloys for electronic devices such as crystal devices that require particularly high reliability. It is affected by various conditions such as bonding temperature, time, atmosphere, etc., but it is greatly affected by the control of the metallographic structure by heat treatment or the like, more specifically, it is common for Au-Ge alloys. By controlling the metal structure by heat treatment or the like based on the vicinity of the composition of crystal points, Au has appropriate wettability, high bonding reliability, and can maintain a good solder volume that contributes substantially to bonding. The present inventors have found that a system solder alloy can be obtained and have completed the present invention.

  That is, the Au—Ge based solder alloy according to the present invention contains Au in an amount of 10.0% by mass or more and 15.0% by mass or less, and is composed of Au except for elements that are inevitably included in the production. A solder alloy having a lamellar structure in which the interval between stripes of a striped structure is 0.01 μm or more and 0.75 μm or less and / or a diameter in the case of a circle, and a minor axis in the case of an ellipse. A metal structure composed of a structure of 01 μm or more and 0.75 μm or less occupies an area of 25% or less with respect to the entire cross section.

  According to the present invention, there is provided an Au-based solder alloy that has a uniform wetting and spreading property and higher bonding reliability than conventional Au-based solder, and can maintain a solder volume that substantially contributes to bonding and sealing. it can. As a result, electronic devices that require extremely high reliability, such as crystal devices, SAW filters, MEMS, etc., in which the solder alloy of the present invention is used as a bonding material or a sealing material, and electronic devices equipped with such devices are increasingly smaller. Even when it is made thinner or thinner, high airtightness and excellent reliability can be maintained.

It is a metallographic photograph of the conventional Au-Ge solder alloy. It is a metallographic photograph of the Au-Ge solder alloy of one specific example of this invention. 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—Ge 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 intensive research on the lamellar structure forming this metal structure, the present inventors have determined the heat treatment conditions during casting, warm rolling, or atomizing after melting of the raw material, as the spacing between the stripes of the lamellar structure. It was found that it can be controlled by adjusting the processing speed and the like, and has a great influence on the solder wettability.

  A solder alloy is generally cast and then rolled, extruded, atomized, pressed, etc. to obtain a product with a predetermined shape. Among these, casting, warm rolling, atomization, etc., particularly affect heat treatment conditions and processing conditions, but the heat treatment conditions, processing conditions such as casting, warm rolling, atomization, etc. have been given priority to productivity. And decided. For this reason, as illustrated in the metal structure of the Au-12.5 mass% Ge solder alloy in FIG. 1, although the lamella structure is shown as a whole, the lamella structure has finely spaced stripes and a lump structure. The structure was a mixture of large crystal grains. When the solder alloy having such a structure is remelted at the time of joining, a lamellar structure composed of fine stripe structures is first melted, and then large massive crystal grains are melted. At this time, since the lamellar structure that has been dissolved first spreads on the substrate and the like, and large crystal grains do not relatively dissolve, the whole may be unevenly spread.

  This large massive crystal is considered to be the influence of the primary crystal due to hypoeutectic and hypereutectic described later. Therefore, the interval between the stripes of the lamella structure is controlled by the heat treatment conditions and the processing speed so that the large crystal grains in the lump form are dissolved in the same manner as the other stripe-like lamellar structures. As a result, there is no clear boundary between the above-described massive crystal grains and the striped lamellar structure adjacent thereto, and the massive crystal grains are taken into the lamella structure. As a result, it is possible to ensure appropriate wettability and to maintain a solder volume that substantially contributes to bonding, and to obtain a solder alloy having high bonding reliability.

  That is, by gradually cooling at the time of casting or by increasing the temperature at the time of rolling, the fine lamellar structure can be reduced. As a result, as shown in FIG. Or by fusing them so that there is no clear boundary between the striped tissue and the mottled non-lamellar tissue adjacent to the striped tissue. A solder alloy having a lamella structure can be obtained. More specifically, a lamellar structure having a stripe interval of 0.01 μm or more and 0.75 μm or less, and / or a diameter in the case of a circle, and a minor axis in the case of an ellipse. A metal structure composed of a circular or elliptical structure of 01 μm or more and 0.75 μm or less occupies 25% or less with respect to a cut surface obtained by cutting the solder in a predetermined direction.

  The requirements regarding the area of the lamella structure described above are numerical values obtained experimentally and experimentally in an actual solder alloy production line. Moreover, the size of the above-described structure and the ratio of the area that they occupy in the cross section of the solder can be calculated by the area calculation function attached to the metal microscope. In other words, arbitrarily select five measurement ranges of 20 μm × 20 μm from a 0.20 mm × 0.20 mm rectangular area when a cross section cut in a predetermined direction with respect to the sample to be measured is viewed with a metal microscope. It can be obtained by averaging the measurement results.

  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. It shall mean the metallographic structure that is formed. 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. It means the metallographic structure. 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. Next, the elements constituting the solder alloy 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. For this reason, Au-based solder is often used for sealing quartz devices and SAW filters, and the solder alloy of the present invention is mainly composed of Au, so that such high reliability is required in the technical field. Provide the solder to which it belongs. However, the metal structure is controlled by heat treatment or the like as described above in order to maintain a proper solder volume that has appropriate wettability and high bonding reliability and also functions effectively as a bonding and sealing. It is necessary to control the metal structure.

<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 356 ° C. Since the Au—Ge-based alloy contains nearly 85 to 90% by mass of Au, which is the most excellent in oxidation resistance, it is very excellent in wettability and bonding reliability. The Ge content is 10.0% by mass or more and 15.0% by mass or less. If the Ge content deviates from this range, the liquidus temperature becomes too high and a melting phenomenon occurs, or the substrate, chip and solder are not uniformly alloyed, resulting in poor bonding. A Ge content of 10.0% by mass or more and 15.0% by mass or less is preferable because it is close to the composition of the eutectic point and enables further excellent bonding.

  The Au—Ge solder alloy is usually used with a composition near the eutectic point, that is, a composition near Au-12.5 mass% Ge. As a result, the solidus temperature becomes 356 ° C. and the crystal becomes finer, so that the wettability is relatively stable. However, when Ge is less than 12.5% by mass, it becomes hypoeutectic, and when Ge exceeds 12.5% by mass, it becomes hypereutectic, so that a primary crystal is generated and mixed with a lamellar structure. For this reason, the wettability varies, and there are portions that spread locally and are difficult to wet. The industrially usable range is 10.0 mass% or more and 15.0 mass% or less near Ge 12.5 mass%, but it is desirable to suppress the generation of primary crystals as much as possible for uniform wetting and spreading. , Ge is preferably 11.5 mass% or more and 13.5 mass% or less.

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

  Various Au—Ge solder alloy samples differing in the proportion of the area occupied by the lamellar structure of a specific size and the Ge content in the solder cross section were prepared and their wettability and reliability were evaluated. Specifically, first, Au and Ge having a purity of 99.999 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 metal structure was controlled by adjusting the amount of water. That is, when cooled rapidly, the crystal becomes finer and a finer lamella structure can be obtained, and conversely when cooled slowly, a lamellar structure with a wide stripe interval is obtained. Furthermore, the metal structure was controlled by controlling the drawing speed of the plate material. On the other hand, the sample made into a ball shape by atomization was annealed in an inert gas, and the metal structure was adjusted by changing the annealing temperature and annealing time for each sample.

  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). Moreover, the area of the lamellar structure | tissue which occupies for a cross section was calculated | required using the digital microscope (VHX-900) made from Keyence. 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, each of the solder mother alloys of Samples 1 to 9, 19 to 27, 28 to 33, and 40 to 43 was processed into a ribbon shape using a warm rolling mill. In addition to the melt casting process, the metal structure was also adjusted in the warm rolling process and controlled so as to obtain the desired metal structure with high accuracy. That is, the metal structure was adjusted by controlling the temperature and rolling speed during rolling and adjusting the heat and time applied to the sample.

  The samples 1 to 9 and 28 to 33 processed into a ribbon shape are punched into a square shape of 1.0 mm × 1.0 mm with a press machine to produce a preform material (punched product), and wet spreadability. Used for evaluation. On the other hand, samples 19 to 27 and 40 to 43 in the form of ribbons are punched into a frame shape with an outer dimension of 1.5 mm × 2.0 mm and a frame width of 150 μm with a press machine to produce a punched product and sealed. Used for evaluation of safety and reliability. Hereinafter, a sample processing method and each evaluation will be specifically described.

<Ribbon manufacturing method>
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. Specifically, the temperature during rolling (roll temperature) was 120 ° C. to 260 ° C., the rolling speed was 0.5 m / min 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.

<Production method of punched product (square shape) and wet spreadability evaluation 1>
Samples 1 to 9 and 28 to 33 processed into a ribbon shape were punched into a square shape of 1.0 mm × 1.0 mm using a pressing machine while supplying pressing oil. Thereafter, the punched sample was washed with alcohol and dried in a vacuum at 40 ° C. for 2 hours to produce a punched product. Using the rectangular punched product thus manufactured, the substrate and the sample were joined, and the wetting spreadability evaluation 1 was evaluated based on the presence or absence of uneven wetting 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.

  With respect to the joined body thus joined, the case where the solder sample and the substrate were properly joined and kept square as shown in FIG. 3A was evaluated as “◯”, and FIG. As shown in FIG. 2, the case where the rectangular shape before joining was not retained and the substrate partially wetted and spread, the case where the substrate could not be joined partially by repelling the solder, or the case where joining was not possible was evaluated as “x”. The evaluation results of the wettability evaluation 1 are shown in Table 2.

<Production method of punched product (frame shape), bonding reliability evaluation 1, bonding reliability evaluation 2>
The samples 19 to 27 and 40 to 43 processed into a ribbon shape were punched into a frame shape having an outer dimension of 1.5 mm × 2.0 mm and a frame width of 150 μm to produce punched products. Using the frame-shaped punched product thus manufactured, the sealing container and the sealing substrate are joined with a solder sample, the leakage state is confirmed to be a joint reliability evaluation 1, and the joined body is heated. A cycle test was conducted to make the joint reliability evaluation 2.

<Joint reliability evaluation 1 (sealing property) of punched product (frame shape)>
In order to confirm the sealing performance by the solder alloy, the sealing container 4 and the sealing lid 5 having the shape shown in FIG. 4 were sealed with each solder alloy sample. A simple die bonder (made by West Bond, MODEL: 7327C) 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. Then, 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 conducted to evaluate the reliability of solder joints. 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 300 ° 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 “◯”.

<Ball manufacturing method>
Next, the prepared master alloys of samples 10 to 18 and 34 to 39 (columns with a diameter of 27 mm) were put into a nozzle of a submerged atomizer, and this nozzle was heated to 300 ° C. above the quartz tube containing oil. (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 300 ° C. and an annealing time of 3 to 120 minutes.

<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. 5, the obtained joined body has a joining form in which the solder alloy 3 is joined by spreading on the surface of the Ni layer 2 of the Cu substrate, and the aspect ratio of the wet-spreading solder alloy is set. Asked. Specifically, the maximum solder wetting spread length shown in FIG. 5 was measured as the major axis X1 and the minimum solder wetting spread length minor axis X2, and the aspect ratio was calculated by the following formula 1.

[Calculation Formula 1]
Aspect ratio = major axis (X1) ÷ minor axis (X2)

  It can be determined that the closer the aspect ratio of the calculation formula 1 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 a portion where the amount of solder is excessive and a portion where there is no solder are formed. Table 3 below shows the measurement results of the aspect ratio of the joined body together with the above-described wettability evaluation 1 (extruding and repelling of solder), bonding reliability evaluation 1 (sealing property), and bonding reliability evaluation 2 (heat cycle test). And in Table 4.

  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 the results are good 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). Met. 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 area of the fine lamellar structure is 25% or less of the entire solder cross section.

  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, 38, 39, 42, and 43, which are Au-12.5Ge mass%, which has been generally used from the past, the wetting and spreading are compared to the samples of the present invention in which the metal structure is controlled within a preferable range. The result was inferior in nature. The samples 32, 33, 38, 39, 42, and 43, which are Au-12.5 Ge mass%, are inferior to the present invention, but they have the same performance as the conventional ones, and further improvement in characteristics due to increasing market demands. It is demanded.

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 (5)

  An Au—Ge based solder alloy containing Ge in an amount of 10.0% by mass or less and 15.0% by mass or less, with the balance being unavoidably included in the manufacturing process. A cross-section of a lamellar structure having an interval of 0.01 μm or more and 0.75 μm or less and / or a metal structure composed of a structure having a diameter in the case of a circle and a structure having a minor axis of 0.01 to 0.75 μm in the case of an ellipse An Au-Ge solder alloy characterized by occupying an area of 25% or less with respect to the whole.   The Au-Ge solder alloy according to claim 1, wherein Ge is contained in an amount of 11.5% by mass to 13.5% by mass.   The Au-Ge solder alloy according to claim 1 or 2, wherein the solder alloy has any one of a frame shape, a sheet shape, a ribbon shape, and a ball shape.   An electronic device, wherein the electronic device is sealed with the Au—Ge solder alloy according to claim 1.   An electronic apparatus, comprising the electronic device according to claim 4.