BDB Adhesive Used In Flexible Electronic Substrate: Preparation And Properties

The demand for electronic equipments is increasing with the development of information technology.Flexible electronic displays are widely used to prepare various electronic devices,such as electronic newspaper,radio-frequency identification tags,wearable electronic equipments,toys,and biomedical devices.However,thermal deformation of flexible electronic substrate is a problem in the manufacture of flexible display.To solve the problem,it is necessary to temporarily fix or bond the flexible electronic substrate to some rigid substrate to avoid the problem of thermal deformation.Vacuum or electrostatic absorption is a popular way to temporarily fix the flexible electronic substrate,but it is expensive,and its application range was narrow.Bonding and debonding(BDB)adhesive is another way to temporarily bond the flexible electronic substrate,which was easily peelable and thermally stable.In this study,a kind of heat and ultraviolet(UV)-induced BDB adhesive was designed and prepared.Its bonding property,debonding property and thermal stability had been studied.On the basis,the proper formula of BDB adhesive and suitable operating conditions for bonding and debonding processes were determined.The BDB adhesive was designed and prepared through blending an epoxy resin,diglycidyl ether of bisphenol A(DGEBA)with an epoxy acrylate resin,bisphenol-A epoxy acrylate resin(BEA).The variation of the chemical structure of DGEBA and BEA in the sequential heat-and UV-curing processes was characterized by FTIR.The FTIR results indicate that DGEBA and BEA successfully took part in the heat-curing and UV-curing processes.A flexible polyimide film could be firmly bonded to a rigid glass substrate by the heat-curing of DGEBA in the adhesive,while the bonded polyimide film could be easily stripped from the glass substrate by the UV-curing of BEA.The influences of the key reaction parameters,such as the mass ratio of epoxy acrylate resin to epoxy resin,content of heat-curing agent,type of diluents,and UV irradiation time,on the bonding and debonding properties of adhesives were systematically investigated.Based on the variation of chemical structure in the curing process,and the dependence of the bonding and debonding properties on the curing conditions,a possible BDB mechanism was proposed.Thermal curing kinetics of diethylenetriamine(DETA)cured DGEBA system was analyzed by differential scanning calorimetry(DSC).The initial temperature of thermal curing reaction was obtained by analyzing the non-isothermal curing DSC curve of DGEBA/DETA system.The mechanism of thermal curing reaction of DGEBA/DETA system was analyzed based on the characteristics of its isothermal curing DSC curve.The effects of temperature and DETA concentration on the isothermal curing reaction were investigated.Based on the mechanism of thermal curing reaction,the experimental results were simulated by dynamic model.The critical curing degree and diffusion factor were introduced to the former model,and the curing kinetic model with the control of diffusion was obtained.According to the isothermal curing DSC curves,suitable curing time of DGEBA/DETA system was decided.Then the key parameters of thermal curing technics,such as temperature,curing time and DETA concentration of DGEBA/DETA system were applied to the preparation of BDB adhesive.Based on the results,the necessary adjustments for the above three parameters were made.At last,the proper thermal curing conditions of BDB adhesive were determined.According to the variation in content of C=C of BDB adhesive in the UV curing process characterized by FTIR,the conversion rate and reaction rate of C=C were calculated.Then UV curing kinetics of BDB adhesive was analyzed.An automatic acceleration process of the UV curing reaction was found at the initial stage,then the reaction rate of C=C slowed down attribute to the gel effect.The effects of photoinitiator concentration and UV light intensity on the conversion rate of C=C,reaction rate of C=C and debonding property of BDB adhesive were investigated.Based on the results,the UV curing conditions of BDB adhesive were optimised.Polymethylepoxysiloxane(PEMS)was synthesized by hydrosilylation reaction between polymethylhydrosiloxane and glycidyl methacrylate,and charactered byFTIR and ~1H NMR.The influences of feed ratio of Si-H to C=C,reaction time,reaction temperature and catalyst concentration on the reaction degree of Si-H and C=C were investigated,and then the reaction conditions were optimized.The thermal stability of BDB adhesive modified with PEMS was investigated by discoloration test and thermogravimetric analysis(TGA).The results showed that with the increase of PEMS concentration,the thermal stability of BDB adhesive was enhanced.Thus,PEMS could effectively improve the thermal stability of BDB adhesive.The storage modulus of the BDB adhesive layer was characterized by dynamic thermomechanical analysis(DMA).The result indicated that PEMS could reduce the storage modulus of the BDB adhesive layer,thus the rigidity of the BDB adhesive layer was improved.Besides,with the increase of PEMS concentration,the elongation at break of BDB adhesive layer developed.The result meat that the brittleness of BDB adhesive layer decreased and the risk of fragmentation of BDB adhesive layer was lowered in application.