SnBi system lead-free solder for electronic packaging and preparation method of SnBi system lead-free solder

Abstract

The invention provides SnBi system lead-free solder for electronic packaging and a preparation method of the SnBi system lead-free solder, the SnBi system lead-free solder comprises, by mass, 30%-58% of Bi, 1%-15% of Sb, 0.01%-3.5% of Ag, 0.001%-2% of Cu, 0.0004%-0.8% of Ni, 0.0005%-2% of In and 35.2%-67% of Sn, the mass fraction ratio of Cu to Ni is 2.5-5: 1, and the sum of the mass percentages of Bi, Sb and Ag is 33%-60%. The SnBi-series lead-free solder has good welding wettability and fine microstructure, after packaging and welding, the expansion rate is larger than 82%, the tensile strength is larger than 60 Mpa, the cold and hot impact resistance test exceeds 500 times, the drop impact resistance exceeds 600 times, and the mechanical strength, the cold and hot cycle resistance and the drop impact resistance of the solder are improved.

Description

Technical Field

[0001] The invention relates to the technical field of electronic packaging solder, in particular to SnBi-based lead-free solder for electronic packaging and a preparation method thereof. Background Art

[0002] With the increasing demand for low-cost and low-temperature soldering processes in the electronic packaging industry, SnBi solder alloys with low cost and low melting point have become the most commonly used brazing materials in the field of low-temperature soldering. However, the SnBi solder alloy currently used in the market is prone to segregation of Bi elements at the β-Sn grain boundaries during the non-equilibrium solidification process after brazing, forming a very brittle Bi-rich phase, which seriously reduces the mechanical strength, thermal cycling performance and drop impact life of the solder joint, posing a great safety hazard to the service reliability of electronic products. Therefore, how to solve the problems of Bi segregation and brittleness of SnBi solder alloys has become a hot research topic in the industry.

[0003] At present, there are open documents such as Chinese patent CN116038175A that disclose a Ni-reinforced Sn-20Bi lead-free solder and its preparation method. Although the Bi content of the brittle property is significantly reduced, the SnBi composition deviates seriously from the eutectic point, resulting in an excessively large paste area of ​​the solid-liquid line, which easily leads to Bi segregation and pad peeling during the welding process. Chinese patent CN109894768A discloses a method for preparing a low-temperature lead-free alloy solder, which uses a very thin alloy skin to wrap the Ce raw material, effectively solving the problem that Ce is easy to oxidize and difficult to add to the alloy solder, but the expensive In is as high as 18-24%, which significantly increases the material cost of the alloy solder.

[0004] It can be seen that in the current research, there are still few research results that can comprehensively improve the comprehensive performance of SnBi solder alloys. Therefore, there is still room for improvement in SnBi lead-free solders. Summary of the invention

[0005] In view of the above technical problems, the present invention discloses a SnBi-based lead-free solder for electronic packaging and a preparation method thereof, which solves the technical problems that the current SnBi-based lead-free solder for electronic packaging is prone to Bi segregation during the brazing process, is highly brittle, and is prone to brittle fracture of solder joints after accidentally falling after welding, as well as has low resistance to cold and hot cycles. The SnBi-based lead-free solder can be used for welding products that are sensitive to temperature or not resistant to high temperatures, such as radiators and LED lighting.

[0006] To this end, the technical solution adopted by the present invention is:

[0007] SnBi lead-free solder for electronic packaging contains the following components and their mass percentages:

[0008] Bi 30%~58%, Sb 1%~15%, Ag 0.01%~3.5%, Cu 0.001%~2%, Ni0.0004%~0.8%, In 0.0005%~2%, Sn 35.2~67%, among which the mass fraction ratio of Cu and Ni is 2.5~5:1, and the sum of the mass percentages of Bi, Sb and Ag is 33%~60%.

[0009] With the above technical solution, the addition range of Bi element is 30-58%. If the Bi content is lower than 30%, the SnBi alloy composition will be far away from the eutectic point, the liquidus of the solder will be significantly increased, and the difference between the liquidus and solidus will become larger, which will easily cause the segregation of Bi in the non-equilibrium solidification process of the molten solder after brazing, and the brittleness of the alloy will increase. If the Bi content is higher than 58%, the interface reaction between Sn and the pad will consume a large amount of Sn, resulting in a large amount of Bi-rich phase in the solder joint, and the brittleness of the alloy will increase.

[0010] The addition of Sb element plays a role of solid solution strengthening in SnBi solder, thereby improving the mechanical strength and toughness of the solder alloy, and at the same time can inhibit the segregation of Bi during the welding process.

[0011] With the addition of Ag element, Ag can form Ag3Sn compound with Sn during the solidification process. A large amount of dispersed Ag3Sn compound can serve as the solidification nucleation element of β-Sn, refining the alloy structure. At the same time, the dispersed Ag3Sn compound can effectively hinder the movement of dislocations when the solder and its solder joints are subjected to mechanical loads, significantly improving the mechanical strength, thermal shock resistance and drop resistance of the SnBi solder alloy.

[0012] It should be pointed out that when the mass percentages of Bi, Sb and Ag satisfy the relationship 33%≤Bi%+Sb%+Ag%≤60%, the SnBiSb solder alloy is a eutectic or near-eutectic composition, with a small pasty area and is not easy to segregate. In addition, when this relationship is satisfied, the synergistic effect of the three elements can optimize the solid solution strengthening and dispersion strengthening effects, and at the same time, the microstructure is fine, thereby achieving the improvement of the tensile strength of the solder alloy, the improvement of the drop impact resistance and the resistance to hot and cold cycles, the suppression of Bi segregation and the improvement of the wettability of the solder, avoiding the inability to achieve these effects simultaneously within the specified content range of a single component element.

[0013] The addition of Cu element can prevent the solder alloy from dissolving the substrate during the brazing process, while refining the microstructure of the solder alloy and improving the toughness of the alloy.

[0014] The addition of Ni replaces some Cu atoms in the interface Cu6Sn5 phase during the welding process, forming a metal compound (Cu, Ni)6Sn5 phase with better toughness and thinner thickness. The mass fraction ratio of Cu and Ni is 2.5-5, and the replacement effect is the best, which significantly inhibits the growth of the interface metal compound, thereby improving the mechanical strength of the solder alloy and its solder joints. In addition, it can also inhibit the corrosion of the solder alloy to the substrate during the brazing process and improve the reliability of the solder joint.

[0015] The addition of In element can form a dispersion-strengthened In3Sn phase in the solder. During the interfacial reaction of solder melting, In atoms can replace Sn atoms in the brittle interfacial Cu6Sn5 phase to form a Cu6(Sn,In)5 phase with better toughness, thereby improving the interfacial toughness of the solder joint and avoiding interfacial brittle fracture of the solder joint.

[0016] The SnBi-based lead-free solder formulated in this technical solution has good solder wettability, excellent tensile strength, better drop impact resistance and thermal cycle resistance, and has preliminarily solved the problems of easy segregation and high brittleness of the existing SnBi-based low-temperature lead-free solder alloys. It has greatly reduced the probability of electronic component pads detaching due to accidental falling and external forces during the use and service of electronic products, as well as the problem of cracks in solder joints after a low number of thermal cycles.

[0017] As a further improvement of the present invention, the composition of the SnBi-based lead-free solder for electronic packaging also includes at least one of the elements P, Ga, Ge, Ce and Nd, and the mass percentage of each component is: P 0-0.1%, Ga 0-0.15%, Ge0-0.15%, Ce 0-0.5%, Nd 0-0.5%.

[0018] By adopting this technical solution, P, Ga, Ge, Ce and Nd elements are added as antioxidant elements. The addition of trace P, Ga, Ge, Ce and Nd elements can be enriched on the surface of the molten solder before the Sn element to form a dense oxide film, thereby improving the antioxidant performance and wettability of the solder, avoiding excessive tin slag and oxidation and blackening of the solder joints.

[0019] As a further improvement of the present invention, the SnBi lead-free solder for electronic packaging further comprises the following components and their mass percentages: P 0.005%-0.1%, Ga 0.005%-0.15%, Ge 0.005%-0.15%, Ce 0.01%-0.5%, and Nd 0.01%-0.5%.

[0020] The present invention also discloses a method for preparing the SnBi-based lead-free solder for electronic packaging as described in any one of the above, comprising the following steps:

[0021] Step S1, vacuum melting a portion of Sn weighed in proportion with P, Ce and Nd to prepare Sn-6P, Sn-5Ce and Sn-3Nd binary master alloys;

[0022] Step S2, vacuum melting Ga and Ge weighed in proportion to prepare a Ga-50Ge binary master alloy;

[0023] Step S3, melting the remaining pure Sn raw material at 400-500° C., then adding weighed Sn-5P, Sn-5Ce, Sn-2Nd and Ga-50Ge binary master alloys in sequence, stirring and keeping warm for 30-60 minutes to obtain a Sn-based main alloy;

[0024] Step S4, cooling the Sn-based main alloy obtained in step S3 to 300-400°C, then adding weighed Bi, Sb, Ag, Cu, Ni and In in sequence, keeping warm and stirring for 60-120 minutes, to obtain the SnBi-based lead-free solder for electronic packaging.

[0025] By adopting this technical solution, Sn is prepared into binary intermediate alloys with P, Ce and Nd respectively, Ga and Ge are prepared into Ga-50Ge binary intermediate alloy, and then a Sn-based main alloy is prepared. In step S4, it can be fused under low temperature conditions to obtain a Sn-Bi alloy.

[0026] As a further improvement of the present invention, the vacuum melting in step S1 is as follows: at a vacuum degree of 10 -2 ~10 -4 Pa vacuum melting furnace, melt at a temperature range of 600-750°C, stir and keep warm for 45-90 minutes.

[0027] As a further improvement of the present invention, the vacuum melting in step S2 is as follows: -2 ~10 -4 Pa vacuum melting furnace, melt at a temperature range of 800-900°C, stir and keep warm for 45-90 minutes.

[0028] As a further improvement of the present invention, in step S3, the molten material is poured or suction-cast into a mold to prepare the SnBi-based lead-free solder for electronic packaging.

[0029] The present invention also discloses the application of the SnBi-based lead-free solder for electronic packaging, which is used in low-temperature soldering of electronic packaging, and further, is suitable for soldering of products such as radiators and LED lighting that are sensitive to temperature or not resistant to high temperatures.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] First, the technical solution of the present invention adjusts the contents of the three elements Sn, Bi and Sb so that the mass percentages of the three elements satisfy 33%≤Bi%+Sb%+Ag%≤60%. Under the synergistic effect of the three elements, the solid solution strengthening and dispersion strengthening effects between the elements are maximized, and the microstructure can be refined at the same time, thereby achieving improved tensile strength of the solder, improved drop impact resistance and thermal cycle resistance, suppressed Bi segregation and improved wettability, thereby avoiding the inability to achieve these effects simultaneously within the specified content range of a single component element.

[0032] Second, the technical solution of the present invention adds and adjusts the content ratio of Cu and Ni elements so that the mass percentage of Cu and Ni is 2.5% to 5%, so that Ni atoms replace Cu atoms in the interface Cu6Sn5 phase to achieve the best effect, forming an intermetallic compound (Cu, Ni)6Sn5 phase with better toughness and thinner thickness, thereby significantly inhibiting the growth of intermetallic compounds at the interface and improving the mechanical strength of the solder alloy and its solder joints.

[0033] Third, the SnBi lead-free solder of the present invention not only has good welding wettability, but also has an expansion rate greater than 82%, a tensile strength greater than 60Mpa, and a thermal shock resistance test of more than 500 times and a drop impact resistance of more than 600 times after packaging and welding, which improves the mechanical strength, drop impact resistance and thermal cycle resistance of the solder, greatly reduces the problem of electronic component pads detaching due to external forces caused by accidental falling of electronic products during use and service, and the problem of cracks in solder joints after a low number of thermal cycles. The comprehensive performance is significantly better than the currently widely used Sn-58Bi solder, and is suitable for the field of low-temperature welding of electronic packaging.

[0034] Fourth, by adopting the method for preparing an intermediate alloy, Sn is prepared into a binary intermediate alloy with P, Ce and Nd respectively, and Ga and Ge are prepared into a Ga-50Ge binary intermediate alloy, which can reduce the loss of antioxidant elements directly added to the solder and greatly improve the effect of adding antioxidant elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a microstructure photograph of the solder alloy prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] The preferred embodiments of the present invention are described in further detail below.

[0037] Example 1

[0038] The high reliability SnBi lead-free solder for electronic packaging has the following components by weight percentage: Bi: 58%, Sb: 1%, Ag: 0.2%, Cu: 0.001%, Ni: 0.0004%, In: 0.0005%, P: 0.005%, Sn: 40.793%. The preparation method comprises the following steps:

[0039] Place the weighed Sn and P in a vacuum chamber with a vacuum degree of 10 -2 Pa vacuum melting furnace, melt at 750 ° C, stir and keep warm for 45 minutes to prepare Sn-5Pr intermediate alloy for standby use; melt weighed 40.698g Sn raw material at 400 ° C in a tin melting furnace, then add weighed 1g Sn-5P binary intermediate alloy, stir and keep warm for 30 minutes to obtain Sn-based main alloy with high oxidation resistance; cool the Sn-based main alloy to 300 ° C, add weighed 580g Bi, 10g Sb, 2g Ag, 0.01g Cu, 0.004g Ni and 0.005g In in sequence, stir and keep warm for 60 minutes, and finally pour or suck-cast into a mold to prepare 1000g Sn-Bi series alloy, that is, the SnBi series lead-free solder for electronic packaging.

[0040] Figure 1 This is a metallographic structure photograph of the solder alloy prepared in this embodiment. It can be observed that the solder alloy in this embodiment has a fine structure.

[0041] Example 2

[0042] The high reliability SnBi lead-free solder for electronic packaging has the following components by weight percentage: Bi: 43%, Sb: 3%, Ag: 0.01%, Cu: 0.005%, Ni: 0.001%, In: 1%, Ga: 0.15%, Ge: 0.15%, Ce: 0.05%, Sn: 52.634%. The preparation method comprises the following steps:

[0043] Place the weighed Sn and Ce in a vacuum chamber with a vacuum degree of 10 -4 Pa vacuum melting furnace at 600 ° C, stirring and keeping warm for 90 minutes to prepare Sn-5Pr intermediate alloy for use; Ga and Ge weighed in proportion are placed in a vacuum furnace with a vacuum degree of 10 -2The invention discloses a method for preparing a Ga-50Ge binary master alloy by melting a weighed Sn raw material in a vacuum melting furnace of 500°C at 800°C, stirring and keeping the mixture warm for 45 minutes, and preparing a Ga-50Ge binary master alloy for standby use; melting a weighed Sn raw material of 516.84g at 500°C in a tin melting furnace, and then sequentially adding weighed Sn-5Ce and 3g Ga-50Ge binary master alloy, stirring and keeping the mixture warm for 60 minutes, and obtaining a Sn-based main alloy with high oxidation resistance; cooling the Sn-based main alloy to 400°C, sequentially adding weighed 430g Bi, 30g Sb, 0.1g Ag, 0.05g Cu, 0.01g Ni and 10g In, stirring and keeping the mixture warm for 120 minutes, and finally pouring or suction casting the mixture into a mold to prepare a 1000g Sn-Bi series alloy, namely the SnBi series lead-free solder for electronic packaging.

[0044] Example 3

[0045] The high reliability SnBi lead-free solder for electronic packaging has the following components by weight percentage: Bi: 44%, Sb: 15%, Ag: 1%, Cu: 1%, Ni: 0.4%, In: 0.2%, P: 0.1%, Ga: 0.005%, Ge: 0.005%, Nd: 0.1%, Sn: 38.19%. The preparation method comprises the following steps:

[0046] Place the weighed Sn, P and Nd in a vacuum chamber with a vacuum degree of 10 -3 Pa vacuum melting furnace at 650 ° C, stirring and keeping warm for 60 minutes, respectively preparing Sn-5P and Sn-2Nd intermediate alloys for use; weighed Ga and Ge in proportion are placed in a vacuum furnace with a vacuum degree of 10 -4 The invention discloses a method for preparing a Ga-50Ge binary master alloy by melting a weighed Sn raw material in a vacuum melting furnace of 10000 ℃ at 900 ℃, stirring and keeping the mixture warm for 90 minutes, and preparing a Ga-50Ge binary master alloy for standby use; melting a weighed Sn raw material of 313.9g at 500 ℃ in a tin melting furnace, and then sequentially adding weighed Sn-5P, 50gSn-2Nd and 0.1gGa-50Ge binary master alloy, stirring and keeping the mixture warm for 60 minutes, and obtaining a Sn-based main alloy with high oxidation resistance; cooling the Sn-based main alloy to 400 ℃, sequentially adding weighed 440gBi, 150gSb, 10gAg, 10gCu, 4gNi and 2gIn, stirring and keeping the mixture warm for 120 minutes, and finally pouring or suction casting the mixture into a mold to prepare a 1000gSn-Bi series alloy, namely the SnBi series lead-free solder for electronic packaging.

[0047] Example 4

[0048] The high reliability SnBi lead-free solder for electronic packaging has the following components by weight percentage: Bi: 30%, Sb: 1%, Ag: 2%, Cu: 0.2%, Ni: 0.08%, In: 2%, P: 0.03%, Ga: 0.1%, Ge: 0.1%, Ce: 0.5%, Nd: 0.01%, Sn: 63.98%. The preparation method comprises the following steps:

[0049] Place the weighed Sn and P, Ce, and Nd in a vacuum chamber with a vacuum degree of 10 -3 Pa vacuum melting furnace at 700 ° C, stirring and keeping warm for 70 minutes, respectively, to prepare Sn-5P, Sn-5Ce and Sn-2Nd intermediate alloys for use; Ga and Ge weighed in proportion are placed in a vacuum furnace with a vacuum degree of 10 -3 The invention discloses a method for preparing a Sn-based main alloy comprising the steps of: melting a weighed Sn raw material of 534.2 g Sn at 460° C. in a vacuum melting furnace of 1000 μm and stirring and keeping the mixture warm for 60 minutes; and then adding weighed Sn-5P, 100 g Sn-5Ce, 5 g Sn-2Nd and 2 g Ga-50Ge binary master alloys in turn, stirring and keeping the mixture warm for 60 minutes to obtain a Sn-based main alloy with high oxidation resistance; cooling the Sn-based main alloy to 390° C., adding weighed 300 g Bi, 10 g Sb, 20 g Ag, 2 g Cu, 0.8 g Ni and 20 g In in turn, stirring and keeping the mixture warm for 80 minutes, and finally pouring or suction casting the Sn-based main alloy into a mold to prepare a 1000 g Sn-Bi series alloy, namely the reliable SnBi series lead-free solder for electronic packaging.

[0050] Example 5

[0051] The high reliability SnBi lead-free solder for electronic packaging has the following components by weight percentage: Bi: 54%, Sb: 2%, Ag: 3.5%, Cu: 2%, Ni: 0.8%, In: 1.5%, Ce: 0.01%, Nd: 0.5%, Sn: 35.69%. The preparation method comprises the following steps:

[0052] Place the weighed Sn, Ce and Nd in a vacuum chamber with a vacuum degree of 10 -3Pa vacuum melting furnace, melt at 700 ° C, stir and keep warm for 60 minutes, respectively prepare Sn-5Ce and Sn-2Nd intermediate alloys for standby use; melt weighed 110g Sn raw material at 450 ° C in a tin melting furnace, then add weighed 2g Sn-5Ce and 250g Sn-2Nd binary intermediate alloys in turn, stir and keep warm for 50 minutes, and obtain a Sn-based main alloy with high oxidation resistance; cool the Sn-based main alloy to 350 ° C, add weighed 540g Bi, 20g Sb, 35g Ag, 30g Cu, 12g Ni and 15g In in turn, stir and keep warm for 80 minutes, and finally pour or suck-cast into a mold to prepare 1000g Sn-Bi series alloy, that is, the SnBi series lead-free solder for electronic packaging.

[0053] Example 6

[0054] The high reliability SnBi lead-free solder for electronic packaging has the following components by weight percentage: Bi: 58%, Sb: 1%, Ag: 1%, Cu: 2%, Ni: 0.8%, In: 2%, Sn: 35.2%. The preparation method comprises the following steps:

[0055] In a tin melting furnace, 352g Sn raw material is melted at 400°C, and weighed 580g Bi, 10g Sb, 10g Ag, 20g Cu, 8g Ni and 20g In are added in sequence, stirred and kept warm for 60 minutes, and finally poured or suction-casted into a mold to prepare 1000g Sn-Bi alloy, i.e., the SnBi lead-free solder for electronic packaging.

[0056] Example 7

[0057] The high reliability SnBi lead-free solder for electronic packaging has the following components by weight percentage: Bi: 30%, Sb: 2.99%, Ag: 0.01%, Cu: 0.001%, Ni: 0.0004%, In: 0.0005%, Sn: 66.9981%. The preparation method comprises the following steps:

[0058] In a tin melting furnace, 669.981g Sn raw material is melted at 400°C, and 300g Bi, 29.9g Sb, 0.1g Ag, 0.01g Cu, 0.004g Ni and 0.005g In are added in sequence, stirred and kept warm for 120 minutes, and finally poured or suction-casted into a mold to prepare 1000g Sn-Bi alloy, i.e., the SnBi lead-free solder for electronic packaging.

[0059] Example 8

[0060] The high reliability SnBi lead-free solder for electronic packaging has the following components by weight percentage: Bi: 40%, Sb: 15%, Ag: 3.5%, Cu: 0.75%, Ni: 0.25%, In: 1%, Sn: 39.5%. The preparation method comprises the following steps:

[0061] In a tin melting furnace, 395g Sn raw material is melted at 400°C, and weighed 400g Bi, 150g Sb, 35g Ag, 7.5g Cu, 2.5g Ni and 10g In are added in sequence, stirred and kept warm for 80 minutes, and finally poured or suction-casted into a mold to prepare 1000g Sn-Bi alloy, i.e., the SnBi lead-free solder for electronic packaging.

[0062] Comparative Example 1

[0063] The raw materials are composed of Bi: 58%, Sn: 42% by weight. The preparation method comprises the following steps:

[0064] In a tin melting furnace, 420 g of Sn raw material was melted at 400°C, and then 580 g of Bi was added and stirred and kept warm for 60 minutes to obtain a Sn-Bi alloy solder.

[0065] Comparative Example 2

[0066] The raw materials are composed of Bi: 58%, Sb: 5%, Ag: 3.5%, Cu: 2%, Ni: 0.8%, In: 1%, Sn: 29.7% by weight. The preparation method comprises the following steps:

[0067] In a tin melting furnace, melt 297g Sn raw material at 400°C, add weighed 580g Bi, 50g Sb, 35g Ag, 20g Cu, 8g Ni and 10g In in sequence, stir and keep warm for 80 minutes, and finally pour or suction cast into a mold to prepare 1000g Sn-Bi alloy solder.

[0068] Comparative Example 3

[0069] The raw materials are composed of Bi: 30%, Sb: 1%, Ag: 0.5%, Cu: 2%, Ni: 0.8%, In: 1%, Sn: 64.7% by weight. The preparation method comprises the following steps:

[0070] In a tin melting furnace, melt 647g Sn raw material at 400°C, add weighed 300g Bi, 10g Sb, 5g Ag, 20g Cu, 8g Ni and 10g In in sequence, stir and keep warm for 80 minutes, and finally pour or suction cast into a mold to prepare 1000g Sn-Bi alloy solder.

[0071] Comparative Example 4

[0072] The raw materials are composed of Bi: 33%, Sb: 1%, Ag: 3.5%, Cu: 1.8%, Ni: 0.8%, In: 1%, Sn: 58.9% by weight. The preparation method comprises the following steps:

[0073] In a tin melting furnace, melt 589g Sn raw material at 400°C, add weighed 330g Bi, 10g Sb, 35g Ag, 18g Cu, 8g Ni and 10g In in sequence, stir and keep warm for 80 minutes, and finally pour or suction cast into a mold to prepare 1000g Sn-Bi alloy solder.

[0074] Comparative Example 5

[0075] The raw materials are composed of Bi: 33%, Sb: 1%, Ag: 3.5%, Cu: 2%, Ni: 0.3%, In: 1%, Sn: 59.2% by weight. The preparation method comprises the following steps:

[0076] In a tin melting furnace, melt 592g Sn raw material at 400°C, add weighed 330g Bi, 10g Sb, 35g Ag, 20g Cu, 3g Ni and 10g In in sequence, stir and keep warm for 80 minutes, and finally pour or suction cast into a mold to prepare 1000g Sn-Bi alloy solder.

[0077] Table 1 shows the solder alloy compositions of Examples 1 to 8 and Comparative Examples 1 to 5, and Table 2 shows the performance comparison of the expansion rate, tensile strength, shear strength and drop impact resistance of the solder alloys of Examples 1 to 5 and Comparative Examples 1 to 5.

[0078] Table 1 Solder alloy compositions of Examples 1 to 8 and Comparative Examples 1 to 5

[0079] Solder Alloy Sn-Bi solder alloy composition Example 1 Sn-58Bi-1Sb-0.2Ag-0.001Cu-0.0004Ni-0.0005In-0.005P Example 2 Sn-43Bi-3Sb-0.01Ag-0.005Cu-0.001Ni-1In-0.15Ga-0.15Ge-0.05Ce Example 3 Sn-44Bi-15Sb-1Ag-1Cu-0.4Ni-0.2In-0.1P-0.005Ga-0.005Ge-0.1Nd Example 4 Sn-30Bi-1Sb-2Ag-0.2Cu-0.08Ni-2In-0.03P-0.1Ga-0.1Ge-0.5Ce-0.01Nd Example 5 Sn-54Bi-2Sb-3.5Ag-2Cu-0.8Ni-1.5In-0.01Ce-0.5Nd Example 6 Sn-58Bi-1Sb-1Ag-2Cu-0.8Ni-2In Example 7 Sn-30Bi-2.99Sb-0.01Ag-0.001Cu-0.0004Ni-0.0005In Example 8 Sn-40Bi-15Sb-3.5Ag-0.75Cu-0.25Ni-1In Comparative Example 1 Sn-58Bi Comparative Example 2 Sn-58Bi-5Sb-3.5Ag-2Cu-0.8Ni-1In Comparative Example 3 Sn-30Bi-1Sb-0.5Ag-2Cu-0.8Ni-1In Comparative Example 4 Sn-33Bi-1Sb-3.5Ag-1.8Cu-0.8Ni-1In Comparative Example 5 Sn-33Bi-1Sb-3.5Ag-2Cu-0.3Ni-1In

[0080] Table 2 Evaluation results of solder alloys of Examples 1 to 8 and Comparative Examples 1 to 5

[0081] Solder Alloy Expansion rate / % Tensile strength / MPa Resistance to thermal shock Anti-drop impact times Example 1 82 64 534 618 Example 2 85 68 552 665 Example 3 87 80 574 610 Example 4 86 73 587 636 Example 5 84 65 560 685 Example 6 83 62 522 609 Example 7 83 64 536 612 Example 8 82 61 541 622 Comparative Example 1 80 48 355 440 Comparative Example 2 82 50 408 456 Comparative Example 3 78 46 384 432 Comparative Example 4 79 45 390 465 Comparative Example 5 81 47 413 471

[0082] As shown in Table 1, under the same test conditions, the SnBi lead-free solder for electronic packaging of the embodiment of the present invention has an expansion rate greater than 82%, a tensile strength greater than 60Mpa, and a thermal shock resistance test and a drop impact resistance number far greater than the commonly used Sn-58Bi eutectic solder. It can be seen that the SnBi lead-free solder for electronic packaging of the present invention has higher wettability, mechanical strength, thermal shock resistance number and drop impact resistance number, and can be used for the welding of electronic products that are not resistant to high temperatures and are sensitive to temperature, such as LEDs and radiators.

[0083] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. SnBi-based lead-free solder for electronic packaging, characterized in that: The ingredients and their mass percentages are: Bi 30%~58%, Sb 1%~15%, Ag 0.01%~3.5%, Cu 0.001%~2%, Ni 0.0004%~0.8%, In0.0005%~2%, Sn 35.2~67%, wherein the mass fraction ratio of Cu and Ni is 2.5~5:1, and the sum of the mass percentages of Bi, Sb and Ag is 33%~60%.

2. The SnBi-based lead-free solder for electronic packaging according to claim 1, characterized in that: The SnBi lead-free solder for electronic packaging also contains at least one of P, Ga, Ge, Ce and Nd elements, and the mass percentage of each component is: P 0-0.1%, Ga 0-0.15%, Ge 0-0.15%, Ce 0-0.5%, Nd 0-0.5%.

3. The SnBi-based lead-free solder for electronic packaging according to claim 2, characterized in that: The SnBi lead-free solder for electronic packaging further comprises the following components and their mass percentages: P 0.005%-0.1%, Ga 0.005%-0.15%, Ge 0.005%-0.15%, Ce 0.01%-0.5%, and Nd 0.01%-0.5%.

4. The method for preparing SnBi-based lead-free solder for electronic packaging according to any one of claims 2 to 3, characterized in that: The steps include: Step S1, vacuum melting a portion of Sn weighed in proportion with P, Ce and Nd to prepare Sn-6P, Sn-5Ce and Sn-3Nd binary master alloys; Step S2, vacuum melting Ga and Ge weighed in proportion to prepare a Ga-50Ge binary master alloy; Step S3, melting the remaining pure Sn raw material at 400-500° C., then adding weighed Sn-5P, Sn-5Ce, Sn-2Nd and Ga-50Ge binary master alloys in sequence, stirring and keeping warm for 30-60 minutes to obtain a Sn-based main alloy; Step S4, cooling the Sn-based main alloy obtained in step S3 to 300-400°C, then adding weighed Bi, Sb, Ag, Cu, Ni and In in sequence, keeping warm and stirring for 60-120 minutes, to obtain the SnBi-based lead-free solder for electronic packaging.

5. The method for preparing SnBi lead-free solder for electronic packaging according to claim 4, characterized in that: The vacuum melting in step S1 is as follows: -2 ~10 -4 Pa vacuum melting furnace, melt at a temperature range of 600-750°C, stir and keep warm for 45-90 minutes.

6. The method for preparing SnBi lead-free solder for electronic packaging according to claim 4, characterized in that: The vacuum melting in step S2 is as follows: -2 ~10 -4 Pa vacuum melting furnace, melt at a temperature range of 800-900°C, stir and keep warm for 45-90 minutes.

7. The method for preparing SnBi lead-free solder for electronic packaging according to claim 4, characterized in that: In step S3, the molten material is poured or suction-cast into a mold to prepare the SnBi-based lead-free solder for electronic packaging.

8. The use of SnBi lead-free solder for electronic packaging according to any one of claims 1 to 3, characterized in that: Used in low temperature welding of electronic packaging.

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