The improvement in wettability by adding Ti as an active element were confirmed by reduction of expulsion of liquid interlayer, elimination of interfacial gap, higher shear strength and favorable fracture path (partially through bond seam and the composite). It was found that not only the Ti content but also the pressure are critical factors affecting interfacial wettability and bond seam microstructure. To optimize both the interlayer composition design route and pressure for joining aluminum matrix composite reinforced with short alumina fiber (as-cast 30 vol pct Al2O3sf/Al), traditional transient liquid phase (TLP) bonding using Al-12Si and Cu interlayer and active-TLP (A-TLP) bonding using an active Ti-containing interlayer (Al-12Si-xTi, x = 0.1, 0.5, and 1 wt pct) under the same condition were compared in terms of interfacial wettability, bond seam microstructure, shear strength, and fracture path. Further, the mechanical strength and reliability of the two TLP bonding joints are reduced owing to the formation of brittle IMCs.
The results of the study indicate that the Cu–Sn and Ni–Sn TLP bonding processes transform the joints fully into Cu6Sn5/Cu3Sn and Ni3Sn4 intermetallic compounds (IMCs), respectively. In this study, the feasibility of Cu–Sn and Ni–Sn TLP bonding technologies as die-attach methods for power electronics packaging applications is examined. In particular, the TLP bonding technology is suitable for use in high temperature environments owing to its low cost and simplicity of the bonding process. Some good candidates for high temperature applications include high-temperature solders such as Au–20Sn, Ag or Cu sinter pastes, and transient liquid phase (TLP) bonding materials. Consequently, the reliability requirements for such modules have become highly stringent and new packaging materials and technologies are required to meet the demands of power electronic modules. Power electronics modules in electric vehicles and hybrid electric vehicles, particularly those containing next-generation power semiconductor devices such as silicon carbide and gallium nitride are operated at high temperatures exceeding 200 ☌. Different substrates and their corresponding interlayers used in TLP bonding are also mentioned where the process has been successfully applied. In the end, some applications are shown where the process can be applied in different sectors. Also, some potential alloy systems are discussed, showing the characteristic features and properties that TLP bonding provides. In this chapter, the history behind TLP is described in brief with special relation to the phase diagram describing the mechanism behind joint forming, classification, and applicable variants. Macro‐ and especially microelectronics, and electronics packaging industries are greatly served by using this joining technique in some advanced applications. Substituting the traditional soldering method, the process has now been used constantly to fabricate different embedded systems, engineering materials, and also been modified for other applications.
Transient liquid phase (TLP) bonding is a versatile joining process which exploits the potentiality of alloy systems to be used for joining a variety of materials.
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