Development and characterization of electrically conductive copper-based adhesive pastes for die attach in microelectronics packaging

Die attach or die bonding is fundamental to multiple types of microelectronics packaging. It consists in the process of attaching a semiconductor die to a package, a substrate such as a PCB or another die. Copper has the necessary characteristics to replace silver in interconnection materials currently present on the market: very similar electrical, thermal and mechanical properties whit the advantage of an extremely lower price. In this research, several electrically conductive, high temperature resistant copper-based adhesive pastes are developed. Different formulations containing copper flakes, epoxy resin and terpineol are investigated. Two different types of epoxy resins are used. The developed adhesive pastes are used in die attach experiments on copper and ceramic substrates. The best conditions for the curing process are studied by building assemblies at different temperatures. The electrical resistivity of the developed adhesive pastes is measured in the order of magnitude of 10-6 Ω•m. The produced assemblies are observed under optical microscope, scanning acoustic microscope, scanning electron microscope. Direct shear tests suggest a shear strength of ca. 10 MPa. Cross sections are analysed to understand the morphology of the paste in the interconnection. DSC curves of paste components and developed pastes are observed to understand the reaction mechanisms at different temperatures. Additional pastes are produced to understand the effects of metal particles protective agents and the metal particles size. This thesis project has been conducted in collaboration with the research group of Prof. Dr. Gordon Elger at the Institute for Innovative Mobility of the Technische Hochschule Ingolstadt (THI)/Ingolstadt University of Applied Sciences (Germany) within the Erasmus+ for Traineeships program. The traineeship period was under the additional supervision of Mr. Sri Krishna Bhogaraju, from April 4th 2022 to September 30th 2022.