TWI752878B - Alloy Ingots for Joining Materials - Google Patents

Abstract

The present invention provides an alloy ingot for a joining material, which can be used as a joining material that can withstand severe temperature fluctuations from extremely high temperature to extremely low temperature environments, and also has excellent joining strength, flexibility properties that can withstand a continuous vibration state, and excellent mechanical strength. material. The present invention solves the above-mentioned problems by an alloy ingot for a joining material, which has an intermetallic compound crystal including Sn, Cu, Ni, and Ge in a parent phase including Sn and a Sn-Cu alloy, and a group of the intermetallic compound crystals 5 to 50 mass % of Cu, 6.5 to 0.1 mass % of Ni, 0.001 to 0.1 mass % of Ge, and the remainder of Sn, the composition of the mother phase is Sn 95 to 99.9 mass %, Cu 5 mass % or less, and inevitable impurities 0.1 mass % or less, the Sn—Cu alloy in the mother phase and at least a part of the intermetallic compound crystals are internally axially bonded.

Description

Alloy Ingots for Joining Materials

The present invention relates to an alloy ingot for a joining material.

As IoT (Internet of Things) is required to continue to develop and save energy, the importance of power semiconductors at the core of its technology is increasing. However, there are many problems in its utilization. Power semiconductors generate a lot of heat and become high temperature because they handle large power with high voltage and large current. Heat resistance-based current Si power semiconductor required corresponds to about 175 deg.] C, and can withstand temperatures of about 200 ℃ of the Si power semiconductor is continuing to develop, in addition, such as secondary SiC or GaN, Ga ₂ O ₃ or the like Generation power semiconductors are required to withstand 250 to 500°C, and when mounted on a vehicle, they are required to withstand severe vibration and continuous operation state (hereinafter also referred to as vibration continuous operation state characteristics).

On the other hand, as for the bonding material, there is no conventional technology that has the high heat resistance required for the next-generation power semiconductors such as the above-mentioned SiC or GaN, and has the characteristics of continuous vibration operation. For example, the SnAgCu-based bonding material (soldering material) disclosed in Patent Document 1 can only be applied to power semiconductors corresponding to about 125° C., and cannot be applied to next-generation power semiconductors. In addition, the low melting point welding materials and welding alloys disclosed in Patent Document 3 and Patent Document 4 do not have the characteristics of continuous vibration operation.

On the other hand, in Patent Document 2, the applicant of the present application proposes a metal particle including an outer shell and a core portion, wherein the core portion includes a metal or an alloy, and the outer shell includes an intermetallic compound, and The core portion is covered, the core portion includes Sn or Sn alloy, and the outer shell includes an intermetallic compound between Sn and Cu. It has been confirmed that the junction formed by the metal particles can maintain a high temperature for a long time even when used in a severe environment with a large temperature fluctuation from a high temperature operation state to a low temperature stop state over a long period of time. Heat resistance, joint strength and mechanical strength. However, brittleness, which is a disadvantage of intermetallic compounds, becomes a hindrance when the joint structure is continuously operated with severe vibration. [Prior Art Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 2007-268569 Patent Document 2: Japanese Patent No. 6029222 Patent Document 3: Japanese Patent No. 6369620 Patent Document 4: International Publication WO2014/084242A1 Pamphlet

[The problem to be solved by the invention]

An object of the present invention is to provide an alloy ingot for a joining material, which is capable of being subjected to severe temperature fluctuations from extremely high temperature to extremely low temperature environments, and has excellent joining strength, flexibility characteristics capable of withstanding vibration and continuous operation, and excellent mechanical properties. The strength of the joint material. [means to solve the problem]

The inventors of the present invention, as a result of repeated and careful investigations, have found that an alloy ingot for a joining material can solve the above-mentioned problems, and the present invention has been completed, and the present invention has been completed. The intermetallic compound of the crystal structure is crystallized, and at least one part of the mother phase and the intermetallic compound crystal is joined by an endoaxial (endotaxial).

That is, the present invention provides an alloy ingot for a joining material, which is an alloy ingot for a joining material having an intermetallic compound crystal containing Sn, Cu, Ni, and Ge in a parent phase containing Sn and a Sn-Cu alloy, wherein It is characterized in that the composition of the intermetallic compound crystal is Cu 5-50 mass %, Ni 6.5-0.1 mass %, Ge 0.001-0.1 mass %, the remainder is Sn, the composition of the mother phase is Sn 95-99.9 mass %, 5 mass % or less of Cu and 0.1 mass % or less of unavoidable impurities, the Sn—Cu alloy in the mother phase and at least a part of the intermetallic compound crystals are internally axially bonded. [Effect of invention]

According to the present invention, it is possible to provide an alloy ingot for a joining material which can withstand severe temperature fluctuations in an extremely high temperature to an extremely low temperature environment, and which has excellent joining strength, flexibility characteristics that can withstand a continuous vibration state, and excellent mechanical properties. The strength of the joint material.

[Form for carrying out the invention]

Hereinafter, the present invention will be described in more detail. First, the syntax used in this specification is as follows, even if there is no particular description. (1) When referring to a metal, not only a single metal element but also an alloy containing a plurality of metal elements and an intermetallic compound may be included. (2) When referring to a single metal element, it does not mean a substance containing only the metal element completely and simply, but also means a case where a trace amount of other substances are contained. That is, it does not mean to exclude those containing a trace amount of impurities that hardly affect the properties of the metal element, and of course it does not mean to exclude, for example, that a part of atoms in the crystal of the parent phase system Sn is substituted with other. elements (eg, Cu). For example, the aforementioned other substances or other elements may be contained in 0 to 0.1 mass % in the target substance. (3) Inner shaft bonding means the precipitation of intermetallic compound crystals in a substance that becomes a metal/alloy (in the present invention, a parent phase containing Sn and Sn-Cu alloy), and in the precipitation, Sn-Cu alloy and metal The inter-compound crystals are joined at the lattice level to form crystal grains. The terminology of the so-called inner axis is well known, and is described in, for example, Nature Chemisry 3(2): 160-6, 2011, the last paragraph of the left column on page 160.

Since the alloy ingot for joining materials of this invention has high toughness, the said subject can be solved. The high toughness is especially based on: intermetallic compounds having a specific composition in the aforementioned parent phase, that is, having intermetallic compound crystals containing Sn, Cu, Ni and Ge; and Sn-Cu alloys in the aforementioned parent phase and At least one part of the said intermetallic compound crystal|crystallization is internal-shaft joined. According to this configuration, the alloy ingot for a joining material can be given a softness characteristic capable of withstanding a continuous vibration state.

The alloy ingot for joining materials of the present invention (hereinafter sometimes referred to as the alloy ingot of the present invention) will be further described.

FIG. 1 is a SEM image of the cross section of the alloy ingot of the present invention embedded with resin and thinly sliced. FIG. 1(b) is a partially enlarged view of FIG. 1(a). Referring to FIG. 1( b ), it can be seen that the alloy ingot 10 has intermetallic compound crystals 120 including Sn, Cu, Ni and Ge in the parent phase 140 including Sn and Sn—Cu alloy. In addition, it has been confirmed that the intermetallic compound crystal 120 contains a crystal structure of a monoorthogonal crystal and a hexagonal crystal. The crystal structure of the intermetallic compound was confirmed by XRD-6100 observation apparatus and database: ICDD (International Centre for Diffraction Data) manufactured by Shimadzu Corporation.

In the alloy ingot of the present invention, the composition of the intermetallic compound crystal is Cu 5 to 50 mass %, Ni 6.5 to 0.1 mass %, Ge 0.001 to 0.1 mass %, and the remainder is Sn, preferably Cu is 40 to 10 mass % %, Ni is 0.3 to 5 mass %, Ge is 0.001 to 0.01 mass %, and the remainder is Sn.

The alloy ingot of the present invention can be produced from, for example, a raw material containing 8 mass % of metallic Cu, 1 mass % of metallic Ni, 0.001 mass % of metallic Ge, and the remainder of which is metallic Sn. For example, the alloy ingot of the present invention is obtained by melting the raw material by high-frequency induction heating in a vacuum, casting it in a nitrogen atmosphere under atmospheric pressure, and cooling and solidifying it.

In order to form the alloy ingot of the present invention, the above-mentioned high-frequency induction heating and cooling solidification conditions are important. For example, the following conditions are mentioned. High-frequency induction heating: Set up a crucible for high-frequency melting in a vacuum chamber capable of reducing the pressure to about 9×10 ^-2 Pa, introduce the above-mentioned raw materials into the crucible, and maintain the pressure reduction to about the above-mentioned degree of pressure reduction. The raw material is subjected to high-frequency induction heating so that the heating temperature is 600° C. to 800° C., the above-mentioned raw material is melted, and the temperature is maintained for 5 to 15 minutes. Cooling and solidification: Next, while flowing nitrogen gas at 15 to 50°C into the tank, the above heating temperature is set to about 400°C or higher under atmospheric pressure, mold casting is performed, and cooling and solidification are performed at 30°C or lower.

Moreover, the ratio of the intermetallic compound crystal in the alloy ingot of this invention is 20-60 mass %, for example, Preferably it is 30-40 mass %. The composition and ratio of the intermetallic compound crystals can be satisfied by conforming to the manufacturing conditions of the alloy ingot.

The alloy ingot of the present invention is obtained by inner-shaft bonding of at least one part of the Sn—Cu alloy and the intermetallic compound crystal in the parent phase. As described above, in the inner shaft joining, an intermetallic compound is precipitated in a substance that becomes a metal/alloy (in the present invention, it is a parent phase containing Sn and a Sn-Cu alloy), and among the precipitation, the Sn-Cu alloy and the intermetallic compound are Crystals are joined at the lattice level to form crystal grains. It is possible to provide the following bonding material: an intermetallic compound in which a specific high-melting-point metal element is substituted and intruded into the Sn-Cu intermetallic compound crystal while forming the inner shaft joint can solve the problem of the brittleness of the intermetallic compound crystal, At the same time, it is possible to suppress a decrease in mechanical strength due to a change in the crystal structure of Sn, which will be described below, and to have a bonding material having high heat resistance, bonding strength, and mechanical strength. Furthermore, the inventors of the present invention confirmed that the Sn—Cu alloy and the intermetallic compound crystal in the parent phase in the weld wire formed by using the alloy ingot of the present invention are maintained in the inner axis.

The crystal structure of Sn is tetragonal in the temperature range from about 13°C to about 160°C (in addition, Sn having a tetragonal crystal structure is referred to as β-Sn.), and in a lower temperature range, the The crystal structure is changed to cubic (in addition, Sn having a cubic crystal structure is referred to as α-Sn.). In addition, the crystal structure of β-Sn changes to an orthorhombic crystal of a high-temperature phase crystal in a temperature region exceeding about 160° C. (In addition, Sn having an orthorhombic crystal structure is referred to as γ-Sn.). Then, especially in the phase transition between tetragonal β-Sn and cubic α-Sn, it is generally known that a large volume change occurs. The joining material (eg, welding wire) produced from the alloy ingot of the present invention contains high-temperature phase crystals even at about 160° C. or lower (eg, even at normal temperature). For example, when the joining material is heated in the joining step, if the joining material is in a semi-molten state in which the joining material is not completely melted, and the intermetallic compound is joined to the inner shaft of the parent phase, even after cooling The temperature region of 160°C or lower also maintains a state containing high temperature phase crystals. Then, even if the temperature of the high-temperature phase crystal system is lowered to a certain extent, the low-temperature phase crystal β-Sn that is transformed into tetragonal crystal is not easily caused, and the Sn that is not transformed into tetragonal crystal is not transformed into α. The phase transition of -Sn, and the large volume change of α-Sn accompanying the phase transition caused by the decrease in temperature did not occur. Therefore, the bonding material system containing Sn having high-temperature phase crystals even at a temperature range of 160° C. or lower (for example, even at room temperature) is compared with other bonding materials containing Sn in composition (that is, even at 160° C. or lower). The temperature region of 2 is also not intended to include high-temperature crystalline phases), and the volume change caused by temperature changes is also reduced. In addition, various metals such as Cu, Ag, Au, and Ni are used for electronic components, and Sn is well bonded to these various metals. Therefore, the joining material produced from the alloy ingot of the present invention contains a high-temperature phase crystalline phase in a wide temperature range (for example, even at normal temperature), and avoids the generation of a tetragonal low-temperature phase β-Sn as much as possible. It is not easy to cause a large volume change from tetragonal β-Sn to cubic α-Sn due to temperature changes, and is also compatible with various metals used in electronic parts. Since it joins, it is useful especially for the joining material of a fine joint.

The above-mentioned effect of suppressing the change in the crystal structure of Sn is well exhibited by the internal axis bonding between the parent phase in the alloy ingot and the crystal of the intermetallic compound.

Further, in the alloy ingot of the present invention, when the inner shaft bonding system is 100% of the entire bonding surface between the parent phase and the intermetallic compound crystal, it is preferably 30% or more, more preferably 60% or more. The ratio of the aforementioned inner shaft engagement can be calculated, for example, as follows. The cross section of the alloy ingot shown in the following Fig. 1 was photographed with an electron microscope, and 50 joint surfaces of the Sn-Cu alloy and the intermetallic compound crystal were randomly sampled. Next, this joint surface was subjected to image analysis, and it was investigated how much inner shaft joint as shown in the following examples exists with respect to the sampled joint surface.

On the other hand, the alloy ingot of the present invention can also be pelletized by a conventional method. The particle diameter of the metal particles obtained as described above is preferably in the range of, for example, 1 μm to 50 μm. The metal particles can be processed into flakes or pastes, and in a state where they are in contact with the object to be joined, maintained at 160°C to 180°C for more than 3 minutes, and solidified on the premise of melting at 235°C to 265°C , so as to form a good bond. In addition, at the time of joining, after holding for about 1 second under reduced pressure (decompression degree of 50cmHg to 100cmHg), it is heated to about 230°C under atmospheric pressure, and then the ambient pressure is maintained at 0.5 to 2MPa at this temperature. Finally, curing is performed at room temperature, whereby a good bond can also be formed. Furthermore, the inventors of the present invention confirmed that the Sn—Cu alloy in the parent phase in the metal particle-based metal particle formed using the alloy ingot of the present invention and the intermetallic compound crystal are maintained in axial bonding.

The sheet of the above-mentioned metal particles can be obtained, for example, by press-bonding the metal particles with a roller as follows. That is, the above-mentioned metal particles are supplied between a pair of crimping rollers that rotate in opposite directions, and heat of about 100° C. to 150° C. is applied to the metal particles by the crimping rollers to press the metal particles. Get flakes. In addition, the above-mentioned paste system can be obtained by mixing metal particles into an organic vehicle. Furthermore, the inventors of the present invention have confirmed that the metal particles processed into flakes or pastes have the same crystal structure as that of the alloy ingot of the present invention.

Furthermore, the sheet or the conductive paste may be mixed with metal particles by adding SnAgCu alloy particles, Cu, Cu alloy particles, Ni, Ni alloy particles or other particles such as mixtures thereof. These other particles can also be coated with metals such as Si, if desired. For example, when combined with Cu or Ni alloy particles having higher conductivity than Sn, a bonding layer having excellent conductivity and suppressed volume change in a relatively wide temperature range can be obtained.

The ratio of the said metal particle in the said sheet or the said conductive paste is 50 mass % or more, for example, Preferably it is 70-80 mass %.

7 is a schematic cross-sectional view for explaining a structure that can be joined using the alloy ingot of the present invention. The substrates 100 and 500 include semiconductor elements, and are, for example, substrates constituting electronic and electrical equipment such as power elements, and the metal/alloy bodies 101 and 501 are integrally provided as electrodes, bumps, terminals, lead conductors, and the like for connection between the substrates 100 and 500 . member. In electronic and electrical equipment such as power elements, the metal/alloy bodies 101 and 501 are generally composed of Cu or an alloy thereof. However, the portions corresponding to the substrates 100 and 500 are not excluded from those composed of metal/alloy bodies. [Example]

The present invention is further described below based on Examples and Comparative Examples, but the present invention is not limited to the following examples.

Example 1 As a raw material, a raw material containing 8 mass % Cu, 1 mass % Ni, 0.001 mass % Ge, and each metal whose remainder is Sn was used, and high-frequency induction heating and cooling solidification were performed under the following conditions to form the material of the present invention. Alloy ingots. High-frequency induction heating: Set up a crucible for high-frequency melting in a vacuum chamber capable of reducing the pressure to about 9×10 ^-2 Pa, introduce the above-mentioned raw materials into the crucible, and maintain the pressure reduction to about the above-mentioned degree of pressure reduction. The raw material was subjected to high-frequency induction heating so that the heating temperature was 650° C., the above-mentioned raw material was melted, and the temperature was maintained for 5 minutes. Cooling and solidification: Next, while flowing nitrogen gas at 15 to 50° C. into the tank for 10 minutes, the heating temperature of the raw material was set to about 400° C. under atmospheric pressure, mold casting was performed, and cooling and solidification were performed at room temperature. The obtained alloy ingot of the present invention was rectangular with a thickness of 2 cm, a length of 20 cm, and a width of 3 cm, and had a cross section as shown in FIG. 1 above. FIG. 2 shows the result of element distribution analysis by EDS with respect to the intermetallic compound at “No, 1” in FIG. 1( b ). From this analysis result, it was confirmed that the composition of the intermetallic compound crystal was 17 to 33 mass % of Cu, 1.8 to 4.22 mass % of Ni, 0.007 mass % of Ge, and the remainder was Sn.

Moreover, the intermetallic compound in the obtained alloy ingot accounts for 30-35 mass % in the alloy ingot.

FIG. 3 is a TEM image and a transmission electron diffraction pattern of the cross-section of the obtained alloy ingot. The transmission electron diffraction pattern in FIG. 3 shows the state of the inner shaft junction. From the transmission electron diffraction pattern in FIG. 3 , it can be confirmed that the Sn—Cu alloy in the parent phase shown by the light color portion and the dark color portion are An intermetallic intra-axial bond comprising Sn, Cu, Ni and Ge is shown. In addition, it was also confirmed that there was no buffer layer between the crystals. In addition, it was confirmed that the lattice constants (and the crystal orientations) of the Sn—Cu alloy and the gold sensitizing compound in the parent phase were identical, and the respective crystals were joined at a continuous lattice level.

Comparative Example 1 Tests were performed based on the description of the examples in the aforementioned Patent Document 3 (Japanese Patent No. 6369620 ). As a raw material, a raw material containing 8 mass % Cu, 1 mass % Ni, 0.001 mass % Ge, and the remainder of which is Sn is used, and the raw material is melted with the set temperature of the melting furnace at 450°C, and then water is circulated. The groove of the rotary casting mold casts the melt. The cooling rate is about 30°C/s. Then, an ultrasonic oscillator was attached to the rotary mold, and 60 kHz ultrasonic waves were applied when the molten solder was cast. The obtained alloy ingot of Comparative Example 1 was a rectangle with a thickness of 2 cm, a length of 20 cm, and a width of 3 cm. FIG. 4 is an SEM image of the cross section of the alloy ingot of Comparative Example 1 embedded with resin and thinly sliced. FIG. 4(b) is a partially enlarged view of FIG. 4(a). Referring to FIG. 4( a ), the alloy ingot of Comparative Example 1 has intermetallic compound crystals 220 including Sn, Cu, Ni and Ge in the parent phase 240 including Sn and Sn—Cu alloy, but as shown in FIG. 4 As shown in (b), a fracture occurred at the interface between the parent phase and the intermetallic compound crystal, and the inner shaft bonding could not be confirmed.

Comparative Example 2 The test was performed based on the method described in the aforementioned Patent Document 4 (International Publication WO2014/084242A1). As a raw material, a raw material containing 8 mass % Cu, 1 mass % Ni, 0.001 mass % Ge, and Sn as the remainder was used, and after melting the raw material, the molten material was cast in the groove of the mold and cooled at room temperature. The obtained alloy ingot of Comparative Example 2 was a rectangle with a thickness of 2 cm, a length of 20 cm, and a width of 3 cm. FIG. 5 is an SEM image of the cross-section of the alloy ingot of Comparative Example 2 embedded with resin and thinly sliced. FIG. 5(b) is a partially enlarged view of FIG. 5(a). Referring to FIG. 5( a ), the alloy ingot of Comparative Example 2 has intermetallic compound crystals 320 including Sn, Cu, Ni, and Ge in the parent phase 340 including Sn and Sn—Cu alloy, but as shown in FIG. 5 As shown in (b), a fracture occurred at the interface between the parent phase and the intermetallic compound crystal, and the inner shaft bonding could not be confirmed.

Example 2, Comparative Examples 3 to 4 The alloy ingots prepared in Example 1, Comparative Example 1, and Comparative Example 2 were used for pressure-bonding processing to prepare sheets with a thickness of 100 μm×15 mm×15 mm. The sheet was baked and attached to a copper foil having a thickness of 300 μm×30 mm×30 mm in a formic acid environment at 260° C. to obtain a test piece. The laminated center portion of this test piece was bent by 190 degrees, and the state of cracks on the surface of the test piece was observed with an optical microscope. This result is shown in FIG. 6 . 6(a) shows that the test piece produced using the alloy ingot produced in Example 1 has no fractures or cracks, maintains the joint (symbol 701), and has the flexibility to maintain the characteristics of the continuous vibration state. 6( b ), it can be seen that the test piece prepared by using the alloy ingot prepared in Comparative Example 1 had a cracked state (symbol 702 ) on the surface of the material that was bent at 190 degrees, which did not correspond to the test in the above-mentioned test. The bending tensile force caused by the cracks, and there is no flexibility to maintain the characteristics of the continuous operation state of vibration. Further, from the results of FIG. 6( c ), it can be seen that the test piece prepared using the alloy ingot prepared in Comparative Example 2 had a cracked state (symbol 703 ) on the surface of the material folded by 190 degrees, which did not correspond to the above-mentioned test. The bending tensile force caused by the cracks, and there is no flexibility to maintain the characteristics of the continuous operation state of vibration.

The present invention has been described above in detail with reference to the accompanying drawings, but the present invention is not limited to these, and it is obvious that various modifications can be conceived based on the basic technical ideas and teachings of those skilled in the art. .

100,500: Substrate 101,501: Alloy/Alloy Body 120, 220, 320: Intermetallic compounds 140, 240, 340: Mother Phase

FIG. 1 is a SEM image of the cross section of the alloy ingot of the present invention embedded with resin and thinly sliced. FIG. 2 is the result of element distribution analysis by EDS of the intermetallic compound crystal in the cross section of the alloy ingot. 3 is a TEM image and a transmission electron diffraction pattern of the cross-section of the alloy ingot obtained in Example 1. FIG. FIG. 4 is an SEM image of the cross section of the alloy ingot of Comparative Example 1 embedded with resin and thinly sliced. FIG. 5 is an SEM image of the cross-section of the alloy ingot of Comparative Example 2 embedded with resin and thinly sliced. 6 is an optical microscope photograph showing the results of a softness property test of the alloy ingots of Example 2 and Comparative Examples 1 and 2. FIG. 7 is a schematic cross-sectional view for explaining a structure that can be joined using the alloy ingot of the present invention.

10: Alloy Ingot

120: Intermetallic compounds

140: Mother Phase

Claims (1)

An alloy ingot for a joining material, which is an alloy ingot for a joining material having an intermetallic compound crystal containing Sn, Cu, Ni, and Ge in a parent phase containing Sn and a Sn-Cu alloy, characterized by: The composition of the intermetallic compound crystal is Cu 5-50 mass %, Ni 6.5-0.1 mass %, Ge 0.001-0.1 mass %, and the remainder is Sn, The composition of the mother phase is Sn 95-99.9 mass %, Cu 5 mass % or less, and unavoidable impurities 0.1 mass % or less, The Sn-Cu alloy in the mother phase and at least a part of the intermetallic compound crystals are internally bonded to each other, The ratio of the said intermetallic compound crystal in the said alloy ingot for joining materials is 20-60 mass %, The alloy ingot for a joining material contains Sn having an orthorhombic crystal structure at a temperature of 160° C. or lower.

Images