Reactive interdiffusion between a lead-free solder and Ti/Ni/Ag thin-film metallizations

Abstract

The reactive interdiffusion between a Sn-3.0wt.%Ag-0.7wt.%Cu solder and thin-film Ti/Ni/Ag metallizations on two semiconductor devices, a diode and a metal-oxide-semiconductor field-effect transistor (MOSFET), and a Au-layer on the substrates are studied. Comprehensive microanalytical techniques, scanning electron microscopy, transmission electron microscopy (TEM), and analytical electron microscopy (AEM) are employed to identify the interdiffusion processes during fabrication and service of the devices. During the reflow process of both diode and MOSFET devices, (1) the Ag layer dissolves in the liquid solder; (2) two intermetallics, (Ni,Cu) 3 Sn 4 and (Cu,Ni) 6 Sn 5 , form near the back metal/solder interface; and (3) the Au metallization in the substrate side dissolves in the liquid solder, resulting in precipitation of the (Au,Ni,Cu)Sn 4 intermetallic during solidification. During solid-state aging of both diode and MOSFET solder joints at 125°C and 200°C, the following atomic transport processes occur: (1) interdiffusion of Cu, Ni, and Sn, leading to the growth of a (Ni,Cu) 3 Sn 4 layer until the Ni layer is completely consumed;(2) interdiffusion of Au, Cu, Ni, and Sn through the (Ni,Cu) 3 Sn 4 layer and unconsumed Ni layer to the Ti layer to form a solid solution; and (3) further interdiffusion of Au, Cu, Ni, and Sn through the (Ni,Cu) 3 Sn 4 layer to from an (Au,Ti,Ni,Cu)Sn 4 layer. The growth of the latter layer continues until the entire Ti layer is consumed.

Thermodynamic and kinetic models for describing microstructure evolution during joining of metals and alloys

“…Computational thermodynamic and CK tools are extensively used for predicting interfacial reactions and interdiffusion during soldering and service. [202][203][204][205][206][207][208][209] Microstructure evolution during soldering has also been linked to failures of solders during service. 210 These failures are affected by phase change as well as recrystallisation behaviours.…”

Al2O3–Al2O3 and Al2O3–Ti Solder Joints—Influence of Ceramic Metallization and Thermal Pretreatment on Joint Properties

“…This multilayer structure generally consists of an adhesion and conduction layer adjacent to the substrate, a diffusion barrier layer and a wetting layer which is in direct contact with the solder alloy. Typical layer structures are Cu/Ni/(Au, Pd), Ti/Ni/Ag, or Ti/W/Au . The coatings are usually applied by sputtering, electroplating, and/or electroless deposition.…”

“…The assembly of high‐performance functional metal–ceramic components often involves different manufacturing steps prior to the joining process, for example, deposition of resistor tracks or contacting of wires involving different temperature–time profiles. It can be assumed that any thermal pretreatment causes diffusion in the interlayer which influences the soldering behavior and finally the mechanical joint properties. However, systematic studies of the influence of thermal pretreatments on the joint properties of premetallized and soldered ceramic–ceramic or ceramic–metal joints are currently lacking.…”