Fluorinated poly polyimide film

Figure 15.24 shows the fabrication process of the optical filter on a fluorinated polyimide substrate. First, the low-thermal-expansion-coefficient PMDA/TFDB poly(amic acid) solution was spin-coated onto a Si substrate and baked. Then alternate TiO2 and SiO2 layers were formed on the polyimide film by ion-assisted deposition. The multilayered polyimide film was diced and peeled off from the Si substrate. In this way, thin optical filters on a fluorinated polyimide substrate are easily fabricated. 

Among various strategies that have been used to synthesize polyimides with lower dielectric constants, the most common approach is to incorporate fluorene, in the form of trifluoromethyl groups, into diamine and dianhydride units that minimize polarizability and increase the free volume [46]. It is well-known that fluorene atom has unique characteristics such as high electronegativity and low electric polarity. These properties give fluorinated polymers (e.g., poly[tetrafluoroethylene]) attractive features such as low water uptake, water and oil repellency, low permittivity, low refractive indices, resistance to wear and abrasion, and thermal and chemical stability. Fluorination is also known to enhance solubility and optical transparency and to lower the moisture absorption of polyimides. Therefore, it is expected that fluorinated polyimides will be widely applied in the electro-optical and semiconductor industries. The polymer series studied was essentially limited mainly to 6F dianhydride because it proved to be the only dianhydride with which many of the fluorinated diamines would form polymer films suitable for physical characterization. 

W.C. Wang, R.H. Vora, E.T. Kang, K.G. Neoh, C.K. Ong, L.F. Chen, Nanoporous ultra-low-K films prepared from fluorinated polyimide with grafted poly(acrylic acid) side chains, Adv. Mater. 16 (1) (2004) 54-57. 

Wang W-C, Vora R H, Kang E-T, Neoh K-G, Ong C-K, Chen L-F (2004) Nanoporous Ultra-low-K Films Prepared from Fluorinated Polyimide with Grafted Poly(acrylic acid) Side Chains. Adv. Mater. 16 54-57. 

Table III lists the properties of perfluorinated polyimides, along with those of partially fluorinated and unfluorinated polyimides. The structure of PMDA/ODA is the same as that of Dupont s Kapton. Because of the direct introduction of fluorines into the aromatic rings and the flexible structure of the lOFEDA component, the polymer decomposition temperatures and Tg s of perfluorinated polyimides are slightly lower than those of conventional poly imides. The thermal stability of these films is nonetheless high enough to withstand the manufacturing process for IC s and muitichip modules.

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