Low temperature soldering material for copper substrates, soldering assembly and method for its production and use

Abstract

The application belongs to the technical field of welding, and particularly relates to a low-temperature soldering material for a copper substrate, a soldering assembly, and a preparation method and application thereof. The soldering material contains the following mass percentages of elements: Bi: 40.0% to 58.0%; Ga: 0.1% to 2.0%; and the rest is Sn. When the soldering material is applied to the copper substrate, a Cu-Ga barrier layer is formed at the soldering interface. The Cu-Ga barrier layer is used to prevent mutual diffusion between Cu and Sn and inhibit the formation of a Bi-rich layer. At the same time, the Cu-Ga barrier layer has good stability, and even after a certain period of aging treatment, the Cu-Ga barrier layer at the soldering interface does not significantly grow, and the formation of a Cu-Sn compound layer is effectively prevented. The Cu-Ga barrier layer is beneficial to guarantee the wettability of the soldering interface, the interface strength is appropriate, the solder joint has high reliability, and the service life is long. The soldering material is suitable for the field of microelectronic packaging.

Description

Technical Field

[0001] This application belongs to the field of welding technology, specifically relating to a low-temperature solder for copper substrates, welding components, their preparation methods and applications. Background Technology

[0002] With the rapid development of microelectronics technology, microelectronic packaging is trending towards lead-free, miniaturized, fine-pitch, and high-reliability designs. Especially with the emergence of high-density packaging technology, solder joint sizes are becoming smaller and packaging structures are becoming more complex. This places higher demands on the mechanical properties and reliability of solders. Currently, the mainstream Sn-Ag-Cu solder alloy has a high melting point (217℃), and the high soldering temperature easily leads to severe substrate warping, causing soldering failure, further resulting in irreversible thermal damage to thermistor devices, and causing a significant increase in energy consumption and carbon emissions throughout the entire industry chain. Consequently, its application in the field of microelectronic packaging is gradually being limited.

[0003] Therefore, low-temperature solders that can meet the microelectronic interconnection requirements of next-generation chip packaging and SMT low-temperature process technology have become the future development trend of microelectronic interconnection materials. Existing low-temperature solders, such as Sn-Bi alloys, are prone to forming intermetallic compounds with Cu elements in Cu substrates during the soldering process, causing element segregation, resulting in solder joint embrittlement and failure, short solder joint life, and low reliability. Summary of the Invention

[0004] The technical objective of this application is to at least solve the problems of solder joint embrittlement failure, short solder joint life, and low reliability that are easily caused by existing Sn-Bi alloys when welding Cu substrates.

[0005] This objective is achieved through the following technical solutions:

[0006] In a first aspect, this application provides a low-temperature solder for copper substrates, wherein the solder comprises the following elemental contents in mass percentage:

[0007] Bi: 40.0%~58.0%;

[0008] Ga: 0.1%~2.0%;

[0009] The rest are Sn;

[0010] When the tin solder is applied to the copper substrate, a Cu-Ga barrier layer is formed at the soldering interface. This Cu-Ga barrier layer contains a Cu-Ga intermetallic compound, which prevents the interdiffusion between Cu and Sn and inhibits the formation of a Bi-rich layer. Simultaneously, the Cu-Ga barrier layer exhibits good stability; even after a certain period of aging treatment, the Cu-Ga barrier layer at the soldering interface does not show significant growth, effectively preventing the formation of a Cu-Sn compound layer.

[0011] In some embodiments of this application, the solder comprises the following elemental contents by mass percentage:

[0012] Bi: 45.0%~58.0%;

[0013] Ga: 0.5%~2.0%;

[0014] The rest are Sn.

[0015] In some embodiments of this application, the solder further comprises an alloying element, wherein the mass percentage content of the alloying element satisfies the following:

[0016] 0 < alloying element ≤ 2.0%;

[0017] (1) The alloying elements include one or more of Sb, Cu, In, Ag, Ni, Zn, and mixed rare earth elements, wherein the mixed rare earth elements include lanthanum-cerium alloys. The alloying elements can optimize the strength and toughness matching relationship of the solder through solid solution strengthening, second-phase particle strengthening, and grain refinement strengthening, thereby further improving the reliability of the solder.

[0018] In some embodiments of this application, the solder comprises the following elemental contents by mass percentage:

[0019] Bi: 45.0%~58.0%;

[0020] Ga: 0.5%~1.5%;

[0021] Alloying elements: 0.1% to 1.5%; the alloying elements include one or more of Sb, Cu, In, Ag, Ni, and Zn;

[0022] The rest are Sn;

[0023] Furthermore, the eutectic melting point of the solder is 130–150°C.

[0024] Secondly, this application provides a method for preparing the low-temperature tin solder described in the first aspect. The preparation method includes: mixing and melting the corresponding raw materials according to the content of each element, casting to form an ingot, and converting the ingot into any one of paste, strip, foil, sheet, wire, powder or ball.

[0025] Thirdly, this application provides a copper-based welding assembly, the welding assembly comprising a copper substrate and a solder layer located on the surface of the copper substrate, the solder layer being obtained by welding with the low-temperature solder described in the first aspect or the low-temperature solder prepared by the method described in the second aspect.

[0026] In some embodiments of this application, a portion of the Ga element in the solder forms a Cu-Ga barrier layer, while the remaining Ga element forms a Ga-rich phase and is distributed in a network form within the Sn matrix or precipitates at Sn phase grain boundaries. This Ga-rich phase serves two purposes: firstly, it refines the grains to improve the strength and toughness of the solder; secondly, the Ga-rich phase precipitated at grain boundaries inhibits the growth of the Sn phase during aging, further reducing the growth rate of intermetallic compounds and thus improving solder reliability.

[0027] In some embodiments of this application, the thickness of the Cu-Ga barrier layer is 1 μm to 8 μm, preferably 1.5 μm to 7.0 μm. A Cu-Ga barrier layer of suitable thickness is beneficial to the solder joint lifespan.

[0028] Fourthly, this application provides a method for preparing the component described in the third aspect, comprising:

[0029] The low-temperature solder melts upon heating to form a molten liquid;

[0030] The copper substrate is brought into contact with the molten liquid to form a solder layer.

[0031] Fifthly, this application provides an application of the low-temperature solder described in the first aspect, the low-temperature solder prepared by the method described in the second aspect, the copper-based welding assembly described in the third aspect, or the copper-based welding assembly prepared by the method described in the fourth aspect in microelectronic packaging. The microelectronic components are conventional components in the art.

[0032] The beneficial effects of the technical solution disclosed in this application are mainly reflected in the following:

[0033] 1. The solder provided in this application has a simple composition and preparation process, and is suitable for welding copper plates. It has good wettability at the welding interface, suitable interface strength, high solder joint reliability, and long service life.

[0034] 2. The solder provided in this application is applicable to the field of microelectronic packaging. Attached Figure Description

[0035] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0036] Figure 1 The microstructure and elemental distribution at the bonding interface of a Cu substrate according to an embodiment of this application are schematically shown, wherein (a) is the microstructure at the bonding interface; (b) is the elemental distribution of Sn; (c) is the elemental distribution of Ga; and (d) is the elemental distribution of Cu.

[0037] Figure 2 The microstructure and elemental distribution at the bonding interface of a Cu substrate according to an embodiment of this application are schematically shown, wherein (a) is the microstructure at the bonding interface; (b) is the elemental distribution of Sn; (c) is the elemental distribution of Ga; and (d) is the elemental distribution of Cu.

[0038] Figure 3 The microstructure and elemental distribution at the welding interface of the Cu substrate in the comparative example are schematically shown, wherein (a) is the microstructure at the welding interface; (b) is the elemental distribution of Sn; (c) is the elemental distribution of Bi; and (d) is the elemental distribution of Cu.

[0039] Figure 4 The microstructure and elemental distribution of the Cu substrate welding interface according to the embodiments of this application after aging treatment at 100°C for 480 hours are schematically shown, wherein (a) is the microstructure at the welding interface after aging treatment; (b) is the Sn elemental distribution; (c) is the Ga elemental distribution; and (d) is the Cu elemental distribution.

[0040] Figure 5 The microstructure and elemental distribution of the Cu substrate welding interface in the comparative example after aging treatment at 100℃ for 480h are schematically shown. (a) Microstructure at the welding interface after aging treatment; (b) Sn elemental distribution; (c) Bi elemental distribution; (d) Cu elemental distribution.

[0041] Figure 6 A scanning electron microscope image of the microstructure of an alloy according to an embodiment of this application is shown schematically. Detailed Implementation

[0042] In existing technologies, Sn-Bi alloys have a eutectic composition of Sn-58Bi (wt.%) and a eutectic temperature of 138℃. They possess advantages such as excellent wetting properties, high strength, and low cost, showing great potential in fields such as thermal devices and SMT packaging. Due to the inherent brittleness of Bi, reasonably reducing the Bi content can significantly improve the plasticity of the alloy without sacrificing its strength. However, reducing the Bi content will worsen the wetting properties, increase the melting point, and significantly increase the melting range. Considering the strength, plasticity, melting characteristics, and wetting properties of the solder alloy, a Bi mass percentage in the range of 40%-58% can yield Sn-Bi solders with good overall performance.

[0043] When Sn-Bi solder is bonded to a Cu substrate, Sn and Cu elements form intermetallic compounds at the welding interface. Simultaneously, the loss of Sn from the solder causes Bi segregation, forming a Bi-rich layer near the welding interface. Due to the inherent brittleness of the Bi-rich phase, the formation of this layer at the welding interface and its subsequent growth during aging often become weak points in the solder joint, making it prone to crack initiation and propagation, ultimately leading to solder joint failure. Research suggests that the formation of the Bi-rich phase is primarily caused by the interdiffusion of Cu and Sn at the welding interface. This interdiffusion thickens the intermetallic compound layer at the interface, and due to Bi's high atomic number and slow diffusion rate, a large amount of Bi phase remains at the interface and grows, eventually forming a Bi-rich layer. Therefore, by hindering the interdiffusion of Cu and Sn at the welding interface, the formation and growth kinetics of the Bi-rich layer can be suppressed, thereby improving solder joint reliability.

[0044] Currently, alloying is commonly used to control the microstructure, suppressing the interdiffusion of Cu and Sn elements, reducing the growth rate of intermetallic compounds at the weld interface, and ultimately inhibiting the formation of Bi-rich layers and improving weld reliability. Common Sn-Bi alloys include those containing Cu, Sb, In, Ag, Ni, Zn, and RE (rare earth elements).

[0045] Specifically, adding a small amount of Cu to the solder can reduce the Cu concentration difference on both sides of the solder interface and inhibit Cu and Sn diffusion; preferably, the mass percentage of Cu is 0 to 2.0%.

[0046] Sb element dissolves into the Bi phase, replacing some Bi atoms and playing a role in solid solution strengthening, inhibiting the diffusion of Bi atoms, and hindering the growth of Bi phase and the formation of Bi-rich layers; preferably, the mass percentage of Sb element is 0 to 2.0%.

[0047] In can replace some Sn atoms in the Cu6Sn5 phase to form Cu6(Sn,In)5, which hinders the dissolution of Cu into the solder and reduces the thickness of the Cu-Sn intermetallic compound; preferably, the mass percentage of In is 0 to 2.0%.

[0048] The Ag3Sn phase formed by Ag and the Sn matrix provides heterogeneous nucleation sites, refines the eutectic structure, and delays the growth rate of Cu-Sn intermetallic compounds; preferably, the mass percentage of Ag is 0 to 2.0%.

[0049] Ni can replace some Cu atoms in the Cu6Sn5 phase to form the (Cu,Ni)6Sn5 phase. The addition of a small amount of Ni can significantly improve the scallop-like structure of the Cu6Sn5 phase and enhance solder reliability. In addition, Ni atoms dissolved in the Bi matrix can effectively inhibit Bi atom diffusion, suppress Bi phase growth, and inhibit the formation of Bi-rich layers. The preferred mass percentage of Ni is 0-2.0%.

[0050] Therefore, appropriate amounts of elements such as Sb, Cu, In, Ag, and Zn can form intermetallic compounds with Sn, playing a role in second-phase particle reinforcement. This significantly improves the strength of the solder and the reliability of the solder joint without compromising its plasticity.

[0051] However, the above-mentioned method of controlling the microstructure by alloying can only slow down the growth rate of intermetallic compounds at the interface to a certain extent, and cannot fundamentally inhibit the formation of Bi-rich layers and improve the reliability of solder joints.

[0052] Therefore, improving the diffusion characteristics of Cu and Sn intermetallic compounds at the welding interface and inhibiting the mutual diffusion of Cu and Sn elements are key to reducing the growth rate of intermetallic compounds, improving the interface morphology, inhibiting the formation of Bi-rich layers, and improving the welding reliability of Sn-Bi alloys.

[0053] To address the aforementioned technical problems, this application provides a low-temperature solder for copper substrates, a soldering assembly, its preparation method, and its application. First, Ga is added to the Sn-Bi based solder. A portion of the Ga preferentially reacts chemically with Cu to form a dense Cu-Ga barrier layer at the soldering interface. This Cu-Ga barrier layer prevents interdiffusion between Cu and Sn and inhibits the formation of a Bi-rich layer. Simultaneously, this Cu-Ga barrier layer exhibits good stability; even after a certain period of aging treatment, the Cu-Ga barrier layer at the soldering interface does not show significant growth, effectively preventing the formation of a Cu-Sn compound layer. Furthermore, the remaining Ga element forms a Ga-rich phase, which is distributed in a network form within the Sn matrix or precipitates at Sn phase grain boundaries. This Ga-rich phase refines the grains to improve the strength and toughness of the solder. Furthermore, the Ga-rich phase precipitated at grain boundaries inhibits the growth of the Sn phase during aging, further reducing the growth rate of intermetallic compounds and improving solder reliability.

[0054] To achieve the aforementioned technical effects, the first aspect of this application is to provide a low-temperature solder for copper substrates, wherein the solder comprises the following elemental contents by mass percentage:

[0055] Bi: 40.0%~58.0%;

[0056] Ga: 0.1%~2.0%;

[0057] The rest are Sn;

[0058] When the tin solder is applied to the copper substrate, a Cu-Ga barrier layer is formed at the soldering interface.

[0059] Furthermore, the solder contains certain essential impurity elements, which are indispensable impurity elements in various metal raw materials. Moreover, these impurity elements have almost no effect on the soldering temperature and interface quality of the solder in this application, and will not be described in detail here.

[0060] In some embodiments, the solder comprises the following elemental contents by mass percentage:

[0061] Bi: 45.0%~58.0%;

[0062] Ga: 0.5%~2.0%;

[0063] The rest are Sn.

[0064] For example, the mass percentage of element Bi includes any one of 40.0%, 40.5%, 41.0%, 41.5%, 42.0%, 42.5%, 43.0%, 43.5%, 44.0%, 44.5%, 45.0%, 45.5%, 46.0%, 46.5%, 47.0%, 47.5%, 48.0%, 48.5%, 49.0%, 49.5%, 50.0%, 50.5%, 51.0%, 51.5%, 52.0%, 52.5%, 53.0%, 53.5%, 54.0%, 54.5%, 55.0%, 55.5%, 56.0%, 56.5%, 57.0%, 57.5%, and 58.0%, or any value that satisfies the above range.

[0065] For example, the mass percentage of element Ga includes any one of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2.0%, or any value that satisfies the above range.

[0066] In some embodiments, the solder further comprises an alloying element, wherein the mass percentage content of the alloying element satisfies the following:

[0067] 0 < alloying element ≤ 2.0%;

[0068] Furthermore, the alloying elements include one or more of Sb, Cu, In, Ag, Ni, Zn, and mixed rare earth elements, wherein the mixed rare earth elements include lanthanum-cerium alloys.

[0069] For example, the mass percentage of the alloying element includes any one of 0.01%, 0.05%, 0.10%, 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, 0.70%, 0.80%, 0.90%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2.0%, or any value within the range described above.

[0070] In some embodiments, the solder comprises the following elemental contents by mass percentage:

[0071] Bi: 45.0%~58.0%;

[0072] Ga: 0.5%~1.5%;

[0073] Alloying elements: 0.1% to 1.5%; the alloying elements include one or more of Sb, Cu, In, Ag, Ni, and Zn;

[0074] Furthermore, the eutectic melting point of the solder is 130–150°C.

[0075] In some embodiments, the solder comprises the following elemental contents by mass percentage:

[0076] Bi: 45.0%~58.0%;

[0077] Ga: 0.5%~1.5%;

[0078] Sb / Cu / In / Ag / Ni:0.1%~1.0%;

[0079] The rest are Sn.

[0080] In some embodiments, the solder comprises the following elemental contents by mass percentage:

[0081] Bi: 45.0%~58.0%;

[0082] Ga: 0.5%~1.5%;

[0083] In: 0.1%~0.8%;

[0084] Ag: 0.1%–0.8%;

[0085] The rest are Sn.

[0086] In some embodiments, the solder comprises the following elemental contents by mass percentage:

[0087] Bi: 45.0%~58.0%;

[0088] Ga: 0.5%~1.5%;

[0089] Cu: 0.8%–1.5%;

[0090] Ni: 0.1%–0.5%;

[0091] The rest are Sn.

[0092] In some embodiments, the solder comprises the following elemental contents by mass percentage:

[0093] Bi: 45.0%~58.0%;

[0094] Ga: 0.5%~1.5%;

[0095] Sb: 0.8%~1.5%;

[0096] Ni: 0.1%–0.5%;

[0097] The rest are Sn.

[0098] In some embodiments, the solder comprises the following elemental contents by mass percentage:

[0099] Bi: 45.0%~58.0%;

[0100] Ga: 0.5%~1.5%;

[0101] Cu: 0.8%–1.5%

[0102] Ag: 0.1%~0.4%

[0103] Ni: 0.1%;

[0104] The rest are Sn.

[0105] The second aspect of this application to achieve the above-mentioned technical effects is to provide a method for preparing the low-temperature tin solder described in the first aspect. The preparation method includes: taking appropriate raw materials according to the content of each element, mixing and melting them, casting them to form an ingot, and converting the ingot into any one of paste, strip, foil, sheet, wire, powder or ball.

[0106] In some embodiments, the preparation method includes the following preparation steps:

[0107] 1) Ingredients: Each metal raw material is prepared according to the stated mass percentage, specifically including elemental Sn, elemental Bi, elemental Ga, and intermediate alloys formed with Sn, such as Sn-Sb, Sn-Cu, Sn-Ag, Sn-Ni, Sn-Zn, and Sn-RE. The purity of the elemental Sn, Bi, and Ga is preferably 99.99 wt.%.

[0108] 2) Melting: The various metal raw materials described in step 1) are mixed and melted. An anti-oxidation solvent is then applied to the surface of the molten alloy, mixed, and kept at a constant temperature to obtain an alloy melt. The anti-oxidation solvent is preferably rosin. The melting is preferably carried out in a vacuum environment.

[0109] 3) Processing and forming: The alloy melt is poured into a mold to form an ingot billet.

[0110] In some embodiments, the vacuum environment is a vacuum melting device, which includes a vacuum melting furnace. Any model of the vacuum melting furnace meets the requirements of this application and will not be described in detail here.

[0111] In some embodiments, after the vacuum process is completed, an inert gas is introduced into the vacuum melting equipment.

[0112] For example, the vacuum melting equipment is filled with inert gas to expel oxygen-containing gas from the vacuum melting equipment.

[0113] In some embodiments, the mixing method includes stirring, which includes mechanical stirring and / or electromagnetic stirring.

[0114] In some embodiments, the conversion includes using conventional powder-making equipment and processes, fiber-making equipment and processes, sheet-making equipment and processes, etc.

[0115] For example, the powder-making equipment and process include centrifugal atomization powder-making equipment and processes conventional in the art.

[0116] For example, the filament-making equipment and process include conventional filament-drawing equipment and processes in the art.

[0117] For example, the wafer fabrication equipment and process include conventional wafer fabrication processes and equipment in the art.

[0118] A third aspect of this application to achieve the above-mentioned technical effects is to provide a copper-based welding assembly, the welding assembly comprising a copper substrate and a solder layer located on the surface of the copper substrate, the solder layer being obtained by welding with the low-temperature solder described in the first aspect or the low-temperature solder prepared by the method described in the second aspect.

[0119] In some embodiments, a portion of the Ga element in the solder forms a Cu-Ga barrier layer, while the remaining Ga element generates a Ga-rich phase and is distributed in a network form in the Sn matrix or precipitates at the Sn phase grain boundaries.

[0120] In some embodiments, the thickness of the Cu-Ga barrier layer is 0.5 μm to 3.0 μm.

[0121] The thickness of the Cu-Ga barrier layer is affected by the Ga content and aging time. According to the following embodiments, the thickness of the Cu-Ga barrier layer is preferably 0.7 μm to 2.5 μm.

[0122] For example, the thickness of the Cu-Ga barrier layer is any one of 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2.9μm, and 3.0μm or any value within the above range.

[0123] A fourth aspect of this application for achieving the aforementioned technical effects is providing a method for preparing the component described in the third aspect, comprising:

[0124] The low-temperature solder melts upon heating to form a molten liquid;

[0125] The copper substrate is contacted with the molten liquid to obtain a solder layer;

[0126] The temperature at which the material melts is 130–155°C.

[0127] The fifth aspect of this application to achieve the above-mentioned technical effects is to provide an application of the low-temperature solder described in the first aspect, the low-temperature solder prepared by the method described in the second aspect, the copper-based welding assembly described in the third aspect, or the copper-based welding assembly obtained by the method described in the fourth aspect in microelectronic packaging.

[0128] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0129] Example 1

[0130] A SnBi58Ga0.1 solder is disclosed. The preparation method of the solder includes: adding Sn metal with a purity of 99.99 wt.% and Bi metal with a purity of 99.99 wt.% to a graphite crucible according to the mass percentage; heating the metal until it is completely melted; then adding Ga metal with a purity of 99.99%; covering the surface of the melt with a layer of rosin to prevent oxidation; heating the alloy melt to 400°C and holding it at that temperature for 60 min; stirring every 15 min to ensure the melt is fully mixed and homogeneous; pouring the metal melt into a mold to form an alloy ingot; and air-cooling to room temperature to obtain the SnBi58Ga0.1 alloy ingot.

[0131] Example 2

[0132] A SnBi45Ga0.5 solder is disclosed, which is the same as that in Example 1 except for the different content of each element.

[0133] Example 3

[0134] A SnBi40Ga1 solder is disclosed, which is the same as that in Example 1 except for the different content of each element.

[0135] Example 4

[0136] A SnBi50Ga2 solder is disclosed, which is the same as that in Example 1 except for the different content of each element.

[0137] Example 5

[0138] A SnBi50Ga0.5Sb1 solder is disclosed, and the preparation method of the solder includes:

[0139] (1) Sn metal with a purity of 99.99% and Sb metal with a purity of 99.99% are added to a medium-frequency induction melting furnace at a mass ratio of 90:10, and the furnace is evacuated to a vacuum of 5×10⁻⁶. -3 Below MPa, after filling with protective gas, heat to 750℃ and hold for 60 minutes. At the same time, use electromagnetic stirring to mix the melt evenly. Finally, perform vacuum casting. After the alloy ingot cools to a certain temperature, SnSb10 master alloy is obtained.

[0140] (2) Sn metal with a purity of 99.99%, Bi metal with a purity of 99.99%, and SnSb10 master alloy were added to a graphite crucible and heated to 400°C. After the metals were completely melted, Ga metal with a purity of 99.99% was added, and a layer of rosin was placed on the surface of the melt. The mixture was kept at this temperature for 60 minutes, and stirred every 15 minutes. Finally, the melt was poured into a mold and air-cooled to room temperature to obtain SnBi50Ga0.5Sb1 alloy ingot.

[0141] Furthermore, by adjusting the content of each metal, solder materials such as SnBi50Ga0.5Sb0.1 and SnBi50Ga0.5Sb0.5 can be produced, which can achieve the same technical effect as in Example 5.

[0142] Example 6

[0143] A SnBi58Ga0.5Cu1 solder is disclosed, and the preparation method of the solder includes:

[0144] (1) Sn metal with a purity of 99.99% and Cu metal with a purity of 99.99% are added to a medium-frequency induction melting furnace at a mass ratio of 90:10, and the furnace is evacuated to a vacuum of 5×10⁻⁶. -3 Below MPa, after filling with protective gas, heat to 1100℃ and hold for 60 min. At the same time, use electromagnetic stirring to mix the melt evenly. Finally, perform vacuum casting. After the alloy ingot cools to room temperature, SnCu10 master alloy is obtained.

[0145] (2) Except for the different alloy ratio and the type of intermediate alloy, step (2) is the same as step (2) in Example 5.

[0146] By adjusting the content of each metal, solder materials such as SnBi58Ga0.5Cu0.1 and SnBi58Ga0.5Cu0.5 can be produced, which can achieve the same technical effect as in Example 6.

[0147] Example 7

[0148] A SnBi58Ga1In1 solder is disclosed. The preparation method of the solder includes: adding Sn metal with a purity of 99.99 wt.%, Bi metal with a purity of 99.99 wt.%, and In metal with a purity of 99.99 wt.% to a graphite crucible according to their respective mass percentages; heating the metals until they are completely melted; then adding Ga metal with a purity of 99.99%; covering the surface of the molten metal with a layer of rosin to prevent oxidation; heating the alloy molten metal to 400°C and holding it at that temperature for 60 minutes, stirring it every 15 minutes to ensure that the molten metal is fully mixed and homogeneous; pouring the molten metal into a mold to form an alloy ingot; and air-cooling it to room temperature to obtain the SnBi58Ga1In1 alloy ingot.

[0149] Example 8

[0150] A SnBi58Ga1Ag1 solder is disclosed, and the preparation method of the solder includes:

[0151] (1) Sn metal with a purity of 99.99% and Ag metal with a purity of 99.99% are added to a medium-frequency induction melting furnace at a mass ratio of 90:10, and the furnace is evacuated to a vacuum of 5×10⁻⁶. -3Below MPa, after filling with protective gas, heat to 1100℃ and hold for 60 minutes. At the same time, use electromagnetic stirring to mix the melt evenly. Finally, vacuum casting is performed. After the alloy ingot cools to room temperature, SnAg10 master alloy is obtained.

[0152] (2) Sn metal with a purity of 99.99%, Bi metal with a purity of 99.99%, and SnAg10 master alloy were added to a graphite crucible and heated to 400°C. After the metals were completely melted, Ga metal with a purity of 99.99% was added, and a layer of rosin was placed on the surface of the melt. The mixture was kept at this temperature for 60 minutes, and stirred every 15 minutes. Finally, the melt was poured into a mold and air-cooled to room temperature to obtain SnBi58Ga1Ag1 alloy ingot.

[0153] Example 9

[0154] A SnBi58Ga1Ni1 solder is disclosed, and the preparation method of the solder includes:

[0155] (1) Sn metal with a purity of 99.99% and Ni metal with a purity of 99.99% are added to a medium-frequency induction melting furnace at a mass ratio of 95:5, and the furnace is evacuated to a vacuum of 5×10⁻⁶. -3 Below MPa, after filling with protective gas, heat to 1100℃ and hold for 60 min. At the same time, use electromagnetic stirring to mix the melt evenly. Finally, perform vacuum casting. After the alloy ingot cools to room temperature, SnNi5 master alloy is obtained.

[0156] (2) Sn metal with a purity of 99.99%, Bi metal with a purity of 99.99%, and SnNi5 master alloy were added to a graphite crucible and heated to 400°C. After the metals were completely melted, Ga metal with a purity of 99.99% was added, and a layer of rosin was placed on the surface of the melt. The mixture was kept at this temperature for 60 minutes, and stirred every 15 minutes. Finally, the melt was poured into a mold and air-cooled to room temperature to obtain SnBi58Ga1Ni1 alloy ingot.

[0157] Example 10

[0158] A SnBi58Ga1In0.5Ag0.5 solder is disclosed, and the preparation method of the solder includes:

[0159] (1) The preparation method of SnAg10 intermediate alloy is the same as step (1) in Example 8;

[0160] (2) Sn metal with a purity of 99.99%, Bi metal with a purity of 99.99%, In metal with a purity of 99.99%, and SnAg10 master alloy were added to a graphite crucible and heated to 400°C. After the metals were completely melted, Ga metal with a purity of 99.99% was added, and a layer of rosin was placed on the surface of the melt. The mixture was kept at this temperature for 60 minutes, and stirred every 15 minutes. Finally, the melt was poured into a mold and air-cooled to room temperature to obtain SnBi58Ga1In0.5Ag0.5 alloy ingot.

[0161] By adjusting the content of each metal, solder materials such as SnBi58Ga1In0.1Ag0.5, SnBi58Ga1In0.8Ag0.5, SnBi58Ga1In0.1Ag0.1, and SnBi58Ga1In0.1Ag0.8 can be produced, which can achieve the same technical effect as in Example 10.

[0162] Example 11

[0163] A SnBi58Ga1Cu1Ni0.1 solder is disclosed, and the preparation method of the solder includes:

[0164] (1) The preparation method of SnCu10 intermediate alloy is the same as step (1) in Example 6;

[0165] (2) The preparation method of SnNi5 intermediate alloy is the same as step (1) in Example 9;

[0166] (3) Sn metal with a purity of 99.99%, Bi metal with a purity of 99.99%, SnCu10 master alloy, and SnNi5 master alloy were added to a graphite crucible and heated to 400°C. After the metals were completely melted, Ga metal with a purity of 99.99% was added, and a layer of rosin was placed on the surface of the melt. The mixture was kept at this temperature for 60 minutes, and stirred every 15 minutes. Finally, the melt was poured into a mold and air-cooled to room temperature to obtain SnBi58Ga1Cu1Ni0.1 alloy ingot.

[0167] By adjusting the content of each metal, solder materials such as SnBi58Ga0.5Cu0.8Ni0.1, SnBi58Ga0.5Cu1.5Ni0.1, and SnBi58Ga0.5Cu1Ni0.5 can be prepared, which can achieve the same technical effect as in Example 11.

[0168] Example 12

[0169] A SnBi58Ga0.5Sb1Ni0.1 solder is disclosed, and the preparation method of the solder includes:

[0170] (1) The preparation method of SnSb10 master alloy is the same as step (1) in Example 5.

[0171] (2) The preparation method of SnNi5 master alloy is the same as step (1) in Example 9.

[0172] (3) Sn metal with a purity of 99.99%, Bi metal with a purity of 99.99%, SnSb10 master alloy, and SnNi5 master alloy were added to a graphite crucible and heated to 400°C. After the metals were completely melted, Ga metal with a purity of 99.99% was added, and a layer of rosin was placed on the surface of the melt. The mixture was kept at this temperature for 60 minutes, and stirred every 15 minutes. Finally, the melt was poured into a mold and air-cooled to room temperature to obtain SnBi58Ga0.5Sb1Ni0.1 alloy ingot.

[0173] By adjusting the content of each metal, solder materials such as SnBi58Ga0.5Sb0.8Ni0.1, SnBi58Ga0.5Sb1.5Ni0.1, and SnBi58Ga0.5Sb0.8Ni0.5 can be produced, which can achieve the same technical effect as in Example 12.

[0174] Example 13

[0175] A SnBi58Ga0.5Cu1.5Ag0.4Ni0.1 solder is disclosed, and the preparation method of the solder includes:

[0176] (1) The preparation method of SnCu10 master alloy is the same as step (1) in Example 6.

[0177] (2) The preparation method of SnAg10 master alloy is the same as step (1) in Example 8.

[0178] (3) The preparation method of SnNi5 master alloy is the same as step (1) in Example 9.

[0179] (4) Sn metal with a purity of 99.99%, Bi metal with a purity of 99.99%, SnCu10 master alloy, SnAg10 master alloy, and SnNi5 master alloy were added to a graphite crucible and heated to 400°C. After the metals were completely melted, Ga metal with a purity of 99.99% was added, and a layer of rosin was placed on the surface of the melt. The mixture was kept at this temperature for 60 minutes, and stirred every 15 minutes. Finally, the melt was poured into a mold and air-cooled to room temperature to obtain SnBi58Ga0.5Cu1.5Ag0.4Ni0.1 alloy ingot.

[0180] Comparative Example 1

[0181] SnBi58 solder has been disclosed, and its preparation method includes:

[0182] Sn metal with a purity of 99.99 wt.% and Bi metal with a purity of 99.99 wt.% were added to a graphite crucible in a mass percentage ratio of 42:58. A layer of rosin was placed on the surface of the molten metal to prevent oxidation. The alloy molten metal was heated to 400℃ and held for 60 min, with stirring every 15 min to ensure thorough mixing. The molten metal was then poured into a mold to form an alloy ingot. After air cooling to room temperature, the SnBi58 alloy ingot was obtained.

[0183] This application also discloses the conversion of the alloy ingots prepared in the above embodiments and comparative examples into any one of paste, strip, foil, sheet, wire, powder or ball. Since these are all prior art, this application will not elaborate on them.

[0184] Tests and experiments:

[0185] (1) The melting point of the alloy was tested using a conventional differential thermal analyzer. The heating rate was set to 10℃ / min, and the melting point of the alloy was taken as the intersection of the extended baseline and the tangent at the maximum slope of the peak. The melting point list is shown in Table 1.

[0186] (2) The alloy solder prepared in the above embodiments and comparative examples is used to weld a copper substrate to obtain a copper-based welding assembly. Specifically, the alloy solder is heated and melted between 135 and 155°C to form a molten liquid; the copper substrate is brought into contact with the molten liquid to obtain a tin solder layer; the tin solder layer includes a welding interface; and the welding interface is subjected to an aging treatment of 100°C for 480 hours, wherein the aging treatment is a continuous aging treatment of 100°C for 480 hours.

[0187] The microstructure of the copper-based welding assembly and the welding interface is as follows;

[0188] (3) Microstructure and elemental distribution in micro-regions were observed using an electron probe microanalysis device. The analytical equipment used was a standard model in the field, and the analytical methods met the corresponding national standards.

[0189] Table 2 and Figures 1 to 6 .

[0190] Table 1. List of solder alloy compositions and melting points in the examples and comparative examples.

[0191] Example Solder alloy composition Alloy melting point (°C) Example 1 SnBi58Ga0.1 137.81 Example 2 SnBi45Ga0.5 143.68 Example 3 SnBi40Ga1 142.72 Example 4 SnBi50Ga2 139.22 Example 5 SnBi50Ga0.5Sb1 140.34 Example 6 SnBi58Ga0.5Cu1 139.27 Example 7 SnBi58Ga1In1 137.11 Example 8 SnBi58Ga1Ag1 137.42 Example 9 SnBi58Ga1Ni1 137.51 Example 10 SnBi58Ga1In0.5Ag0.5 137.33 Example 11 SnBi58Ga1Cu1Ni0.1 140.27 Example 12 SnBi58Ga0.5Sb1Ni0.1 139.46 Example 13 SnBi58Ga0.5Cu1.5Ag0.4Ni0.1 139.12 Comparative Example 1 SnBi58 138.24

[0192] Table 2. Characterization and properties of the weld interfaces of each solder alloy in the examples and comparative examples.

[0193]

[0194]

[0195] Figure 1, Figure 2 Microstructure and elemental distribution diagrams of the solder-Cu substrate interface in Examples 1 and 4 are shown respectively. Figure 1 , Figure 2 It can be seen that a continuous Cu-Ga intermetallic compound was formed at the welding interface. The thickness of the Cu-Ga barrier layer composed of this Cu-Ga intermetallic compound is 0.5 μm to 3.0 μm, and no Cu-Sn intermetallic compound was observed to form. At the same time, no Bi-rich layer was formed near the welding interface, indicating that the dense Cu-Ga intermetallic compound effectively inhibited the diffusion of Cu and Sn elements, played the role of diffusion barrier layer, and effectively inhibited the formation of Bi-rich layer. Figure 3 The microstructure and elemental distribution diagram at the interface between the solder and the Cu substrate in Comparative Example 1 are shown in the figure. Figure 3 It can be seen that the welding interface is still a Cu-Sn intermetallic compound.

[0196] Figure 4 The image shows the microstructure and elemental distribution of the weld interface after aging treatment in Example 1, combined with... Figure 4 It can be seen that after a long period of aging treatment, the welding interface is still a Cu-Ga compound layer and no significant growth has occurred. No Cu-Sn compound layer has been formed. This indicates that during the aging process, the Cu-Ga barrier layer can still effectively inhibit the mutual diffusion of Cu and Sn elements, reduce the growth rate of intermetallic compounds, inhibit the formation of Cu-Sn intermetallic compounds and the formation of Bi-rich layers.

[0197] Figure 5 The image shows the microstructure and elemental distribution of the weld interface in Comparative Example 1 after aging treatment. Figure 5 It can be seen that the thickness of the Cu-Sn compound layer is significantly increased, and it exhibits a distinct scallop-like structure.

[0198] Figure 6 Microstructure diagrams of Example 4 are provided, combined with Figure 6 It is known that Ga in the alloy precipitates in the form of Ga-rich phase within the Sn phase grains and at grain boundaries, which plays a role in refining the grains, which is beneficial to improving the strength and toughness of the solder. In addition, it hinders grain growth during the aging process, further reducing the growth rate of intermetallic compounds and improving the reliability of the solder.

[0199] In summary, the solder provided in this application has a simple composition, a straightforward preparation process, and is suitable for soldering copper plates. It exhibits good wettability at the solder interface, suitable interface strength, high solder joint reliability, and a long lifespan. It is applicable to the field of microelectronic packaging.

[0200] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” as used herein may also include the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not construed as requiring them to be performed in a particular order described or illustrated unless the order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

[0201] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A low temperature tin solder for copper substrates, characterized by, The solder contains the following elemental contents by mass percentage: Bi: 40.0%~58.0%; Ga: 0.1%~2.0%; The rest are Sn.

2. The low temperature tin solder of claim 1, wherein, The solder contains the following elemental contents by mass percentage: Bi: 45.0%~58.0%; Ga: 0.5%~2.0%; The rest are Sn.

3. A method of producing the low-temperature tin solder according to any one of claims 1 to 2, characterized by, The preparation method includes: taking appropriate raw materials according to the content of each element, mixing and melting them, casting them into an ingot, and converting the ingot into any one of paste, strip, foil, sheet, filament, powder or ball.

4. A copper-based welding assembly, characterized in that, The welding assembly includes a copper substrate and a solder layer located on the surface of the copper substrate, the solder layer being obtained by welding with the low-temperature solder of any one of claims 1 to 2 or the low-temperature solder prepared by the method of claim 3.

5. The copper-based welding assembly according to claim 4, characterized in that, In the solder, some of the Ga element forms a Cu-Ga barrier layer, while the remaining Ga element generates a Ga-rich phase and is distributed in a network form in the Sn matrix or precipitates at the Sn phase grain boundaries.

6. The copper-based welding assembly according to claim 5, characterized in that, The thickness of the Cu-Ga barrier layer is 0.5 μm to 3.0 μm.

7. The copper-based welding assembly according to claim 6, characterized in that, The thickness of the Cu-Ga barrier layer is 0.7 μm to 2.5 μm.

8. A method for preparing the component according to any one of claims 4 to 5, characterized in that, include: The low-temperature solder melts upon heating to form a molten liquid; The copper substrate is brought into contact with the molten liquid to form a solder layer.

9. The application of a low-temperature solder as described in any one of claims 1 to 2, or a low-temperature solder prepared by the method of claim 3, or a copper-based welding assembly as described in any one of claims 4 to 7, or a copper-based welding assembly prepared by the method of claim 8, in microelectronic packaging.

Images