Preparation And Properties Of Advanced Polyimide With Low Coefficient Of Thermal Expansion

As the development of advanced technology on the fields of electronics and microelectronics, the integrity, preciseness and reliability of electron devices like integrated circuit are rapidly improved as well. Therefore, substrate material in electronic packages with excellent performance is required to protect and support the electron devices. The most intelligent choice for substrate material in electronic packages goes to polymer insulated material that expresses perfect combination properties, in which is the polyimide (PI) stand out with the best heat resistance. Polyimide materials have controllable molecular structure and exhibit good mechanical property, thermal property, outstanding dielectric performance and environmental friendly while processing, which have lead to wide attention. In order to guarantee the reliability of electron devices, substrate material in electronic packages demand low coefficient of thermal expansion (CTE) to fit with heat-conducting layer (copper.et al) and avoid crack, split or layer separation in case of the raise of temperature while electron devices are operation. In this thesis, a new type of diamine monomer 2-(4-Aminophenyl)-5-aminobenzimidazole is introduced to prepare a serial of polyimide films with different diamine monomers and concentration to optimize mechanical property, thermal property and reduce CTE with control. Different kinds of tests and analysis are made on the prepared PI films to investigate the beneficial effect after modification. Main work in this thesis is listed below:A rigid monomer p-phenylene diamine (PDA) and a flexible monomer 4,4’-diaminodiphenyl ether (ODA) with ether link, together with 3,3’,4,4’-biphenyltetracarboxylic dianhydride (BPDA) are selected to synthesis serials of copolymerization BPDA-PDA-ODA and blending BPDA-PDA/BPDA-ODA polyimide films. The results demonstrate that the property of copolymerization BPDA-PDA-ODA films are a little better than that of blending polyimide films, and the tensile strength, heat resistance and dimensional stability are improved as the proportion of PDA raises.And then, a new type of diamine monomer BIA is added in with fixed ratio PDA:ODA= 7:3 to fabricate quaternary BPDA-(PDA+ODA)-BIA benzimidazole PI films. According to the results of characterization, the flexibility of quaternary PI films is significantly improved as the concentration of BIA goes up and the elongation at break reaches 40.4% with excellent thermal resistance and low coefficient of thermal expansion (CTE). This kind of PI films can be used efficiently in flexible circuit board and flexible substrate of electronic package.In order to remove the strong influence of flexible monomer ODA, ternary BPDA-PDA-BIA benzimidazole polyimide films are prepared in this thesis and investigate the effect of BIA on PI films. The mechanical property, thermal property, hydrogen bond interaction and CTE are analyzed by universal material machine, dynamic thermomechanical analyzer, FTIR spectrometer and thermomechanical analyzer. The new kind of ternary benzimidazole polyimide films express outstanding comprehensive properties that the tensile strength reach 288.7 MPa, thermal stability is improved significantly and the CTE value is reduced by 70% which is down to 10.83 ppm/K. In applications for substrates of electron package material, these PI films can meet the demand of suitable CTE with metal (as copper) with extraordinary mechanical property and thermal resistance.CTE of PI films fabricated in this thesis has a gradient which is from 10.83 ppm/K to 43.14 ppm/K. So that it is able to prepare an expected high performance PI films with a definite CTE value by adjusting the structure and proportion of different monomers. These new PI films with excellent property in this thesis will bright prospect for future electron application.