Study On The Preparation And Properties Of Conductive Adhesive Filled With Multi-component Fillers For Green Packaging

In order to meet the development trend to miniaturization, facilitation and integration of electronic packaging products, combined with the investigation of conductive adhesive, the mixture of micron-filler and nano-filler was adopted to improve the electronic property of conductive adhesive. The synergistic effect of the micron and nano fillers could achieve high conductive property when the content of the filler was low and perfect conductive adhesive could be obtained. Combined with the theoretical analysis and experimental results, the fabrication parameters of conductive filler were optimized, the effects of conductive filler and curing reaction on the properties of conductive adhesive were studied systematically, the computational formula of conductive adhesive was optimized and the bulk resistivity of conductive adhesive was calculated. At last, the conductive mechanism was analyzed.Cu powders coated by nano-Ag layer with different shapes were fabricated through chemical plating and the effect of Cu powders shapes on resistance to oxidation was analyzed; the silver nanowire was prepared through polyol method, the effects of parameters and control agents on the growth of silver nanowire were investigated and the optimized parameters were obtained. In order to reduce the pores in the resin matrix and improve the toughness of resin, curing agent and antifoaming agents were added into the resin system. The curing parameters were investigated from the point of curing reaction kinetics. Based on the analysis result, characteristic temperatures of the system with 0℃ as heating rate were reckoned. The initial curing temperature was 105℃, the peak curing temperature was 137℃, and the terminal curing temperature was 169℃.The conductive filler composed of Cu powders coated by nano-Ag layer and silver nanowire and resin matrix were mixed to fabricate conductive adhesive. The effects of conductive filler(content, shape, size and component) and resin matrix(curing temperature and curing time) on the electrical property of conductive adhesive were investigated, then the optimized formula was obtained. The results showed that, with the increase of conductive filler content, the bulk resistivity of conductive adhesive decreased with two discontinuities; the nanometer effect of nano conductive filler could reduce the discontinuities of the conductive adhesive; and the conductive filler composed of Cu powder coated by nano-Ag layer and silver nanowire could reduce the bulk resistivity and percolation threshold of conductive adhesive. When the conductive adhesive was cured at 170℃ for 60 min using Cu powder coated by nano-Ag layer and silver nanowire as conductive filler and the content of filler was 60 wt.%, the lowestbulk resistivity was 6.53×10-5Ω·cm, while the shear strength of the adhesive was5.36 MPa.Combined with the theoretical calculation and experimental results, the conductive mechanism of the conductive adhesive was studied. The results show that contact conduction and tunnel conduction are the main conductive types. When the content of conductive filler is lower than the percolation threshold, the tunnel conduction is the conductive type and few conductive particles could contact, the bulk resistivity is high;when the content of conductive filler is higher than the percolation threshold, the contact conduction is the conductive type and majority of conductive particles can contact, the bulk resistivity is low.