JP5461125B2 - Lead-free high-temperature bonding material - Google Patents

Description

  The present invention relates to a lead-free high-temperature bonding material used in a high-temperature environment that is equal to or higher than a general soldering temperature.

  The high-temperature solder can ensure the strength of the connecting portion even in the soldering temperature range of the Sn—Pb solder alloy which is a general joining solder material. Therefore, for example, the inside of the semiconductor device is soldered with a typical high-temperature solder Pb-5Sn solder (melting point: 310 to 314 ° C.), and then reflow soldering for connecting the semiconductor device itself to the substrate is performed inside the semiconductor device. In order not to melt the soldering portion, a temperature hierarchical connection in which a general-purpose Sn-37Pb eutectic solder having a low melting point (melting point: 183 ° C.) is applied.

In recent years, in order to deal with environmental problems, lead-free products are required by the RoHS Directive that regulates specific harmful substances such as Pb contained in electronic devices in the EU. As the solder for reflow, Sn—Ag—Cu eutectic alloy (melting point: 227 ° C.) has been put into practical use instead of Sn-37Pb eutectic solder. However, Au-20Sn (melting point: 280 ° C.) is known as a high temperature solder required to have a melting point higher than these reflow solders. However, the cost and mechanical properties of Pb—Sn solder are lower. Since it is inferior in terms of use, it has hardly been used and other component systems have not been put into practical use. Therefore, even in the RoHS directive, Pb high-temperature solder is excluded from application.

  Regarding the development of a high-temperature solder alloy, for example, Japanese Patent Application Laid-Open No. 2003-260587 (Patent Document 1) describes Sn—Cu based solder. According to this method, a material in which Sn powder and Cu powder are mixed is used as a solder paste. During high-temperature soldering, Sn powder melts and contributes to soldering, and at the same time, reacts with Cu powder and has a high melting point Sn—Cu. An intermetallic phase is formed. This compound phase functions to maintain the strength of the soldered part without melting during reflow.

However, according to the invention of Patent Document 1 described above, since the powder that is practically used is about 10 μm in size, all of the Cu powder does not react and is generated at the interface between the joint Sn powder and the Cu powder. Since the structure of the intermetallic phase is formed on the surface of the Cu powder, it is rough and varies in strength. Furthermore, since much Cu powder must be used for emphasizing strength, there are problems such as a large influence of Sn powder and a decrease in soldering characteristics. In addition, since the formation of intermetallic compounds is due to the diffusion reaction between melted Sn and solid state Cu, the rate of formation of the Cu ₆ Sn ₅ intermetallic compound phase that contributes to strength maintenance is slow, and it takes time to react. There is also a problem.

  On the other hand, it has been studied to add fine particles of a powder to a solder material to improve the characteristics. For example, as shown in WO 2006/126564 (Patent Document 2), particles having a size of less than 1 μm are soldered. It is added for the purpose of refining the subsequent structure, and it is not added for the purpose of an alloy reaction for obtaining a joint portion of an intermetallic compound as in Patent Document 2 described above.

  Therefore, the inventors disclosed in Japanese Patent Application Laid-Open No. 2008-178909 (Patent Document 3) an alloy composed of two types of elements A and B. Element A has a higher melting point than element B and is stable at room temperature composed of element B. A bonding material produced by supersaturating solid solution of element A in a room temperature stable phase composed of element B in an alloy having a room temperature stable phase AmBn composed of a phase and elements A and B (m and n are values inherent to the alloy system) Is used to maintain the bonding strength even at the reflow temperature of Pb-Sn eutectic solder and Sn-Ag-Cu lead-free solder by maintaining the temperature at which the supersaturated solid solution decomposes and the room temperature stable phase AmBn precipitates I found out that I can do it.

The object of the present invention is to ensure the bonding strength at the time of general soldering, and the Sn phase remains at a constant ratio in a material in which the element A is Cu and the element B is Sn. Therefore, for example, when using a rapidly solidified SnCu powder as a joining material for joining a semiconductor element and a heat sink or a material for joining a member exposed to a high temperature environment, the temperature becomes higher than the reflow temperature, and the liquid phase state Sn may flow out of the junction.
JP 2003-260587 A WO2006 / 126564 JP 2008-178909 A

  As described above, there is no practical non-Pb bonding material that can maintain the strength without securing the solderability on the higher temperature side than the reflow temperature and without flowing the molten Sn liquid phase.

An appropriate amount of Cu-based powder having a diameter of less than 1 μm (hereinafter referred to as submicron) is mixed with the rapidly solidified SnCu alloy powder according to Patent Document 3 described above. Since the submicron powder has a large specific surface area and high reactivity, it contains Cu ₆ Sn ₅ and Cu ₃ Sn in the joint by further reacting with the added Cu-based powder and extra Sn in addition to the precipitation reaction from the supersaturated solid solution. Increase organizational ratio. As a result, although the joining temperature is the same as the normal solder joining temperature, a joined portion in which Sn in the liquid phase does not flow out can be obtained while securing a high temperature strength even after the joining at a temperature higher than the reflow.

However, Cu submicron powder is expensive regardless of the production method such as pulverization or gas phase reaction, but the specific surface area of copper oxide (Cu ₂ O, CuO) or surface-oxidized Cu is also cheaper. When using submicron powders with a large particle size, the effect of the oxide layer can be reduced compared to general powders, and the metal caused by the reaction between Cu and Sn, such as Cu ₆ Sn ₅ or Cu ₃ Sn, in contact with molten Sn Intermetallic compound formation occurs. Furthermore, when the solder flux is added, the solder flux acts not only on the oxide layer on the surface of the solder powder but also on the reducing action of copper oxide at the same time.

From the above, when submicron powder is used even with Cu oxide or surface oxidized Cu powder, in addition to the supersaturated precipitation reaction, the entire joined portion is made Cu ₆ Sn ₅ or Cu by reaction with the above-mentioned added Cu powder and excess Sn. ₃ Increases the proportion of tissue containing Sn. As a result, it is possible to obtain a joint that can secure high-temperature strength without melting even at a temperature higher than reflow after joining, and prevent Sn from flowing out, even though the joining temperature is the same as the normal solder joining temperature. I found.

The gist of the invention is that
(1) A particle diameter of less than 1 μm composed of any one or more of a powder composed of Sn and / or a powder composed of a SnCu alloy, and copper powder having copper, copper oxide, cupric oxide, and a surface oxide layer. The SnCu alloy is a material comprising a mixture of copper fine powder, and the SnCu alloy comprises , by mass%, Cu of 38% or less, the balance being Sn and inevitable impurities, and the Sn powder and / or SnCu. a powder of an alloy, the mixing ratio of the fine the copper fine powder, a mass ratio, 7.00: 3.00 to 9.95: bonding material for lead-free high temperature which comprises using a material that is 0.05 .

(2) a powder consisting of powder and / or SnCu alloy consisting Sn, copper, copper oxide, cupric oxide, copper powder that have a surface oxide layer either one or less than 1μm of two or more The lead-free high-temperature bonding material according to claim 1, wherein a flux is mixed with a material obtained by mixing copper fine powder having a particle size .

(3) a powder consisting of powder and / or SnCu alloy consisting Sn, copper, copper oxide, cupric oxide, copper powder that have a surface oxide layer either one or less than 1μm of two or more The lead-free high-temperature bonding material according to claim 2, wherein 1 to 30% by mass of flux is added to a material obtained by mixing copper fine powder having a particle size .

  Although the material of the present invention has a bonding temperature that is the same as the normal solder bonding temperature, it is possible to obtain a bonded portion in which excess molten Sn does not flow out while securing high temperature strength even at a temperature higher than the reflow after bonding. The present invention provides a material, and can be used as a lead-free high-temperature bonding material corresponding to high-temperature solder, brazing material for bonding high-temperature members, sealing material filling through holes exposed to high temperatures, and the like.

The present invention will be described in detail below.
As the Sn powder, a powder produced by an atomizing method or a pulverizing method may be used. The SnCu powder is produced by a rapid cooling method such as an atomizing method, a melt span method, or an underwater spinning method so as to have Sn and a Cu alloy composition of 38% by mass or less. The shape at that time is not particularly limited, and may be powder, wire, bar, ribbon, plate or the like. In the SnCu alloy having the composition range of the present invention, the Sn phase and the Cu ₆ Sn ₅ intermetallic compound are present in a proportion according to the equilibrium diagram unless quenched.

  However, by rapid cooling, Cu is forcibly dissolved in the Sn phase rather than the original composition ratio, the Sn phase ratio apparently increases, and this Sn solid solution melts at around 230 ° C., which is almost equivalent to the original Sn phase. In addition, the Sn phase that contributes to good soldering and melts forms an intermetallic compound with Cu and / or copper oxide and / or cupric oxide and / or Cu powder having a surface oxide layer. Happens.

  As described above, the rapid cooling method includes the atomizing method and the melt span method, and the helium gas atomizing method and the melt span method are particularly effective as the rapid cooling means. However, centrifugal atomization, argon atomization, and nitrogen gas atomization are very effective means for mass production of solder powder, and the cooling rate depends on the particle size of the powder after atomization, and is a means. The fine grains belong to the category of the present invention. Further, for example, a wire is obtained by an underwater spinning method. In addition, a bar wire can be obtained by the mid-spinning method and straightening or drawing.

The optimum Cu content in the SnCu alloy is 38% or less. The reason is determined by the balance between the amount of Sn solid solution contributing to soldering while ensuring wettability and the amount of Cu ₆ Sn ₅ intermetallic compound contributing to maintaining the strength after soldering. For application to the purpose of the present invention material amount, if the Cu amount exceeds 38%, even if the quenching method is used, the amount of Cu ₆ Sn ₅ intermetallic compound produced is greatly increased, and the amount of Sn solid solution that contributes to soldering The wettability deteriorates and good soldering becomes difficult, so the upper limit was made 38%. Further, if the Cu amount is less than 10%, Cu and / or copper oxide, cupric oxide, Cu having a surface oxide layer are provided to ensure the amount of Cu ₆ Sn ₅ intermetallic compound that contributes to maintaining the strength after soldering. Since the mixing amount of powder submicron powder tends to increase, it is preferably 10 to 32%.

  Submicron Cu powder with Cu and / or copper oxide, cupric oxide, and surface oxide layer is made by the same method as SnCu, then submicron by pulverization etc., or reaction or liquid phase in gas phase There are a technique obtained directly from the reaction inside, a technique obtained directly from vapor obtained by melting a metal under vacuum or reduced pressure, and the like. In any case, it is necessary to uniformly disperse with Sn or SnCu powder, and to secure a specific surface area in order to promote the reaction to form an intermetallic compound of Sn and Cu, and is applied as a material of the present invention. Therefore, it is required to have a particle size of submicron or less. The sub-micron particle size needs to be 1 μm or less. When it exceeds 1 μm, it becomes difficult to uniformly disperse when mixing with Sn or SnCu powder and to secure a specific surface area for promoting the reaction. Therefore, the thickness is set to 1 μm or less.

  As the flux, a general soldering flux may be used as long as it is a rosin-based or chloride-based flux whose reducing action is effective at 150 to 350 ° C. The flux is usually used to adjust the viscosity of the solder paste and remove the oxide film of the solder ball to ensure the wettability. In the present invention, the Cu-based oxide has a copper oxide / cupric oxide / surface oxide layer. It is also used to obtain a reducing action of powder.

  The mixing ratio of SnCu powder and Cu and / or copper oxide, cupric oxide, Cu powder having a surface oxide layer is set to 7.00: 3.00 to 9.95: 0.05. The mixing ratio of Cu and / or copper oxide, cupric oxide, and Cu powder having a surface oxide layer is determined by the balance with the Sn amount of the SnCu powder. However, if it is less than 7.00: 3.00, Cu becomes excessive, and Cu clusters are formed at the joint. This does not melt at a normal soldering temperature such as 250 ° C., so it does not contribute to the joining, and the strength of the whole joint is reduced. When 9.95: 0.05 or more, formation of the CuSn intermetallic compound in the joint structure after melting and solidification becomes insufficient, the remaining Sn phase becomes too much, and the joint portion surrounding the Sn phase with the CuSn intermetallic compound is formed. Since it becomes difficult to obtain, it is set to 7.00: 3.00 to 9.95: 0.05.

  The flux adjusts the viscosity of the solder paste and promotes the formation of CuSn intermetallic compounds in the joint structure after melting and solidification. In order to exert the reduction effect of the oxide layer and oxide on the powder surface, the weight ratio with respect to the powder mixture is 1% or more. However, if it exceeds 30%, the flux residue remains inside the joint structure, which becomes a void, and the strength of the whole joint is reduced.

  As the above-mentioned flux, for example, a rosin flux, a water-soluble flux containing zinc chloride, etc., has the action of removing oxides on the surface of parts and patterns, preventing reoxidation during soldering, and reducing the surface tension of molten solder, What improves solderability. Furthermore, an activator such as an acid anhydride that further enhances the action of the flux and improves solderability may be added.

  The bonding material controlled in the above range can form a sufficient bonding portion at a normal soldering temperature. In addition, since the obtained joint is formed of CuSn intermetallic compound, the bonding strength is ensured at a normal soldering temperature, and the liquid phase Sn is surrounded by the CuSn intermetallic compound. Does not reach.

FIG. 1 shows a paste made by mixing Sn ₂₅ Cu solder powder and Cu ₂ O submicron powder (mixing ratio 9: 1), adding 15% by weight of chloride-based flux, and this is 250 ° C. in the atmosphere. It is a photograph which shows the cross-sectional observation state by the electron microscope of the junction part formed by heating. As shown in this figure, FIG. 1A is a cross-sectional photograph taken by an electron microscope showing a mixed state, and FIG. 1B is a cross-sectional photograph taken by an electron microscope after mixing and heating at 250 ° C. Thus, the results were subjected to cross-sectional observation with an electron microscope, the components were analyzed with EDS, and the tissue was identified. In the mixed state, the Sn ₂₅ Cu solder powder and the Cu ₂ O submicron powder do not react, and the Cu ₂ O submicron powder is agglomerated on the outside of the powder. it is found that a Cu ₆ Sn ₅ phase.

Hereinafter, the present invention will be specifically described with reference to examples.
FIG. 2 is a photograph showing a state in which a mixed paste of SnCu powder, Cu ₂ O submicron powder and flux according to the present invention is heated to bond Cu plates together, the cross section is polished, and the cross section is observed with an electron microscope. . That is, a mixed paste of Sn ₂₅ Cu powder and Cu ₂ O submicron powder was prepared at 9.5: 0.5 to obtain the material of the present invention. The material of the present invention was applied between Cu plates, heated at 250 ° C. and held for 15 minutes, and then cooled to room temperature to join the Cu plates together. The bonded cross section was indexed and polished, and observed with an electron microscope.

As shown in FIG. 2, a joint was obtained that spreads on the Cu plate and has Cu ₃ Sn at the interface with Cu and a Cu ₆ Sn ₅ phase inside. Since this junction does not show Sn, the melting point is 415 ° C. or higher. Therefore, the material of the present invention was able to join members by heating at 250 ° C., and had a heat resistance equal to or higher than a normal soldering temperature, and a joined portion having no extra Sn phase was obtained. Similarly, the inventive material and the comparative material were each joined, then cut along a cross section, and observed with a metal microscope and a scanning electron microscope (SEM). The results are shown in Table 1.

The wettability shown in Table 1 indicates that the Cu plate and the joint are in surface contact, and a Cu ₃ Sn intermetallic compound indicating that Sn and Cu are sufficiently diffused is formed as ◯, and only point contact. In the case of △, the absence of point contact was evaluated as x without wettability. The bonding strength was determined by reheating the above-mentioned bonding material (bonding area 5 mm ² ) to 350 ° C. and holding it for 15 minutes, then applying a high temperature shear test to the bonded portion by applying a load to the Cu plate, and setting a shearing force of 5.0 N or more as “◯”. Less than that, it was set as x with insufficient strength.

表１に示すＮｏ．１〜１３は本発明例であり、Ｎｏ．１４〜２０は比較例である。

No. shown in Table 1. Nos. 1 to 13 are examples of the present invention. 14 to 20 are comparative examples.

  As shown in Table 1, Example No. of the present invention. Nos. 5 to 7 are obtained by mixing Cu-based submicron powder only with Sn powder. Nos. 8 to 9 are obtained by mixing two or three Cu-based submicron powders and then mixing them with Sn and / or SnCu alloy powders. Nos. 10 to 13 are obtained by mixing Sn powder and SnCu powder and then mixing Cu-based submicron powder.

  As shown in Table 1, Comparative Example No. No. 14 has high Cu in the Sn and / or SnCu alloy powder, so there is no wettability at 250 ° C., and the bonding strength at 350 ° C. is weak. Comparative Example No. No. 15 has wettability at 250 ° C. due to low Cu in the Sn and / or SnCu alloy powder, but the bonding strength at 350 ° C. is weak. Comparative Example No. Since No. 16 has a large particle size of submicron powder, the wettability at 250 ° C. is only point contact, and the bonding strength at 350 ° C. is weak.

  Comparative Example No. Since No. 17 has no mixing of submicron powder, it has wettability at 250 ° C., but the bonding strength at 350 ° C. is weak. Comparative Example No. No. 18 has a large particle size of the submicron powder, a low mixing ratio with the submicron powder, and no flack, so that there is no wettability at 250 ° C. and the bonding strength at 350 ° C. is weak.

  Comparative Example No. No. 19 has high Cu in Sn and / or SnCu alloy powder, and does not have wettability at 250 ° C. Further, since the mixing ratio with the submicron powder is low, the bonding strength at 350 ° C. is weak. Comparative Example No. No. 20 is high in Cu in Sn and / or SnCu alloy powder, the wettability at 250 ° C. is point contact, the mixing ratio with submicron powder is low, and the flack or activator is high. The bonding strength of is weak. On the other hand, No. which is an example of the present invention. Since Nos. 1 to 13 satisfy all the conditions of the present invention, it is understood that the wettability and the bonding strength are excellent.

Mixed SnCu powder and Cu ₂ O submicron powder, adding a flux, and heated to a photograph showing a state in which cross-sectional observation with an electron microscope the formation of the joint. Mixed paste was heated joining Cu plates are of SnCu powder and Cu ₂ O submicron powder and the flux according to the present invention is a photograph showing a state where the cross-sectional observation with an electron microscope polishing the cross-section.

Claims (3)

A fine copper particle having a particle diameter of less than 1 μm, consisting of any one or more of a powder composed of Sn and / or a powder composed of an SnCu alloy, and copper powder having copper, copper oxide, cupric oxide and a surface oxide layer. It is a material formed by mixing powder, and the SnCu alloy is composed of the powder of Sn and / or the SnCu alloy, with the mass%, Cu being 38% or less and the balance being Sn and inevitable impurities. powder, the mixing ratio of the fine the copper fine powder, a mass ratio, 7.00: 3.00 to 9.95: lead-free high temperature bonding material, which comprises using a material that is 0.05. A powder consisting of powder and / or SnCu alloy consisting Sn, copper, copper oxide, cupric oxide, either one or a particle size of less than 1μm of two or more of the copper powder that have a surface oxide layer The lead-free high-temperature bonding material according to claim 1, wherein a flux is mixed with a material obtained by mixing copper fine powder . A powder consisting of powder and / or SnCu alloy consisting Sn, copper, copper oxide, cupric oxide, either one or a particle size of less than 1μm of two or more of the copper powder that have a surface oxide layer The lead-free high-temperature bonding material according to claim 2, wherein 1 to 30% by mass of flux is added to a material obtained by mixing copper fine powder .

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