Preparation And Properties Of Polyimide Coatings

In recent years, with the rapid development of microelectronics industry, it urgently needs the thermal stability, mechanical properties, coefficient of thermal expansion(CTE), dielectric constant, water absorption and adhesion of packaging materials to be further improved. Due to the excellent comprehensive properties, polyimide(PI) insulating coating has been widely used in the field of microelectronics for it can meet microelectronics industrial performance requirements to a great degree. It is called PI coating. However, traditional PI coating has some inherent disadvantages, such as higher CTE, higher dielectric constant, higher water absorption and weaker adhesion. Therefore, improve these properties of PI coating has become an important reasearch direction for research workers.In this paper, PI coatings of BTDA-PMDA-ODA and BTDA-PMDA-HQDPA-ODA type were firstly prepared. In order to enhance the properties of this material, we modified the latter by adding 1,3-bis(3-aminopropyl)tetramethyldisiloxane)(GAPD) and SiO2 nanoparticles. And we used sol-gel and blending method to prepare PI/SiO2 hybrid coatings respectively. PI films and PI composite plates with different substrates were acquired via the conventional thermal imidization process. Chemical structures, mechanical properties, CTE, thermal properties, surface morphology, contact angles, insulation resistance and water absorption of PI films were characterized by fourier transform infrared spectroscopy(FTIR), nuclear magnetic resonance(1H-NMR), X-ray photoelectron spectroscopy(XPS), electronic universal tensile testing machine, thermo mechanical analysis(TMA), thermogravimetric(TG), differen-tial scanning calorimetry(DSC), scanning electron microscopy(SEM), energy dispersive X-ray spectrometry(EDX), atomic force microscopy(AFM), contact angle measurement and insulation resistance measurement. The adhesion between cured coatings and various substrates was determined by cross-cut test, cooking test and lap shear strength test.The results showed that:when n(BTDA):n(PMDA):n(HQDPA)=4:1:20, the PI coating of BTDA-PMDA-HQDPA-ODA type has the best comprehensive properties, with 129.82MPa of tensile strength,523.59℃ of the initial decomposition temperature(Tsta),270.76℃ of the glass transition temperature(Tg),0 of adhesion level on aluminum, copper and silicon substrates, high insulating resistance and lower than 1% of water absorption. But its high CTE(45.8×10-6/℃) and poor adhesion on SiO2 substrate still need to be improved. The introduction of GAPD to PI mainchain can effectively improve the adhesion between PI coating and SiO2 substrate. When n(GAPD)=n(ODA)/40, organosiloxane modified PI coating has the optimal comprehensive properties, it can basically meet the needs of industrial applications except its high CTE(51.6×10-6/℃). The introduction of SiO2 nanoparticles can effectively reduce the CTE of PI coating. Sample A PI/SiO2-15 which was prepared by sol-gel method has the best comprehensive properties, its CTE was decreased to 23.0×10-6/℃, which is similar to the CTE of aluminum and copper. In addition, its tensile strength is 100.86MPa, its Tsta is 520.31℃ and its Tg is 277.26℃, it also has excellent adhesion on various substrates and good insulation. Furthermore, its water absorption can be as low as 0.30%. So this modified hybrid coating can fully meet the needs of microelectronics applications.