Research Of Three-layer Flexible Copper Clad Laminate Adhesive

The three-layer flexible copper clad laminate(3L-FCCL)as the substrate materials of flexible printed circuit board,was widely used in most of electronic products such as folding mobile phones,digital cameras,laptops and LCD TV.FCCL was also known as adhesive FCCL which was composed of insulation film,copper foil and adhesive,and the adhesive directly affected the performance of the FCCL.In this paper,EP-CTBN prepolymer was prepared with E-44 epoxy resin as substrate and carboxyl-terminated acrylonitrile-butadiene rubber(CTBN)as toughening agent through the graft copolymerization method.The performance of FCCL and epoxy adhesive modified with CTBN by different methods,which including physical blending,block copolymerization and graft copolymerization,were compared.The effect of CTBN content on the properties of epoxy adhesive and FCCL was also discussed.The results showed that EP-CTBN copolymer was formed by stable chemical bonds though esterification reaction between hydroxyl of E-44 and carboxyl of CTBN during copolymerization process.It found that,the epoxy adhesive modified by graft copolymerozation had better comprehensive properties than that by physical blending and block copolymerization.The thermal stability of epoxy adhesive modified by graft copolymerozation increased with the increase of the content of CTBN along with the increase of the peel strength of FCCL,but the folding resistant of FCCL first increased and then decreased.And when the CTBN content increased to 50 wt %,the peel strength of FCCL reached 1.30 N/mm and the folding number was 5149 times.In order to further improve the peel strength of FCCL,polyamide acid(PAA)was added to epoxy adhesive in this article,and the performance of epoxy adhesive and FCCL were measured.It showed that,PAA played an important rolein improving adhesion of epoxy adhesive,but it had slight bad influence on the thermal stability of epoxy adhesive.And the secondary amide and carboxyl group participated in the curing reaction of E-44.Within a certain range,the peel strength of FCCL had a larger increase with the increase of the content of PAA,but the folding resistance decreased.When the PAA content is 8 wt%,the peel strength of FCCL reached to 1.75 N/mm,folding number was 3261 times,these properties all meet the requirements of FCCL industry.SEM analysis showed that,a brittle peel was performed on the cured unmodified epoxy adhesive.A not uniform two-phase structure was formed during the curing process of epoxy adhesive modified by physical blending,which would make the crack grow smoothly.The epoxy adhesive modified by block copolymerization had better toughness because of formed homogeneous after curing.The epoxy adhesive modified by graft copolymerozation had best toughness with a large number of uniformly distributed pores forming.And the pores of epoxy adhesive doped with PAA depth in adhesive inside,which led to higher peel strength of FCCL.