Inter-substrate microstructure formation by electroplating bonding technology

Abstract

This paper explores the technological capabilities as well as theoretical limitations of electroplating bonding technology (EBT). EBT is of particular interest for the fabrication of complex three-dimensional electrical components (e.g. inductors, high frequency antennae, etc) as well as high aspect ratio mechanical structures with exotic geometrical features. Two separate substrates, each containing identical arrays of 150 µm tall copper microstructures, are aligned and then joined together using electrodeposition of copper under forced convection conditions to form 300 µm long structures that mechanically and electrically link the two substrates. Theoretical and experimental approaches are used to develop this bonding system. Mass transfer calculations of diffusion and convection are performed to predict optimal fabrication conditions. To demonstrate the ability to predict optimal plating conditions, a test coupon mimicking a chip-scaled interconnect system with 256 chip interconnects is designed, fabricated and characterized. The mechanical and electrical connectivity are verified by formation of daisy-chained test beds. The electrical testing of the bonded system shows an excellent conductivity of 0.097 Ohm/test row. Thermal-cycling-accelerated aging tests are performed over a temperature range from −55 to +125 °C. Electroplating bonded structures show excellent mechanical stability as well as electrical performance.