CN115383349B - Method for obtaining high-toughness lead-free tin-bismuth solder by microalloying regulation and control microstructure - Google Patents
Method for obtaining high-toughness lead-free tin-bismuth solder by microalloying regulation and control microstructure Download PDFInfo
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- 229910000679 solder Inorganic materials 0.000 title claims abstract description 59
- JWVAUCBYEDDGAD-UHFFFAOYSA-N bismuth tin Chemical compound [Sn].[Bi] JWVAUCBYEDDGAD-UHFFFAOYSA-N 0.000 title claims abstract description 41
- 238000000034 method Methods 0.000 title claims abstract description 23
- 230000033228 biological regulation Effects 0.000 title claims abstract description 14
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 161
- 239000000956 alloy Substances 0.000 claims abstract description 161
- 229910052751 metal Inorganic materials 0.000 claims abstract description 33
- 239000002184 metal Substances 0.000 claims abstract description 32
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 8
- 238000005275 alloying Methods 0.000 claims abstract description 7
- 238000002844 melting Methods 0.000 claims description 38
- 230000008018 melting Effects 0.000 claims description 37
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 18
- 238000010438 heat treatment Methods 0.000 claims description 16
- 238000005266 casting Methods 0.000 claims description 15
- 238000002360 preparation method Methods 0.000 claims description 14
- 229910052718 tin Inorganic materials 0.000 claims description 14
- 239000012535 impurity Substances 0.000 claims description 9
- 229910052757 nitrogen Inorganic materials 0.000 claims description 9
- BLOIXGFLXPCOGW-UHFFFAOYSA-N [Ti].[Sn] Chemical compound [Ti].[Sn] BLOIXGFLXPCOGW-UHFFFAOYSA-N 0.000 claims description 7
- SMZOUWXMTYCWNB-UHFFFAOYSA-N 2-(2-methoxy-5-methylphenyl)ethanamine Chemical compound COC1=CC=C(C)C=C1CCN SMZOUWXMTYCWNB-UHFFFAOYSA-N 0.000 claims description 5
- NIXOWILDQLNWCW-UHFFFAOYSA-N 2-Propenoic acid Natural products OC(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 claims description 5
- RSWGJHLUYNHPMX-UHFFFAOYSA-N Abietic-Saeure Natural products C12CCC(C(C)C)=CC2=CCC2C1(C)CCCC2(C)C(O)=O RSWGJHLUYNHPMX-UHFFFAOYSA-N 0.000 claims description 5
- KHPCPRHQVVSZAH-HUOMCSJISA-N Rosin Natural products O(C/C=C/c1ccccc1)[C@H]1[C@H](O)[C@@H](O)[C@@H](O)[C@@H](CO)O1 KHPCPRHQVVSZAH-HUOMCSJISA-N 0.000 claims description 5
- KHPCPRHQVVSZAH-UHFFFAOYSA-N trans-cinnamyl beta-D-glucopyranoside Natural products OC1C(O)C(O)C(CO)OC1OCC=CC1=CC=CC=C1 KHPCPRHQVVSZAH-UHFFFAOYSA-N 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 3
- 229910052709 silver Inorganic materials 0.000 claims description 3
- 238000003466 welding Methods 0.000 abstract description 25
- 238000004377 microelectronic Methods 0.000 abstract description 4
- 238000004806 packaging method and process Methods 0.000 abstract description 4
- 230000005496 eutectics Effects 0.000 description 17
- 230000000052 comparative effect Effects 0.000 description 15
- 230000008569 process Effects 0.000 description 10
- 239000000463 material Substances 0.000 description 7
- 238000001000 micrograph Methods 0.000 description 7
- 229910001152 Bi alloy Inorganic materials 0.000 description 5
- 238000003723 Smelting Methods 0.000 description 5
- 229910020830 Sn-Bi Inorganic materials 0.000 description 5
- 229910018728 Sn—Bi Inorganic materials 0.000 description 5
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 5
- 239000000758 substrate Substances 0.000 description 5
- 229910006640 β-Sn Inorganic materials 0.000 description 5
- 229910006632 β—Sn Inorganic materials 0.000 description 5
- 229910002056 binary alloy Inorganic materials 0.000 description 4
- 229910052797 bismuth Inorganic materials 0.000 description 3
- 230000018109 developmental process Effects 0.000 description 3
- 238000004090 dissolution Methods 0.000 description 3
- 230000004907 flux Effects 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- 229910017944 Ag—Cu Inorganic materials 0.000 description 2
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 229910020888 Sn-Cu Inorganic materials 0.000 description 2
- 229910019204 Sn—Cu Inorganic materials 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 2
- 230000006399 behavior Effects 0.000 description 2
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 2
- 230000009977 dual effect Effects 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 229910052738 indium Inorganic materials 0.000 description 2
- 229910000765 intermetallic Inorganic materials 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 229910001316 Ag alloy Inorganic materials 0.000 description 1
- 229910016331 Bi—Ag Inorganic materials 0.000 description 1
- 101100136092 Drosophila melanogaster peng gene Proteins 0.000 description 1
- 241001562081 Ikeda Species 0.000 description 1
- 229910001035 Soft ferrite Inorganic materials 0.000 description 1
- 239000011157 advanced composite material Substances 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 229910000905 alloy phase Inorganic materials 0.000 description 1
- 239000003963 antioxidant agent Substances 0.000 description 1
- 230000003078 antioxidant effect Effects 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000006023 eutectic alloy Substances 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 239000005022 packaging material Substances 0.000 description 1
- 230000035882 stress Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 230000003313 weakening effect Effects 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
- B23K35/40—Making wire or rods for soldering or welding
Abstract
The method for obtaining high-toughness lead-free tin-bismuth solder by micro-alloying regulation and control microstructure is characterized in that on the basis of SnBi40 alloy, three or more micro-alloy elements are added in the form of low-melting-point or easily-dissolved intermediate alloy and metal, so that the solder alloy maintains a reticular structure; the microalloy elements are more than three of Ni, sb, in, ag, cu, and the microalloy element content is 0.05wt.% or 0.075wt.% of Ni0.05wt.% or 0.3wt.% of Sb, 0.1wt.% or 0.3wt.% of In, 0.1wt.% of Ag and 0.05wt.% of Cu. The high-toughness lead-free tin-bismuth solder prepared by the invention has excellent mechanical property and reliability, and is suitable for the low-temperature welding field of microelectronics and photovoltaic packaging.
Description
Technical Field
The invention relates to a method for obtaining high-toughness lead-free tin-bismuth solder by multi-element microalloying regulation and control microstructure, belonging to the technical field of materials for microelectronic interconnection and photovoltaic solder strip welding.
Background
With the development of lead-free, fine-pitch and multifunctional microelectronic product packaging structures, the current main solder Sn-Cu system, sn-Ag system and Sn-Ag-Cu system alloys for board-level interconnection have higher melting points, so that the problems of larger heat input, easy bending deformation after welding of printed circuit boards and substrates and the like are caused, and the use of the main solder is gradually limited. In the photovoltaic industry, along with the rapid development of heterojunction batteries, development of lead-free solders matched with a low-temperature welding process is needed. Therefore, low temperature lead-free tin-based solders will be a future trend in microelectronic interconnects and photovoltaic packaging materials.
Compared with Sn-Cu alloy, sn-Ag alloy and Sn-Ag-Cu alloy, the Sn-Bi solder has lower melting point (eutectic temperature is 138 ℃), excellent wettability and unique advantages in aspects of heat sensitive components, LED packaging and mixed interconnection. Compared with the SnBi 45-SnBi 58 solder with high Bi element content and the SnBi40 solder with high extensibility, the SnBi40 has lower melting point (Cai S, luo X, peng J, et al, analysis mechanism of various Sn-xBi alloys under tensile tests [ J ]. Advanced Composites and Hybrid Materials,2021,20 ]) compared with the SnBi 17-SnBi 25 solder with low Bi element content, so that the SnBi40 bulk alloy has better mechanical property under the condition of low-temperature welding. After the Bi content in the alloy is reduced to 40wt.%, the Bi content can be reduced to improve the toughness of the alloy under the condition of low strain rate compared with the SnBi58 eutectic alloy, but the toughness of the SnBi40 alloy is not obviously improved under the condition of high strain rate.
The tin-based solder block alloy is finally applied in the form of welding spots, and the main problems of the welding spots in the service process are as follows: (1) After the welding spot ages, intermetallic compounds (IMCs) at the interface between the welding flux and the Cu substrate grow up, and the reliability of the welding spot is reduced. According to previous studies (Belyakov S A, nishimura T, akaiwa T, et al Role of Bi, sb and In in microstructure formation and properties of Sn-0.7Cu-0.05Ni-X BGA interconnections [ C)]The growth rate of IMC In the aging process can be reduced by adding elements such as Ni, sb, in and the like into the alloy of the formula I/2019 International Conference on Electronics Packaging (ICEP) 2019; (2) In the welding process and the service process, cu element of the substrate gradually diffuses into the interface and the solder, so that an interface IMC layer is thickened, the reliability of a welding spot is reduced, trace Cu element is usually added into the solder alloy to reduce the dissolution of the Cu element, and patent CN 111182999A of Qianzhen metal industry Co Ltd mentions that the Cu-containing solder alloy can inhibit the diffusion of Cu atoms of the substrate into the interface and the solder, thereby reducing the solubility of the Cu element; (3) During the service process of the welding spot, bi element inside the welding spot gradually gathers at the Interface, the welding spot is likely to fail at the Interface because of the brittleness of Bi phase, and the addition of trace Ag element can inhibit the Bi element from gathering at the Interface (Zhang Q K, zou H F, zhang Z F. Informants of Substrate Alloying and Reflow Temperature on Bi Segregation Behaviors at Sn-Bi/Cu Interface [ J ]]Journal ofElectronic Materials,2011,40 (11): 2320-2328.) therefore, to obtain a solder joint with excellent reliability, the solder alloy needs to be multi-alloyed (CN 106216872B), but the type and content of added elements affect the alloying effect, except that Sb and In are solid-dissolved In the matrix, the rest of the elements mainly form IMC with the tin matrix, and excessive amounts of IMC cause damage to the mechanical properties of the alloy, such as slightly increased strength by adding Ag, more plastic degradation, and damage toughness (Yang T, zhao X, xiong Z, et al im)provement of microstructure and tensile properties of Sn-Bi-Ag alloy by heterogeneous nucleation ofβ-Sn on Ag 3 Sn[J]Materials Science and Engineering A,2020,785.). Therefore, the control of the alloy element type and content for multi-element microalloying is a key to improving the reliability of the welding spot.
Therefore, the reliability of the SnBi40 welding spot can be improved through multi-element microalloying. The SnBi40 binary block alloy consists of a hard tin-bismuth eutectic structure and a soft beta-Sn phase, wherein the tin-bismuth eutectic structure forms a network structure. After addition of Cu elements of different contents (x=0.1 to 1.0), the tin-bismuth eutectic structure changes from a network structure (networked structure) to an island structure (isolated structure), the strength is slightly improved, but the elongation is significantly reduced, resulting in a decrease in toughness of the alloy (Wu X, xia M, li S, et al microstructure and mechanical behavior of Sn-40Bi-xCu alloy [ J ]. Journal of Materials Science Materials in Electronics,2017,28 (20): 15708-15717.). The phenomenon of weakening of the strong plastic match resulting from this structural transformation is also observed in dual phase steels (Terda D, ikeda G, park M H, et al Reason for high strength and good ductility in dual phase steels composed of soft ferrite and hard martensite [ J ]. IOP Conference Series: materials Science and Engineering,2017, 219:01008.).
Disclosure of Invention
The invention aims to provide a method for obtaining high-toughness lead-free tin-bismuth solder by multi-element microalloying and maintaining a reticular structure, so as to improve the toughness of the tin-bismuth solder and solve the problem that the toughness of SnBi40 is not remarkably improved after the toughness is improved by two orders of magnitude under a low strain rate compared with that of SnBi 58.
The invention aims at realizing the following technical scheme:
the method for obtaining high-toughness lead-free tin-bismuth solder by micro-alloying regulation and control microstructure is characterized in that on the basis of SnBi40 alloy, three or more micro-alloy elements are added in the form of low-melting-point or easily-dissolved intermediate alloy and metal, so that the solder alloy maintains a reticular structure; the microalloy elements are more than three of Ni, sb, in, ag, cu, and the microalloy element content is 0.05wt.% or 0.075wt.% of Ni0.05wt.% or 0.3wt.% of Sb, 0.1wt.% or 0.3wt.% of In, 0.1wt.% of Ag and 0.05wt.% of Cu.
The method for obtaining the high-toughness lead-free tin-bismuth solder by micro-alloying regulation microstructure comprises the following steps:
(1) Preparing low-melting-point or easily-dissolved intermediate alloys SnNi0.05, snAg3 and SnCu10 respectively;
(2) Adding at least one of SnNi0.5, snCu10 and SnAg3 intermediate alloy and metal Sn, bi, in, sb into a lead-free titanium tin furnace for melting, covering the surface of the alloy with acrylic acid modified rosin, heating the alloy to 400+/-3 ℃, preserving heat for 30min, and casting into a mould to prepare an alloy ingot, thus obtaining the high-toughness lead-free tin-bismuth solder.
Further, the preparation method of the SnNi0.5 master alloy in the step (1) comprises the following steps: sn and Ni with the purity of 99.99wt.% are respectively added into a vacuum smelting furnace according to the mass ratio of 95.5:0.5, and the vacuum is pumped to 3 multiplied by 10 -3 Pa, charging nitrogen, heating to 1400 ℃ for melting, preserving heat for 30min, and then vacuum casting to prepare SnNi0.5 intermediate alloy, wherein the melting point of the intermediate alloy is 430 ℃;
the preparation method of the SnCu10 intermediate alloy comprises the following steps: adding Sn and Cu with the purity of 99.99wt.% into a vacuum smelting furnace according to the mass ratio of 90:10, and vacuumizing to 3X 10 -3 Pa, charging nitrogen, heating to 1100 ℃ for melting, preserving heat for 30min, and then vacuum casting to prepare the SnCu10 intermediate alloy, wherein the melting point of the intermediate alloy is 450 ℃;
the preparation method of the SnAg3 intermediate alloy comprises the following steps: respectively adding Sn and Ag with the purity of 99.99wt.% into a vacuum melting furnace according to the mass ratio of 97:3, and vacuumizing to 3X 10 -3 Pa, charging nitrogen, heating to 960 ℃ for melting, preserving heat for 30min, and then vacuum casting to prepare the SnAg3 intermediate alloy, wherein the melting point of the intermediate alloy is 235 ℃.
The invention has the following advantages:
(1) The alloy with the network structure and the island structure has the alloy strength with the network structure close to the alloy strength with the island structure under the condition that the phase area fractions of the tin-bismuth eutectic phase and the beta-Sn phase are consistent, and the network structure can greatly improve the elongation of the alloy. Compared with the eutectic structure, the high-toughness lead-free tin-bismuth solder with the network structure has the maximum tensile strength improvement rate of about 24.45 percent, the elongation rate is obviously improved, and the improvement rate can reach 73.81 percent at the highest under the condition of high strain rate; under the condition of low strain rate, compared with the tin-bismuth alloy with the eutectic structure and the island structure, the tensile strength of the tin-bismuth alloy is still kept above 40MPa, and the elongation is improved to 68.70 percent at maximum;
(2) According to the invention, the addition amount of trace alloy elements is strictly controlled, so that a net structure is formed, the obtained net structure still has net structure characteristics after the trace alloy elements are added, and the mechanical properties of the alloy are still higher than those of tin-bismuth alloy with island-shaped structures and eutectic structures;
(3) In the process of obtaining the reticular structure through multi-element microalloying, ni, sb, in, ag, cu elements with fixed content are added, so that the problems of too fast growth of IMC, bi segregation, cu dissolution and the like are solved, and the reliability of welding spots is improved;
(4) In the process of forming welding spots by using the welding flux, the melting temperature of the high-toughness lead-free tin-bismuth welding flux alloy is lower than 180 ℃, so that the low-temperature welding requirement can be met;
(5) The method of the invention firstly prepares the intermediate alloy with low melting point and easy dissolution of SnNi0.5 alloy, snAg3 and SnCu10, and then adds low melting point metal elements such as Sn, bi and the like according to the alloy proportion. Compared with the preparation mode of adding Ni, ag and Cu high-melting-point metal simple substances separately for many times, the preparation method has the advantages of simple and convenient process, high metal utilization rate and even alloy components, and the obtained lead-free tin-bismuth solder has more excellent mechanical properties.
Drawings
FIG. 1 is a graph showing comparison of fracture energy of the alloys obtained under test conditions in which the elongation rate is 3mm/min for 7 alloys of examples 1 to 4 and comparative examples 1 to 3;
FIG. 2 is a graph showing comparison of fracture energy of the alloys obtained under test conditions in which the elongation rate is 0.03mm/min for the 7 alloys of examples 1 to 4 and comparative examples 1 to 3;
FIG. 3 is a microstructure scanning electron microscope image of the alloy of example 1;
FIG. 4 is a microstructure scanning electron microscope image of the alloy of example 2;
FIG. 5 is a microstructure scanning electron microscope image of the alloy of example 3;
FIG. 6 is a microstructure scanning electron microscope image of the alloy of example 4;
FIG. 7 is a microstructure scanning electron microscope image of the alloy of comparative example 1;
FIG. 8 is a microstructure scanning electron microscope image of the alloy of comparative example 2;
FIG. 9 is a microstructure scanning electron microscope image of the alloy of comparative example 3.
FIG. 10 is a drawing of a tensile fracture Scanning Electron Microscope (SEM) with a strain rate of 0.03mm/min for the alloy of example 2;
FIG. 11 is a drawing of a tensile fracture Scanning Electron Microscope (SEM) with a strain rate of 0.03mm/min for the alloy of example 3;
FIG. 12 is a drawing of a tensile fracture Scanning Electron Microscope (SEM) with a strain rate of 0.03mm/min for the alloy of example 4;
FIG. 13 is a drawing of a tensile fracture Scanning Electron Microscope (SEM) with a strain rate of 0.03mm/min for the alloy of comparative example 3;
FIG. 14 is a DSC graph of the alloy of example 1;
FIG. 15 is a DSC graph of the alloy of example 2;
FIG. 16 is a DSC graph of the alloy of example 3;
FIG. 17 is a DSC graph of the alloy of example 4.
Detailed Description
The present invention will be described in further detail by way of examples, but the scope of the present invention is not limited to the examples.
The method for obtaining the high-toughness lead-free tin-bismuth solder by the multi-element microalloying regulation microstructure comprises the following steps of:
firstly, preparing SnNi0.5, snCu10 and SnAg3 intermediate alloy according to mass percent;
and secondly, adding at least one of SnNi0.5, snCu10 and SnAg3 intermediate alloy and metal Sn, bi, in, sb into a lead-free titanium tin furnace according to a certain alloy proportion for melting, and covering an antioxidant on the alloy surface to reduce the oxidation of the alloy surface and improve the metal utilization rate. Heating the alloy to 400 ℃, preserving heat for 30min, and casting into a die to prepare an alloy ingot.
Example 1
A SnBi40 alloy was prepared whose microstructure consisted of a hard tin-bismuth eutectic structure and a soft β -Sn phase, wherein the tin-bismuth eutectic structure forms the network structure shown in fig. 3. The preparation method of the alloy comprises the following steps: and respectively placing the d Sn metal with the purity of 99.99wt.% and the Bi metal with the purity of 99.99wt.% into a lead-free titanium tin furnace, scattering 10g of acrylic acid modified rosin on the upper layer of the metal, heating the metal to 400 ℃, preserving the heat for 30min, and casting into a mould to prepare the SnBi40 alloy ingot.
Example 2
Preparing a high-toughness lead-free tin-bismuth solder alloy, wherein the lead-free solder comprises the following components in percentage by mass: 40% of Bi, 0.05% of Ni, 0.1% of Sb, 0.1% of In, and the balance of Sn and unavoidable impurities. The microstructure of the alloy still maintains a network structure formed by the eutectic structure of tin and bismuth, as shown in figure 4. The steps for preparing the solder are as follows:
(1) Adding Sn metal with the purity of 99.99 percent and Ni metal with the purity of 99.99 percent into a vacuum smelting furnace according to the alloy proportion of 99.5:0.5, and vacuumizing to 3 multiplied by 10 -3 Pa, charging nitrogen, heating to 1400 ℃ for melting, preserving heat for 30min, and then vacuum casting to prepare SnNi0.5 intermediate alloy, wherein the melting point of the intermediate alloy is 430 ℃;
(2) And adding Sn metal with the purity of 99.99%, sb metal with the purity of 99.99%, in metal with the purity of 99.99%, bi metal with the purity of 99.99% and SnNi0.5 intermediate alloy into a lead-free titanium tin furnace according to the calculated alloy ratio for melting. And the surface of the alloy is covered with acrylic acid modified rosin to reduce oxidation of the surface of the metal and improve the utilization rate of the metal. Heating the alloy to 400 ℃, preserving heat for 30min, and casting into a die to prepare the SnBi40Ni0.05Sb0.1In0.1 lead-free solder alloy ingot.
Example 3
Preparing a high-toughness lead-free tin-bismuth solder alloy, wherein the lead-free solder comprises the following components in percentage by mass: 40% of Bi, 0.075% of Ni, 0.3% of Sb, 0.3% of In, and the balance of Sn and unavoidable impurities. Its microstructure has a pronounced network structure characteristic, as shown in fig. 5. The preparation method is the same as in example 2 except that the alloy proportions are different.
Example 4
Preparing a high-toughness lead-free tin-bismuth solder alloy, wherein the lead-free solder comprises the following components in percentage by mass: 40% of Bi, 0.1% of Sb, 0.1% of Ag, 0.1% of In, 0.05% of Cu, and the balance of Sn and unavoidable impurities. Its microstructure still has significant network characteristics as shown in fig. 6. The preparation method of the lead-free solder comprises the following steps:
(1) Adding Sn metal with the purity of 99.99 percent and Cu metal with the purity of 99.99 percent into a vacuum smelting furnace according to the alloy proportion of 90:10, and vacuumizing to 3 multiplied by 10 -3 Pa, charging nitrogen, heating to 1100 ℃ for melting, preserving heat for 30min, and then vacuum casting to prepare the SnCu10 intermediate alloy, wherein the melting point of the intermediate alloy is 450 ℃;
(2) Adding Sn metal with the purity of 99.99% and Ag metal with the purity of 99.99% into a vacuum melting furnace according to the alloy proportion of 97:3, and vacuumizing to 3 multiplied by 10 -3 Pa, charging nitrogen, heating to 960 ℃ for melting, preserving heat for 30min, and then vacuum casting to prepare SnAg3 intermediate alloy, wherein the melting point of the intermediate alloy is 235 ℃;
(3) Sn metal with the purity of 99.99 percent, sb metal with the purity of 99.99 percent, in metal with the purity of 99.99 percent, bi metal with the purity of 99.99 percent, snAg3 intermediate alloy and SnCu10 intermediate alloy are added into a lead-free titanium tin furnace according to the calculated proportion for melting. Covering the surface of the alloy with acrylic acid modified rosin, heating the alloy to 400 ℃, preserving heat for 30min, and casting into a mould to prepare SnBi40Sb0.1Ag0.1In0.1Cu0.05 lead-free solder alloy ingots.
Comparative example 1
A lead-free tin bismuth solder alloy, the lead-free solder comprising, in mass percent: 40% of Bi, 0.1% of Ni, 0.5% of Sb, 0.5% of In, and the balance of Sn and unavoidable impurities. The alloy of comparative example 1 was identical in kind, but the content of micro-alloying elements was increased, compared to the high toughness lead-free tin-bismuth solders of example 2 and example 3, resulting in the alloy not forming a significant network structure, as shown in fig. 7. The preparation was the same as in example 2, except that the content of the microalloy element was increased.
Comparative example 2
A lead-free tin bismuth solder alloy, the lead-free solder comprising, in mass percent: 40% of Bi, 0.897% of Sb, 0.374% of Ag0.2%, 0.2% of Cu, and the balance of Sn and unavoidable impurities. The total amount of microalloying elements of comparative example 2 (Sb 0.897% + ag0.374% + Cu 0.2%) is higher than in examples 2, 3 and 4. The microalloy element content is too high, resulting in the alloy failing to form a significant network structure, see fig. 8. The preparation was the same as In example 4 except that In metal was not added and the content of the microalloy element was increased.
Comparative example 3
A common lead-free tin-bismuth solder alloy comprises, in mass percent: 58% of Bi, and the balance of Sn and unavoidable impurities. The alloy structure mainly comprises a tin-bismuth eutectic structure with a non-network structure and a beta-Sn phase, and is shown in figure 9. The preparation method is the same as in example 1 except that the alloy proportions are different.
Test:
(1) The alloy ingots of examples 1 to 4 and the alloy ingots of comparative examples 1 to 3 were cut into drawn samples having a length of 16mm, a thickness of 1mm, and a gauge length of 5mm, respectively;
(2) The tensile strength and elongation of the alloys were measured on a high throughput tensile testing apparatus, and the tensile rates of the tensile tests for the above examples and comparative examples were each tested at 3mm/min and 0.03mm/min, respectively. Three tensile samples were tested for each data point and averaged as shown in table 1 and the stress strain curves of the tensile samples were integrated to obtain the alloy fracture energy as shown in fig. 1 and 2. Under high-low strain rate, the high-toughness lead-free tin-bismuth solder obtained through the multi-element microalloying regulation microstructure has the elongation higher than that of the binary alloy of SnBi40 and SnBi58, and the effective multi-element microalloying regulation forms a network structure, and the fracture energy of the corresponding alloy is obviously higher than that of other alloys with excessive microalloying elements. The tensile fracture of the alloy of examples 2, 3, 4 with the network structure is in ductile fracture mode, and the fracture morphology of the alloy of comparative example 3 is in brittle fracture mode, see fig. 10-13, because the alloy of examples 2, 3, 4 with the network structure has higher toughness than the eutectic structure alloy.
(3) Melting point of the alloy was measured on a differential thermal analyzer at a heating rate of 5 c/min and the sample was measured under argon and the results are shown in fig. 14-17. The melting point of the pentatomic tin-bismuth alloy with the net structure is not obviously increased by the multi-element microalloying regulation and control, and the numerical value of the pentatomic tin-bismuth alloy is close to that of the SnBi40 binary alloy, so that the high-toughness lead-free tin-bismuth solder with the microalloying regulation and control microstructure can be matched with the welding process of the SnBi40 binary alloy in the actual welding process, and the low-temperature welding requirement is met.
TABLE 1 comparison of mechanical Properties of solder alloys
Phase area fraction statistics:
the alloy samples of example 4 and comparative example 2 were taken 3 times each, and the area fractions of the tin-bismuth eutectic structure (white phase region) and the β -Sn phase (gray phase region) were counted using Image J software to average the values, as shown in table 2. The ratio of the area fraction of the eutectic structure of tin and bismuth to the beta-Sn phase of the alloy containing the network structure is about 0.49, which is consistent with the corresponding ratio of the alloy containing the island structure. By combining the performance data of the alloy, it can be demonstrated that compared with other SnBi40 alloys, the ratio of the area fractions of the Sn-Bi eutectic structure and the beta-Sn phase of the five-membered Sn-Bi alloy with the network structure is not changed significantly by multi-element microalloying regulation and control, but the toughness of the five-membered Sn-Bi alloy with the network structure is improved significantly, and further, the network structure performance is improved excellently under the condition of consistent phase area fractions.
TABLE 2 alloy phase area fraction statistics
The invention realizes the aim that the toughness of the SnBi40 solder can be obviously improved under the condition of high strain rate by utilizing a method of multi-element microalloying and forming a reticular structure. Under the condition of not changing the melting point and the phase fraction, the invention obtains a net structure with more uniform deformation through multi-element microalloying regulation and control, rather than forming an island structure or eutectic structure with uneven deformation. Under the condition of increasing the strain rate, the elongation of the alloy is still obviously improved compared with that of the SnBi40 binary alloy under the condition of keeping the strength performance, so that the toughness of the solder alloy is improved, and further the problem that the toughness of the SnBi40 is not obviously improved after the toughness of the alloy is improved by two orders of magnitude under the condition of increasing the strain rate compared with that of the SnBi58 under the low strain rate is solved.
The above embodiments are only some, but not all, embodiments of the present invention. Based on the SnBi40 alloy, the invention adds more than three micro-alloy elements In the form of low-melting point or easily-dissolved intermediate alloy and metal to ensure that the solder alloy maintains a net structure, wherein the micro-alloy elements are more than three of Ni, sb, in, ag, cu, and the content of the micro-alloy elements is Ni0.05wt.% or 0.075wt.%, sb0.1 wt.% or 0.3wt.%, in0.1 wt.% or 0.3wt.%, ag0.1 wt.%, and Cu0.05 wt.%, which belong to the protection scope of the invention.
The percentages stated in the present invention are mass percentages unless otherwise indicated.
The vacuum smelting furnace, the lead-free titanium tin furnace and the like are all devices in the prior art.
Claims (3)
1. The method for obtaining the high-toughness lead-free tin-bismuth solder by microalloying regulation and control microstructure is characterized in that on the basis of SnBi40 alloy, microalloying elements are added in the form of low-melting-point or easily-dissolved intermediate alloy and metal, so that the solder alloy maintains a network structure; the micro-alloy elements are more than three of Ni, sb, in, ag, cu, and the obtained high-toughness lead-free tin-bismuth solder comprises 40% of Bi, 0.05% of Ni, 0.1% of Sb, 0.1% of In, the balance of Sn and unavoidable impurities, or 40% of Bi, 0.075% of Ni, 0.3% of Sb, 0.3% of In, the balance of Sn and unavoidable impurities, or 40% of Bi, 0.1% of Sb, 0.1% of Ag, 0.1% of In, 0.05% of Cu, and the balance of Sn and unavoidable impurities.
2. The method for obtaining the high-toughness lead-free tin-bismuth solder by micro-alloying control microstructure according to claim 1, comprising the following steps:
(1) Preparing low-melting-point or easily-dissolved intermediate alloys SnNi0.05, snAg3 and SnCu10 respectively;
(2) Adding both SnCu10 and SnAg3 intermediate alloy or SnNi0.5 intermediate alloy and metal Sn, bi, in, sb into a lead-free titanium tin furnace for melting, covering the surface of the alloy with acrylic acid modified rosin, heating the alloy to 400+/-3 ℃, preserving heat for 30min, and casting into a mould to prepare an alloy ingot, thus obtaining the high-toughness lead-free tin-bismuth solder.
3. The method for obtaining the high-toughness lead-free tin-bismuth solder by the microalloying control microstructure according to claim 2, wherein the preparation method of the SnNi0.5 master alloy in the step (1) is as follows: adding 99.99wt.% Sn and Ni into a vacuum melting furnace according to the mass ratio of 95.5:0.5, and vacuumizing to 3×10 -3 Pa, charging nitrogen, heating to 1400 ℃ for melting, preserving heat for 30min, and then vacuum casting to prepare SnNi0.5 intermediate alloy, wherein the melting point of the intermediate alloy is 430 ℃;
the preparation method of the SnCu10 intermediate alloy comprises the following steps: adding 99.99wt.% Sn and Cu into a vacuum melting furnace according to a mass ratio of 90:10, and vacuumizing to 3×10 -3 Pa, charging nitrogen, heating to 1100 ℃ for melting, preserving heat for 30min, and then vacuum casting to prepare the SnCu10 intermediate alloy, wherein the melting point of the intermediate alloy is 450 ℃;
the preparation method of the SnAg3 intermediate alloy comprises the following steps: adding 99.99wt.% Sn and Ag into a vacuum melting furnace according to a mass ratio of 97:3, and vacuumizing to 3×10 -3 Pa, charging nitrogen, heating to 960 ℃ for melting, preserving heat for 30min, and then vacuum casting to prepare the SnAg3 intermediate alloy, wherein the melting point of the intermediate alloy is 235 ℃.
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