Z.L. Li

Rapid formation of Ni3Sn4 joints for die attachment of SiC-based high temperature power devices using ultrasound-induced transient liquid phase bonding process

High melting point Ni3Sn4 joints for the die attachment of SiC-based high temperature power devices was successfully achieved using an ultrasound-induced transient liquid phase (TLP) bonding process within a remarkably short bonding time of 8s. The formed intermetallic joints, which are completely composed of the refined equiaxial Ni3Sn4 grains with the average diameter of 2μm, perform the average shear strength of 26.7MPa. The sonochemical effects of ultrasonic waves dominate the mechanism and kinetics of the rapid formation of Ni3Sn4 joints.

Control Al/Mg intermetallic compound formation during ultrasonic-assisted soldering Mg to Al

To prevent the formation of Al/Mg intermetallic compounds (IMCs) of Al3Mg2 and Al12Mg17, dissimilar Al/Mg were ultrasonic-assisted soldered using Sn-based filler metals. A new IMC of Mg2Sn formed in the soldered joints during this process and it was prone to crack at large thickness. The thickness of Mg2Sn was reduced to 22u202fμm at 285u202f°C when using Sn-3Cu as the filler metal. Cracks were still observed inside the blocky Mg2Sn. The thickness of Mg2Sn was significantly reduced when using Sn-9Zn as the filler metal. A 17u202fμm Mg2Sn layer without crack was obtained at a temperature of 200u202f°C, ultrasonic power of Mode I, and ultrasonic time of 2u202fs. The shear strengths of the joints using Sn-9Zn was much higher than those using Sn-3Cu because of the thinner Mg2Sn layer in the former joints. Sn whiskers were prevented by using Sn-9Zn. A cavitation model during ultrasonic assisted soldering was proposed.

Homogeneous (Cu, Ni) 6 Sn 5 intermetallic compound joints rapidly formed in asymmetrical Ni/Sn/Cu system using ultrasound-induced transient liquid phase soldering process

Homogeneous (Cu, Ni)6Sn5 intermetallic compound (IMC) joints were rapidly formed in asymmetrical Ni/Sn/Cu system by an ultrasound-induced transient liquid phase (TLP) soldering process. In the traditional TLP soldering process, the intermetallic joints formed in Ni/Sn/Cu system consisted of major (Cu, Ni)6Sn5 and minor Cu3Sn IMCs, and the grain morphology of (Cu, Ni)6Sn5 IMCs subsequently exhibited fine rounded, needlelike and coarse rounded shapes from the Ni side to the Cu side, which was highly in accordance with the Ni concentration gradient across the joints. However, in the ultrasound-induced TLP soldering process, the intermetallic joints formed in Ni/Sn/Cu system only consisted of the (Cu, Ni)6Sn5 IMCs which exhibited an uniform grain morphology of rounded shape with a remarkably narrowed Ni concentration gradient. The ultrasound-induced homogeneous intermetallic joints exhibited higher shear strength (61.6u202fMPa) than the traditional heterogeneous intermetallic joints (49.8u202fMPa).

Wetting mechanism of Sn to Zr 50.7 Cu 28 Ni 9 Al 12.3 bulk metallic glass assisted by ultrasonic treatment

In this work, pure Sn was used to wet Zr50.7Cu28Ni9Al12.3 bulk metallic glasses (BMGs) assisted by ultrasonic treatment. Without ultrasonic treatment, pure Sn showed a non-wetting condition to BMG. Ultrasonic vibration facilitated the wetting of Sn to BMG. Prior to ultrasonication for 30u202fs, only physical adsorption formed at the Sn/BMG interface. Increasing ultrasonic time led to the alteration of the bond at the Sn/BMG interface from point contact to local surface contact, and to diffusion layer. Two bonding modes of order-order and order-disorder were discovered at the Sn/BMG interface. Cu content was higher than the other elements near the bonding interface. Longer diffusion distances of Sn into the BMG were obtained at high ultrasonic power, high temperature and large dip depth.

Reduction of intermetallic compounds in ultrasonic-assisted semi-solid brazing of Al/Mg alloys

ABSTRACT An ultrasonic-assisted semi-solid brazing method was used to control Mg/Al intermetallic compounds (IMCs). Zn–20.95Al, which has a large semi-solid temperature range of 60°C, was chosen as filler metal. Oxide films on the Al/Mg surfaces were removed despite the semi-solid state of the filler metal at 430°C. Al–Mg–Zn IMCs were observed inside the joint at 667u2009W and 5u2009s. The IMCs was reduced as ultrasonication time was prolonged. At high power of 1000u2009W, short ultrasonication time was needed to guarantee that no IMCs remained inside the joint. Otherwise, new IMCs formed because of serious cavitation erosion on substrates. Ultrasonication time of 20u2009s was unable to completely eliminate IMCs and solid phases at 423°C.

A Comparative Study on the Microstructure and Mechanical Properties of Cu 6 Sn 5 and Cu 3 Sn Joints Formed by TLP Soldering With/Without the Assistance of Ultrasonic Waves

In this study, the microstructure and mechanical properties of Cu6Sn5 and Cu3Sn intermetallic joints, formed by the transient liquid phase (TLP) soldering process with and without the assistance of ultrasonic waves (USWs), were compared. After the application of USWs in the TLP soldering process, Cu-Sn intermetallic compounds (IMCs) exhibited a novel noninterfacial growth pattern in the molten solder interlayer. The resulting Cu6Sn5 and Cu3Sn joints consisted of refined equiaxed IMC grains with average sizes of 3 and 2.3xa0µm, respectively. The Cu6Sn5 grains in the ultrasonically soldered intermetallic joints demonstrated uniform mechanical properties with elastic modulus and hardness values of 123.0 and 5.98xa0GPa, respectively, while those of Cu3Sn grains were 133.9 and 5.08xa0GPa, respectively. The shear strengths of ultrasonically soldered Cu6Sn5 and Cu3Sn joints were measured to be 60 and 65xa0MPa, respectively, higher than that for reflow-soldered intermetallic joints. Ultrasonically soldered Cu6Sn5 and Cu3Sn joints both exhibited a combination of transgranular and intergranular fractures during shear testing.