Study On Conducting Polypyrrole Films For Electromagnetic Interference Shielding

The electromagnetic interference (EMI) brought a lot of harm to the world. And the broad use of epoxy molding compound (EMC) in electronic packaging materials produced more and more EMI problems. According to the status and development trend of EMI shielding materials, polypyrrole (PPy) shows a favorable application in EMI shielding because of its high electrical conductivity, outstanding stability and easy doping. In this study, insulating epoxy molding compound were used as the substrates for the depositing of PPy films. Conducting polypyrrole films with high electrical conducting and EMI shielding effectiveness and Fe₃O₄/PPy composite film with both magnetoconductivity and electrical conductivity were synthesized on the surface of EMC substrate attached with silane self-assembled monolayers (SAMs) by chemical polymerization, after the epoxy resin substrate surface being treated with contamination removing, coarsening and silane coupling agent modifying processes. The homogeneous, continuous and compact PPy film and Fe₃O₄/PPy composite film with EMI shielding effectiveness made the study have very important significance.Contamination removing and coarsening treatment condition were studied, the roughness degree of EMC substrates is the best at the coarsening temperature of 85℃for 30min. The silane content, pH value of silane coupling agent and dipping time of substrates in silane solution influence the quality of silane SAMs. Dipping time always is in the range of 10s～20min.The original concentration of pyrrole solution and oxidant FeCl₃ solution decide the rate of pyrrole polymerization and over oxidation reaction, and influence the polymerization time and the thickness, conductivity and morphology of PPy films greatly. The forming mechanism of PPy films on the surface of EMC substrates and silane self-assembled monolayers were discussed. Lots of experiments show that PPy films have favorite proerties when the concentration of pyrrole solution and FeCl₃ solution are 4.82mol/L and 1.8mol/L separately. And the measured EMI SE value of PPy film is about 22dB at the range of 30MHz～250MHz frequency and 17.5dB～20dB at the range of 250MHz～1.5GHz.There is the optimum doping concentration every dopant. Doping anion can make the PPy molecular chains arrange more regular, increase the concentration and move ratio of charge carrier in PPy chain at this saturation state. As a result, conductivity and compactness of PPy film have prominent increase. Such as, conductivity of PPy films doped by I2, HClO₄, SDBS and STS are all above 35S/cm, and calculated SE value is more than 20dB. Among them, the SE value of I2-doped PPy film get to 37dB at low frequency and 26dB at high frequency.Fe₃O₄/PPy composite films holding with magnetoconductivity and electrical conductivity were synthesized. Its saturation magnetization strength is 10.59emu/g. Particles of Fe₃O₄ with uniform size dispersed in the composite film. Fe₃O₄/PPy composite films with different conductivity show varied EMI shielding effectiveness. The SE values of composite films are more than 25dB at low frequency, and SE near to 100dB at 10GHz when the content of Fe₃O₄ is 1.0g.