Nano-Ag Filled Anisotropic Conductive Adhesives (ACA) with Self-Assembled Monolayer and Sintering Behavior for High

Recently, anisotropic conductive adhesives (ACAs) have attracted increasing interests in electronic packaging industry due to the advantages of ultra fine pitch capability potential (pitch <20 mum due to the availability of micro-sized conductive particles), low processing temperatures, low stress on substrate, environmentally friendly, etc. In this study, effects of nano silver (Ag) particles on electrical properties of ACA formulations were investigated. The nano Ag particles exhibited sintering behavior at significantly lower temperatures (<200degC) than the melting point (Tm of Ag is 960degC). The sintered nano Ag particles significantly reduced the ACA joint resistance and enhanced the current carrying capability of ACAs. The reasons for the enhanced performance of ACA were attributed to the increased contact area and improved interfacial contact between nano Ag and bond pads by sintering and compressing processes of the ACA. In addition, different types of self-assembled monolayers (SAMs) were used to treat nano Ag fillers. Thermogravimetric analyzer (TGA), differential scanning calorimeter (DSC), contact angle and photoacoustic Fourier Transfer Infrared (FTIR) results indicated the SAMs were well coated on the nano Ag particles. Furthermore, 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 the improved interface properties of the high performance ACA for potential microprocessor applications