Interfacial Reaction and Mechanical Properties of Sn-Bi Solder joints

Abstract

Sn-Bi solder with different Bi content can realize a low-to-medium-to-high soldering process. To obtain the effect of Bi content in Sn-Bi solder on the microstructure of solder, interfacial behaviors in solder joints with Cu and the joints strength, five Sn-Bi solders including Sn-5Bi and Sn-15Bi solid solution, Sn-30Bi and Sn-45Bi hypoeutectic and Sn-58Bi eutectic were selected in this work. The microstructure, interfacial reaction under soldering and subsequent aging and the shear properties of Sn-Bi solder joints were studied. Bi content in Sn-Bi solder had an obvious effect on the microstructure and the distribution of Bi phases. Solid solution Sn-Bi solder was composed of the β-Sn phases embedded with fine Bi particles, while hypoeutectic Sn-Bi solder was composed of the primary β-Sn phases and Sn-Bi eutectic structure from networked Sn and Bi phases, and eutectic Sn-Bi solder was mainly composed of a eutectic structure from short striped Sn and Bi phases. During soldering with Cu, the increase on Bi content in Sn-Bi solder slightly increased the interfacial Cu6Sn5 intermetallic compound (IMC)thickness, gradually flattened the IMC morphology, and promoted the accumulation of more Bi atoms to interfacial Cu6Sn5 IMC. During the subsequent aging, the growth rate of the IMC layer at the interface of Sn-Bi solder/Cu rapidly increased from solid solution Sn-Bi solder to hypoeutectic Sn-Bi solder, and then slightly decreased for Sn-58Bi solder joints. The accumulation of Bi atoms at the interface promoted the rapid growth of interfacial Cu6Sn5 IMC layer in hypoeutectic or eutectic Sn-Bi solder through blocking the formation of Cu6Sn5 in solder matrix and the transition from Cu6Sn5 to Cu3Sn. Ball shear tests on Sn-Bi as-soldered joints showed that the increase of Bi content in Sn-Bi deteriorated the shear strength of solder joints. The addition of Bi into Sn solder was also inclined to produce brittle morphology with interfacial fracture, which suggests that the addition of Bi increased the shear resistance strength of Sn-Bi solder.

Dynamic Observation of Interfacial IMC Evolution and Fracture Mechanism of Sn2.5Ag0.7Cu0.1RE/Cu Lead-Free Solder Joints during Isothermal Aging

“…In the literature, investigating the reliability of isothermal aging of Sn-based lead-free solder joints has become an area of interest. Many scholars have studied the isothermal aging characteristics of SnAgCu/Cu [21][22][23][24][25], In-48Sn/Cu [26,27], and Sn-Bi/Cu [28,29] solder joints. They have focused on the growth kinetics of the interfacial IMC and the mechanical properties of solder joints during isothermal aging.…”

Conduction Path Formation Mechanism of Solderable Polymer Composites with Low-Melting-Point Alloy/High-Melting-Point Alloy Mixed Filler

“…As the HMPA mixes into the LMPA, the interconnection properties (e.g., ductility, fracture toughness) of the SPC joints can be enhanced because of a change in the microstructure arising from reduced total Bi content within the conduction path. 9) Figure 1 shows the newly proposed interconnection mechanism using an SPC with an LMPA/ HMPA mixed filler. During the reflow process, the viscosity of the polymer composite gradually decreases, and the oxide…”

Intermetallic Compound Layer Growth at the Interface between Sn-Ag and ENImAg Surface Finish

“…These alloys have a low melting temperature at 180 , which is 63Sn-37Pb and 60Sn-40Pb at the eutectic composition and near eutectic temperature, respectively. Many manufacturer's concern about the disadvantages of Sn-Pb, which is causing the environmental and human health affected due to the toxicity of Pb [7]- [12]. Due to these problems, lead-free candidate alloys such as the Sn-Ag are believed can replace the Sn-Pb solders.…”