Study Of Soldering Mechanism Between Active Solder Sn3.5Ag4Ti(Ce,Ga) And GaAs Substrate At Low Temperature

Gallium arsenide(GaAs) compound semiconduction material is one of the most important optoelectronic materials, and the most important microelectronic material after silicon. It has been widely used in optical communcations, mobile communictions and other important areas. However GaAs is commonly known as non-wettable matericals in conventional soldering system because of its stable chemical properties. Before soldering it should be make mental surface treatment. Currently, the active solder has been able to soldering some non-wetting material directly with simple peocess, and not require pre-metal and shielding gas. Active soldering is an important way to impore GaAs device package. Achieving the low temperature active soldering of GaAs can solve many problems of GaAs device package such as solder price, environmental protection, soldering technology, and has a great significance for the industry applications.The microstructure, the element distribution and the phase of interface recation between GaAs/Sn3.5Ag4Ti(Ce,Ga)/GaAs have been investigated by using scanning electron microscopy(SEM) 、 transmission electron microscope(TEM) and energy-dispersive spectroscopy(EDS) in this work. The mechanical properties of joints have been evaluated through the shear testing. The experiment results show that active solder Sn3.5Ag4Ti(Ce,Ga) can wet the GaAs substrate well at 250℃ in air; Ti element segregates at the interface at soldering process. With the increase of soldering time, the segregation become more obvious; Ga4Ti5 phase is formed at the interface. The shear strength of the joints is measured to be 15.25 MPa, 17.43 MPa, 23.32 MPa with soldering time of 1min, 30 min, 60 min respectively, which can well meet the requirements of the standard for the shear strength of die attachment.The mechanism of low temperature active soldering of GaAs/Sn3.5Ag4Ti(Ce,Ga)/GaAs has been analyzed based on diffusion kinetics, active adsorption theory and reaction thermodynamics theory. The results show that due to the Brownian movement and Dussan-Davis movement, some Ti atoms will move to solid-liquid interface from interal solder at the initial stage of soldering. There is a stronge active adsorption between GaAs substrate and Ti atoms located in the solid-liquid interface. The adsorption force is about 13.88J/m2(N/m) and consistent with the SV? direction. This adsorption make Ti atoms segregation at the interface and is the main reason for wetting. The interfacial reaction 4GaAs+9Ti=Ga4Ti5+4AsTi will take place because of its lowest Gibbs free energy, which is the main mechanism of low temperature active soldering.