Nano and micro materials in a Pb-free world

This paper examines the use of nano and micro materials in the area of “Pb-free” technology. A variety of Pb-free materials for advanced organic packaging have been developed. These include capacitors as embedded passives, highly conducting nano-micro media for Z-interconnects, lead free assembly paste, and Z-interconnects suitable for Pb-free assembly. The electrical properties of capacitors fabricated from BaTiO₃-epoxy nanocomposites showed a stable capacitance over a temperature range from 20°C to 120°C. Low resistivity paste, with volume resistivity in the range of 10^-4 ohm-cm to 10^-5 ohm-cm depending on composition, particle size, and loading can be used as conductive joints for high frequency and high density interconnect applications. A variety of metals including Cu, Ag, LMP (low melting point) and LMP-coated Cu fillers have been used to make lead free electrically conducting adhesive technology as an alternative to solders. The mechanical strength of the various Pb-free conducting pastes was characterized by the measurement of tensile strength. Most of the conducting pastes exhibited no fail even up to 1500 PSI. Reliability of the Pb-free structures was ascertained by IR-reflow, thermal cycling, PCT (Pressure Cooker Test) and solder shock. All capacitors experienced less than 5% change after 3X, Pb-free IR reflow and 1000 cycles of thermal cycling (ATC, DTC). Altogether, this is a new direction in the development of Pb-free Packages and more specifically in the development of substrates with Z-interconnects suitable for Pb-free assembly.