Preparation Of Composite Conductive Microspheres And Their Effects On Anisotropic Conductive Adhesive Film

In the modern trend of rapid development of electronic devices,the traditional soldering technology of tin soldering has been gradually replaced by various new packaging processes.Among them,Anisotropic conductive adhesive film(ACF)is a new type of packaging material with simple process and environmental friendliness,which is widely used in flexible circuits,ultra-fine pitch interconnects,etc.Aiming at the problems of high cost and easy delamination of the existing pure metal fillers,and the small contact radius of core-shell structured composite microspheres with hard cores,this thesis prepares core-shell structured composite conductive microspheres suitable for ACF using flexible polystyrene microspheres(PS)as the core and high conductivity metals as the shell.The thesis prepared micron-sized PS@Ag core-shell composite conductive microspheres by chemical plating,and systematically analyzed the effects of different reducing agents on the monodispersity,coating effect and shell morphology of the composite conductive microspheres.At the same time,this thesis investigates the effects of reductant concentration,silver source and chemical plating time on the microscopic morphology of the composite microspheres during the plating process.The experimental protocol was improved by using multiple sensitisation to increase the number of activation sites to improve the coating morphology and reduce the free silver in the bath.The optimum process conditions for this solution were obtained by chemical plating with the reducing agent hydrazine hydrate at 30 mmol/L for 0.75 h at a molar ratio of 3:1 of silver ammonia to PS microspheres.The resulting composite microspheres have good monodispersity,sphericity and a complete shell structure.The silver shell thickness of the composite microspheres was about 91 nm.This thesis also presents a simple electrostatic self-assembly method for the preparation of PS@Au core-shell structured composite conductive microspheres with uniform and continuous shell layers.At present,most of the gold-coating research on polymer microspheres uses surface functional group modification to achieve gold sol coating,and the microsphere pretreatment and sol preparation steps are relatively complicated.In this thesis,the electrostatic selfassembly method is used to reduce the surface of the microspheres in situ by utilizing the reducibility of stannous ions.This method is simple and efficient,and the obtained microspheres have high monodispersity,good sphericity,and uniform and dense shell.The thesis investigates the effects of chloroauric acid concentration,self-assembly time and other factors on the morphology of microspheres,and the problem of dissolution and rupture of microspheres respectively was solved.The best solution for this problem is electrostatic selfassembly for 10 h at a concentration of 10 mmol/L of chloroauric acid.The best preparation method obtained in the experiment is electrostatic self-assembly for10 h at the concentration of chloroauric acid of 10 mmol/L.In the experiment,the prepared two core-shell composite microspheres were used as conductive fillers to prepare ACF,so as to explore the effect of filler ratio on the electrical and mechanical properties of ACF.The test results show that increasing the filler ratio enhances the electrical conductivity of ACF.When the filler ratio reaches 25 wt%,further increasing the filler ratio ACF electrical properties are not significantly improved,while ACF mechanical properties will be significantly decreased.Considering all the influencing factors,the conductive filler content of 20 wt% was determined as the best filler ratio for this thesis.At this filler content,the contact resistances of ACF prepared with PS@Ag and PS@Au was 0.65 Ω and 1.95 Ω,fully meeting the requirements of commercial conductive adhesives.The maximum stress it can withstand in the tensile fracture test is 54.55 N,and the peel strength is 296 N/m.