low-Ag Lead-free Solder Research Articles

Effect of Bi addition on the shear strength and failure mechanism of low-Ag lead-free solder joints

To optimize the mechanical properties of low-Ag lead-free solder, different amount of Bi element was added into the Sn–1.0Ag–0.5Cu (SAC105) to form SAC105-xBi (0 ≤ x ≤ 4) solder alloy. The microstructural evolution and shear fracture of SAC105-xBi solder joints were systematically investigated to clarify the failure mechanism after reflow and after 175 °C aging compared to SAC305. It was found that Bi element could provide solution strengthening and second-phase strengthening in the low-Ag SAC solder joints depending on the amount of added Bi element. The shear strength after reflow increased from 34.79 to 70.16 MPa with the increase of Bi addition from x = 0.0 to x = 4.0, while that after aging at 175 °C for 168 h increased from 28.97 MPa (x = 0.0) to 55.02 MPa (x = 4.0). The thickness of IMC decreased with the addition of Bi, and excessive Bi would precipitate in the matrix when the Bi content reached 2 wt% or even form brittle Bi barrier layer after 4 wt% addition. During shear tests, three kinds of fracture mode including ductile fracture, quasi-cleavage fracture, and cleavage brittle fracture were observed, and three kinds of failure position including solder matrix, Cu6Sn5/solder interface, and Cu3Sn/Cu interface were revealed. The failure mechanism of different solder joints was closely related to the coupling effects among the Bi amount in the matrix, the thicknesses of IMC, and the status of Kirkendall voids, which significantly affected the reliability of SAC solder joints. Finally, SAC105-1.0Bi solder alloy was considered having the most suitable Bi addition with anticipated comprehensive properties compared with SAC305.

Tensile and Fatigue strength of Bi added low Ag lead-free solder

Tensile and Fatigue strength of Bi added low Ag lead-free solder

Bi添加低銀鉛フリーはんだの引張挙動

The purpose of this study is to investigate the effect of Bi addition to Ag-free and low Ag lead-free solder on their mechanical properties. The specimens used in this study were SC07 and SAC107 with and without Bi. Tensile tests for their specimens were carried out at various temperature (25, 80, and 120°C) under 1.0×10-3 s-1 strain rate. The addition of Bi into SC07 and SAC107 caused to increase their tensile strength. This is because Bi is dissolved in the primary Sn as a solid solution. The addition of Bi has no effect on their elongation. When test temperature increased, the addition of Bi had an effect on their tensile strength.

Effect of Bi Addition on Microstructures, Properties and Interfacial Intermetallic Compound Growth of Low-Ag Sn-Cu Lead-Free Solder

The research on a new low-Ag lead-free solder has become a hot spot in the field of electronic packaging. In this work, the effects of Bi addition on microstructure, melting temperature, wettability of low-Ag solder, shear strength of solder joint and the growth of interfacial intermetallic compound (IMC) before and after thermal cycling were investigated. A moderate amount of Bi element resulted in the microstructural refinement and melting temperature reduction of Sn-0.2Ag-0.7Cu solder. Wetting test results showed that a small amount of Bi produced the significant effect on improving the wettability. In addition, it is shown that the thickness of interfacial IMC during thermal cycling decreased first and then increased; the shear strength of solder joint increased with the increase of Bi.

Effect of Strain Rate on Tensile Properties of Miniature Size Specimens of Several Lead-Free Alloys

The effect of strain rate on tensile properties of several lead-free solder was investigated using miniature size specimens. High-temperature lead-free solder which are Sn-Cu and Sn-Sb alloys were prepared. Moreover, low-Ag lead-free solder which are Sn-1Ag-0.7Cu (SAC107, mass%) based alloys were prepared. Sn-3Ag-0.5Cu (SAC305) was also prepared for comparison. Tensile strength is proportion to the logarithm of strain rate in all solder investigated. Although 0.1% proof stress decreases at high strain rate in high-temperature solder, it scarcely changes in low-Ag solder. Elongation somewhat increases with increasing strain rate in high-temperature solder. It increases with increasing strain rate in low-Ag solder although it is lower than that of SAC305. Chisel point fracture mainly occurred except Sn-13Sb. In Sn-13Sb, brittle fracture occurred and thus elongation was lower than those of other solder. Sn-8.5Sb and Sn-1Ag-0.7Cu-1Bi-0.2In show mechanical properties similar to SAC305.

低 Ag鉛フリーはんだの実力

低 Ag鉛フリーはんだの実力

Tensile properties and wettability of SAC0307 and SAC105 low Ag lead-free solder alloys

In this article, the tensile properties of low Ag lead-free solder alloys, SAC0307 and SAC105, are examined under various strain rates and temperatures. The wettability of these solders on Cu pad is also characterized by using different fluxes. The SAC305 and Sn37Pb solder alloys are also studied for comparison. Our results show that the properties of all solder alloys are dependent on the strain rate and temperature. The ultimate tensile strength increases monotonously with the increment of strain rate. Both SAC0307 and SAC105 alloys possess lower strength and higher elongation ratio than SAC305 and Sn37Pb alloys. For all the fluxes used in this study, the SAC0307 and SAC105 alloys show the similar wettability to SAC305, whereas worse than that of Sn37Pb alloy. Increasing the activity of the flux does not improve the wettability of the SAC solder alloys on Cu pad effectively.