CN114932337A

CN114932337A - SnAgCuBiIn series lead-free solder alloy, and design method and preparation method thereof

Info

Publication number: CN114932337A
Application number: CN202210657627.9A
Authority: CN
Inventors: 董自强; 游康东; 元皓; 陈悠扬; 杨体鑫; 孙安康; 王刚; 彭巨擘; 蔡珊珊; 罗晓斌; 刘晨
Original assignee: R & D Center Of Yunnan Tin Industry Group Holdings Co ltd; University of Shanghai for Science and Technology
Current assignee: R & D Center Of Yunnan Tin Industry Group Holdings Co ltd; University of Shanghai for Science and Technology
Priority date: 2022-06-10
Filing date: 2022-06-10
Publication date: 2022-08-23

Abstract

The invention discloses a SnAgCuBiIn series lead-free solder alloy, a design method and a preparation method thereof, wherein the solder alloy comprises 1.0-5.5% of Ag, 0.5-1.0% of Cu, 0.5-5.0% of Bi, 0.4-4.0% of In, 0-1.0% of Ti, 0-0.5% of Ni and the balance of Sn. The invention relates to a solder alloy design method, which utilizes machine learning to assist the design of solder components, collects experimental data first and obtains an initial data set of the solder alloy components and mechanical properties; then, screening alloy components with larger mechanical property correlation by adopting the maximum mutual information coefficient and the Pearson correlation coefficient; then modeling and training by using a gradient descent tree algorithm; the model is verified by adopting a leave-one-out cross verification method; inputting the virtual sample into a machine learning model to obtain a prediction result; and performing systematic test verification to obtain the solder alloy with excellent performance. The preparation method adopts a method of combining a high-flux vacuum arc melting furnace and an electromagnetic induction furnace for melting. The invention obviously improves the mechanical property and the wettability of the solder alloy, has higher strength and better creep resistance, brazing property and oxidation resistance, and has good application prospect.

Description

SnAgCuBiIn series lead-free solder alloy, and design method and preparation method thereof

Technical Field

The invention belongs to the technical field of electronic micro-connection and packaging materials, and relates to a SnAgCu series high-reliability lead-free solder alloy, and a design and preparation method thereof.

Background

The tin-lead (Sn-Pb) alloy solder has the advantages of excellent welding performance, high reliability, easy preparation, low price and the like, and has been used for more than 50 years in the field of electronic component packaging. However, since Pb and Pb compounds pollute the environment and are harmful to human health, Sn-Pb solder is gradually banned, and lead-free solder becomes the main development trend of electronic packaging and micro-connection at present. With the continuous development of the electronic industry, the miniaturization and multi-functionalization of electronic products have promoted the development of electronic packaging technology towards high density, high functionality and high integration. As substrates become smaller and smaller, pad sizes and pad spacings become narrower and narrower, and the mechanical, electrical and thermodynamic loads they carry become heavier, more severe challenges are presented to their reliability.

To solve these problems, it is required to develop a lead-free solder alloy having a low melting point, high strength and good creep resistance. Among the conventional lead-free solders, Sn-Ag-cu (sac) solder alloys have excellent overall properties and have become the lead-free solder alloys of international standards. The SAC alloy has different composition standards in each country, and the European Union advocates that the composition is controlled to be near Sn3.8Ag0.7Cu (SAC387), and that the compositions recommended by the Japan society for electronics and information technology industries are two types, Sn3.0Ag0.5Cu (SAC305) and Sn3.5Ag0.7Cu. The Sn-Ag-Cu alloy has a near eutectic alloy composition and a melting point in the range of 183 ℃ to 232 ℃. Wherein Ag and Sn form Ag ₃ Sn intermetallic compound is favorable for improving the mechanical property and reliability of the solder. The Cu in the solder can slow down the dissolution and diffusion of the substrate Cu into the solder to a certain extent, and the thickness of the intermetallic compound interface layer is reduced. Taking high-silver alloy SAC387 as an example, the high-silver alloy SAC387 has good wettability and wide application, but still has low strength, cold and hot fatigue resistance and creep deformation performance which need to be improved, and cannot meet the use requirements under special harsh service environments.

The material research and development concept of the material genome integrates a material database, material calculation and a high-throughput experiment, accelerates the research and development process of a new material, and realizes the double reduction of research and development cost and research and development period. The application of Machine Learning (ML) to the research and development of new materials is an important means of a material genome research and development technology, and the method comprises the steps of constructing a material data set, training a model in a flexible and highly nonlinear mode, searching the relation between different factors and performance in material design, and simultaneously combining expert field knowledge to rapidly design the new materials according to performance requirements.

Disclosure of Invention

In order to solve the problems of the prior art, the invention aims to overcome the defects in the prior art, and provides the SnAgCuBiIn series lead-free solder alloy, the design method and the preparation method thereof, which are used for carrying out the preferred component range and the design development of the high-reliability lead-free solder alloy.

In order to achieve the purpose of the invention, the invention adopts the following technical scheme:

a SnAgCuBiIn series lead-free solder alloy comprises, by weight, 1.0-5.5% of Ag, 0.5-1.0% of Cu, 0.5-5.0% of Bi, 0.4-4.0% of In, 0-1.0% of Ti, 0-0.5% of Ni, and the balance of Sn.

Preferably, the SnAgCuBiIn series lead-free solder alloy comprises, by weight, 3.0-4.0% of Ag, 0.5-0.7% of Cu, 1.0-3.5% of Bi, 0.5-3.5% of In, 0.1-0.8% of Ti, 0.1-0.2% of Ni, and the balance of Sn.

Further preferably, the composition and content of the snagcubin series lead-free solder alloy of the invention are calculated by weight percentage, and the alloy further comprises at least one or more of the following alloy elements: ce is less than or equal to 0.2 percent and Ge is less than or equal to 0.2 percent.

Further preferably, the composition and content of the snagcubin series lead-free solder alloy of the present invention are calculated by weight percentage, and the alloy further includes at least one or more of the following alloy elements: 0.1-0.2% Ce, 0.05-0.2% Ge.

The invention relates to a design method of SnAgCuBiIn series lead-free solder alloy, which utilizes machine learning to assist the design of the components of the lead-free solder, and the method comprises the following steps:

(1) collecting experimental data to obtain an initial data set of lead-free solder alloy components and mechanical properties;

(2) screening alloy components with large correlation with mechanical properties by adopting a maximum Mutual Information Coefficient (MIC) and a Pearson correlation Coefficient (Pearson correlation Coefficient);

(3) taking alloy components as input and mechanical properties as output, and modeling and training by using a Gradient Boosting Decision Tree (GDBT) algorithm; the model is verified by adopting a leave-one-out cross verification method;

(4) designing alloy component combination and step length, constructing a virtual sample by adopting a permutation and combination mode, and inputting the virtual sample into a machine learning model to obtain a prediction result; and (4) performing systematic test verification on the edge points of the virtual sample space to obtain the solder alloy with excellent performance.

The invention relates to a preparation method of SnAgCuBiIn series lead-free solder alloy, which adopts a mode of combining high-flux vacuum arc melting and induction melting to prepare the alloy, and the preparation method comprises the following steps:

a. in a high-flux vacuum arc melting furnace, materials containing metal Ti, Ni, Ce, Ge and Sn with the mass fraction of not less than 99.9 percent are used as alloy component raw materials to respectively prepare Sn-Ti intermediate alloy, Sn-Ni intermediate alloy, Sn-Ce intermediate alloy and Sn-Ge intermediate alloy with the mass fraction of Sn-5 percent Ti, Sn-4 percent Ni, Sn-7 percent Ce and Sn-5 percent Ge;

in the process of preparing the intermediate alloy, firstly, the furnace of a high-flux vacuum arc melting furnace is vacuumized when the vacuum degree is not higher than 1 multiplied by 10 ^-3 Introducing protective argon gas to be not less than 0.5atm under Pa, loading current to 110A, and igniting pure Ti metal to consume residual oxygen in the furnace; then placing the prepared alloy component raw materials into a smelting station, loading current to 110-120A, igniting metal in the smelting station until the alloy component raw materials are completely molten, turning over the alloy after the alloy is completely cooled after arc extinguishing, re-melting and cooling, and repeatedly smelting for 4 times to ensure that the alloy components are uniform to obtain an intermediate alloy for later use;

b. according to the prepared target SnAgCuBiIn series lead-free solder alloy component, calculating and weighing pure metal Sn, Ag, Cu, Bi and In raw materials with the mass fraction not less than 99.9 percent and the intermediate alloy prepared In the step a, and preparing materials;

b, smelting by using a vacuum induction furnace, repeating the same operations of vacuumizing and argon filling In the step a for 3 times before smelting, removing oxygen In the furnace, and finally smelting In an argon environment, wherein when the alloy is smelted, raw materials of pure metals Sn, Ag, Cu, Bi and In are put into a crucible, heated to be not lower than 300 ℃, and kept warm for 15-20 minutes; and then, according to the component design requirements, placing the Sn-Ti intermediate alloy, the Sn-Ni intermediate alloy, the Sn-Ce intermediate alloy and the Sn-Ge intermediate alloy into a crucible, heating to be not lower than 500 ℃, preserving the heat for 20-30 minutes, cooling to be not higher than 300 ℃, casting the alloy liquid into a stainless steel mold, and cooling and molding to obtain the finished product of the SnAgCuBiIn series lead-free solder alloy.

Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:

1. the invention guides the design of the high-performance lead-free solder alloy by a fusion machine learning method, optimizes the alloy components and accelerates the material research and development process;

2. the invention prepares the intermediate alloy by utilizing the high-flux vacuum arc melting, solves the problems of uneven alloy components and infusibility caused by metals with higher melting points, improves the reliability of the melting, has higher preparation efficiency, and can simultaneously prepare various alloys with different components in a high-flux vacuum arc melting furnace;

3. according to the invention, alloy design is guided according to the screening result of the machine learning model, meanwhile, a certain amount of Ag, Cu, Bi, In, Ti and Ni elements are added into the solder alloy simultaneously by combining expert field knowledge, so that the strength and creep resistance of the solder alloy are obviously improved, and the possibility of internal shear fracture of a welding spot under severe service conditions is reduced;

4. the experimental verification shows that the addition of Bi and In elements can effectively improve the strength and creep resistance of the solder, and the simultaneous addition of the Bi and In elements has excellent synergistic strengthening effect; in general, excessive addition of Bi element causes a part of Bi element to be precipitated in the form of a precipitate phase during alloy solidification, and Bi precipitates are easily coarsened in an environment with constantly changing temperature, thereby adversely affecting the mechanical properties of the solder alloy; in the invention, the solid solubility of Bi In the Sn matrix can be obviously increased by adding In with the mass fraction of 2.8%, and the coarsening of Bi precipitates is effectively reduced, so that the adverse effect on the alloy performance is reduced; meanwhile, the increase of the solid solubility of Bi in the Sn matrix means that the solid solution strengthening effect of Bi can be enhanced, and the creep resistance of the alloy can be further improved;

5. the addition of trace Ce and Ge in the invention can further improve the oxidation and corrosion resistance of the solder alloy, simultaneously can keep better melting property and wetting property, and is beneficial to improving the dimensional stability and the drop resistance of the soldered joint after welding, thereby enhancing the reliability of the soldered joint under severe service conditions.

Drawings

FIG. 1 is a general flow chart of the alloy design of the present invention.

Fig. 2 is a graph of the results of the maximum mutual information coefficient and pearson correlation coefficient of the present invention.

FIG. 3 is a graph of the distribution of points selected in the virtual space and the trend of mechanical properties varying with the content of ingredients in the present invention.

FIG. 4 is a graph showing the trend of mechanical properties of the experimental sample of the present invention according to the content of the components.

FIG. 5 is a differential thermal analysis chart of the solder alloy of example 8 of the present invention.

Fig. 6 is a drawing graph of a solder alloy of example 5 of the present invention.

Fig. 7 is a graph of the wetting angle of the solder alloy of example 3 of the present invention.

FIG. 8 is a metallographic structure chart of a solder alloy according to example 4 of the present invention.

FIG. 9 is a metallographic structure chart of a solder alloy according to example 6 of the present invention.

FIG. 10 is a graph comparing oxidation resistance of inventive examples and comparative samples.

Detailed Description

The invention aims to guide alloy design by utilizing a machine learning method, and improve the mechanical property and creep resistance of the solder alloy on the premise of ensuring good wettability by adding alloy elements such as Bi, In, Ni, Ti and the like and additionally containing at least one or more of Ce, Ge and the like on the basis of the SnAgCu-based lead-free solder alloy. The invention aims to solve the problem of developing a lead-free solder alloy with good wettability, good weldability, excellent mechanical property and high reliability, and improving the service performance of a welding device in a harsh environment.

The invention takes the improvement of the comprehensive mechanical property of the solder alloy as a starting point, and optimizes and improves the traditional lead-free tin-based solder. In the field of electronic packaging, the final application effect of the lead-free solder is embodied in the reliability of the prepared welding device, and when the lead-free solder is used, because a welding spot joint is frequently influenced by stress strain and thermal shock, a welding spot can generate cracks at the connection part of a solder alloy or a substrate so as to generate fracture failure. Therefore, the improvement of the comprehensive mechanical property of the solder alloy is beneficial to reducing the possibility of failure of the solder or the welding spot under severe service conditions, such as high load and alternating thermal stress. The better wettability can enhance the combination firmness degree of the solder alloy and the substrate, and further improve the reliability of the welding spot. The invention combines the machine learning technology, and simultaneously adds a plurality of trace alloy elements in the SnAgCu system to achieve the effect of improving the comprehensive mechanical property of the solder.

As shown in FIG. 1, the present invention firstly guides the design of lead-free solder alloy by machine learning, and the machine learning method is further described in detail with reference to the attached drawings:

64 pieces of experimental data were collected as an initial data set, and the designed alloy components were Sn, Ag, Cu, Bi, In, Sb, Ti, Ni, Zn, and Al, and were combined In mass%. Mechanical properties include tensile strength and elongation at break.

The results of screening alloy elements using the maximum mutual information coefficient and the pearson correlation coefficient are shown In FIG. 2, and the involved components are Sn, Bi, In, Sb, Ti, Ni, Zn and Al. From the results, Bi and In have the largest correlation with mechanical properties, and therefore, alloy design is performed using the snagcubin system as a basic system In the following.

Arranging and combining the SnAgCuBiIn alloy with the set step size of 0.1 percent to obtain 2091 virtual samples. And inputting the virtual sample into the model to obtain a prediction result, and selecting points to carry out experimental verification. Fig. 3 is a trend graph of the prediction result of the mechanical property of the virtual sample with the change of the component content, fig. 4 is a trend graph of the experimental result of verifying the mechanical property of the sample with the change of the component content, and the component range of the alloy is optimized according to the results of fig. 3 and fig. 4.

The lead-free solder alloy in the embodiment of the invention is preferably composed of the following elements in percentage by weight: 3.0-4.0% of Ag, 0.5-0.7% of Cu, 1.0-3.5% of Bi and 0.5-3.5% of In. Furthermore, at least one of the following alloying elements is contained: 0.1-0.8% of Ti, 0.1-0.2% of Ni, 0.1-0.2% of Ce and 0.05-0.2% of Ge.

Meanwhile, the invention also carries out relevant measurement and screening on the melting point of the solder. The melting point temperature of the solder is an important parameter index for determining a reflow soldering process, the reflow soldering peak temperature of the solder is usually 25 ℃ higher than the melting point of the solder, and the reflow soldering peak temperature is too high and is easy to generate irreversible damage to a PCB and an electronic component. As during soldering, reflow peak temperatures exceeding the PCB's glass transition temperature can cause board warpage or localized material softening. On the other hand, taking the most widely used lead-free solder SAC305 as an example, if the new lead-free solder is prepared with a melting temperature much higher than that of the SAC305, it may be necessary to replace reflow equipment or to make a new process flow, adding additional cost. Therefore, the melting temperature of lead-free solder should match the operating temperature of current soldering equipment to the greatest possible extent.

The melting point testing device used in the following examples of the present invention was a synchronous thermal analyzer (STA-DTA) manufactured by Chinesco corporation, and the test sample was 15mg of solder alloy powder, the heating rate was 5 ℃/min, and the cooling rate was 10 ℃/min. The solidus temperature of the solder alloy taken by the invention is the starting point of the peak of the heating curve, and the liquidus temperature is the temperature of the peak point of the heating curve.

The preferred solder oxidation performance was also tested in the embodiments of the present invention. The oxidation resistance test of the solder was carried out by thermogravimetric analysis in STA-DTA equipment, the weight of the sample was 30mg, and the sample was kept at a constant temperature of 280 ℃ for 60min, and the result was expressed as the percentage of the weight gain of the sample.

The preferred solder is also tested for its wetting properties in the embodiments of the present invention. The solder wettability refers to the wettability of molten solder on a base material, and the solder with good wettability can ensure that the connection between an electronic device and a substrate is firmer and the reliability of a welding point is improved. The wetting property of solder can be measured by wetting angle, wetting force, wetting time, wetting area, etc. The main factors affecting wettability include: the composition of the solder and the base material, the temperature, the intermetallic compound formed at the interface, the flux, the surface state of the base material, the surface active material, and the like.

In the embodiment of the invention, the wetting angle is used for measuring the wettability of the solder, the size of a red copper sheet used in the experiment is 30mm multiplied by 1mm, and after an oxide layer and oil stains on the surface are removed by sand paper, the red copper sheet is immersed in acetone for ultrasonic cleaning; making lead-free solder into 0.2g of block with deviation of +/-1%, and then putting the block into ethanol for ultrasonic cleaning; selecting soldering flux, placing solder in the center of the red copper sheet, coating the soldering flux, ensuring that the red copper sheet is horizontally placed in a reflow soldering machine, and setting a heating temperature curve; after cleaning the spread sample, measuring the wetting angle of the spread sample by using a wetting angle measuring instrument; 3 replicates of each sample were taken and averaged.

The embodiment of the invention tests the creep property of the optimized solder. In the embodiment of the invention, the steady-state creep rate of the solder is tested by using an iMicro type nanoindenter manufactured by KLA company. The sample size was 5X 3mm and the sample was ground, polished and ultrasonically cleaned prior to testing to give the sample a better flatness. Experimental parameters: strain rate of 0.05s ^-1 The maximum load is 50mN, the load retention time is 5min, the dot layout is 3 x 3, and 9 dots are distributed in the whole screen, so that the data uniformity and the effectiveness are ensured.

The invention analyzes the optimized solder components, and the alloy elements added in the embodiment have the following functions:

1. the effect of adding Ag in the embodiment of the invention is as follows:

a certain amount of Ag can improve the wettability of the solder alloy, and Ag and Sn can generate Ag ₃ The Sn intermetallic compound is distributed in a Sn matrix in a network form, so that the strength of the solder alloy is enhanced. Meanwhile, the liquidus temperature of the solder is reduced, and the melting interval is reduced. The Ag content of the solder alloy is controlled to be 1.0-5.5%.

2. The effect of adding Cu in the embodiment of the invention is as follows:

the addition of copper to the solder alloy inhibits the dissolution of copper elements on the substrate into the solder matrix during solderingThereby suppressing or reducing the generation of a brittle intermetallic compound layer at the interface. Meanwhile, because the dissolution of copper element is reduced, the supersaturated state of copper in the welding liquid can be inhibited in the welding process, thereby reducing the coarse Cu ₆ Sn ₅ Phase formation, reduced coarse Cu ₆ Sn ₅ The probability of phase induced cracking. Meanwhile, the Cu element also has a certain grain refining effect. The Cu content of the solder alloy is controlled to be 0.5-1.0%.

3. The effect of adding Bi in the embodiment of the invention is as follows:

the Bi element is dissolved into the Sn basal body in a solid way to cause the solid solution strengthening effect, so that the strength of the solder alloy can be obviously enhanced, the creep resistance of the solder alloy is improved, the liquidus and solidus temperatures of the solder are reduced, and meanwhile, the Bi also reduces the surface tension of the liquid solder, thereby improving the wetting property of the solder. When the Bi content is less than 1%, the solid solution strengthening effect is not obvious, and the strength of the solder is not greatly improved. When the content of Bi exceeds 5.0%, the strength of the solder is greatly improved, but the plasticity is sharply reduced, and the addition of Bi in an excessive content increases the melting range of the solder, which is disadvantageous to the welding process. The Bi content of the solder alloy of the present invention is controlled to 0.5 to 5.0%, and more preferably 1.0 to 3.5%.

4. The effect of adding In the embodiment of the invention is as follows:

the addition of In can obviously reduce the melting point of the solder; in can be dissolved In Sn matrix to play a role of solid solution strengthening, and simultaneously can refine the alloy structure, improve the uniformity of the distribution of strengthening phases In the alloy, and further improve the mechanical property and the welding reliability of the solder alloy. When the In content is less than 0.4%, the solid solution amount of In relative to Sn is small, and the solid solution strengthening effect is insignificant. In is an easily-oxidized element, and when the content of In is more than 4.0%, the oxidation resistance of the solder alloy is reduced, so that the solder alloy is yellowed, and voids are easily generated during welding. The In content of the solder alloy of the present invention is controlled to 0.4 to 4.0%, and more preferably 0.5 to 3.5%.

In the invention, when the addition amount of the Bi element reaches 3.5%, a Bi-containing precipitate phase is separated under an electron microscope, and the separated phase can obstruct dislocation motion to a certain extent, thereby improving the alloy strength. On the other hand, in practical use of solder, Bi-containing precipitates in the solder tend to coarsen in an environment where the temperature is constantly changing, adversely affecting the mechanical properties of the solder alloy, and the alloy has reduced plasticity, and tends to cause stress concentration and cracks in the solder joint.

In the invention, the problem that Bi educt is easy to coarsen can be effectively solved by adding 3.5 percent of Bi and 2.8 percent of In at the same time. The solid solubility of the Bi element in the Sn matrix is certain at room temperature, in the process of alloy solidification, the excessive Bi element cannot be completely dissolved in the Sn matrix in a solid solution mode, and part of Bi is separated out in the form of a precipitation phase and distributed at the final solidification position, a grain boundary and other positions. In the invention, the solid solubility of Bi In the Sn matrix can be obviously increased by adding 2.8 percent of In, the coarsening of Bi precipitates is effectively reduced, and the adverse effect on the alloy performance is further reduced. The increase in the solid solubility of Bi in the Sn matrix means that the solid-solution strengthening effect of Bi is enhanced, and the creep resistance of the alloy can be further improved.

The effect of adding Ti in the examples of the invention is as follows:

the alloy structure of the solder is refined, and the strength and the plasticity of the solder are improved. However, when the content of Ti exceeds 1.0%, coarse intermetallic compounds Ti are formed ₂ Sn ₃ And the plasticity and the toughness of the solder are reduced. The content of Ti in the invention is controlled to be 0-1.0%.

The effect of adding Ni in the embodiment of the invention is as follows:

ni may form Ni with Sn ₃ Sn、Ni ₃ Sn ₂ 、Ni ₃ Sn ₄ The three intermetallic compounds have the function of precipitation strengthening, and can reduce the dissolution of Cu into the solder, thereby inhibiting the growth of the intermetallic compounds at the interface with the copper substrate caused by high-temperature aging, and being beneficial to improving the shear strength and the shock resistance of the prepared solder joint. However, when the Ni content is higher than 0.2%, the melting point of the solder alloy can be improved, and the Ni content of the solder alloy is controlled to be 0-0.5%.

In the examples of the inventionThe effect of adding Ce and Ge is as follows: the addition of a small amount of Ce can play a role in refining grains and improving tissues, but the addition of excessive Ce can generate CeSn ₃ The tensile strength and the elongation of the alloy are reduced, and the content of the Ce element in the embodiment of the invention is controlled to be 0-0.2%. Ge element has high-strength oxygen-philic skin effect, promotes the solder surface to form a barrier layer in the welding process, can hinder the further oxidation of solder, improves the spreading rate of solder. When the Ge content is too high, a large amount of CeO may be caused ₂ The surface tension of the solder is increased, so that the wettability of the solder is reduced, and the content of Ge element in the embodiment of the invention is controlled to be 0-0.2%.

The present invention will be described in further detail below. In the following description, the% of the solder alloy composition is a mass percentage unless otherwise specified.

The above-described embodiments are further illustrated below with reference to specific examples, in which preferred embodiments of the invention are detailed below:

example 1

In this embodiment, a snagcubin high reliability lead-free solder alloy consists of, by weight, 5.0% Ag, 0.5% Cu, 2.0% Bi, 0.6% In, and the balance Sn. The lead-free solder has a solidus line of 209.1 deg.C, a liquidus line of 215.3 deg.C, a tensile strength of 76.7MPa, an elongation at break of 26.0%, and a wetting angle of 38.2 deg.

Example 2

This embodiment is substantially the same as embodiment 1, and is characterized in that:

in this embodiment, a snagcubin high reliability lead-free solder alloy consists of, by weight, 3.8% Ag, 0.7% Cu, 0.5% Bi, 0.8% In, and the balance Sn. The lead-free solder has a solidus line of 213.0 deg.C, a liquidus line of 217.5 deg.C, a tensile strength of 49.2MPa, an elongation at break of 29.1%, and a wetting angle of 35.3 deg.

Example 3

This embodiment is substantially the same as the above embodiment, and is characterized in that:

in this embodiment, a snagcubin high reliability lead-free solder alloy consists of, by weight, 3.8% Ag, 0.7% Cu, 3.5% Bi, 2.8% In, and the balance Sn. The lead-free solder has a solidus line of 200.1 ℃, a liquidus line of 207.7 ℃, a tensile strength of 85.1MPa, an elongation at break of 20.7% and a wetting angle of 28.8 degrees.

Example 4

in this embodiment, a SnAgCuBiInNi high reliability lead-free solder alloy consists of, by weight, 3.8% Ag, 0.7% Cu, 2.5% Bi, 3.1% In, 0.1% Ni, and the balance Sn. The lead-free solder has a solidus of 205.9 ℃, a liquidus of 215.3 ℃, a tensile strength of 80.4MPa, an elongation at break of 18.2% and a wetting angle of 34.3 °.

Example 5

in this embodiment, a SnAgCuBiInNi high reliability lead-free solder alloy consists of, by weight, 5.5% Ag, 0.7% Cu, 2.0% Bi, 0.4% In, 0.2% Ni, and the balance Sn. The lead-free solder has a solidus line of 209.0 ℃, a liquidus line of 215.0 ℃, a tensile strength of 76.2MPa, an elongation at break of 24.6% and a wetting angle of 35.7 °.

Example 6

in this example, a SnAgCuBiInTi high reliability lead-free solder alloy consists of, by weight, 3.8% Ag, 0.7% Cu, 3.0% Bi, 1.0% In, 0.2% Ti, and the balance Sn. The lead-free solder has a solidus line of 207.6 ℃, a liquidus line of 218.3 ℃, a tensile strength of 85.7MPa, an elongation at break of 19.0% and a wetting angle of 33.6 degrees.

Example 7

in this embodiment, a SnAgCuBiInTiNi high reliability lead-free solder alloy comprises, by weight, 3.8% Ag, 0.7% Cu, 2.5% Bi, 1.8% In, 0.1% Ti, 0.2% Ni, and the balance Sn. The lead-free solder has a solidus line of 207.0 deg.C, a liquidus line of 213.2 deg.C, a tensile strength of 77.9MPa, an elongation at break of 17.5%, and a wetting angle of 34.2 deg.

Example 8

in this embodiment, a snagcubinitice high reliability lead-free solder alloy consists of, by weight, 3.8% Ag, 0.7% Cu, 3.0% Bi, 1.0% In, 0.2% Ti, 0.2% Ce, and the balance Sn. The lead-free solder has a solidus of 208.0 ℃, a liquidus of 213.8 ℃, a tensile strength of 79.5MPa, an elongation at break of 20.0% and a wetting angle of 35.6 deg.

Example 9

in this embodiment, the composition of the SnAgCuBiInNiCeGe high reliability lead-free solder alloy comprises, by weight, 1.0% Ag, 0.5% Cu, 3.0% Bi, 2.0% In, 0.1% Ni, 0.2% Ce, 0.05% Ge, and the balance Sn. The lead-free solder has the solidus line of 195.3 ℃, the liquidus line of 213.7 ℃, the tensile strength of 72.7MPa, the elongation at break of 22.0 percent and the wetting angle of 36.2 degrees.

Example 10

in this embodiment, a SnAgCuBiInNiCe high reliability lead-free solder alloy consists of, by weight, 3.8% Ag, 0.7% Cu, 2.5% Bi, 3.1% In, 0.1% Ni, 0.1% Ce, and the balance Sn. The lead-free solder has a solidus line of 203.1 ℃, a liquidus line of 210.5 ℃, a tensile strength of 72.9MPa, an elongation at break of 20.7% and a wetting angle of 34.9 °.

TABLE 1 table of performance data of lead-free solder alloys of examples 1 to 10

Table 1 compares the melting characteristics, mechanical properties and wetting properties of some of the examples with the comparative samples: the alloy melting temperature of the embodiment of the invention is generally lower than the melting temperature of SAC387 and SAC305, and the temperature requirement of the basic reflow soldering process is met; compared with the SAC387, the alloy strength of the embodiment has the lifting effect of 59-87 percent, and compared with the SAC305, the alloy strength of the embodiment has the lifting effect of 76-108 percent; in the aspect of wettability, the wetting angle of the alloy of the embodiment is generally smaller than that of SAC387 and SAC305, which shows that the embodiment has better wettability, is beneficial to enhancing the firmness degree of a welding spot and a substrate and improves the reliability of the welding spot.

Table 2 compares the creep stress indices of the examples and comparative samples: the larger the creep stress index, the better the creep resistance of the alloy. As can be seen from table 2, the creep stress index of the alloy of example is generally higher than that of the comparative sample, and the creep resistance of the alloy of example is improved due to the strengthening effect of the added multiple alloy elements, such as the solid solution strengthening effect of Bi and In elements, the precipitation strengthening effect of Ni elements, and the structure refining strengthening effect of Ti elements.

TABLE 2 comparison of creep properties of solder alloys according to some examples of the invention

The test sample was 15mg of the solder alloy powder prepared in example 8, the heating rate was 5 deg.C/min, and the cooling rate was 10 deg.C/min. The solidus temperature of the solder alloy taken by the invention is the starting point of the peak of the heating curve, and the liquidus temperature is the temperature of the peak point of the heating curve. FIG. 5 is a differential thermogram of the solder alloy of example 8. As can be seen from FIG. 5, in example 8, the solidus temperature was 208.0 ℃ and the liquidus temperature was 213.8 ℃.

Mechanical testing was performed on the solder alloy of example 5. fig. 6 is a tensile graph of the solder alloy of example 5 of the present invention and a comparison with the examples. From fig. 6, it is understood that example 5 has high strength and good toughness, the tensile strength is 76.2, and the elongation at break is 24.6.

The wetting properties of the solder of example 3 of the present invention were also tested. Measuring the wettability of the solder by using a wetting angle, wherein the size of a red copper sheet used in the experiment is 30mm multiplied by 1mm, and after removing an oxide layer and oil stains on the surface by using sand paper, immersing the red copper sheet into acetone for ultrasonic cleaning; making lead-free solder into 0.2g of block with deviation of +/-1%, and then putting the block into ethanol for ultrasonic cleaning; selecting soldering flux, placing solder in the center of a red copper sheet, coating the soldering flux, ensuring that the red copper sheet is horizontally placed in a reflow soldering machine, and setting a heating temperature curve; after the spread sample is cleaned, measuring the wetting angle of the spread sample by using a wetting angle measuring instrument; 3 specimens were measured for each sample and the average value was taken. Fig. 7 is a wetting angle diagram of a solder alloy in example 3 of the present invention. As can be seen from fig. 7, the wetting angle of example 3 on the copper sheet was 28.8 °, and example 3 had good wetting properties.

Microscopic observations of the solders prepared in examples 4 and 6 were made, and fig. 8 is a metallographic structure diagram of a solder alloy of example 4 of the present invention. FIG. 9 is a metallographic structure drawing of a solder alloy according to example 6 of the present invention. As is clear from fig. 8 and 9, examples 4 and 6 have intermetallic compounds uniformly distributed, and these intermetallic compounds can inhibit dislocation movement and effectively improve the tensile strength of the solder.

FIG. 10 is a comparison of oxidation resistance of the examples and comparative samples: in FIG. 10, A1 is a comparative sample SnAg3.8Cu0.7, A2 is example 10: snag3.8cu0.7bi2.5in3.1ni0.1ce0.1, a3 for example 9: snag1.0cu0.5bi3.0in2.0ni0.1ce0.2ge0.05, a4 is example 6: SnAg3.8Cu0.7Bi3.0In1.0Ti0.2. It can be seen from fig. 10 that the percentage weight gain of the example is significantly less than that of the comparative sample at the same oxidation time, indicating that the high temperature oxidation resistance of the solder alloy of the present invention is superior to that of the comparative sample.

In summary, the above embodiments of the present invention are designed and manufactured for high reliability lead-free solder alloys. The alloy comprises the following components in percentage by weight: 1.0-5.5% of Ag, 0.5-1.0% of Cu, 0.5-5.0% of Bi, 0.4-4.0% of In, 0-1.0% of Ti, 0-0.5% of Ni and the balance of Sn; in addition, the alloy contains 1 or more selected from Ce and Ge according to the situation, and the rest is Sn. The design method of the high-reliability lead-free solder alloy of the embodiment of the invention comprises the following steps: collecting relevant experimental data as an initial data set; screening the key gold elements by using the maximum mutual information coefficient and the Pearson correlation coefficient; taking alloy components as input and mechanical properties as output, and modeling by using a gradient descent tree algorithm; and constructing a virtual sample, calculating by a reliable machine learning model to obtain a prediction result, and preferably selecting the alloy component range according to the prediction result. The preparation method of the lead-free solder alloy comprises the following steps: refractory metal with higher melting point and pure tin metal are prepared into intermediate alloy by utilizing a high-flux electric arc melting furnace, and then pure Sn, Ag, Cu, Bi, In and various intermediate alloys with proper amount are weighed according to design components and mixed and melted In an induction melting furnace. The invention solves the problems of lower strength and poorer creep resistance of the traditional lead-free solder, guides alloy design through machine learning, combines a high-flux experimental method, and obviously improves the mechanical property and the wettability of the solder alloy by utilizing multi-element alloying and the interaction strengthening effect of multiple elements such as Bi, In and the like. The finally obtained solder alloy has higher strength and creep resistance, better brazing property and oxidation resistance and good application prospect.

The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made according to the purpose of the invention, and all changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention shall be made in the form of equivalent substitution, so long as the invention is in accordance with the purpose of the invention, and the invention shall fall within the protection scope of the present invention as long as the technical principle and the inventive concept of the present invention are not departed from the present invention.

Claims

1. A SnAgCuBiIn series lead-free solder alloy is characterized in that: comprises 1.0-5.5% Ag, 0.5-1.0% Cu, 0.5-5.0% Bi, 0.4-4.0% In, 0-1.0% Ti, 0-0.5% Ni, and the balance Sn.

2. The snagcubin-based lead-free solder alloy of claim 1, wherein: comprises (by weight percent) Ag 3.0-4.0%, Cu 0.5-0.7%, Bi 0.5-3.5%, In 0.5-3.5%, Ti 0.1-0.8%, Ni 0.1-0.2%, and Sn In balance.

3. The SnAgCuBiIn-based lead-free solder alloy of claim 1 or 2, wherein the solder alloy further comprises, in weight percent, at least one or more of the following alloying elements: ce is less than or equal to 0.2 percent and Ge is less than or equal to 0.2 percent.

4. The SnAgCuBiIn series lead-free solder alloy according to claim 3, wherein the composition and content of the solder alloy in percentage by weight, the alloy further comprises at least one or more of the following alloying elements: 0.1-0.2% Ce, 0.05-0.2% Ge.

5. The method for designing the SnAgCuBiIn series lead-free solder alloy as set forth in claim 1, wherein the lead-free solder composition design is assisted by machine learning, the method comprising the steps of:

(3) taking alloy components as input and mechanical properties as output, and modeling and training by using a gradient descent tree algorithm; the model is verified by adopting a leave-one-out cross verification method;

6. The preparation method of the SnAgCuBiIn series lead-free solder alloy of claim 1, which is characterized in that the alloy preparation is carried out by adopting a mode of combining high-flux vacuum arc melting and induction melting, and the preparation method comprises the following steps:

in the process of preparing the intermediate alloy, firstly, the furnace of a high-flux vacuum arc melting furnace is vacuumized when the vacuum degree is not higher than 1 multiplied by 10 ^-3 Introducing protective argon to be not less than 0.5atm when Pa, loading current to 110A, and igniting pure Ti metal to consume residual oxygen in the furnace; then placing the prepared alloy component raw materials into a smelting station, loading current to 110-120A, igniting metal in the smelting station until the alloy component raw materials are completely molten, turning over the alloy after the alloy is completely cooled after arc extinguishing, remelting and cooling the alloy, and repeatedly smelting for 4 times to ensure that the alloy components are uniform to obtain intermediate alloy for later use;