Novel nanotechnology for environmentally friendly interconnect materials in microelectronic packaging applications

Recently, anisotropic conductive adhesives (ACAs) have attracted increasing interests as environmentally friendly materials in electronic packaging industry because they are lead-free, require fewer processing steps, such as fluxing and cleaning (reducing processing cost), allow a low processing temperature (enabling the use of heat-sensitive and low-cost components and substrates), and fine pitch interconnect capability (enabling the miniaturization of electronic devices). In this study, effects of nano silver (Ag) particles on electrical properties of ACA formulations were firstly investigated. It is discovered that nano silver (Ag) particles exhibited sintering behavior at significantly lower temperatures (<200°C) than the melting point (Tm of Ag is 960°C). The sintered nano Ag particles significantly reduced the ACA joint resistance and enhanced the current carrying capability of ACAs. In addition, a novel approach of self-assembled monolayers (SAMs) was used to treat nano Ag fillers to improve the interface properties of ACA joints. These SAM-treated ACAs were thermally stable at processing temperatures of the ACA samples. By introducing the novel SAM materials into the interfaces between nano metal fillers and the substrate bond pads, the conductivity and current carrying capability of ACAs were further improved due to the stronger bonding between nano fillers and SAM and consequently, it improved interface properties of the high performance ACA for potential microprocessor applications. This improvement enabled the possibility of replacing lead-containing solder interconnects in electronic industry.