SnBiSb series low-temperature lead-free solder and its preparation method

Abstract

A SnBiSb series low-temperature lead-free solder and a preparation method thereof, which belongs to the technical field of low-temperature soldering. The lead-free solder includes by weight the following composition: 32.8-56.5% of Bi, 0.7-2.2% of Sb, with the remainder being Sn, wherein the weight percentages of Bi and Sb satisfy a relationship of b=0.006a2−0.672a+19.61+c, wherein the symbol a represents the weight percentage of Bi, the symbol b represents the weight percentage of Sb, and the range of c is −1.85≤c≤1.85. The solder alloy has a peritectic or near peritectic structure with a low melting point, and has an excellent mechanical performance and reliability, and applicable to the field of low-temperature soldering.

Claims

1. A SnBiSb series lead-free solder, comprising: by weight 32.8%-45% of Bi, 0.7%-2.2% of Sb, 0.01%-2.5% of Ce, 0.05%-2.0% of Ti, and Sn, wherein a weight percentage of Bi and a weight percentage of Sb satisfy a relationship of b=0.006a.sup.20.672a+19.61+c, wherein a is the weight percentage of Bi, b is the weight percentage of Sb, and a range of c is −1.85≤c≤1.85, and wherein the SnBiSb series lead-fee solder does not contain Mg, and the SnBiSb series lead-free solder has peritectic or near-peritectic structure, and a tensile strength of 92.43 to 108.05 MPa.

2. The SnBiSb series lead-free solder according to claim 1, wherein the Bi is 41.8%-45% by weight and the Sb is 0.7%-2.0% by weight.

3. The SnBiSb series lead-free solder according to claim 1, wherein the range of c is 0.008≤c≤1.5.

4. The SnBiSb series lead-free solder according to claim 1, wherein the SnBiSb series lead-free solder further comprises one or more metal elements selected from the group consisting of Cu, Ni, Ag, and In.

5. The SnBiSb series lead-free solder according to claim 4, wherein the SnBiSb series lead-free solder comprises: 0.01%-0.8% of Cu by weight, 0.03%-1.5% of Ni by weight, 0.1%-1% of Ag by weight, 0.05%-1% of In by weight.

6. A preparation method for the SnBiSb series lead-free solder of claim 1, comprising the following steps: step (1) preparing a master alloy; master alloy comprises Bi-Sb, or Bi-Sb and one or more selected from the group consisting of Sn-Ce, Sn-Ti, Sn-Cu, Sn-Ni and Sn-Ag; step (2) melting the master alloy and metals Sn and Bi, or melting the master alloy, the metals Sn and Bi and one or more selected from the group consisting of Sn-Ce, Sn-Ti, Sn-Cu, Sn-Ni, Sn-Ag and In in a melting furnace at an alloy ratio; covering a surface of an alloy with an anti-oxidation solvent, heating the alloy to a temperature of 250° C.-500° C.; maintaining the temperature for 10 minutes-20 minutes; removing oxide slag on the surface; and pouring into a mold to obtain an alloy ingot of the SnBiSb series lead-free solder, and wherein the lead-fee solder does not contain Mg.

7. The preparation method for the SnBiSb series lead-free solder according to claim 6, wherein a method for preparing the master alloy of Bi-Sb comprises the following steps: placing separately Bi and Sb having a purity of 99.99 wt.% into a vacuum melting furnace at the alloy ratio; performing vacuum treatment to 1×10.sup.−2 to 1×10.sup.−1 Pa; charging nitrogen; heating a mixture of Bi and Sb to a temperature of 650° C:-700° C. to be melted, and performing electromagnetic stirring at the same time to make a composition of Bi and Sb uniform; and performing vacuum casting, so as to obtain the master alloy of Bi-Sb; and a method for preparing the master alloys of Sn-Ce, Sn-Ti, Sn-Cu, Sn-Ni, and Sn-Ag comprises the following steps: placing separately Sn and Ce, or Sn and Ti, or Sn and Cu, or Sn and Ni, or Sn and Ag having a purity of 99.99 wt.% into the vacuum melting furnace at the alloy ratio; performing vacuum treatment to 1×10.sup.−2 to 1×10.sup.−1 Pa; charging nitrogen; heating separately a mixture of Sn and Ce, or Sn and Ti, or Sn and Cu, or Sn and Ni, or Sn and Ag to a temperature of 400° C.-1650° C. to be melted, and performing electromagnetic stirring at the same time to make a composition of Sn and Ce, or Sn and Ti, or Sn and Cu, or Sn and Ni, or Sn and Ag uniform; and then performing vacuum casting, so as to obtain the master alloy of Bi-Sb, Sn-Ce, Sn-Ti, Sn-Cu, Sn-Ni or Sn-Ag.

8. The preparation method for the SriBiSb series lead-free solder according to claim 6, wherein the anti-oxidation solvent is rosin or KCL-LiCl fused salt.

9. A welding spot or welding seam formed by using the SnBiSb series lead-free solder of claim 1.

10. The welding spot or welding seam according to claim 9, wherein the welding spot or welding seam is formed by using solder paste reflux, wave soldering or heat fusion welding, wherein the heat fusion welding comprises a preformed soldering lug, soldering strip, soldering ball and soldering wire, and the alloy of the welding spot or welding seam comprises by weight the following composition: 32.8%-45% of Bi, 0.7%-2.2% of Sb, 0.01%-1.5% of Cu, 0.03%-2.0% of Ni, Ag 0.1%-1.5% of Ag, 0.01%-2.5% of Ce, 0.05%-2.0% of Ti, 0%-1% of In, with the remainder being Sn.

11. The preparation method for the SnBiSb series lead-free solder according to claim 6, wherein the Bi is 41.8%-45% by weight and the Sb is 0.7%-2.0% by weight.

12. The preparation method for the SnBiSb series lead-free solder according to claim 6, wherein the range of c is 0.008≤c≤1.5.

13. The preparation method for the SriBiSb series lead-free solder according to claim 6, therein the SriBiSb series lead-free solder further comprises one or more metal elements selected from the group consisting of Cu, Ni, Ag and In.

14. The preparation method for the SnBiSb series lead-free solder according to claim 13, wherein the SnBiSb series lead-free solder comprises: 0.01%-0.8% of Cu by weight, 0.03%-1.5% of Ni by weight, 0.1%-1% of Ag by weight, 0.05%-1% of In by weight.

15. The preparation method for the SnBiSb series lead-free solder according to claim 6, wherein a method for preparing the master alloy of Bi-Sb comprises the following steps: placing separately Bi and Sb having a purity of 99.99 wt% into a vacuum melting furnace at the alloy ratio; performing vacuum treatment to 1×10.sup.−2 to 1×10.sup.−1 Pa; charging nitrogen; heating a mixture of Bi and Sb to a temperature of 650° C.-700° C. to be melted, and performing electromagnetic stirring at the same time to make a composition of Bi and Sb uniform; and performing vacuum casting, so as to obtain the master alloy of Bi-Sb; and a method for preparing the master alloys of Sn-Ce, Sn-Ti, Sn-Cu, Sn-Ni, and Sn-Ag comprises the following steps: placing separately Sn and Ce, or Sn and Ti, or Sn and Cu, or Sn and Ni, or Sn and Ag having a purity of 99.99 wt.% into the vacuum melting furnace at the alloy ratio; performing vacuum treatment to 1×10.sup.−2 to 1×10.sup.−1 Pa; charging nitrogen; heating separately a mixture of Sn and Ce, or Sn and Ti, or Sn and Cu, or Sn and Ni, or Sn and Ag to a temperature of 400° C.-1650° C. to be melted, and performing electromagnetic stirring at the same time to make a composition of Sn and Ce, or Sn and Ti, or Sn and Cu, or Sn and Ni, or Sn and Ag uniform; and then performing vacuum casting, so as to obtain the master alloy of Bi-Sb, Sn-Ce, Sn-Ti, Sn-Cu, Sn-Ni or Sn-Ag.

16. The preparation method for the SnBiSb series lead-free solder according to claim 6, wherein the anti-oxidation solvent is rosin or KCL-LiCl fused salt.

17. The preparation method for the SnBiSb series lead-free solder according to claim 9, wherein the Bi is 41.8%-45% by weight and the Sb is 0.7%-2.0% by weight.

18. The preparation method for the SnBiSb series lead-free solder according to claim 9, wherein the range of c is 0.008<c<1.5.

19. The preparation method for the SnBiSb series lead-free solder according to claim 9, wherein the SnBiSb series lead-free solder further comprises one or more metal elements selected from the group consisting of Cu, Ni, Ag and In.

20. The preparation method for the SnBiSb series lead-free solder according to claim 19, wherein the SnBiSb series lead-free solder comprises: 0.01%-0.8% of Cu by weight, 0.03%-1.5% of Ni by weight, 0.1%-1% of Ag by weight, 0.05%-1% of In by weight.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an SEM image of the structure of the solder alloy prepared according to example 2 of the present invention.

(2) FIG. 2 shows the DSC test result of the solder alloy prepared according to example 10 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(3) A lead-free solder alloy according to the present invention comprises Bi, Sb and Sn, of which the composition by weight is: 32.8-56.5% of Bi, 0.7-2.2% of Sb, with the remainder being Sn, wherein the weight percentages of Bi and Sb in the solder alloy satisfy a relationship of b=0.006a2−0.672a+19.61+c, wherein the symbol a represents the weight percentage of Bi, the symbol b represents the weight percentage of Sb, and the range of c is −1.85≤c≤1.85. The range of c is preferably −1.85≤c≤−0.001 or 0.001≤c≤1.85 or −1.5≤c≤−0.005 or 0.005≤c≤1.5 or −1.5≤c≤−0.008 or 0.008≤c≤1.5, more preferably −1.0≤c≤−0.05 or 0.05≤c≤1.0 or −0.5≤c≤−0.05 or 0.05≤c≤0.5.

(4) A preparation method for the alloy includes the following steps: (1) preparing a Bi—Sb master alloy; (2) preparing separately master alloys of Sn—Ce, Sn—Ti, Sn—Cu, Sn—Ni, and Sn—Ag according to a certain ratio; (3) melting in a melting furnace the Bi—Sb master alloy, metals Sn and Bi, and/or the master alloys prepared in the second step, and/or metal In according to a certain alloy ratio, covering a surface of the alloy with an anti-oxidation solvent, heating to a temperature of 200-500° C., maintaining the temperature for 10 to 20 minutes, removing oxide slag on the surface, pouring into a mold to obtain an ingot of SnBiSb series lead-free solder alloy.

Example 1

(5) A lead-free solder alloy used in the field of low-temperature soldering is provided, the lead-free solder alloy comprising by weight: 41.8% of Bi, 2.1% of Sb, with the remainder being Sn and inevitable impurities, wherein the lead-free solder alloy has a near peritectic structure, with a melting point of the alloy being 142.9-150.8° C. A preparation method for the lead-free solder alloy includes the following steps:

(6) 1) placing metals Bi and Sb having a purity of 99.99 wt. % into a vacuum melting furnace at an alloy ratio of 80:20 by weight, performing vacuum treatment to 1×10.sup.−1 Pa, charging nitrogen and then heating the alloy to a temperature of 650-700° C. to be melted, performing electromagnetic stirring at the same time to make the alloy composition uniform, and then performing vacuum casting, so as to obtain a Bi—Sb20 master alloy;

(7) 2) melting the prepared Bi—Sb master alloy together with metals Sn and Bi at an alloy ratio in the melting furnace, covering a surface of the alloy with an anti-oxidation solvent, which can be selected from rosin or LiCl-KCL fused salt, heating the alloy to a temperature of 250° C., maintaining the temperature for 10 minutes, removing oxide slag on the surface, pouring into a mold to obtain an ingot of SnBi41.8Sb2.1 lead-free solder alloy.

Example 2

(8) A lead-free solder alloy used in the field of low-temperature soldering is provided, the lead-free solder alloy comprising by weight: 50% of Bi, 1.0% of Sb, with the remainder being Sn and inevitable impurities, wherein the lead-free solder alloy has a peritectic structure, with a melting point being 140.6-143.8° C. The lead-free solder alloy is prepared in the same manner as in Example 1, except that the alloy ratio is different.

(9) FIG. 1 shows an SEM image of the structure of the solder alloy prepared in this example. It can be seen from the figure that the alloy has a peritectic structure.

Example 3

(10) A lead-free solder alloy used in the field of low-temperature soldering is provided, the lead-free solder alloy comprising by weight: 55% of Bi, 0.8% of Sb, 0.01% of Ce, 0.05% of Ti, with the remainder being Sn and inevitable impurities, wherein the lead-free solder alloy has a near peritectic structure, with a melting point being 142.9-146.2° C. A preparation method for the lead-free solder alloy includes the following steps:

(11) 1) placing metals Bi and Sb having a purity of 99.99 wt. % into a vacuum melting furnace at an alloy ratio of 80:20 by weight, performing vacuum treatment to 1×10.sup.−2 Pa, charging nitrogen and then heating the alloy to a temperature of 650-700° C. to be melted, performing electromagnetic stirring at the same time to make the alloy composition uniform, and then performing vacuum casting, so as to obtain a Bi—Sb20 master alloy;

(12) 2) placing separately metals Sn and Ce, Sn and Ti having a purity of 99.99 wt. % into a vacuum melting furnace at a certain alloy ratio, performing vacuum treatment to 1×10.sup.−2 Pa, charging nitrogen and then heating separately the alloys to temperatures of 690-780° C. and 1550-1650° C. to be melted, performing electromagnetic stirring at the same time to make the alloy composition uniform, and then performing vacuum casting, so as to obtain separately Sn—Ce10 and Sn—Ti20 master alloys;

(13) 3) melting the prepared Bi—Sb, Sn—Ce, and Sn—Ti master alloys together with metals Sn and Bi at an alloy ratio in the melting furnace, covering a surface of the alloy with an anti-oxidation solvent (rosin or KCL-LiCl fused salt), heating the alloy to a temperature of 400° C., maintaining the temperature for 15 minutes, removing oxide slag on the surface, pouring into a mold to obtain an ingot of SnBi55Sb0.8Ce0.01Ti0.05 lead-free solder alloy.

Example 4

(14) A lead-free solder alloy used in the field of low-temperature soldering is provided, the lead-free solder alloy comprising by weight: 44.2% of Bi, 1.7% of Sb, 0.05% of Ce, 0.1% of Ti, with the remainder being Sn and inevitable impurities, wherein the lead-free solder alloy has a near peritectic structure, with a melting point of the alloy being 145.2-150.5° C. The lead-free solder alloy is prepared in the same manner as in Example 3, except that the alloy ratio is different.

Example 5

(15) A lead-free solder alloy used in the field of low-temperature soldering is provided, the lead-free solder alloy comprising by weight: 44.2% of Bi, 1.7% of Sb, 0.1% of Ce, 0.8% of Ti, 0.01% of Cu, 0.03% of Ni, with the remainder being Sn and inevitable impurities, wherein the lead-free solder alloy has a near peritectic structure, with a melting point of the alloy being 147.5-152.9° C. A preparation method for the lead-free solder alloy includes the following steps:

(16) 1) placing metals Bi and Sb having a purity of 99.99 wt. % into a vacuum melting furnace at an alloy ratio of 80:20 by weight, performing vacuum treatment to 1×10.sup.−2 Pa, charging nitrogen and then heating the alloy to a temperature of 650-700° C. to be melted, performing electromagnetic stirring at the same time to make the alloy composition uniform, and then performing vacuum casting, so as to obtain a Bi—Sb20 master alloy;

(17) 2) placing separately metals Sn and Ce, Sn and Ti, Sn and Cu, Sn and Ni having a purity of 99.99 wt. % into a vacuum melting furnace at a certain alloy ratio, performing vacuum treatment to 1×10.sup.−2 Pa, charging nitrogen and then heating separately the alloys to temperatures of 690-780° C., 1550-1650° C., 750-820° C., and 900-1100° C. to be melted, performing electromagnetic stirring at the same time to make the alloy composition uniform, and then performing vacuum casting, so as to obtain separately Sn—Ce10, Sn—Ti20, Sn—Cu20, Sn—Ni5 master alloys;

(18) 3) melting the prepared Bi—Sb, Sn—Ce, Sn—Ti, Sn—Cu, Sn—Ni master alloys together with metals Sn and Bi at an alloy ratio in the melting furnace, covering a surface of the alloy with an anti-oxidation solvent (rosin or KCL-LiCl fused salt), heating the alloy to a temperature of 450° C., maintaining the temperature for 15 minutes, removing oxide slag on the surface, pouring into a mold to obtain an ingot of SnBi44.2Sb1.7Ce0.1Ti0.8Cu0.01Ni0.03 lead-free solder alloy.

Example 6

(19) A lead-free solder alloy used in the field of low-temperature soldering is provided, the lead-free solder alloy comprising by weight: 56.5% of Bi, 0.7% of Sb, 0.5% of Ce, 1.0% of Ti, 0.03% of Cu, 0.07% of Ni, 0.1% of Ag, with the remainder being Sn and inevitable impurities, wherein the lead-free solder alloy has a near peritectic structure, with a melting point of the alloy being 146.1-154.3° C. A preparation method for the lead-free solder alloy includes the following steps:

(20) 1) placing metals Bi and Sb having a purity of 99.99 wt. % into a vacuum melting furnace at an alloy ratio of 80:20 by weight, performing vacuum treatment to 1×10.sup.−2 Pa, charging nitrogen and then heating the alloy to a temperature of 650-700° C. to be melted, performing electromagnetic stirring at the same time to make the alloy composition uniform, and then performing vacuum casting, so as to obtain a Bi—Sb20 master alloy;

(21) 2) placing separately metals Sn and Ce, Sn and Ti, Sn and Cu, Sn and Ni, Sn and Ag having a purity of 99.99 wt. % into a vacuum melting furnace at a certain alloy ratio, performing vacuum treatment to 1×10.sup.−2 Pa, charging nitrogen and then heating separately the alloys to temperatures of 690-780° C., 1550-1650° C., 750-820° C., 900-1100° C., 800-900° C. to be melted, performing electromagnetic stirring at the same time to make the alloy composition uniform, and then performing vacuum casting, so as to obtain separately SnCe10, SnTi20, SnCu20, SnNi5, SnAg20 master alloys;

(22) 3) melting the prepared Bi—Sb, Sn—Ce, Sn—Ti, Sn—Cu, Sn—Ni, Sn—Ag master alloys together with metals Sn and Bi at an alloy ratio in the melting furnace, covering a surface of the alloy with an anti-oxidation solvent (oil bath), heating the alloy to a temperature of 450° C., maintaining the temperature for 15 minutes, removing oxide slag on the surface, pouring into a mold to obtain an ingot of SnBi56.5Sb0.7Ce0.5Ti1Cu0.03Ni0.07Ag0.1 lead-free solder alloy.

Example 7

(23) A lead-free solder alloy used in the field of low-temperature soldering is provided, the lead-free solder alloy comprising by weight: 45% of Bi, 1.5% of Sb, 1.0% of Ce, 1.5% of Ti, 0.1% of Cu, 0.5% of Ni, 0.5% of Ag, with the remainder being Sn and inevitable impurities, wherein the lead-free solder alloy has a near peritectic structure, with a melting point of the alloy being 144.9-152.7° C. It is prepared in the same manner as in Example 6, except that the alloy ratio is different.

Example 8

(24) A lead-free solder alloy used in the field of low-temperature soldering is provided, the lead-free solder alloy comprising by weight: 42.3% of Bi, 2.0% of Sb, 1.5% of Ce, 1.5% of Ti, 0.5% of Cu, 1.2% of Ni, 0.8% of Ag, 0.05% of In, with the remainder being Sn and inevitable impurities, wherein the lead-free solder alloy has a near peritectic structure, with a melting point of the alloy being 148.5-158.7° C. A preparation method for the lead-free solder alloy includes the following steps:

(25) 1) placing metals Bi and Sb having a purity of 99.99 wt. % into a vacuum melting furnace at an alloy ratio of 80:20 by weight, performing vacuum treatment to 1×10.sup.−2 Pa, charging nitrogen and then heating the alloy to a temperature of 650-700° C. to be melted, performing electromagnetic stirring at the same time to make the alloy composition uniform, and then performing vacuum casting, so as to obtain a Bi—Sb20 master alloy;

(26) 2) placing separately metals Sn and Ce, Sn and Ti, Sn and Cu, Sn and Ni, Sn and Ag having a purity of 99.99 wt. % into a vacuum melting furnace at a certain alloy ratio, performing vacuum treatment to 1×10.sup.−2 Pa, charging nitrogen and then heating separately the alloys to temperatures of 690-780° C., 1550-1650° C., 750-820° C., 900-1100° C., 800-900° C. to be melted, performing electromagnetic stirring at the same time to make the alloy composition uniform, and then performing vacuum casting, so as to obtain separately SnCe10, SnTi20, SnCu20, SnNi5, SnAg20 master alloys;

(27) 3) melting the prepared Bi—Sb, Sn—Ce, Sn—Ti, Sn—Cu, Sn—Ni, Sn—Ag master alloys together with metals In, Sn and Bi at an alloy ratio in the melting furnace, covering a surface of the alloy with an anti-oxidation solvent (rosin), heating the alloy to a temperature of 500° C., maintaining the temperature for 15 minutes, removing oxide slag on the surface, pouring into a mold to obtain an ingot of SnBi42.3Sb2Ce1.5Ti1.5 Cu0.5Ni1.2Ag0.8In0.05 lead-free solder alloy.

Example 9

(28) A lead-free solder alloy used in the field of low-temperature soldering is provided, the lead-free solder alloy comprising by weight: 42.3% of Bi, 2.0% of Sb, 2.5% of Ce, 2.0% of Ti, 0.8% of Cu, 1.5% of Ni, 1.0% of Ag, 1.0% of In, with the remainder being Sn and inevitable impurities, wherein the lead-free solder alloy has a near peritectic structure, with a melting point of the alloy being 150.1-159.3° C. The lead-free solder alloy is prepared in the same manner as in Example 8, except that the alloy ratio is different.

Example 10

(29) A lead-free solder alloy used in the field of low-temperature soldering is provided, the lead-free solder alloy comprising by weight: 42.3% of Bi, 2.0% of Sb, 0.5% of Ag, with the remainder being Sn and inevitable impurities, wherein the lead-free solder alloy has a near peritectic structure, with a melting point of the alloy being 144.8-146.9° C. A preparation method for the lead-free solder alloy includes the following steps:

(30) 1) placing metals Bi and Sb having a purity of 99.99 wt. % into a vacuum melting furnace at an alloy ratio of 80:20 by weight, performing vacuum treatment to 1×10.sup.−2 Pa, charging nitrogen and then heating the alloy to a temperature of 650-700° C. to be melted, performing electromagnetic stirring at the same time to make the alloy composition uniform, and then performing vacuum casting, so as to obtain a Bi—Sb20 master alloy;

(31) 1) placing metals Sn and Ag having a purity of 99.99 wt. % into a vacuum melting furnace at a certain alloy ratio, performing vacuum treatment to 1×10.sup.−2 Pa, charging nitrogen and then heating the alloy to a temperature of 500-650° C. to be melted, performing electromagnetic stirring at the same time to make the alloy composition uniform, and then performing vacuum casting, so as to obtain a SnAg20 master alloy;

(32) 3) melting the prepared Bi—Sb, Sn—Ag master alloys together with metals Sn and Bi at an alloy ratio in the melting furnace, covering a surface of the alloy with an anti-oxidation solvent (KCL-LiCl fused salt), heating the alloy to a temperature of 500° C., maintaining the temperature for 20 minutes, removing oxide slag on the surface, pouring into a mold to obtain an ingot of SnBi42.3Sb2Ag0.5 lead-free solder alloy.

(33) FIG. 2 shows DSC test results of the solder alloy prepared in the example 10. It can be seen from the figure that its melting point is 144.8-146.9.

Comparative Example 1

(34) A lead-free solder alloy used in a low temperature is provided, the lead-free solder alloy comprising by weight: 58% of Bi, 42% of Sn, with a melting point of the solder alloy being 138° C.

Comparative Example 2

(35) A lead-free solder alloy used in a low temperature is provided, the lead-free solder alloy comprising by weight: 57% of Bi, 1.0% of Ag, with the remainder being Sn, and the melting point of the solder alloy being 138-140° C.

(36) Test Experiment

(37) 1. Measurement of Melting Point

(38) The test for melting point is performed under a heating rate of 10° C./min by using an STA409PC differential scanning calorimeter (TA Instrument), wherein the mass of the sample is 30 mg, data processing is performed automatically by software calculation, and a peak temperature of the DSC curve is recorded as the melting point value of the solder alloy.

(39) 2. Conditions for Wettability Test

(40) An alloy having a mass of 0.6 g is obtained and mixed with a certain amount of flux, and then placed on an oxygen free copper plate having a size of 30×30×0.3 mm (oxide and dirt are removed from the surface of the copper plate), and then the copper plate is placed on a flattening oven to be heated to 180° C., and then cooled to room temperature to form a welding spot after the solder has been melted and spread. The spread area of the welding spot is measured using a CAD software.

(41) 3. Sample Preparation

(42) Tensile samples and copper welded samples are prepared and tested with reference to Japanese Industrial Standards JIS Z 3198.

(43) 4. Mechanical performance data are measured on a universal material testing machine of the type AG-50KNE in accordance with methods in GB/T228-2002, wherein the stretching speed is 5 mm/min, and three samples are tested for each data point to obtain average values.

(44) 5. Reliability assessment method: Vibration experiments are carried out on copper sheet welded samples with weights having a weight of 2 kg; the number of vibrations when the welding spot of the copper sheet welded sample breaks are recorded; and 10 samples are tested for each data point to obtain average values.

(45) TABLE-US-00001 TABLE 1 Comparison of melting point and wetting performance of solder alloy alloy melting point spread area solder alloy composition (° C.) (μm.sup.2) Example 1 SnBi41.8Sb2.1 142.9-150.8 64.2 Example 2 SnBi50Sb1 140.6-143.8 65.9 Example 3 SnBi55Sb0.8Ce0.01Ti0.05 142.9-146.2 63.1 Example 4 SnBi44.2Sb1.7Ce0.05Ti0.1 145.2-150.5 70.2 Example 5 SnBi44.2Sb1.7Ce0.1Ti0.8 147.5-152.9 71.6 Cu0.01Ni0.03 Example 6 SnBi56.5Sb0.7Ce0.5 146.1-154.3 73.5 Ti1Cu0.03Ni0.07Ag0.1 Example 7 SnBi45Sb1.5Ce1Ti1.5Cu0.1 144.9-152.7 74.9 Ni0.5Ag0.5 Example 8 SnBi42.3Sb2Ce1.5Ti1.5Cu0.5Ni1.2 148.5-158.7 76.7 Ag0.8In0.05 Example 9 SnBi42.3Sb2Ce2.5Ti2Cu0.8 150.1-159.3 78.5 Ni1.5Ag1In1 Example 10 SnBi42.3Sb2Ag0.5 144.8-146.9 72.1 Comparative SnBi58 138 60.5 Example 1 Comparative SnBi57Ag1 138-140 65 Example 2

(46) TABLE-US-00002 TABLE 2 Comparison of mechanical performance of solder alloy Number of Tensile vibra- strength tion Solder alloy composition (MPa) shocks Example 1 SnBi41.8Sb2.1 92.43 14380 Example 2 SnBi50Sb1 98.89 15200 Example 3 SnBi55Sb0.8Ce0.01Ti0.05 95.62 11636 Example 4 SnBi44.2Sb1.7Ce0.05Ti0.1 102.71 12701 Example 5 SnBi44.2Sb1.7Ce0.1Ti0.8Cu0.01Ni0.03 101.07 12989 Example 6 SnBi56.5Sb0.7Ce0.5Ti1Cu0.03Ni0.07 98.25 11050 Ag0.1 Example 7 SnBi45Sb1.5Ce1Ti1.5Cu0.1Ni0.5Ag0.5 108.05 12123 Example 8 SnBi42.3Sb2Ce1.5Ti1.5Cu0.5Ni1.2Ag0.8 102.68 13576 In0.5 Example 9 SnBi42.3Sb2Ce2.5Ti2Cu0.8Ni1.5Ag1In1 104.77 13900 Example SnBi42.3Sb2Ag0.5 100.23 11000 10 Com- SnBi58 73.62 9230 parative Example 1 Com- SnBi57Ag1 61 9808 parative Example 2

(47) Using the SnBiSb series low-temperature lead-free solder of the present invention, it is possible to form welding spot or welding seam with common solder paste reflux, wave soldering, or heat fusion welding, wherein the heat fusion welding includes preformed soldering lug, soldering strip, soldering ball and soldering wire etc., and in addition to the solder composition, the welding spot or welding seam alloy also includes other substrate alloying elements, such as but not limited to Cu, Ag, Ni, Au. The resulted welding spot or welding seam alloy comprises by weight the following composition: Bi 32.8-56.5%, Sb 0.7-2.2%, Cu 0.01-1.5%, Ni 0.03-2.0%, Ag 0.1-1.5%, Ce 0-2.5%, Ti 0-2.0%, In 0-1%, with the remainder being Sn and small amount of inevitable substrate alloying elements.

(48) Compared with the prior art, the solder alloy prepared according to the present invention has a peritectic or near peritectic structure with a low melting point, thereby fundamentally solves the problem of brittleness and poor reliability of SnBi solder, while having excellent mechanical performance and reliability, and thus applicable to low-temperature soldering field.