Papers by Keyword: Lead-Free Solder

Abstract: The Influence of alloy composition on tensile properties of Sn-Bi, Sn-Bi-Cu and Sn-Bi-Ni lead-free solder alloys were investigated. It is found that the elongation of Sn-Bi alloys depend on Bi content, and Sn-40wt% Bi alloy has the highest elongation. The addition of Cu and Ni improves the ductility of Sn 35-45wt% Bi alloys. The fine microstructure of Sn-Bi-Cu or Ni alloys have an effect on the ductility of Sn-Bi based alloys. The elongation increases with decreasing strain rate and increasing temperature. Cu and Ni added to Sn-Bi alloy showed the super plasticity behavior at low strain rate and high temperature (more than 333 K). Moreover, strain rate sensitivity ‘m’ increases with temperature.

Abstract: Tensile properties of Sn-5Sb (mass%) and Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge (mass%) were investigated using miniature size specimens and obtained results were compared. Tensile strength of both alloys increase with increasing the strain rate and decrease with increasing the temperature. Although similar dependency to the temperature is observed in 0.1% proof stress, the effect of the strain rate on it is obscure. The tensile strength and the 0.1% proof stress of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge are higher than those of Sn-5Sb. The elongation of Sn-5Sb is relatively stable at the range from 0.4 to 0.6. The elongation of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge which is approximately 0.3, is inferior to that of Sn-5Sb. On the basis of investigation of stress exponent, n, it was clarified that dispersion strengthening by Ag₃Sn particulates in Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge is effective to prevent the degradation of creep resistance compared with Sn-5Sb that is strengthened by solid-solution of Sb in β-Sn phases and dispersion of SbSn compounds.

Abstract: The effect of bismuth (Bi) micro-alloying additions on wettability and mechanical properties of Sn-0.7Cu lead-free solder were explored. This paper also investigates the influences of various Bi percentages on the suppression of intermetallic compound formation. Scanning electron microscope (SEM) was used to observe the microstructure evolution of solder joint including the thickness of interfacial intermetallic layers. Overall, with the addition of Bi to Sn-0.7Cu solder, the size of primary Cu₆Sn₅ become smaller and suppresses the thickness of interfacial intermetallic compound between solder and the Cu substrate. Microhardness value and wetting properties also increased with Bi addition which resulted in smaller size of β-Sn and Cu₆Sn₅.

Abstract: In this research, we investigated the influence of indium and antimony additions on the microstructure, mechanical and thermal properties of Sn-3.0Ag-0.5Cu lead free solder alloys. The results revealed that the addition of 0.5 wt.%InSb into SAC305 solder alloys resulted to a reduced melting temperature by 3.8 °C and IMCs phases formed new Ag₃(Sn,In) and SnSb in the Sn-rich matrix with a decreased grain size of 28%. These phases improved the mechanical properties of solder alloys. In addition, the mechanical properties of SAC305 solder alloys increased by adding 0.5 wt.%InSb, resulting in an increase of ultimate tensile strength of 24%, but the percent elongation decreased to 45.8%. Furthermore, the Vickers microhardness slightly increased of the SAC305 solder alloys.

Abstract: The effect of cooling rate on the microstructural and mechanical properties of Sn-0.3Ag-0.7Cu-0.05Ni lead-free solder alloy was studied. The microstructure of specimens was characterized by using an optical microscope (OM) and an energy dispersive X-ray spectroscopy (EDX). The mechanical properties were performed by using a universal testing machine (UTM). The results showed that the cooling rate of water-cooled specimens was about 2.37 °C/s and the cooling rate of mold-cooled specimens was about 0.05 °C/s. To compare the different cooling rates, it was found that the grain size of water-cooled specimens was finer than that of the mold-cooled specimens, this resulted in an increment of mechanical properties of solder alloy. A higher tensile strength (33.10 MPa) and a higher elongation (34%) were observed when water-cooled and mold-cooled systems were used, respectively. The microstructure of Sn-0.3Ag-0.7Cu-0.05Ni lead-free solder alloy solidified by both cooling systems exhibited three phases: β-Sn, Ag₃Sn and (Cu,Ni)₆Sn₅ IMCs.

Abstract: In design of the electronic device, FEM analyses considering the creep deformation of solder joints in-situ should be conducted to evaluate the strength reliability. The indentation test is one of effective method to evaluate the creep deformation in microscopic region. However, the result obtained by the indentation test does not coincide with that obtained by the tensile creep test. To solve the problem, the method to determine the suitable area for the indentation test had also been proposed by using the numerical test. To apply the proposed method for the actual indentation test, the homogeneity of specimen should be considered. In this paper, the analyses of the proposed indentation tests were conducted by using the homogeneous and inhomogeneous specimen models of Sn-3.0Ag-0.5Cu. Three types of the deformation behavior were given for the initial phase and the indenter was pushed into in the specimen at the three locations. As a result, it was found that there was not difference in the distribution of the principal stress caused by variation in the indent location. However, the proposed method can successfully determine the reference area except for the case when the deformation behaviors of the constituent phases have a large difference.

Abstract: This paper investigates the fatigue results in low cycle fatigue region obtained from a miniaturized specimen having a 6mm gage length, 3mm diameter and 55mm total length. Fatigue tests were performed for two type lead-free solders using horizontal-type electrical servo hydraulic push-pull fatigue testing machine. Materials employed were Sn-3.0Ag-0.5Cu and Sn-5Sb. The results from Sn-3.0Ag-0.5Cu were compared with those obtained using a bulk specimen in a previous study. Relationship between strain range and number of cycles to failure of the small-sized specimen agreed with those of the bulk specimens. The testing techniques are applicable to Sn-5Sb following the Manson-Coffin law. These results confirm that the testing technique proposed here, using small-sized specimen, is suitable to get fruitful fatigue data for lead-free solder compounds.

Abstract: The fracture strengths of thin solder joints were investigated experimentally and with Finite Element Analysis. Due to a constraining effect, thin solder joints can carry loads which are much higher than the ultimate tensile strength of bulk solder material. On the other hand, thin solder joints show a tendency of being brittle. In fact, the tensile properties show a dependence on the quality of the intermetallic compound at the interface to the base material. Consequently, the size of microscopic defects in the intermetallic compound has a dominant influence on the fracture stress. This behavior could nicely be explained with Finite Element simulations based on strain gradient elasticity.

Abstract: To create a high reliability solder joint using IMCs dispersed in the joint, the joints with four types of lead-free solder were investigated. The joint with Sn-3.0Ag-0.7Cu-5.0In (mass%) has high die shear force compared to other joints investigated, and the joint with the Ni-electroplated Cu bonded at 300 ^oC for 30 min showed the maximum die shear force due to formation of a large number of fine IMCs. In the joint with Sn-0.7Cu-0.05Ni (mass%), uniform dispersion of a large number of IMCs was achieved, although the die shear force of the joint is lower than that of the joint with Sn-3.0Ag-0.7Cu-5.0In. In the joint with Sn-5.0Sb (mass%), a solder area was remained in the center of the joint although a large number of columnar IMCs form at the joint interface. The die shear force of the joint with Sn-5.0Sb increased with increasing the bonding time due to formation and growth of IMCs. In the joint with Sn-3.0Ag-0.5Cu (mass%), IMCs formed at the joint interface and did not disperse in the entire joint.

Abstract: Tensile and low cycle fatigue properties of Sn-5Sb (mass%) solder were investigated with miniature size tensile specimens. The effect of temperature and strain rate on tensile properties and the effect of temperature on low cycle fatigue properties were examined. Tensile strength increases with increasing strain rate regardless of temperature investigated. For elongation, the effect of temperature on it is negligible although it slightly increases with increasing strain rate. The low cycle fatigue life of Sn-5Sb obeys by the Manson-Coffin’s equation. The effect of temperature on the fatigue life is negligible in the temperature range from 25 ^oC to 150 ^oC. In the low cycle fatigue test with a high total strain range of 4%, cracking at phase boundary mainly occurs regardless of temperature investigated. In the case of a low total strain range of 0.4%, ductile fracture mainly occurs, and cracking at phase boundary with generation of grooves also occurs at high temperature.