Influence of Nanoparticles, Low Melting Point (LMP) Fillers, and Conducting Polymers on Electrical, Mechanical, and Reliability Performance of Micro-Filled Conducting Adhesives for Z-Axis Interconnections

This paper discusses micro-filled epoxy-based conducting adhesives modified with nanoparticles, conducting polymers, and low melting point (LMP) fillers for z-axis interconnections, especially as they relate to package level fabrication, integration, and reliability. A variety of conducting adhesives with particle sizes ranging from 80 nm to 15 μm were incorporated as interconnects in printed wiring board (PWB) or laminated chip carrier (LCC) substrates. SEM and optical microscopy were used to investigate the micro-structure, and conducting and sintering mechanisms. Volume resistivity of modified adhesives is in the range of 10
^-5
to 10
^-6
ohm-cm. Adhesives formulated with a conducting polymer exhibited tensile strength with Gould's JTC-treated Cu ≥ 3800 PSI, and as low as 1800 PSI for a conducting polymer-LMP based system. There was no delamination of conductive joints after 3X IR-reflow, pressure cooker test (PCT), and solder shock. Among all, the conducting polymer modified micro-filled adhesives showed the highest mechanical strength. The paper also describes a combinatorial approach to the synthesis of LMP coated particles. Several conductive adhesives were used in a z-axis interconnect construction for a laminate chip carrier and printed wiring board (PWB). The present process allows fabrication of z-interconnect conductive joints having diameters in the range of 55-300 microns. The processes and materials used to achieve smaller feature dimensions, satisfy stringent registration requirements, and achieve robust electrical interconnections are discussed.