Research Projects

Due to its excellent electrical insulation, mechanical stiffness, and good thermal conductivity, Alumina can be used as a substrate to package electrical components used in harsh environments such as automotive and space. Presently, the low temperature-cofired ceramic (LTCC) technique is popular; however, the electrical conductivity of gold/silver paste is relatively lower. Although Silicon and glass interposers have been demonstrated in the past, the fabrication of alumina interposers has not been demonstrated yet due to the difficulty in machining hard and brittle alumina. The alumina interposer can withstand higher temperatures and external stresses. This project will demonstrate the fabrication of Alumina interposer technology by using cost-effective ‘cleanroom-free’ steps for the first time in India. A novel ultrasonic machining technique will create multiple through-holes and embedded redistribution lines simulataneously. The target etches rate of the ultrasonic technique will be more than 10 times more than the etch rate obtained by plasma etching. The opening dimensions of through-holes will be less than 0.1 mm. An electroless technique will be tried to deposit the conductive seed layer in through-holes. This will be the first attempt to deposit a conductive seed layer in alumina without using any additional adhesion layer. Instead of expensive chemical treatment, local roughening will be carried out to obtain stronger adhesion between electroless metal and alumina. Through-holes and embedded RDLs will be filled by a proprietary bottom-up electroplating technique. Post-deposition annealing will be investigated to obtain stress-free metal layers. In this project, direct Cu-Cu bonding will be established to ensure air-tight packaging. In electronic packaging applications such as space and automotive, maintaining long-term functionality is the key requirement. The traditional solder-based bonding (Cu-Sn-Cu) can crack under higher mechanical shock waves, which are generated during the launching of satellites. A 10 micrometer thick bonding pad will be created on individual dies by electroplated copper. The top surface of copper pads will be smoothened by polished, and a surface-protecting film will be deposited on top of copper pads. The proposed work is well aligned with the Indian Semiconductor Mission (ISM), under which packaging is classified as one of the four verticals. The successful execution of this project will be helpful in creating high-performance Integrated passive devices (IPDs), inductors, metal-insulator-metal (MIM) capacitors, thin film resistors, etc., by eliminating parasitic capacitance and extremely low substrate loss. Alumina-based interposers will integrate devices, surface mount components, and IPDs directly on the interposers.