Abstract
The invention provides an alloy, preferably a lead-free solder alloy, comprising: from 35 to 59% wt Bi; from 0 to .0 wt % Ag; from 0 to 1.0% wt Au; from 0 to 1.0% wt Cr; from 0 to 2.0% wt In; from 0 to 1.0% wt P; from 0 to 1.0% wt Sb; from 0 to 1.0% wt Sc; from 0 to 1.0% wt Y; from 0 to 1.0% wt Zn; from 0 to 1.0% wt rare earth elements; one or more of: 10 from greater than 0 to 1.0% wt Al; from 0.01 to 1.0% wt Ce; from greater than 0 to 1.0% wt Co; from greater than 0 to .0% wt Cu; from 0.001 to 1.0% wt Ge; from greater than 0 to .0% wt Mg; from greater than 0 to 1.0% wt Mn; from 0.01 to 1.0% wt Ni; and from greater than 0 to 1.0% wt Ti, and the 1 balance Sn, together with any unavoidable impurities.
Claims
1.-20. (canceled)
21. A lead-free solder alloy, comprising: from 35 to 59 wt % Bi; from greater than 0 to 1.0 wt % Cu; from 0.003 to 0.5 wt % Co; from 0.01-1.0 wt % Ag; optionally from 0 to 1.0 wt % Au; from 0 to 1.0 wt % Cr; from 0 to 2.0 wt % In; from 0 to 1.0 wt % P; from 0 to 1.0 wt % Sb; from 0 to 1.0 wt % Sc; from 0 to 1.0 wt % Y; from 0 to 1.0 wt % Zn; from 0 to 1.0 wt % rare earth elements; from greater than 0 to 1.0 wt % Al; from 0.01 to 1.0 wt % Ce; from 0.001 to 1.0 wt % Ge; from greater than 0 to 1.0 wt % Mg; from greater than 0 to 1.0 wt % Mn; from 0.01 to 1.0 wt % Ni; and from greater than 0 to 1.0 wt % Ti, and the balance Sn, together with any unavoidable impurities.
22. An alloy according to claim 1, comprising from 57 to 59 wt % Bi.
23. An alloy according to claim 1 wherein the concentration of Sn is from 41 to 43 wt %.
24. A lead-free solder alloy, comprising: from 35 to 59 wt % Bi; from 0.01 to 1.0 wt % Ag; from 0.01 to 0.05 wt % Ni; and balance Sn, together with any unavoidable impurities.
25. The alloy of claim 1 consisting essentially of: from 35 to 59 wt % Bi; from greater than 0 to 1.0 wt % Cu; from 0.01 to 0.07 wt % Co; from 0.01-0.8 wt % Ag; balance Sn; and unavoidable impurities.
26. The alloy of claim 1 consisting of: from 35 to 59 wt % Bi; from greater than 0 to 1.0 wt % Cu; from 0.01 to 0.07 wt % Co; from 0.01-0.8 wt % Ag; balance Sn; and unavoidable impurities.
27. The alloy of claim 25 consisting essentially of: from 35 to 59 wt % Bi; from 0.05 to 0.5 wt % Cu; from 0.02 to 0.04 wt % Co; from 0.01-0.8 wt % Ag; balance Sn; and unavoidable impurities.
28. The alloy of claim 26 consisting of: from 35 to 59 wt % Bi; from 0.05 to 0.5 wt % Cu; from 0.02 to 0.04 wt % Co; from 0.01-0.8 wt % Ag; balance Sn; and unavoidable impurities.
29. The alloy of claim 1 consisting essentially of: from 57 to 59 wt % Bi; from 0.1 to 0.3 wt % Cu; from 0.02 to 0.04 wt % Co; from 0.01-0.8 wt % Ag; balance Sn; and unavoidable impurities.
30. The alloy of claim 1 consisting of: from 57 to 59 wt % Bi; from 0.1 to 0.3 wt % Cu; from 0.02 to 0.04 wt % Co; from 0.01-0.8 wt % Ag; balance Sn; and unavoidable impurities.
31. The alloy of claim 1 consisting of: from 35 to 59 wt % Bi; from 0.05 to 0.5 wt % Cu; from 0.01 to 0.07 wt % Co; from 0.01 to 1.0 wt % Ag; balance Sn; and unavoidable impurities.
34. The alloy of claim 24 consisting of: from 35 to 59 wt % Bi; from 0.01-1.0 wt % Ag; from 0.025 to 0.05 wt % Ni; and balance Sn, together with any unavoidable impurities.
Description
[0184] The invention will now be described, by way of example only, with reference to the following drawings in which:
[0185] FIG. 1 is a plot showing the results of the Charpy Impact Test on three alloys according to the first aspect of the invention and a reference example;
[0186] FIG. 2 is a plot showing the results of the Charpy Impact Test on three alloys according to the first aspect of the invention and three reference examples;
[0187] FIG. 3 is a plot of linear spread in mm on a copper organic solderability preservative (OSP) of a number of alloys according to the present invention and a reference example.
[0188] FIG. 4 is a plot showing the results of the Bulk Shear Test for a number of alloys according to the present invention and a number of reference examples.
[0189] FIG. 5 is a plot showing the results of the Hardness Test for a number of alloys according to the present invention and a number of reference examples.
[0190] FIG. 6 is a plot of yield strengths of a number of alloys according to the present invention and a number of reference examples.
[0191] FIG. 7 is a plot of tensile strengths of a number of alloys according to the present invention and a number of reference examples.
[0192] FIG. 8 is a plot showing the results of the Bulk Shear Test for a number of alloys according to the present invention when incorporated onto a chip component and a number of reference examples.
[0193] FIG. 9 is a plot showing the results of the Lead Pull Test for a number of alloys according to the present invention when incorporated onto a Quad Flat Package (QFP) component and a number of reference examples.
[0194] FIG. 10 is a plot of thermal conductivities of a number of alloys according to the present invention and a number of reference examples.
[0195] FIGS. 11-13 show electron microscope images of the microstructures of Sn57.6Bi0.4Ag, Sn57.45Bi0.5Ag0.05Ni and Sn57.4Bi0.5Ag0.1Ce, respectively.
[0196] FIG. 14 shows the time for Cu dissolution of a number of alloys according to the present invention and a number of reference examples.
[0197] FIG. 15 shows the results of drop shock testing for a number of alloys according to the present invention and a reference example.
[0198] FIG. 16 shows the results of thermal fatigue testing for a number of alloys according to the present invention and a number of reference examples.
[0199] FIG. 17 shows the results of thermal fatigue testing for a number of alloys according to the present invention and a number of reference examples.
[0200] Referring to FIG. 1, the Charpy Impact Test was carried out (sample size 551015 mm) on four alloys (from left to right): Sn57.5Bi0.5Ag, Sn57.4Bi0.5Ag0.1Ce, Sn57.495Bi0.5Ag0.005Ge and Sn57.45Bi0.5Ag0.05Ni. The results indicate that the presence of Ce, Ge and Ni results in the alloys exhibiting an increase in impact energy of from approximately 10 to 12% compared to the Sn57.5Bi0.5Ag base alloy.
[0201] Referring to FIG. 2, the Charpy Impact Test was carried out (sample size 551010 mm) on six alloys (from left to right): Sn58Bi, Sn57.5Bi0.5Ag, Sn45Bi, Sn57.4Bi0.5Ag0.1Ce, Sn57.4555Bi0.5Ag0.005Ge and Sn57.45Bi0.5Ag0.05Ni. The results indicate that a reduction in the level of Bi and the addition of Ag, Ce, Ge and Ni improves the toughness of the alloys. Charpy Impact Tests carried out on the alloys Sn57.54Bi0.4Ag0.03Ni0005Mn, Sn57.75Bi0.2Cu0.03Ni, Sn57.7Bi0.2Cu0.03Co, Sn45Bi0.03Ni and Sn45Bi0.1Cu0.034Co indicated that each of these alloys exhibit an impact energy in excess of 225 kJ. Sn57.7Bi0.2Cu0.03Co exhibited an impact energy in excess of 230 kJ.
[0202] Referring to FIG. 3, linear spreads were determined for the alloys (from left to right): Sn57.6Bi0.4Ag, Sn57.5Bi0.5Ag0.005Ge, Sn57.5Bi0.5Ag0.05Ni and Sn57.5Bi0.5Ag0.05Ce. the results demonstrate that the alloys of the present invention exhibit improved wettability compared to their base SnBiAg alloy. Similar results were obtained for the alloys Sn58Bi0.2Cu0.03Ni, Sn58Bi0.2Cu0.03Co and Sn58Bi0.4Ag0.03Ni, for both samples manufactured on the laboratory and 400 kg scales.
[0203] Referring to FIGS. 4-7, it is demonstrated that the alloys of the present invention exhibit increased shear strength, hardness, yield strength and tensile strength in comparison to their base SnBiAg alloy. In FIG. 4, the bulk shear test results are shown for the following alloys (from left to right): Sn45Bi, Sn58Bi, Sn57.6Bi0.4Ag, Sn58Bi0.5Ag0.5Ce, Sn58Bi0.5Ag0.005Ge, Sn57.6Bi0.4Ag0.02Ti, Sn57.6Bi0.4Ag0.02Ti0.05Ni. Sn45Bi0.2Cu0.005Mn, Sn58Bi0.005Al, Sn58Bi0.005Mn and Sn57.75Bi0.2Cu0.05Ni. In FIG. 5, the hardness values are shown for the following alloys (from left to right): Sn58Bi, Sn58Bi0.4Ag0.02Ti, An58Bi0.4Ag0.02Ti0.05Ni, Sn58Bi0.005Al, Sn58Bi0.2Cu0.02Ni, Sn58Bi0.2Cu0.02Ni0.005Ge, Sn58Bi0.005Mn, Sn58Bi0.4Ag0.005Mn and Sn58Bi0.4Ag0.05Ni0.005Mn. In FIG. 6 the yield strength values are shown for the following alloys (from left to right) Sn57.5Bi0.5Ag, Sn45Bi, Sn57.5Bi0.5Ag0.05Ce, Sn57.5Bi0.5Ag0.005Ge, Sn57.5Bi0.5Ag0.05Ni and Sn57.5Bi0.5Ag0.05(Ce, Ni)0.005Ge. In FIG. 7 the tensile strengths are shown for the following alloys (from left to right) Sn57.5Bi0.5Ag, Sn45Bi, Sn57.5Bi0.5Ag0.05Ce, Sn57.5Bi0.5Ag0.005Ge, Sn57.5Bi0.5Ag0.05Ni and Sn57.5Bi0.5Ag0.05(Ce, Ni)0.005Ge.
[0204] Referring to FIG. 8, it is demonstrated that the improvement in shear strength is also exhibited by the alloys when incorporated onto a chip component. The results are shown for the following alloys (from left to right): Sn57.6Bi0.4Ag, Sn57.6Bi0.4Ag0.05Ni, Sn57.6Bi0.4Ag0.005Ge and Sn57.6Bi0.4Ag0.05Ce
[0205] Referring to FIG. 9, it is demonstrated that the when the alloys are incorporated onto QFP components, the force required to pull the lead from the chip after soldering increases in comparison to their base SnBiAg alloy. In FIG. 9 the results are shown for the following alloys (from left to right) Sn57.6Bi0.4Ag, Sn57.6Bi0.4Ag0.05Ni, Sn57.6Bi0.4Ag0.005Ge and Sn57.6Bi0.4Ag0.05Ce.
[0206] Referring to FIG. 10, it is demonstrated that the alloys of the present invention exhibit improved thermal conductivity in comparison to their base SnBi/SnBiAg alloy. The results are shown for the alloys Sn58Bi (smaller squares), Sn57.5Bi0.5Ag (triangles), Sn57.5Bi0.5Ag0.05Ce (larger squares) and Sn57.5Bi0.5Ag0.05Ni (diamonds).
[0207] Referring to FIGS. 11-13, it is demonstrated that small additions of certain elements have the advantageous effect of refining the microstructure, leading to, for example, enhanced mechanical properties. Electron micrograph images of the alloys Sn57.8Bi0.2Cu0.03Ni and Sn57.8Bi0.2Cu0.03Co show microstructures which are still further refined.
[0208] Referring to FIG. 14, it is demonstrated that the alloys Sn58Bi0.2Cu0.06 and Sn58Bi0.2Cu0.03Co exhibit very low Cu dissolution. Accordingly, since these alloys also exhibit high electrical conductivity, they are particularly suitable for photovoltaic applications. The results in FIG. 14 are shown for the alloys (from left to right): Sn58Bi0.4Ag, Sn58Bi0.4Ag0.03Ni, Sn58Bi0.4Ag0.03Ti, Sn58Bi0.4Ag0.007Mn, Sn58Bi0.2Cu0.06Ni, Sn58Bi0.2Cu0.03Co, Sn45Bi, Sn45Bi0.1Cu, Sn45Bi0.02Ni and Sn45Bi0.1Cu0.06Co.
[0209] Referring to FIG. 15, drop shock test results are indicated for the alloys Sn58BiCu0.2Ni0.06 (circles, average number of drops to failure: 324.5), Sn58BiCu0.2Co0.03 (squares, average number of drops to failure 289.9), Sn58Bi0.04Ag (diamonds, average number of drops to failure 174.7) and Sn58Bi0.4Ag0.05Ni (triangles, average number of drops to failure 259.0). The drop shock test followed JEDEC standard JESD22-B111 (test conditions: 1500 Gs, 0.5 millisecond duration, half-sine pulse). Boards were populated with Ball Grid Array (BGA) components on all 15 available positions. The results indicate that the alloys of the present invention exhibit improved drop shock resistance compared to the Sn58Bi0.4Ag alloy.
[0210] Referring to FIG. 16, thermal fatigue testing was carried out on the alloys Sn58Bi (diamonds), Sn57.6Bi0.4Ag (filled triangles), Sn57.6Bi0.4Ag0.03Ni (hollow circles), Sn57.6Bi0.4Ag0.0033Ge (hollow triangles), Sn57.6Bi0.4Ag0.056Ce (squares) and Sn45Bi (crosses). The thermal cycling conditions corresponded to standard TC3/NTC-C (40 to 125 C.; 10 minute dwell time). The alloys of the present invention exhibited very little variation in shear strength after 1500 cycles compared to those of the Sn58Bi and Sn45Bi alloys. In addition, no cracks were observed after 1500 cycles for any of the alloys of the present invention.
[0211] Referring to FIG. 17, thermal fatigue testing was carried out on the alloys Sn57.6Bi0.4Ag (diamonds, 3.sup.rd highest shear force after 1000 cycles), Sn58Bi (squares, 5.sup.th highest shear force after 1000 cycles), Sn57.6Bi0.2Cu0.03Ni (triangles, highest shear force after 1000 cycles), Sn57.6Bi0.2Cu0.03Co (dark circles, 2.sup.nd highest shear force after 1000 cycles), Sn57.6Bi0.4Ag0.03Ni (crosses, lowest shear force after 1000 cycles) and Sn57.1Bi0.9Ag (light circles, 4.sup.th highest shear force after 1000 cycles). The thermal cycling conditions were the same as those used for the testing shown in FIG. 16. 36 BGA84 boards were used for testing per alloy. Only 26 of the SnBi0.4Ag boards and 24 of the Sn58Bi boards survived 1000 cycles. In comparison, all 36 boards of Sn57.6Bi0.2Cu0.03Ni, Sn57.1Bi0.9Ag and Sn57.6Bi0.4Ag0.03Ni, and 35 board of Sn57.6Bi0.2Cu0.03Co, survived 1000 cycles.
[0212] The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.
