The Preparation And Properties Of Photo-thermal Co-curing Electrically Conductive Adhesive

The electrically conductive adhesive（ECA）has outstanding advantages such as high line resolution,good wettability and simple process,which can meet the requirements of miniaturization and high integration of current electronic components in the electronic packaging field.Thermal-curing is the earliest and most widely used curing method in ECA field,but there are a series of shortcomings,such as high curing temperature,long curing time,high energy consumption,which are easy to damage electronic components in the curing process and are not suitable for thermal sensitive substrates.UV-curing technology can quickly cure the ECA at room temperature,but UV light is easy to be absorbed or scattered by the fillers,which affects the polymerization reaction caused by the photo-initiator.Therefore,the performance of UV-curing ECAs is generally poor.The photo-thermal dual-curing technology combines thermal polymerization with photo polymerization.In the process of photo-thermal dual-curing,the ECA is precured by photo curing process,and then is cured completely by thermal curing process,which overcomes the deficiency of single curing method.However,the step-by-step curing process is complicated and the curing time is still too long.The photo-thermal co-curing technology can use the irradiation heat and the reaction heat of photo polymerization to induce the thermal polymerization reaction,and the ECA can be cured completely under the effect of photo-thermal synergy.This curing method makes efficient use of the heat generated during the curing process.Therefore,the ECA can be completely cured in a few minutes and the method of photo-thermal co-curing is a new curing method with simple process,high efficiency,energy saving and environmental friendly.In this paper,two kinds of photo-thermal co-curing technologies are applied to the preparation of ECAs,and the ECA can be cured in one step.The specific research results are as follows:（1）The UV-thermal co-curing technology was applied to the preparation of the ECA,and the curing mechanism of the UV-thermal co-cured ECA was explored.During the reaction,irradiation heat provided by the curing system and reaction heat of photo polymerization were used to induce the thermal polymerization reaction,and the ECA was completely cured within6 min.The effects of curing conditions,Ag@Cu content,Ag@Cu modification method,type of photocuring resin and active diluent,the ratio of resin:active diluent on the properties of UV-thermal co-cured ECAs were investigated.The results showed that the combination of photo-initiators increased the photo initiation efficiency,which was beneficial to improve the curing degree of the ECA.Due to the limited UV-thermal co-curing effect,the upper limit of Ag@Cu content in UV-thermo co-cured ECA was 47.5 wt%.The modification of Ag@Cu with silane coupling agent could promote the dispersion of Ag@Cu in the polymer,which could improve the conductivity and shear strength of the ECA.The ratio of the resin:active diluent could affect the viscosity of ECA,which influenced the dispersion of Ag@Cu in the polymer and the properties of the ECA.The active diluent containing nitrogen heterocycle structure was conducive to the dispersion of Ag@Cu,and the bifunctional active diluent was conducive to the improvement of the crosslinking density of the ECA,so the combination of the both could improve the performance of the ECA.The bulk resistivity and shear strength of the prepared UV-thermol co-cured ECA could reach 6.63×10^-3Ω·cm and 3.65 MPa,respectively.UV-thermal co-cured ECA makes more efficient use of the heat energy generated in the reaction process on the basis of step-to-step photo-thermal dual-curing technology,which is an efficient and simple method to prepare ECAs.（2）NIR-thermal co-cured ECAs were prepared by applying upconversion nanoparticle-assisted NIR photopolymerization（UCAP）technology in the field of ECAs.The mechanism of NIR-thermal co-curing was explored.UCNP could convert the NIR light into UV-vis light as the internal light source,thereby exciting the photoinitiator to generate active species and initiate photopolymerization of epoxy acrylic resin.In the meanwhile,the photo-thermal effect of NIR rapidly increased the system temperature to initiate the thermal curing of ECAs.Owing to the synergistic combination of high penetration depth and photo-thermal effect of NIR light,ECAs could be fully cured in one-step.In addition,the effects of curing conditions and Ag@Cu content on the properties of ECAs were also explored.It was showed that ECA could be cured completely within 4 min by controlling UCNP content and irradiation dose.The upper limit content of Ag@Cu in the NIR-thermal co-cured ECAs was 70 wt%,which was higher than that of the highest Ag@Cu content（47.5 wt%）in the UV-thermal co-cured ECAs.Compared with UV-thermal co-cured ECAs,the curing time of NIR-thermal co-cured ECAs was shortened from 6 min to 4 min,which indicated that the photo-thermal conversion efficiency of NIR-thermal co-curing process was higher,so the NIR-thermal co-cured ECAs could be cured more efficiently.In addition,NIR-thermal co-curing ECAs have lower bulk resistivity(8.45×10^-4Ω·cm)and higher shear strength（6 MPa）,which is a more efficient ECA curing method.