Preparation Of Modified Epoxy Based Electrically Conductive Adhesives With Polyimide And Study On Curing Reaction Kinetics Of The System

With the miniaturization of electronic components and the rapid development of printed circuit board, conductive connections by welding, riveting technique are more gradually replaced by conductive adhesives. The most important part of conductive adhesives is the choice of adhesive matrix.Epoxy adhesive has an excellent performance such as low shrinkage, electrical insulation properties, mixing performance and so on. However, because of their low extension, brittleness, it is not appropriate to use in structural parts, the brittleness of epoxy curing material greatly restrict its application. Polyimides (PI) especially aromatic polyimides have excellent properties of resistance to abrasion, thermal stability, radiation resistance, high dimensional stability. But pure PI have shortcomings of poor adhesion, higher processing temperatures and so on. Modified epoxy resin with PI can integrate the advantage of epoxy adhesive and PI, which has good thermal stability and adhesion. Polyimide containing four phenolic hydroxyl has good solubility, and as a result of the existence of phenolic hydroxyl groups, it can react with epoxy group and form a covalent bond, thereby it can enhancing the compatibility of the two and get a good toughening effect.This article mainly contains five parts:(1) preparation of the the monomer of hydroxyl polyimide (2) synthesis and performance test of a series of hydroxyl polyimide films (3) preperation and performance test of epoxy resin modified with hydroxyl polyimide (4) preperation and performance test of conductive adhesives (5) study on the curing reaction kinetics of epoxy resin modified with hydroxyl polyimide.Firstly,2,2-bis[4-(2,4-dinitrophenoxy)phenyl]propane (BDNPPP) were synthesized by the nucleophilic substitution of 2,4-dinitrochlorobenzene with diphenol in the presence of N,N-dimeth-ylformamide, then BDNPPP was reduced into 2,2-bis[4-(2,4-diaminophenoxy)phenyl]propane (BDAPPP) in the reduction system of Pd/C and hydrazine hydrate. The properties of the monomer were characterized by FTIR and DSC.Secondly, The polyamic acid solutions were prepared by BDAPPP,4,4'-ODA, maleic anhydride, and aromatic dianhydride including pyromelitic dianhydride (PMDA),4,4'-oxydiphtha-lie anhydride (ODPA),3,3',4,4'-tetracarboxylicbenzo phenone dianyhydride (BTDA), 3,3',4,4'-tetracarboxylic biphenyl dianhydride (BPDA), and the corresponding forties kinds of polyimide films were prepared by thermal imidization of the polyamic acids in the solvent (DMAc). The tests of machanical performance, DSC, TGA, FT-IR, contacting angle and water absorbance were performed on the seies of polyimide films. The results showed that the PI film (BDAPPP-44ODA-MA-ODPA) had the best overall performance.Then, we prepared adhesives with ES216 mixed with the linear polyimide and maleimide-based polyimide respectively. Besides, its'tensile strength, gel time, water absorption and TGA were tested. The results showed that the adhesive prepared by ES216 and linear polyimide had a better performance than the other one. A study on curing reaction kinetics of the better adhesive was also carried out. The curing process were studied by the non-isothermal differential scanning calorimeter (DSC), the kinetics of the curing processes were analyzed by Kissinger, Crane and Arrhenius equations. Curing kinetics parameters were evaluated. The results showed the activation energy and the order of reaction of the system were 63.24kJ/mol and 0.95.The conductive adhesive was made by the better adhesive and 73% modified flake silver powder PA-1. Silver conductive adhesive's volume receptivity, tensile shear strength and curing properties were studied systemically. The volume receptivity was tested by intelligent DC-low receptivity and the result was 10.45×10-4Ω·cm, the strength was tested by materials testing machine and the tensile shear strength of the cured conductive adhesive was 21.1MPa. The TGA analysis showed that the decomposition rate inflection point was 363.6℃, which suggested that the single component modified epoxy based conductive adhesive have excellent property of heat-resistance. The volume receptivity and the tensile shear strength didn't change after one month, which indicated the conductive adhesive had a long term usage at the room temperature.