Research

Flip chip bonding is one of the most popular techniques to connect chip with the substrate in high density packaging. Different kind of underbump metallizations, such as Ni/Cu/Au or Cu/Ni(P) are used to interect with Sn-based solder material. The growth of intermetallic product phase that are developed during soldering and grown during application by solid-state diffusion is of prime ineterest, since the life of the product depends on the growth and morphological features of these phases. Research is in progress to study the diffusion controlled growth in these systems.

Nb3Sn superconductor is one of the most important superconductors in applications. This is grown by bronze technique, where Nb3Sn phase forms between Nb and Cu(Sn) alloy by diffusion controlled process. Study is going on to determine growth kinetics of the phase and to determine diffusion parameters in this system. Further to shed lights on atomic mechanism of diffusion other superconductors with A15 structure, such as V3Si, Nb3Au, V3Au. In these phases, we shall determine tracer diffusion coefficients following diffusion couple technique.

Cu interconnects have replaced Al interconnects in fast switching devices because of superior conductivity and electromigration resistance. In this project, study will be carried on different aspects, like interaction of diffusion barrier layer with Cu and Si, texture evolution in Cu after deposition and the effect of alloying elements on different properties. This work is in collaboration with Mr. G.V. Mahesh and Dr. Satyam Suwas.

High temperature materials play a crucial role in the performance of gas turbine in land-based application and aircraft engines. Although, inlet gas temperature in the turbine combustor is around 1450-1500 °C, presently, maximum operating temperature that can be reached is only 1150 °C using third generation Ni-based single crystal alloys (3GXs). Cooling air is used to decrease gas temperature because of lack of a suitable material. Presently, there is a challenging task for material scientists to develop an alloy, which can be exposed at much higher service temperature. The increase in operating temperature will decrease specific fuel consumption and cooling air requirement. On the other hand, there is also an added interest to reduce weight of the turbine blade. With decrease in weight, centrifugal stress required on the rotor can be decreased which will further help to increase overall efficiency. Niobium-based silicides have potential to replace Ni-based superalloys, because of their low density and high strength at elevated temperature. Creep properties of these alloys are found to be comparable with Ni-based super alloys. Research is going on to study the effect of alloying elements on different physical and mechanical properties in this system.

Diffusion controlled interactions in the solid-state when one solid reacts with another solid, liquid or gas to produce solid product layer is important from both the viewpoint of academic interest and industrial application. In recent times, we found different unknown but characteristic marker behaviour (for example bifurcation of the marker plane in Ag-Zn system). These findings not only helped us to gain better understanding but also to develop physico-chemical approach. Following physico-chemical approach one can understand/predict the morphological evolution. Research is going on for better understanding in this area.

Backscattered Electron Image (BEI) of a diffusion zone developed between Zn and Ag after reaction in argon at 370C for 5 hrs. ThO2-particles were used as inert Kirkendall markers between the initial end-members. Two well-defined Kirkendall-marker planes (K1 and K2) emerged upon the interaction.

There is a continuous effort to improve the properties of Ni-based superalloys used in gas turbines in aerospace applications. We are studyng the effect of alloying elements, such as Pt, Re etc. to understand the effect on diffusion and mechanical properties. In this project, our aim is first to determine diffusion parameters, like, interdiffusion coefficients, intrinsic diffusion coefficients and tracer diffusion coefficients both in binary and ternary systems. Indentation technique will be followed to study the relative change in the mechanical properties with the change in alloying elements.

These systems are important for high temperature applications. We shall concentrate our studies in these systems to determine diffusion parameters, such as, interdiffusion coefficients, intrinsic diffusion coefficients and tracer diffusion coefficients.

Designing of new alloys with much improved properties is always required for different applications. To achieve a property balance, very frequently we need to produce alloy with different elements. In this respect, the classical diffusion multiple technique can be used as the first step to accelerate alloy-design. This technique is useful for acquiring knowledge on the variation of mechanical properties with composition, from a limited number of experiments. Different compositions will be coupled at elevated temperature and annealed for certain time so that diffusion controlled reaction product layers form with varying compositions of different elements. Composition profile is measured with the help of Electron Probe MicroAnalysis (EPMA) and instrumented nanoindentation is used to evaluate hardness and elastic modulus at a submicron scale. This way one can correlate mechanical properties with the variation of composition in interdiffusion zone. Accordingly, few selected alloy compositions can be considered for further study to develop processing techniques and to study mechanical properties for the purpose of finding a suitable alloy for application.