High temperature lead-free micro-metallurgical solder, solder paste and methods of preparation and soldering and solder joints

Abstract

High-temperature lead-free micro-metallurgical solder, comprising A alloy powder and B alloy powder; the melting point of the A alloy and the melting point of the B alloy differ by 70-150 DEG C; the mass percentage of the A alloy powder is 30-10%, and the mass percentage of the B alloy powder is 70-90%. The welding temperature curve is completed in three stages, namely, a heating stage, a micro-metallurgical welding stage, and a cooling stage; the temperature range of the micro-metallurgical temperature set in the micro-metallurgical welding stage is 【280-350 DEG C】; the holding time in the micro-metallurgical welding stage is 120-240 seconds; the alloy component design of the high-temperature lead-free micro-metallurgical solder is matched with specific reflow temperature and time, a micro-metallurgical process occurs when the solder joint is formed, a large amount of intermetallic compound is generated, the low-melting-point Sn phase is consumed, the service temperature of the solder joint is improved, the packaging strength and the load capacity of temperature cycling of the solder joint are increased, and a high-reliability lead-free high-temperature solder joint is obtained.

Description

Technical Field

[0001] This invention relates to the field of brazing solder manufacturing technology, specifically to a lead-free micrometallurgical solder, solder paste, preparation and welding method, and solder joint for high-temperature welding. Background Technology

[0002] The soldering materials used in the packaging of microelectronic and power semiconductor devices must first consider the application temperature environment of the soldered product. Existing solders, to withstand medium to high temperatures, typically use lead-based solders with a high melting point and a lead content of over 90%. However, considering environmental friendliness, the RoHS Directive, promulgated on July 1, 2006, has banned the use of lead-based solders in the electronic interconnect and electronic packaging industries. There is a need to replace SnPb solder alloys with lead-free solder alloys. However, existing lead-free solder alloys either cannot meet the requirements of medium to high temperature soldering or contain a high content of valuable precious metals, thus resulting in high costs. Developing a low-cost, lead-free medium-to-high temperature solder remains a problem to be solved.

[0003] In existing technologies, when soldering components onto a printed circuit board (PCB), the same board may be exposed to multiple reflows. The temperature set in the reflow soldering equipment during soldering is typically higher than the melting point of the solder to create a temperature or energy difference that allows the solder joints to melt and complete the soldering process. Therefore, during multiple reflows, the solder joints that have already been soldered need to have medium-to-high temperature tolerance to withstand the repeated reflow soldering process and prevent any functional failure. If the melting point of the solder joints that have already been soldered is low, they will melt again during reflow soldering, thus affecting the reliability of the solder joints.

[0004] Especially in some high-reliability applications, solder joints need to withstand a wide temperature range and should not melt again during reflow or service. Instead, they should be able to resist the effects of temperature and time under reflow and service conditions.

[0005] Therefore, developing a lead-free high-temperature solder that can withstand suitable welding temperatures during the soldering process, withstand multiple reflows and temperature cycling under service conditions, and also take into account price and process implementation conditions is very challenging.

[0006] Definitions:

[0007] The use of the term "alloy" in this invention application is intended to refer to a solid product with metallic properties obtained by mixing and melting one metal with one or more other metals or non-metals, and then cooling and solidifying it. Summary of the Invention

[0008] The technical solution of this invention overcomes the shortcomings of the prior art. Taking the packaging process as a breakthrough and combining it with a specific solder formula, it solves the problem that the difference between the service temperature and the soldering temperature of lead-free high-temperature solder after soldering is not sufficient. It develops a high-temperature lead-free micrometallurgical solder that can achieve lead-free soldering under high temperature conditions and has reliable temperature cycle load capability.

[0009] The technical solution to the above-mentioned technical problem in this application is a high-temperature lead-free micrometallurgical solder, comprising alloy A powder and alloy B powder; the melting point difference between alloy A and alloy B is 70℃~150℃; the mass percentage of alloy A powder is 30%~10% and the mass percentage of alloy B powder is 70%~90%.

[0010] Alloy A includes Sn-Ag-Cu alloys; the mass percentages of each component in the Sn-Ag-Cu alloy are Sn: 95.5%-99%, Ag: 0.3%-3.8%, and Cu: 0.5%-0.7%.

[0011] Alloy A includes Sn-Sb alloys, in which the mass percentages of each component are Sn: 89.5%-95%, Sb: 5%-10%, and Ni: 0%-0.5%.

[0012] Alloy B includes a Sn-Sb-Ag-Cu alloy, in which the mass percentages of each component are Sn: 37%-42%, Sb: 35%-50%, Ag: 12%-15%, Cu: 0%-6%, and Bi: 0%-3%. The mass percentages of Sn, Sb, Ag, and Cu in alloy B satisfy the following relationship: a = 1.463b + 0.366c + 1.558d + e, where a is the mass percentage of Sn, b is the mass percentage of Sb, c is the mass percentage of Ag, d is the mass percentage of Cu, and e ranges from -0.4 to -0.2.

[0013] The aforementioned high-temperature lead-free micrometallurgical solder also includes C alloy powder; the C alloy includes Sn-Sb alloy, in which the mass percentages of each component are Sn: 89.5%-95%, Sb: 5%-10%, Ni: 0%-0.5%; the mass percentages of A alloy powder are 25%-5%, the mass percentages of B alloy powder are 70%-90%, and the mass percentages of C alloy powder are 25%-5%.

[0014] The particle size of alloy A powder is 1μm to 50μm; the particle size of alloy B powder is 1μm to 50μm; the particle size of alloy C powder is 1μm to 50μm.

[0015] The aforementioned high-temperature lead-free micrometallurgical solder also includes micro / nano D metal powder; the melting point of the micro / nano D metal is greater than 400℃; the mass percentage of A alloy powder is 10%–27%, the mass percentage of B alloy powder is 70%–87%, and the mass percentage of D metal powder is 0.1%–3%.

[0016] The aforementioned high-temperature lead-free micrometallurgical solder includes any one of the following technical features: Feature TC1: D metal is Ag; Feature TC2: D metal is Cu; Feature TC3: D metal is Fe; Feature TC4: D metal is Ce; Feature TC5: D metal is Ni; Feature TC6: D metal is Co; Feature TC7: D metal is Mn; Feature TC8: D metal is silver-clad copper AgCu, with a component mass ratio of Ag 10%–30% and Cu 70%–90%.

[0017] The particle size of alloy A powder is 1μm to 50μm; the particle size of alloy B powder is 1μm to 50μm; and the particle size of micro / nano metal D powder is 100nm to 10μm.

[0018] The technical solution to the above-mentioned technical problem in this application can also be a high-temperature lead-free micrometallurgical solder paste, including the above-mentioned high-temperature lead-free micrometallurgical solder.

[0019] The technical solution to the above-mentioned technical problem in this application can also be a method for preparing high-temperature lead-free micrometallurgical solder, wherein alloy A powder and alloy B powder are prepared separately; the melting point difference between alloy A and alloy B is 70-150℃; alloy A powder and alloy B powder are mixed to form micrometallurgical solder powder; the mass percentage of alloy A powder is 10%-30% and the mass percentage of alloy B powder is 70%-90%.

[0020] The above-mentioned method for preparing high-temperature lead-free micrometallurgical solder involves preparing C alloy powder separately; mixing A alloy powder, B alloy powder and C alloy powder to form micrometallurgical solder powder; the mass percentage of A alloy powder is 25% to 5%, the mass percentage of B alloy powder is 70% to 90%, and the mass percentage of C alloy powder is 25% to 5%.

[0021] The above-mentioned method for preparing high-temperature lead-free micrometallurgical solder involves preparing micro / nano D metal powder separately, wherein the melting point of the micro / nano D metal is greater than 400℃; the size of the micro / nano D metal powder is 100nm to 10μm (micrometers); and mixing A alloy powder, B alloy powder and D metal powder to form micrometallurgical solder powder; wherein the mass percentage of A alloy powder is 10% to 27%, the mass percentage of B alloy powder is 70% to 87%, and the mass percentage of D metal powder is 0.1% to 3%.

[0022] The above-mentioned method for preparing high-temperature lead-free micrometallurgical solder is based on micrometallurgical solder powder, which is then mixed with a matching flux or solder paste to form micrometallurgical solder paste or solder adhesive.

[0023] The technical solution to the above-mentioned technical problem in this application can also be a high-temperature lead-free micrometallurgical soldering method, which is based on the above-mentioned high-temperature lead-free micrometallurgical solder or the above-mentioned high-temperature lead-free micrometallurgical solder paste. The soldering temperature curve is completed in three stages: heating stage, micrometallurgical soldering stage, and cooling stage. The temperature range set for the micrometallurgical temperature in the micrometallurgical soldering stage is [280℃~350℃]. The micrometallurgical stage is maintained for 120 seconds to 240 seconds. The micrometallurgical encapsulated solder undergoes a micrometallurgical process during soldering.

[0024] In the high-temperature lead-free micrometallurgical welding method, the temperature in the heating stage is raised from 25℃ to 280℃ at a rate of 3℃ / second to 6℃ / second and a heating time of 45 seconds to 90 seconds; the temperature in the cooling stage is lowered from 350℃ to 80℃ at a rate of 3℃ / second to 8℃ / second.

[0025] The technical solution to the above-mentioned technical problem in this application can also be a solder joint formed by high-temperature lead-free micrometallurgical welding. The solder joint composition includes a Sn-Sb-Ag-Cu alloy, in which the mass percentages of each component are Sn: 37%-42%, Sb: 28%-44%, Ag: 8%-13%, Cu: 0%-7%, Bi: 0%-3%, and 0-0.1% of other metals, including any one or more of Ni, Fe, Co, Mn, Ce, and Au. The mass percentages of Sn, Sb, Ag, and Cu in the solder joint alloy satisfy the following relationship: a = 1.463b + 0.366c + 1.558d + e, where a is the mass percentage of Sn, b is the mass percentage of Sb, c is the mass percentage of Ag, d is the mass percentage of Cu, and e ranges from -0.3 to -0.3.

[0026] Compared with existing technologies, one of the beneficial effects of this invention is that the multi-alloy component solder with stepped melting points includes at least two separately prepared alloy powders, unlike traditional single alloy powders. This technology, combined with welding process control, utilizes the melting point difference between the two alloys. During welding, in addition to the conventional melting process to form a new alloy, a micro-metallurgical process occurs where liquid molten alloy and solid alloy coexist. Furthermore, by combining temperature control and rationally controlling the time of the micro-metallurgical process, not only does atomic diffusion occur between the solder and the pad, producing intermetallic compounds, but atomic diffusion also occurs between the metal powders with different melting points within the solder, generating a large number of intermetallic compounds. This further improves the connection reliability of the welded position and enhances its high-temperature resistance.

[0027] Compared with the prior art, one of the beneficial effects of the present invention is that alloys with different melting points are separately powdered, and then the different alloy powders are mixed together according to a set component ratio to be used as high-temperature lead-free micrometallurgical solder. Since the melting point temperature difference of different alloys is large enough, such solder, when combined with specific micrometallurgical welding temperature and time during the welding process, forms a solder joint containing a large number of intermetallic compounds, which refines the grains, prevents the grain growth rate of the solder joint during service, increases the resistance to dislocation movement between grains, increases the encapsulation strength of the solder joint, and increases the reliability of the solder joint.

[0028] Compared with the prior art, one of the beneficial effects of the present invention is that the micrometallurgical packaging solder contains metal powders with different melting points. During the heating process, the relatively low melting point A alloy powder or C alloy powder melts first, while the relatively high melting point B alloy powder or D metal powder remains solid. The medium-temperature molten metal connects with the high-temperature metal particles to form a structure similar to human muscles and skeleton, which improves the solder's anti-collapse performance. Anti-collapse performance is particularly important in the narrow-pitch high-density packaging of microelectronic integrated circuits, reducing the risk of short circuits caused by solder bridging.

[0029] Compared with the prior art, one of the beneficial effects of the present invention is that, due to the sufficient melting point difference between alloy powder A and alloy powder B, alloy powder B and alloy powder C, alloy powder A and metal powder D, alloy powder B and metal powder D, and alloy powder C and metal powder D, micro-metallurgical processes can occur between various powders. Atomic diffusion bonding occurs between metal atoms of different components, generating a large number of intermetallic compounds, forming intermetallic compounds with higher melting points and more stable structures.

[0030] Compared with the prior art, one of the beneficial effects of the present invention is that the time for micro-metallurgical welding is controlled at at least 120 seconds, providing sufficient time for the above process, allowing the liquid molten alloy and the solid alloy or metal to coexist for a long enough time, so as to more fully complete the above micro-metallurgical process, and realize the application of medium-temperature encapsulation and high-temperature service of the welded parts.

[0031] Compared with the prior art, one of the beneficial effects of the present invention is that the combination of multiple component alloys enhances the micrometallurgical process, the atomic diffusion bonding is more complete and has richer layers, resulting in higher strength of the final weld.

[0032] Compared with the prior art, one of the beneficial effects of the present invention is that the alloy composition design, combined with a specific reflow curve, causes a micro-metallurgical process during the formation of solder joints, generating a large number of intermetallic compounds, which can increase the solder joint encapsulation strength and temperature cycle load capacity.

[0033] Compared with the prior art, one of the beneficial effects of the present invention is that powders of different particle sizes can form a suitable interface state during the welding process. The size of the micro-nano D metal powder is smaller than that of the A alloy powder and B alloy powder, forming a large number of nucleation particles, refining the grains, and making it easier for the high melting point D metal powder to diffuse evenly, which is conducive to the formation of more intermetallic compounds. Attached Figure Description

[0034] Figure 1 Here are the component tables for the examples and comparative examples;

[0035] Figure 2 These are graphs showing the test results of the examples and comparative examples;

[0036] Figure 3 This is a bar chart showing the test results of the examples and comparative examples;

[0037] Figure 4 This is a display of the welding temperature profile of a high-temperature lead-free micrometallurgical solder.

[0038] Figure 5 This is a display of the welding temperature profile of a high-temperature lead-free micrometallurgical solder.

[0039] Figure 6 This is an SEM image of the solder joint after high-temperature lead-free micrometallurgical welding in Example 4;

[0040] Figure 7 This is the EDS image of the solder joint after high-temperature lead-free micrometallurgical welding in Example 4;

[0041] Figure 8 This is an SEM image of Example 4 after high-temperature lead-free micrometallurgical soldering and four reflow temperature shocks in a reflow oven at a packaging temperature of 260°C.

[0042] Figure 9 This is the EDS image of Example 4 after high-temperature lead-free micrometallurgical soldering and four reflow temperature shocks in a reflow oven at a packaging temperature of 260°C. Detailed Implementation

[0043] The invention will be further described in detail below with reference to the accompanying drawings.

[0044] As used herein, the term "prepared from" is synonymous with "comprising". The terms "comprising", "having", "containing", or any other variation thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such a composition, step, method, article, or apparatus. The conjunction "composed of" excludes any unnamed elements, steps, or components.

[0045] If used in a claim, this phrase will make the claim closed, excluding materials other than those described, except for conventional impurities associated with them. When the phrase “consisting of…” appears in a clause of the body of a claim rather than immediately following it, it limits only the element described in that clause; other elements are not excluded from the claim as a whole. When a quantity, concentration, or other value or parameter is expressed as a range, preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including the ranges “1 to 4,” “1 to 3,” “1 to 2,” “1 to 2 and 4 to 5,” “1 to 3 and 5,” etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range. Singular forms include plural objects of discussion unless clearly indicated by the context. The terms "optional" or "any one" mean that the following description of a matter or event may or may not occur, and the description includes both the occurrence and non-occurrence of the event. Approximate terms in the specification and claims modify quantities to indicate that the invention is not limited to that specific quantity, but also includes acceptable modifications close to that quantity that do not alter the relevant essential functionality. Accordingly, the use of "about," "approximately," etc., to modify a numerical value means that the invention is not limited to that precise numerical value. In some instances, approximate terms may correspond to the precision of the instrument used to measure the value. In this application's specification and claims, scope definitions can be combined and / or interchanged, unless otherwise stated, these scopes include all subscopes contained therein. Furthermore, the indefinite articles "a" and "an" preceding elements or components of the invention are not restrictive in terms of the quantity (i.e., the number of times) required for the elements or components. Therefore, "an" or "an" should be interpreted as including one or at least one, and singular elements or components also include plural forms, unless the quantity clearly refers to the singular form.

[0046] The technical solution of this application can solve the problem that the difference between the service temperature and the welding temperature of lead-free high-temperature solder after welding is not sufficient. A high-temperature lead-free micrometallurgical solder has been developed, which can realize lead-free welding under high temperature conditions and has reliable temperature cycling load capacity.

[0047] The embodiments of this application involve the following various alloy powders.

[0048] Alloy powder 1 is a Sn-Ag-Cu alloy; the mass percentage of each component in the Sn-Ag-Cu alloy is Sn 96.5%, Ag 3%, and Cu 0.5%. Alloy powder 1 has a melting point of 217℃-219℃.

[0049] Alloy powder 2 is a Sn-Ag-Cu alloy; the mass percentage of each component in the Sn-Ag-Cu alloy is Sn 99%, Ag 0.3%, and Cu 0.7%. Alloy powder 2 has a melting point of 227℃.

[0050] Alloy powder 3 is a Sn-Sb alloy, with the following mass percentages of components: Sn: 95% and Sb: 5%. Alloy powder 3 has a melting point of 235℃-240℃.

[0051] Alloy powder 4 is a Sn-Sb alloy, with the following mass percentages of components: Sn: 90% and Sb: 10%. Alloy powder 4 has a melting point of 240℃-245℃.

[0052] Alloy powder 5 is a Sn-Sb alloy, with the following mass percentages of components: Sn: 89.5%, Sb: 10%, and Ni: 0.5%. Alloy powder 5 has a melting point of 247℃-253℃.

[0053] Alloy powder 1 is a Sn-Sb-Ag-Cu alloy, with the following mass percentages of each component: Sn: 37%, Sb: 49.4%, and Ag: 13.6%; the melting point of alloy powder 1 is 369℃-390℃.

[0054] Alloy B powder 2 is a Sn-Sb-Ag-Cu alloy, with the following mass percentages of each component: Sn: 42%, Sb: 40%, Ag: 12%, Cu: 6%; the melting point of alloy B powder 2 is 332-356℃.

[0055] Alloy B powder 3 is a Sn-Sb-Ag-Cu alloy, with the following mass percentages of each component: Sn: 41%, Sb: 35%, Ag: 15%, Cu: 6%, and Bi: 3%. Alloy B powder 3 has a melting point of 331-349℃.

[0056] The mass percentages of Sn, Sb, Ag, and Cu in alloy B satisfy the following relationship:

[0057] a = 1.463b + 0.366c + 1.558d + e, where a is the mass percentage of Sn, b is the mass percentage of Sb, c is the mass percentage of Ag, d is the mass percentage of Cu, and e ranges from -0.4 to -0.2, preferably -0.3 to -0.2. This alloy composition ensures a suitable melting point for alloy B, providing sufficient intermetallic compounds for high-temperature lead-free solder joints in micrometallurgy, thus providing the material basis for micrometallurgy. If e is less than -0.4, there are relatively fewer Sn atoms, resulting in a higher melting point, increased alloy hardness, but insufficient wettability and ductility. If e is greater than -0.2, there are relatively more Sn atoms, which can easily lead to the formation of low-melting-point phases, reducing the temperature resistance of the solder joint.

[0058] C alloy powder 2 is a Sn-Sb alloy, with the following mass percentages of components: Sn: 90% and Sb: 10%. The melting point of C alloy powder 2 is 240℃-245℃.

[0059] C alloy powder 1 is a Sn-Sb alloy, with the following mass percentages of components: Sn: 89.5%, Sb: 10%, and Ni: 0.5%. The melting point of C alloy powder 1 is 247℃-253℃.

[0060] Metal powder 1 (D) is Ag. Metal powder 1 has a melting point of 961℃.

[0061] Metal powder D2 is Cu. Metal powder D2 has a melting point of 1083℃.

[0062] D metal powder 3 is Fe. D metal powder 3 has a melting point of 1535℃.

[0063] D metal powder 4 is Co. D metal powder 4 has a melting point of 1495℃.

[0064] D metal powder 5 is silver-coated copper AgCu, with a component mass ratio of 10% to 30% Ag and 70% to 90% Cu, and a melting point >900℃.

[0065] like Figure 1 Ten different embodiments are shown, and the specific descriptions of each embodiment are as follows. In each embodiment, alloy powder A, alloy powder B, alloy powder C, and metal powder D are powders prepared separately. The solder paste prepared from the components of each embodiment is processed using... Figure 4 or Figure 5 Welding was performed using the temperature profile shown. Shear force experiments were then conducted on the weld joints under different temperature loads. The experimental conditions were that the R0603 resistor was mounted on copper pads, and the heating element was stepped. Shear force data for the R0603 was measured at room temperature and at 250°C. Figure 2 As shown; Figure 3 yes Figure 2The bar chart shows that the embodiments in this application demonstrate better performance and a consistent improvement in reliability, whether under normal temperature or high temperature conditions.

[0066] Example 1 of high-temperature solder: It includes alloy A powder 1 and alloy B powder 2; the mass percentage of alloy A powder 1 is 10%; the mass percentage of alloy B powder 2 is 90%. The temperature range set for the micrometallurgical welding stage is [280℃~360℃]; the duration of the micrometallurgical stage is 180 seconds.

[0067] Example 2 of high-temperature solder: It includes alloy A powder 1 and alloy B powder 2; alloy A powder 1 accounts for 20% of the mass; alloy B powder 2 accounts for 80% of the mass. The temperature range set for the micrometallurgical welding stage is [280℃~360℃]; the micrometallurgical stage is maintained for 200 seconds.

[0068] Example 3 of high-temperature solder: It includes alloy A powder 1 and alloy B powder 2; the mass percentage of alloy A powder 1 is 30%; the mass percentage of alloy B powder 2 is 70%. The temperature range set for the micrometallurgical welding stage is [280℃~360℃]; the duration of the micrometallurgical stage is 240 seconds.

[0069] Example 4 of high-temperature solder: It includes alloy A powder 2 and alloy B powder 3; the mass percentage of alloy A powder 2 is 15%; the mass percentage of alloy B powder 3 is 85%. The temperature range set for the micrometallurgical welding stage is [280℃~350℃]; the duration of the micrometallurgical stage is 200 seconds.

[0070] Example 5 of high-temperature solder: It includes alloy A powder 4 and alloy B powder 3; alloy A powder 4 accounts for 20% by mass and alloy B powder 3 accounts for 80% by mass. The temperature range set for the micrometallurgical welding stage is [280℃~350℃]; the micrometallurgical stage is maintained for 180 seconds.

[0071] Example 6 of high-temperature solder: It includes alloy A powder 5 and alloy B powder 1; alloy A powder 5 accounts for 15% by mass and alloy B powder 1 accounts for 85% by mass. The temperature range set for the micrometallurgical welding stage is [280℃~360℃]; the micrometallurgical stage is maintained for 150 seconds.

[0072] Example 6 of high-temperature solder: includes alloy A powder 5 and alloy B powder 1; alloy A powder 1 accounts for 15% by mass, and alloy B powder 2 accounts for 85% by mass. The temperature range set for the micrometallurgical welding stage is [280℃~360℃]; the micrometallurgical stage is maintained for 150 seconds.

[0073] Example 7 of high-temperature solder: includes alloy A powder 1, alloy C powder 1, and alloy B powder 2; alloy A powder 1 accounts for 10% by mass, alloy C powder 1 accounts for 10% by mass, and alloy B powder 2 accounts for 80% by mass. The temperature range set for the micrometallurgical welding stage is [280℃~350℃]; the micrometallurgical stage is maintained for 160 seconds.

[0074] Example 8 of high-temperature solder: Includes alloy A powder 1, alloy C powder 2, alloy B powder 1, and alloy B powder 1; alloy A powder 1 accounts for 15% of the mass, alloy C powder 2 accounts for 15% of the mass, and alloy B powder 1 accounts for 70% of the mass. The temperature range set for the micrometallurgical welding stage is [280℃~345℃]; the micrometallurgical stage duration is 120 seconds.

[0075] Example 9 of high-temperature solder: It includes alloy A powder 1, alloy B powder 2, and metal D powder 1; alloy A powder 1 accounts for 14% of the mass, alloy B powder 2 accounts for 85% of the mass, and metal D powder 1 accounts for 1% of the mass. The temperature range set for the micrometallurgical welding stage is [280℃~350℃]; the micrometallurgical stage is maintained for 180 seconds.

[0076] Example 10 of high-temperature solder: It includes alloy A powder 6, alloy B powder 2, and metal D powder 3; alloy A powder 6 accounts for 20% by mass, alloy B powder 2 accounts for 79% by mass, and metal D powder 3 accounts for 1% by mass. The temperature range set for the micrometallurgical welding stage is [280℃~340℃]; the micrometallurgical stage is maintained for 180 seconds.

[0077] Example 11 of high-temperature solder: It includes alloy A powder 6, alloy B powder 3, and metal D powder 2; alloy A powder 6 accounts for 18% by mass, alloy B powder 3 accounts for 80% by mass, and metal D powder 2 accounts for 2% by mass. The temperature range set for the micrometallurgical welding stage is [280℃~345℃]; the micrometallurgical stage is maintained for 120 seconds.

[0078] Example 12 of high-temperature solder: It includes alloy A powder 4, alloy B powder 3, and metal D powder 3; alloy A powder 4 accounts for 14.9% by mass, alloy B powder 3 accounts for 85% by mass, and metal D powder 3 accounts for 0.1% by mass. The temperature range set for the micrometallurgical welding stage is [280℃~345℃]; the micrometallurgical stage is maintained for 120 seconds.

[0079] Example 13 of high-temperature solder: It includes alloy A powder 4, alloy B powder 3, and metal D powder 4; alloy A powder 4 accounts for 14.9% of the mass, alloy B powder 3 accounts for 85% of the mass, and metal D powder 4 accounts for 0.1% of the mass. The temperature range set for the micrometallurgical welding stage is [280℃~345℃]; the micrometallurgical stage is maintained for 120 seconds.

[0080] To illustrate the technical effect, a comparative experiment was designed, and the experimental data are as follows: Figure 1 The table is shown below.

[0081] Comparative Example 1: Includes alloy powder A 1, alloy powder C 2, and alloy powder B 2; alloy powder A 1 accounts for 10% of the mass; alloy powder C 2 accounts for 10% of the mass; alloy powder B 2 accounts for 80% of the mass. The temperature range set for the welding stage is [280℃~350℃]; the holding time is shortened to 30 seconds.

[0082] Comparative Example 2: Includes alloy powder A 1, alloy powder C 2, and alloy powder B 2; alloy powder A 1 accounts for 10% of the mass; alloy powder C 2 accounts for 10% of the mass; alloy powder B 2 accounts for 80% of the mass. The temperature range set for the welding stage is increased to [280℃~370℃]; the holding time is 80 seconds.

[0083] Comparative Example 3: Includes Alloy A powder 6; Alloy A powder 6 accounts for 100% of the total mass. The temperature range set for the welding stage is [280℃~285℃]; the welding stage duration is 40 seconds.

[0084] Comparative Example 4: Includes alloy B powder 2; alloy B powder 2 accounts for 100% of the total mass. The temperature range set for the welding stage is [280℃~380℃]; the holding time is 30 seconds.

[0085] Comparative Example 5 included a high-lead 925 alloy, with the following mass percentages of components: Sn: 5%, Pb: 92.5%, and Ag: 2.5%. The temperature range set for the reflow soldering stage was [280℃~340℃]; the reflow soldering stage duration was 40 seconds.

[0086] Comparative Example 6 included commercially available instant liquid phase solder; the instant liquid phase solder accounted for 100% of the total mass. The temperature range set for the soldering stage was [300℃~320℃]; the stage duration was 150 seconds.

[0087] like Figure 4As shown, a lead-free micrometallurgical soldering method for high-temperature soldering is based on the micrometallurgical encapsulated solder composition of Example 1. The soldering temperature curve is completed in three stages: a heating stage, a micrometallurgical soldering stage, and a cooling stage. The micrometallurgical temperature setting range for the micrometallurgical soldering stage is [280℃~360℃]; the micrometallurgical stage holding time is 120 seconds to 240 seconds; the micrometallurgical encapsulated solder undergoes a micrometallurgical process during soldering. The temperature in the heating stage is increased from 25℃ to 280℃ at a heating rate of 3℃ / second to 6℃ / second, and the heating time is 45 seconds to 90 seconds; the temperature in the cooling stage is decreased from 350℃ to 80℃ at a cooling rate of 3℃ / second to 8℃ / second.

[0088] like Figure 5 As shown, a lead-free micrometallurgical soldering method for high-temperature soldering is based on the solder composition of Example 4. The soldering temperature curve is completed in three stages: heating stage, micrometallurgical soldering stage, and cooling stage. The temperature range set for the micrometallurgical temperature in the micrometallurgical soldering stage is [280℃~350℃]. The duration of the micrometallurgical stage is 120 seconds to 240 seconds. The micrometallurgical solder undergoes a micrometallurgical process during soldering.

[0089] like Figure 6 , Figure 7 As shown, the images are SEM (Scanning Electron Microscope) and EDS (Energy Dispersive Spectrometer) images of the micrometallurgical solder joints after reflow in Example 4. (EDS is used to analyze the elemental composition and content in micro-regions of materials.) Figure 6 , Figure 7It can be clearly seen that intermetallic compounds are distributed at the pad interface and within the filler matrix. At the solder-pad interface, the final intermetallic compound Cu3Sn has formed near the Cu pad, while more Cu6Sn5, Sn3Sb2, and Cu3Sn intermetallic compounds have formed near the solder. Different melting point metal powders in the solder matrix have formed different intermetallic compounds such as Cu6Sn5, Sn3Sb2, Ag3Sn, and SnSb matrix + β-Sn. Sb atoms are dissolved in β-Sn, leading to lattice distortion, increasing resistance to dislocation movement, and producing a solid solution strengthening effect, thereby improving the bonding strength of the micrometallurgical solder joint. A large number of intermetallic compounds are dispersed in the matrix; the diffuse Bi-rich dots improve the phase transformation growth of the intermetallic compounds, reduce the formation of rod-shaped Ag3Sn, presenting a dotted structure, and inhibit the rapid growth of Cu6Sn5, forming a network structure and strengthening the solder joint alloy. Low-melting-point metal powder preferentially reacts with the solder pads to form intermetallic compounds. The presence of these intermetallic compounds at the interface consumes the low-melting-point β-Sn phase. Combined with the micrometallurgical bonding of the high-melting-point matrix of the micrometallurgical solder, this ensures the high-temperature resistance of the micrometallurgical solder joint. Simultaneously, the dispersed Bi-rich structure absorbs the creep stress of the solder joint, giving it strong resistance to creep and thermal fatigue.

[0090] After high-temperature lead-free micrometallurgical soldering, the packaged device underwent four reflow cycles in a reflow oven at a packaging temperature of 260℃. Cross-sectional SEM+EDS analysis was performed on the solder joints. Figure 8 , Figure 9 As shown, after multiple reflows at 260℃, there was no significant increase in the intermetallic compound at the interface, indicating that the amount of β-Sn in the micrometallurgical solder joint matrix was insufficient, which also ensured the high-temperature service reliability of the solder joint.

[0091] The weld alloy obtained by this technology includes a Sn-Sb-Ag-Cu alloy, in which the mass percentages of each component are Sn: 37%-42%, Sb: 28%-44%, Ag: 8%-13%, Cu: 0%-7%, Bi: 0%-3%, and 0-0.1% of other metals, including any one or more of Ni, Fe, Co, Mn, Ce, and Au.

[0092] Furthermore, the mass percentages of Sn, Sb, Ag, and Cu in the solder joint alloy satisfy the following relationship: a = 1.463b + 0.366c + 1.558d + e, where a represents the mass percentage of Sn, b represents the mass percentage of Sb, c represents the mass percentage of Ag, d represents the mass percentage of Cu, and e ranges from -0.3 to e ≤ 0. This alloy composition ensures a suitable melting point for the micrometallurgical lead-free high-temperature solder joint, allowing it to withstand multiple reflow peak temperatures of 260–280°C and prolonged high-temperature service. This alloy ratio provides sufficient intermetallic compounds for the micrometallurgical high-temperature lead-free solder joint, a necessary condition for its long-term high-temperature service. A value e less than -0.3 indicates relatively fewer Sn atoms, resulting in higher alloy hardness, insufficient wettability, and poor creep resistance. A value e greater than 0 indicates relatively more Sn atoms, leading to the appearance of low-melting-point phases in the solder joint, affecting its high-temperature service performance. The Sn content within the aforementioned range is suitable and can maintain the alloy composition conditions required for micrometallurgical welding, ultimately forming a highly reliable high-temperature lead-free solder joint.

[0093] In the existing technology, the conventional approach in the solder preparation process is to design a multi-element alloy after the welding temperature requirement is determined. After the multi-element alloy design is completed, the various elemental metals that make up the multi-element alloy are melted together to form the final alloy powder for welding. This approach is reliable and can design conventional solders.

[0094] However, solders used in certain special applications have specific welding temperature requirements. For example, the welding temperature may be high, but the solder should be able to withstand even higher temperatures after welding. High-temperature solders, in particular, need to withstand high temperatures during welding. During high-temperature reflow soldering, to achieve a melting temperature of 340℃-360℃, the welding equipment temperature is typically set even higher, such as 390℃-410℃. This places higher demands on the service temperature of the weld after welding. Soldering materials face a new challenge in balancing the need to significantly increase the welding temperature with the requirement to increase the service temperature after welding. The relatively low welding temperature coupled with the need to withstand high temperatures after welding presents a contradiction. Typically, once the alloy design is completed, the melting point of the alloy after melting at the welding temperature is fixed relative to the welding temperature. Therefore, its maximum service temperature is limited by the alloy's melting point.

[0095] This application abandons the simple method of co-melting all alloys and breaks through conventional thinking by utilizing the properties of alloys to design a multi-alloy component solder with stepped melting points. The multi-alloy component solder with stepped melting points includes at least two separately prepared alloy powders. By combining welding process control and utilizing the melting point difference between the two alloys, the advantages of each alloy are brought into play. During welding, in addition to the conventional melting process to form a new alloy, a micro-metallurgical process occurs where liquid molten alloy and solid alloy coexist. Furthermore, by combining temperature control and rationally controlling the time of the micro-metallurgical process, not only does atomic diffusion occur between the solder and the pad, producing intermetallic compounds, but atomic diffusion also occurs between the metal powders with different melting points within the solder, producing a large number of intermetallic compounds. This further improves the connection reliability at the welding position and enhances its high-temperature service capability.

[0096] Alloys with different melting points are powdered separately, and then the different alloy powders are mixed together according to a set component ratio to be used as medium-temperature lead-free micrometallurgical solder. Because the melting point temperature difference between different alloys is large enough, such solder, when combined with specific micrometallurgical welding temperature and time during the welding process, forms a solder joint containing a large number of intermetallic compounds, which refines the grains, inhibits the grain growth rate of the solder joint during service, increases the resistance to dislocation movement between grains, increases the encapsulation strength of the solder joint, and increases the reliability of the solder joint.

[0097] Micrometallurgical packaging solder contains metal powders with different melting points. During the heating process, the relatively low melting point A alloy powder or C alloy powder melts first, while the relatively high melting point B alloy powder or D metal powder remains solid. The medium-temperature molten metal connects with the high-temperature metal particles to form a structure similar to human muscles and skeleton, which improves the solder's anti-collapse performance. Anti-collapse performance is particularly important in the narrow-pitch high-density packaging of microelectronic integrated circuits, reducing the risk of short circuits caused by solder bridging.

[0098] The micrometallurgical encapsulation solder contains relatively low-melting-point alloy A powder and relatively high-melting-point alloy B powder. This allows for reflow soldering at encapsulation temperatures not exceeding the melting point of alloy B. The process involves alloy A atoms melting first to erode alloy B, with alloy B atoms occupying or replacing some atoms in alloy A, providing solid solution strengthening of reinforcing elements. The resulting intermetallic compounds provide precipitation strengthening. Ultimately, a multi-element alloy solder joint is formed. Compared to traditional solder paste, this significantly improves the solder joint's creep resistance and aging resistance reliability. It not only reduces encapsulation soldering temperatures, saving energy, but is also environmentally friendly.

[0099] The micrometallurgical encapsulation solder contains B alloy powder and D metal powder with relatively high melting points. During the micrometallurgical process, due to the sufficient melting point difference between A alloy powder and B alloy powder, B alloy powder and C alloy powder, A alloy powder and D metal powder, B alloy powder and D metal powder, and C alloy powder and D metal powder, micrometallurgical processes can occur between various powders. Atomic diffusion bonding occurs between metal atoms of different components, producing a large number of intermetallic compounds, forming intermetallic compounds with higher melting points and more stable structures.

[0100] Furthermore, the micrometallurgical welding time is controlled to be at least 120 seconds, providing sufficient time for the liquid molten alloy and solid alloy or metal to coexist, allowing for a more complete micrometallurgical process and enabling medium-temperature encapsulation and high-temperature service applications. Micrometallurgical high-temperature solder represents a breakthrough in the industry's high-temperature lead-free solder technology, providing a new application method for high-temperature lead-free solder that can replace high-lead solder.

[0101] The combination of multiple alloy components enhances the micrometallurgical process, resulting in more complete atomic diffusion bonding with richer layers, thus leading to higher final weld strength.

[0102] Solder paste based on micrometallurgical encapsulation solder is fundamentally different from traditional solder paste products. The micrometallurgical encapsulation solder in this application involves a micrometallurgical process during soldering. Not only does the solder and the pad undergo atomic diffusion to produce intermetallic compounds, but metal powders with different melting points between the solders also undergo atomic diffusion to produce a large number of intermetallic compounds.

[0103] Micrometallurgical encapsulation solder boasts a simple preparation and application process, high production efficiency, and significant application value. It revolutionizes traditional solder design, which typically involves alloy design, metallurgical melting of all metals to form an alloy, powder preparation, solder paste production, solder paste alloy powder, secondary melting, and solidification into a fixed alloy solder joint. Micrometallurgical encapsulation solder, however, is based on a fundamental metal alloy design. Alloys with different melting points are melted separately, powdered individually, mixed, and then solder paste is prepared. The solder melts, undergoes a micrometallurgical process at the solder joint, and solidifies to form a new alloy solder joint. This component design, combined with specific micrometallurgical welding temperatures and times, results in a micrometallurgical process during solder joint formation, generating numerous intermetallic compounds that increase the solder joint's encapsulation strength and temperature resistance.

[0104] The above description is merely an embodiment of this application and does not limit the scope of this application. Any equivalent structural or procedural transformations made based on the content of the application specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of protection of this application.

Claims

1. A high-temperature lead-free micrometallurgical solder, characterized in that, Includes alloy A powder and alloy B powder; The melting point difference between alloy A and alloy B is 70℃~150℃; The mass percentage of alloy A powder is 30%~10%, and the mass percentage of alloy B powder is 70%~90%. Alloy B includes Sn-Sb-Ag-Cu alloys, in which the mass percentages of each component are Sn: 37%-42%, Sb: 35%-50%, Ag: 12%-15%, Cu: 0%-6%, and Bi: 0%-3%. Furthermore, the mass percentages of Sn, Sb, Ag, and Cu in alloy B satisfy the following relationship: e = a - 1.463b - 0.366c - 1.558d, where a is the mass percentage of Sn, b is the mass percentage of Sb, c is the mass percentage of Ag, d is the mass percentage of Cu, and the value of e ranges from -0.4 to -0.

2.

2. The high-temperature lead-free micrometallurgical solder according to claim 1, characterized in that, Alloy A includes Sn-Ag-Cu alloy; the mass percentage of each component in Sn-Ag-Cu alloy is Sn: 95.5%-99%, Ag: 0.3%-3.8%, Cu: 0.5%-0.7%.

3. The high-temperature lead-free micrometallurgical solder according to claim 1, characterized in that, Alloy A includes Sn-Sb alloys, in which the mass percentages of each component are Sn: 89.5%-95%, Sb: 5%-10%, and Ni: 0%-0.5%.

4. The high-temperature lead-free micrometallurgical solder according to claim 1, characterized in that, It also includes C alloy powder; C alloys include Sn-Sb alloys, in which the mass percentages of each component are Sn: 89.5%-95%, Sb: 5%-10%, and Ni: 0%-0.5%. The mass percentage of alloy powder A is 25%~5%, the mass percentage of alloy powder B is 70%~90%, and the mass percentage of alloy powder C is 25%~5%.

5. The high-temperature lead-free micrometallurgical solder according to claim 4, characterized in that, The particle size of alloy A powder is 1μm~50μm; The particle size of alloy B powder is 1μm~50μm; The particle size of C alloy powder ranges from 1μm to 50μm.

6. The high-temperature lead-free micrometallurgical solder according to claim 1, characterized in that, It also includes micro / nano D-metal powder; The melting point of micro / nano D-metals is greater than 400℃; The mass percentage of alloy powder A is 10%~27%, alloy powder B is 70%~87%, and metal powder D is 0.1%~3%.

7. The high-temperature lead-free micrometallurgical solder according to claim 6, characterized in that, Includes any one of the following technical features: Characteristic TC1: D metal is Ag; Characteristic TC2: D metal is Cu; Characteristic TC3: D metal is Fe; Characteristic TC4: D metal is Ce; Characteristic TC5: D metal is Ni; Characteristic TC6: D metal is Co; Characteristic TC7: D metal is Mn; Characteristic TC8: D metal is silver-plated copper AgCu, with a mass ratio of Ag 10%~30% and Cu 70%~90%.

8. The high-temperature lead-free micrometallurgical solder according to claim 6, characterized in that, The particle size of alloy A powder is 1μm~50μm; The particle size of alloy B powder is 1μm~50μm; The size of the micro / nano D metal powder is 100 nm to 10 μm.

9. A high-temperature lead-free micrometallurgical solder paste, characterized in that, Includes the high-temperature lead-free micrometallurgical solder as described in any one of claims 1 to 8.

10. A method for preparing high-temperature lead-free micrometallurgical solder, characterized in that, Used to prepare alloy A and alloy B powders in the high-temperature lead-free micrometallurgical solder according to any one of claims 1 to 8; A alloy powder and B alloy powder were prepared separately. The melting point difference between alloy A and alloy B is 70~150℃; A alloy powder and B alloy powder are mixed to form micrometallurgical welding powder; The mass percentage of alloy A powder is 10%~30%, and the mass percentage of alloy B powder is 70%~90%.

11. The method for preparing high-temperature lead-free micrometallurgical solder according to claim 10, characterized in that, Prepare C alloy powder separately; A alloy powder, B alloy powder and C alloy powder are mixed to form micrometallurgical welding powder; The mass percentage of alloy powder A is 25%~5%, the mass percentage of alloy powder B is 70%~90%, and the mass percentage of alloy powder C is 25%~5%.

12. The method for preparing high-temperature lead-free micrometallurgical solder according to claim 10, characterized in that, Micro-nano D metal powders were prepared separately, with melting points greater than 400℃; the size of the micro-nano D metal powders ranged from 100 nm to 10 μm. A alloy powder, B alloy powder and D metal powder are mixed to form micrometallurgical welding powder; The mass percentage of alloy powder A is 10%~27%, alloy powder B is 70%~87%, and metal powder D is 0.1%~3%.

13. The method for preparing high-temperature lead-free micrometallurgical solder according to any one of claims 10 to 12, characterized in that, Based on micrometallurgical solder powder, a matching flux or soldering adhesive is added and stirred to form micrometallurgical solder paste or solder adhesive.

14. A high-temperature lead-free micrometallurgical welding method, characterized in that, Based on any one of claims 1 to 8, the high-temperature lead-free micrometallurgical solder is described above. Or based on the high-temperature lead-free micrometallurgical solder paste described in claim 10; The welding temperature profile is completed in three stages: the heating stage, the micrometallurgical welding stage, and the cooling stage. The temperature range for the micrometallurgical welding stage is 280℃~350℃. The micrometallurgical stage is maintained for 120 to 240 seconds. Micrometallurgical encapsulated solder undergoes a micrometallurgical process during soldering.

15. The high-temperature lead-free micrometallurgical welding method according to claim 14, characterized in that, During the heating phase, the temperature rises from 25℃ to 280℃ at a rate of 3℃ / second to 6℃ / second, and the heating time is 45 seconds to 90 seconds. During the cooling phase, the temperature drops from 350℃ to 80℃ at a rate of 3℃ / second to 8℃ / second.

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