Interfacial Reactions and Mechanical Properties of Sn–58Bi Solder Joints with Ag Nanoparticles Prepared Using Ultra-Fast Laser Bonding

Abstract

The effects of Ag nanoparticle (Ag NP) addition on interfacial reaction and mechanical properties of Sn–58Bi solder joints using ultra-fast laser soldering were investigated. Laser-assisted low-temperature bonding was used to solder Sn–58Bi based pastes, with different Ag NP contents, onto organic surface preservative-finished Cu pads of printed circuit boards. The solder joints after laser bonding were examined to determine the effects of Ag NPs on interfacial reactions and intermetallic compounds (IMCs) and high-temperature storage tests performed to investigate its effects on the long-term reliabilities of solder joints. Their mechanical properties were also assessed using shear tests. Although the bonding time of the laser process was shorter than that of a conventional reflow process, Cu–Sn IMCs, such as Cu6Sn5 and Cu3Sn, were well formed at the interface of the solder joint. The addition of Ag NPs also improved the mechanical properties of the solder joints by reducing brittle fracture and suppressing IMC growth. However, excessive addition of Ag NPs degraded the mechanical properties due to coarsened Ag3Sn IMCs. Thus, this research predicts that the laser bonding process can be applied to low-temperature bonding to reduce thermal damage and improve the mechanical properties of Sn–58Bi solders, whose microstructure and related mechanical properties can be improved by adding optimal amounts of Ag NPs.

Mechanical Response of Cu/Sn58Bi-xNi/Cu Micro Solder Joint with High Temperatures

“…To improve the performance of Sn58Bi lead-free solder, a large amount of research based on experimental approaches has been proposed; for example, nanoparticles, metal compounds, and trace elements were added to Sn58Bi lead-free solder [11][12][13][14][15]. Jeong et al [16] studied the effects of different Ag nanoparticle (Ag-NP) content on the interface reaction and mechanical properties of Sn58Bi solder joints. The addition of an appropriate amount of Ag-NPs inhibits the growth of the interfacial intermetallic compound (IMC) and reduces the brittle fracture of the interface.…”

Microstructure Evolution and Shear Strength of Tin-Indium-xCu/Cu Joints

“…Tin-lead (Sn-Pb) alloy is the most widely used solder in electronic packaging because of its low cost, good wettability, acceptable electrical conductivity, and good mechanical properties [6]. In recent years, the Sn-Pb alloy has been replaced by Pb-free alloys, such as Sn-Au, Sn-Ag-Cu, Sn-Cu, Sn-Ag, Sn-Bi, and Sn-In, owing to the toxicity of Pb [7][8][9][10][11]. Most of the Pb-free alloys have higher melting temperatures (T m ) than the eutectic Sn-37Pb alloy (183 • C), e.g., Sn-3.5Ag (T m = 221 • C), Sn-3.0Ag-0.5Cu (T m = 217 • C), and Sn-9Zn (T m = 198 • C), [7,12].…”

“…Therefore, studies on low-melting-temperature alloys and their joint reliabilities are necessary. According to JIS Z 3282:2017, the solidus temperature of low-meting-temperature alloys is less than 150 • C. Among the Pb-free alloys, Sn-58Bi (T m = 138 • C), and In-48Sn (T m = 118 • C), are the most promising candidates for low-temperature soldering applications [8][9][10][11]. However, the eutectic Sn-58Bi alloy with a reflow temperature of 180 • C [13,14] is not suitable for substrates (in flexible electronics) that require a low operating temperature (<180 • C), such as heat-stabilized polyethylene terephthalate and heat-stabilized polyethylene naphthalate [1,2,15].…”