Electrically Conductive Adhesives Based On Epoxy Resins Modified By Polyimide Powder With Carboxyl Groups

Electrically conductive adhesive is prepared from epoxy adhesive and high electrical conductive silver particles.Because of its environmental, non-toxic and low-cost,it takes place of tin-lead welding.It meets the need of semiconductor packages,wire connection among electronic components,repair printed circuit board wiring and connect conductive composite materials.Epoxy adhesive is a class of high performance engineering adhesives,formulated from epoxy resin,curing agents,diluent,enhancers and fillers.However,with the development of technology, market requirements are no longer confined to its original performances,such as its heat resistance,adhesive properties.Epoxy adhesive has excellent performances such as low shrinkage, electrical insulation properties and so on.However, because of their low extension, brittleness, it is not appropriate to use in structural parts. The brittleness of epoxy cured greatly restrict its applications. 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.Modified the epoxy adhesive with the polyimide, the advantages of epoxy and polyimide both can be integrated. Not only improve its heat resistance, but also improve its bonding properties, toughness, etc. Because this polyimide can be introduced by functional groups with active groups, which prepared the functional polyimide adhesive, to enhance the value of potential applications. In recent years, carboxyl containing polyimide epoxy adhesive has some researches both at internal and abroad.The subject is mainly divided into six parts:(1) Preparation and characterize of carboxyl containing polyimide monomer; (2) Preparation of the carboxyl containing polyimide film and its performances testing and research; (3) Development of epoxy adhesive; (4) Development of the modified carboxyl containing polyimide epoxy adhesive system;(5) Study on the curing reaction kinetics of epoxy resin modified with carboxyl containing polyimide;(6)Preparation of the conductive adhesive and its performances testing.Prepare 3,5-bis (4-nitrophenoxy) benzoic acid (35BNPBA) with 3,5-dihydroxybenzoic acid (35DHBA), potassium carbonate(K2CO3)and hydroquinone (PCNB) as raw materials in toluene and N,N-dimethylformamide (DMF) solvent mixture by the nucleophilic substitution reaction; and achieve 35BAPBA with further reduction by using of activated carbon, hydrazine hydrate, ferric chloride. Characterize mixture by using of DSC, FT-IR.Then, polymerization of the corresponding polyamic acid by the synthesized 35BAPBA monomer reacting with pyromellitic dianhydride (PMDA),3,3',4,4'-diphenyl ether dianhydride (ODPA),3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA),biphenyl dianhydride (BPDA) respectively.and obtain corresponding polyimide films by further cyclization, test the poly polyimide films'DSC, TGA, FTIR, contact angle, water absorption, mechanical. The results show that polyimide films have excellent performances.Modify ES216-type epoxy adhesive with 35BAPBA/ODPA-PI polyimide, then test its tensile shear strength, gel time, water absorption,weight loss and other performances. The results show that, ES216 type epoxy resin adhesive modified with 35BAPBA/ODPA-PI polyimide has excellent overall performances.Study its curing reaction kinetics. The activation energy of systerm is 72.5kJ/mol, the order of reaction is 0.9. Added 73% PA-1 into the epoxy, Silver conductive adhesive's volume receptivity, tensile shear strength and curing properties are studied systemically. Volume receptivity is 2.5×10-3Ω·cm; strength is 22.0 MPa. The volume receptivity and the tensile shear strength has not big changing after a long time,which indicates the conductive adhesive has a long term usage under high temperature.