Patent Application
20180079036
This application is based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2016-184922, filed on Sep. 22, 2016, the entire content of which is incorporated herein by reference.
This disclosure relates to a solder material and an electronic component manufactured using this solder material.
In production of an electronic component such as a surface acoustic wave device and a crystal resonator, a solder material is heavily used. For example, when a surface acoustic wave chip or a crystal vibration chip is housed in a container to airtightly seal this container with a lid member, the solder material is used as an airtight sealing material. The electronic component thus airtightly sealed is used mounted on a wiring board. In this regard, the solder material is also used as a connection material. The electronic component thus mounted on the wiring board is sometimes molded with resin together with other components to be modularized. Also when this module is mounted on a substrate of the electronic device, the solder material is used as a connection material.
A typical example of the conventional solder material includes one consist mainly of lead and tin, and one consist mainly of gold and tin, one consist mainly of tin-copper-argentum, and similar one. The one consist mainly of tin-copper-argentum is expected since the one matches a request for lead-free and eliminates the need for using expensive gold. For example, International Publication No. WO2014/024715 discloses, as a solder material consist mainly of tin-copper-argentum, a solder material consist of antimony-argentum-copper-, at least one material selected from aluminum, iron, and titanium, and the remaining portion made up by tin.
On the other hand, the inventors according to this application have been also seriously proceeding study for a solder material including Sn (tin), Sb (antimony), Cu (copper), Ag (argentum), and In (indium). This material also has advantages such that this material matches the request for lead-free and eliminates the need for using gold.
However, the study by the inventors has proved that, in the case of this solder material, although details will be described below, there is the following problem unless the composition is properly performed.
That is, it has been proved that, when airtight sealing, for example, between the container that houses the crystal vibration chip and the lid member is performed using this solder material, a considerable low-melting-point phase occurs in the hardened solder depending on a cooling condition after soldering. This low-melting-point phase causes to generate trouble, for example, as described below. For example, the crystal resonator is, in most cases, used by being mounted on the wiring board with the solder material (the composition does not matter). Further, the crystal resonator is sometimes modularized in a state mounted on the wiring board. Therefore, for example, in the case of the crystal resonator using the solder material as the airtight sealing material, the above-described low-melting-point phase is influenced by heat when the crystal resonator is soldered to the wiring board or heat when the crystal resonator is modularized. Thus, this causes a case where an airtight sealing portion is remelted to break the airtight sealing state of the crystal resonator. Further, when the above-described low-melting-point phase occurs on a solder-bonding portion between the crystal resonator and the wiring board, remelting also occurs at this bonding portion, thus possibly causing deterioration of bonding quality between the crystal resonator and the wiring board.
A need thus exists for a solder material and an electronic component which are not susceptible to the drawback mentioned above.
According to an aspect of this disclosure, there is provided a solder material. The solder material includes 25 to 45 mass % of Sn, 30 to 40 mass % of Sb, 3 to 8 mass % of Cu, 25 mass % or less of Ag, and 1.3 to 6 mass % of In.
The foregoing and additional features and characteristics of this disclosure will become more apparent from the following embodiments considered with reference to the accompanying drawings.
The following description describes an embodiment of this disclosure with reference to the drawings. Each drawing used in the descriptions is merely illustrated schematically for understanding the disclosure. In each drawing used in the descriptions, like reference numerals designate corresponding or identical elements, and therefore such elements will not be further elaborated here. Content rates, temperatures, cooling speeds, and a similar factor described in the following embodiment are merely preferable examples within the scope of the disclosure. Therefore, the disclosure is not limited to only the following embodiment.
An experiment by the inventors has proved that, at a solder material including Sn, Sb, Cu, Ag, and In, depending on a difference of a cooling speed for hardening after melting of the solder material, a considerable low-melting-point phase occurs in the solder after hardening.
Specifically, when the solder material is contacted to a metal having a large thermal capacity to rapidly cool the solder material immediately after the solder material is melted (the cooling speed is estimated to be 50° C./second or more), and when the solder material is cooled such that the cooling speed is varied into 20° C./second, 10° C./second, 5° C./second, 3.5° C./second, and 1° C./second by variously changing a profile of a reflow furnace, differential scanning calorimetry (DSC) characteristics of respective specimens obtained in the respective cooling conditions have been measured. Then, it has been proved that the slower the cooling speed is, the more the considerable low-melting-point phase occurs.
The cooling condition of the solder material when an electronic component is manufactured using the solder material can be set by manufacturing equipment such as the reflow furnace and a solder sealing device. However, although the cooling speed is expected to be fast as much as possible such that the low-melting-point phase is hard to occur, if load to the equipment is considered, there is a limit. Thus, the cooling speed is 5° C./second at the fastest, and preferably 3.5° C./second. Therefore, the solder material where the low-melting-point phase does not occur at such cooling speeds is preferred.
In such case, it has been proved that, in a composition of a solder material of this disclosure, especially when the content rate of In is properly set, even if the cooling speed after the solder material is melted is slowed to 5° C./second, and further to 3.5° C./second, the considerable low-melting-point phase does not substantially occur at a hardened product.
From the perception as described above, the solder material of this disclosure includes 25 to 45 mass % of Sn, 30 to 40 mass % of Sb, 3 to 8 mass % of Cu, 15 to 25 mass % of Ag, and 1.3 to 6 mass % of In (preferably 1.3 to 5 mass %, and more preferably 1.5 to 4 mass %). In the following, a description will be specifically given.
In this solder material, Sn has a role that governs a solidus temperature that is a temperature where the solder material starts melting. The content of Sn is determined corresponding a purpose of use from a range of 25 to 45 mass % (25 mass % or more, and 45 mass % or less).
Sb has a role that controls a eutectic point of this solder material. Specifically, for example, at this solder material including Ag and Cu, the eutectic point is likely to increase. However, if Sb is applied, the eutectic point can be reduced. However, if the content of Sb is excess, Sb recrystallizes to scatter in the melted solder, thus deteriorating a quality of the solder material. Therefore, considering them, the content of Sb is determined from a range of 30 to 40 mass % (30 mass % or more, and 40 mass % or less).
Cu has a role that accustoms a hardened product of this solder material. Here, to accustom means to strengthen binding of the respective metals in the solder material to one another. If the amount of Cu is excess, since a melting temperature of the solder material tremendously increases, and a hardness of the hardened product after soldering increases, it is not preferred. Therefore, considering them, the content of Cu is determined from a range of 3 to 8 mass % (3 mass % or more, and 8 mass % or less).
Ag has a role that keeps stability of bonding of the solder material. Here, good bonding stability means that the hardened product after soldering using this solder material has a high mechanical strength. More specifically, the good bonding stability means that, when a container is airtightly sealed to a lid member using this solder material at the electronic component such as a crystal resonator, a bonding strength of the container to the lid member is high. However, if the content of Ag is excess, crystallization of Ag is likely to occur inside the hardened product, and therefore wettability of the solder gets worse. Moreover, increase of the content of Ag causes a cost increase. If the content of Ag is excess, there is a property that the solidus temperature that is the temperature where the solder material starts melting is likely to be influenced by a temperature of a melting point of Sn. In other words, reduction of the amount of Ag can control decrease of the solidus temperature of this solder material. Therefore, considering them, the content of Ag is good to be 25 mass % or less, and preferably determined from a range of 15 to 25 mass % (15 mass % or more, and 25 mass % or less).
In has a role that governs a liquidus temperature that is a temperature where the solder material is completely melted. Specifically, as the content of In increases, a trend that the liquidus temperature increases is indicated. However, as the content of In increases, a trend that the liquidus temperature becomes unstable is indicated. On the other hand, if the content of In is too little, the wettability of the solder material decreases. Therefore, for example, bondability of the container to the lid member when airtightly sealing is deteriorated to decrease a sealing yield rate. As a specified matter, at this solder material, the low-melting-point phase is likely to occur in the hardened product as the cooling speed after melting slows. However, properly setting this content of In ensures effect that this low-melting-point phase is less likely to occur. That is, properly setting the content of In can enlarge a degree of freedom of the cooling condition in a work that cools and hardens the solder material. Therefore, considering these matters and a result of an experiment in working examples and comparative examples, which are described later, a content X of In is 1.3 mass %≦X≦6 mass %, preferably 1.3 mass %≦X≦5 mass %, and more preferably 1.5 mass %≦X≦4 mass %.
The solder material of this disclosure can further include other materials in addition to Sn, Sb, Cu, Ag, and In.
First, as a preferred form, Si (silicon) and Ti (titanium) can be included. Including Si and Ti makes a gradient of a differential scanning calorimetry curve steep. The reason is conceivable that applying Si and Ti makes crystal that constitutes the solder fine to make particles that constitute the solder fine, thus making change from solid to liquid apparent. If the contents of Si and Ti are too little, the above-described miniaturization of the particles cannot be obtained. If the contents of Si and Ti are excess, Si and Ti themselves are less likely to remain as the crystal. Therefore, the amounts of Si and Ti are determined considering them. According to the experiment by the inventors, the contents of Si and Ti are each good to be 0.1 mass % or less, and preferably 0.05 mass % or less. Ti is hard to have a property that is like to become dross. Thus, increase of the amount of Ti possibly increases viscosity of the solder material. Therefore, the content of Ti is, as described above, 0.1 mass % or less, preferably 0.05 mass % or less, and more preferably 0.03 mass % or less.
As described above, at the solder material of this disclosure including Si and Ti, the change from solid to liquid becomes apparent, thus further reducing a probability that melting of the solder material is insufficient and a probability that a part thought to have been secured with the solder material is peeled off without sufficiently hardening.
As another form of additional elements, the solder material of this disclosure may include, for example, one or a plurality of elements selected from Ni, Fe, Mo, Cr, Mn, Ge, and Ga in a range that does not exceed 1 mass % (in a case of a plurality of elements, in ranges that each do not exceed 1 mass %) to improve fluidity of the solder and to improve the mechanical strength of the solder material.
The following describes an exemplary method for manufacturing the solder material of this disclosure. First, each of Sn, Sb, Cu, Ag, and In is individually pulverized using a known crusher such as a turbo mill, a roller mill, a centrifugal force pulverizer, and a pulverizer to obtain powder of each metallic material.
Next, the powder of the respective metallic materials manufactured as described above is weighted to each fulfill a predetermined content in this disclosure, specifically, the composition shown in Table 1 described below, and then, mixed.
Next, this mixture is melted, for example, in a heated crucible to form molten metal. Next, the molten metal is granulated, for example, by known centrifugal atomization. The centrifugal atomization continuously supplies the above-described molten metal in the crucible on a rotary disc that rotates at high speed to circumferentially atomize the molten metal by centrifugal force of the rotary disc. This atomized molten metal is cooled in a predetermined atmosphere to be hardened, thus obtaining microparticulated solder material. If a diameter of this microparticle is too large, printability on a substrate of solder paste that is generated gets worse. If the diameter of this microparticle is too small, wettability to an applied product of the solder paste gets worse when the solder paste is heated. Therefore, it is good to manage workmanship of the above-described processed product to manufacture respective microparticles such that each microparticles have a grain diameter whose average particle diameter is in a range of 5 μm to 50 μm at a sphere-equivalent diameter, using a known particle size distribution measurement method such as particle image measuring and zeta potential measuring.
The solder material of this disclosure, a paste-like solder material is obtained by mixing such a microparticulated solder material and a flux. As the flux used when the solder paste is constituted, for example, flux including tackifier resin such as rosin, a thixotropic agent, an activator, and a solvent can be used. Regardless of difference of degree of activity of the flux, various fluxes can be used.
The following describes an exemplary electronic component manufactured using the paste-like solder material prepared as described above.
Bonding of the substrate body to the lid member of the crystal resonator is performed as follows. At around an edge portion of the substrate body 11 or 21 that mounts the crystal vibration chip 3, a paste of the solder material of this disclosure is applied, for example, by screen printing. Next, the lid member 12 or 22 is placed on this substrate body 11 or 21. Next, this specimen is set on a heatable sealing device, and then, the lid member and the substrate body are sealed by applying predetermined heat, for example, while applying pressure. A sealing atmosphere is a predetermined gas atmosphere such as a reduced-pressure atmosphere or a nitrogen atmosphere. Thus, the crystal resonator as the electronic component airtightly sealed with the solder material of this disclosure can be obtained. The solder material may be used in a state where the solder material is preliminary applied and melted on the lid member.
The electronic component to which this disclosure is applicable is not limited to the crystal resonator. This disclosure is applicable to various ones on which solder sealing is desired to be perfonned, such as a surface acoustic wave filter and a sensor.
The electronic component in this disclosure is not limited to the above-described crystal resonator or the like that has used the solder material of this disclosure as a sealing material. The electronic component in this disclosure also includes a substrate that mounts the electronic component. The substrate is constituted by soldering the electronic component such as the crystal resonator to a wiring board with the solder material of this disclosure. For example, the electronic component of this disclosure also includes an electronic component mounting substrate where the mounting terminal (not illustrated) of the crystal resonator and a connecting terminal on a wiring board (not illustrated) in
5-1. Experiment by DSC Measurement
The following experiment of the working examples and the comparative examples has been performed to confirm an effect that can reduce remelting danger. The solder material of this disclosure has this effect.
Solder materials of the working examples and the comparative examples having compositions shown in Table 1 have been prepared by the above-described manufacturing method.
Next, each of the solder materials of these working examples and comparative examples have been melted at a temperature of 475° C., and then, cooled at a cooling speed of 5° C./second to be hardened. Here, the reason that has melted the solder materials at the temperature of 475° C. is for surely melting the respective solder materials of the working examples and the comparative examples. Therefore, this temperature is merely one example.
Next, on the respective hardened specimens, a differential scanning calorimetry has been perfoll ied. Then, a solidus temperature, a liquidus temperature, and a liquid phase rate and a solid phase rate at 280° C. for each specimen have been obtained. These results are shown in Table 1. A DSC device used in the measurement is Thermo Plus EVOII/DSC8230 (manufactured by Rigaku). The measurement has been performed by a method normalized in Japanese Industrial Standard Z3198-1. For the liquid phase rate and the solid phase rate, taking a whole peak area in the DSC measurement result as 100%, a peak area ratio at less than 280° C. is the liquid phase rate, and a peak area ratio at 280° C. or more is the solid phase rate. The reason that the temperature of 280° C. is set in calculation of the liquid phase rate and the solid phase rate is, since a melting point of a gold-tin alloy currently generally used is 280° C., for easily determining whether the solder material of this disclosure can assure a heat resistance equal to or more than a heat resistance of the gold-tin alloy or not.
As apparent from
Meanwhile, as apparent from
Therefore, at the specimen of the working example, it is found that even if heat is applied again after melting and hardening, remelting is less likely to occur. That is, it is found that, even when the cooling speed in melting and hardening at the first time is set to 5° C./second, a feasible relatively fast speed, remelting in reheating can be prevented. Although a DSC characteristic diagram is omitted, at the solder materials of the respective working examples, even when the cooling speed after the solder material is melted is set to 3.5° C./second, similarly to the case where the cooling speed is 5° C./second, the low-melting-point phase does not substantially occur. This can be confirmed in the experiment by the inventors.
5-2. Experiment at Electronic Component
The following describes a result that has confirmed the effect of this disclosure by the second exemplary crystal resonator described with reference to
First, the second exemplary crystal resonators illustrated in
Table 2 shows each yield rate that the quality item after sealing has been passed through the reflow furnace for several times. As seen from Table 2, when the content rate of In is 1.5 mass % or more, and 4 mass % or less, even though the number of reflow is increased, the yield rate is maintained at 100%. Even when the content rate of In is 1.3 mass % or more, and 6 mass % or less, the yield rate is ensured to some extent. Thus, it can be said to be applicable to a product by proper manufacturing condition or the like. In contrast, at the specimen whose content of In exceeds 7 mass %, even after the reflow at the first time, the failure occurs. As the number of reflow increases, the failure occurs. When the content of In is 6 mass %, after the reflow at the fifth time, the failure occurs.
Examining these results in
5-3. Confirmatory Experiment of Wettability
Using the solder materials of the comparative example and the working example used in the above-described sealing experiment, according to a method normalized in Japanese Industrial Standard Z3284-4:204, evaluation of solder wettability has been performed.
From this result in
Therefore, also from the aspect of wettability, a lower limit of the content of In is good to be 1.3 mass %, and more preferably 1.5 mass %. If the wettability is poor, melting and bonding of the solder, for example, when the crystal resonator is airtightly sealed is not properly performed, thus reducing the yield rate after sealing. Also in the context of the results in
5-4. Experimental Result of Addition of Si and Ti
The following describes an experimental result where Si and Ti have been added as additional trace elements. At the solder material of the working example 1, the content of Ag is reduced by 0.01 mass %, and alternatively, 0.05 mass % of Si and 0.05 mass % of Ti are included, thus adjusting a solder material of a working example 15.
Next, this material is, similarly to the above-described working examples, melted at the temperature of 475° C., and then, cooled at the cooling speed of 5° C./second to be hardened. Next, on the hardened specimen, the differential scanning calorimetry has been performed.
The solder material including Si and Ti has a heat flow peak larger than that of the solder material without Si and Ti, and moreover, has a gradient of a differential scanning calorimetry curve steeper than that of the solder material without Si and Ti. This means that the change from solid to liquid becomes apparent. Thus, it can be said that melting and hardening of the solder material can be more properly performed.
To embody this disclosure, it is preferable that the content of Ag is 15 to 25 mass %. The content of In is preferably 1.3 to 5 mass %, and more preferably 1.5 to 4 mass %. A cooling condition after the solder material of this disclosure is heated and melted is preferably a cooling speed faster than a cooling speed of 3.5° C./second, and more preferably a cooling speed faster than a cooling speed of 5° C./second. Such cooling speed can reduce possibility that the low-melting-point phase occurs at a hardened product.
According to the solder material of this disclosure, the occurrence of the low-melting-point phase after hardening can be reduced, thus ensuring prevention of the above-described trouble even if the heat reaches, for example, the electronic component airtightly sealed and connected to the substrate using this solder material. Therefore, this can provide an inexpensive solder material that has high reliability, and matched the request for lead-free.
The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-184922 | Sep 2016 | JP | national |
