Study On The Interconnection Mechanism Of TLP Bonding Process In Cu/Sn/Ni System

High power devices has been rapidly developed and widely used, which is on the basis of Si C, a new generation of broadband semiconductor materials. It is necessary to put forward a new challenge to the packaging technology and materials, and to develop the chip bonding technology which can provide reliable interconnection at high temperature has become one of the most important research directions in the field of packaging technology. Though high melting point solder alloy and nano silver paste have been developed, there are some problems, such as high cost, complex process, and so on. Transient liquid phase（TLP） technique is applied to deal with the technology challenge The method can be at a lower sintering temperature formation have the characteristics of high melting point of the metal compound joint, can meet the requirements of reliability, high temperature solder joint or joints. The process can form metal compounds joint with high melting point at lower soldering temperature, which can meet the requirement of high temperature reliability of solder joint.TLP technique were applied to complete the interconnection of joint in Cu/Sn/Cu, Ni/Sn/Ni and Cu/Sn/Ni system in this paper. It became possible to obtain an intermetallic compound joint in a very short period of time, due to the introduction of ultrasound on the TLP technique. The microstructure, morphology, mechanical properties and thermal stability of the interface metallurgical reaction and thermal stability were studied.The joint of all intermetallic compound was finally obtained by prolonging the reaction time in the Cu/Sn/Cu and Ni/Sn/Ni system. With the increase of isothermal reaction time, the diffusion mechanism was changed from grain boundary diffusion to bulk diffusion, and the growth rate of intermetallic compound layer decreased with time. There were differences about the nucleation and growth process in the two systems. Cu3 Sn and Cu6Sn5 intermetallic compounds were nucleated at the solid-liquid interface in the Cu/Sn/Cu system, while the nucleation process of Ni₃Sn₄ intermetallic compounds occurs in the solid-liquid interface and liquid Sn solder. The Jackson factor of Cu6Sn5, Cu3 Sn and Ni₃Sn₄ intermetallic compounds are different, which lead to different morphology of the crystal. Compared with the traditional solder joint, the shear strength of the intermetallic compound joint was relatively high, so it can meet the requirements of the mechanical properties of the package interconnect.There formed Cu concentration gradient in liquid Sn solder due to the interaction of Cu and Ni, in the metallurgical reaction process of Cu/Sn/Ni system. There is a great difference in Sn/Ni and Sn/Cu interface. With the increase of the reaction temperature, the type of the solid-liquid interface was changed from the rough interface to the interface with small plane characteristics. The melting temperature of the metal compound joint was 418.4oC, which can satisfy the requirement of the thermodynamic stability. The average joint shear strength as the soldering temperature increased slightly reduced, the maximum shear strength was 31.4MPa.It became possible to obtain an intermetallic compound joint in a very short period of time, due to the introduction of ultrasound on the TLP technique. Because of the ultrasonic cavitation and acoustic streaming effect, the metallurgical reaction behavior at the interface was completely different from the traditional welding method, Blasting of a cavitation bubble caused a huge energy release, which promoted the dissolution and diffusion of metal substrate, breaking the equilibrium solubility limit. With the extension of ultrasonic treatment time, the over saturation of Ni and Cu in liquid phase Sn solder was increased, promoted the formation of the intermetallic compounds joint.