Study On Blocking Performance Of Polyimide Packaging Used For Implantable Electronic Devices

With the increasing development of implantable electronic devices(IEDs),they are expected to have higher lifetime.Due to the emergence of energy harvesters,the problem of energy supply of the devices would be solved in the future.By then,reliability of packaging materials will become a key factor limiting the longtime of IEDs.Organic materials have gradually become the research focus of packaging materials due to their low permeability and good flexibility.Recent researches about them are focused on biocompatibility and preparation.However,there are few studies on their retardation performance and there is no research on the degradation mechanism of the coating’s retardation performance.Based on these,polyimide is used as research objects and simulated body fluids are used as the research medium in our work.Measurement parameters such as water absorption,porosity,contact angle,etc.,combined with the observation of surface morphology and the result of Electrochemical Impedance Spectroscopy are used to study the blocking performance of polyimide on water and chloride ions.In addition,the effect of macromolecules on the blocking performance is investigated,and the degradation mechanism of the coating’s retardation performance is proposed.Based on these,a kind of method is proposed to improve retardation performance.The specific research results are as follows:1.The transport process of water molecules in polyimide when immersed in simulated body fluids includes four stages:Water absorption increase rapidly in the first stage which is caused by surface wetting;The transmission of free water in the coating follows FICK’s law in the second stage;In the third stage,the water absorption rate increased suddenly due to the formation of bound water.;In the fourth stage,the coating is saturated with water.Cl-reaches the interface between the coating and the substrate after the coating is saturated with water,and once it reaches the interface,the concentration of Cl-will increase exponentially.The biological macromolecules will be adsorbed on the surface of the substrate to prevent the transmission of water in the coating.2.When corrosive particles such as water reach the interface of the substrate,the coating will fail due to blistering caused by small adhesion of the coating on the substrate.Reducing the thickness of the coating can reduce the defects caused by the volatilization of the solvent,and can improve the blocking performance.Studies have shown that the characteristics of the water transport process in the polyimide coating with a thickness of 15 μm are the same as those of a polyimide coating with a thickness of 30 μm,but the retardation performance is significantly improved.Moreover,the 30 μm coating made by spinning the 15 μm coating twice has better retardation performance.