High temperature tolerance polyimides

For aerospace applications, several advanced sealants have been mentioned cyanosilicones (123),fluoroalkyl-arylenesiloxanylene (FASIL) (124), phosphonitrilic fluo-roelastomers (PNF ) (125,126), flexible polyimide (127), tetrafluoroethylene oxide phenylquinoxaline elastomer (FEX) (128), perfluoroalkyl ethers (129), etc. These advanced sealants have been used for fuel tank sealing, channel sealing, filleting, aerodynamic smoothing, and other assemblies. Basically, they should be high-temperature serviceable, fault-tolerant, and adhere well to metals and/or composites. 

Some general conclusion from these studies are (1) Cu/PI TFML structures have excellent thermal and mechanical stability under extremes of temperature, humidity, and radiation (2) the adhesion of polyimide is highly dependent on interface chemistry and surface preparation (3) PI rapidly absorbs and desorbs water, which has an appreciable effect on its dielectric properties and thus the electrical charactersitics of TFML interconnections the electrical design tolerances must accommodate these variations or the package must be hermetically sealed (4) properly baked and sealed TFML packages can maintain MIL-STD internal moisture levels of less than 5000 ppm at 100°C. 

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