| In recent years,with the remarkable growth of the market and application of flexible stretchable micro-electronic products,it has become one of the hot research topics to find a fast and low-cost method to combine electronic devices with flexible substrates.The physical method,including vacuum evaporation and plane lithography,and the chemical method,which is represented by electroplating and electroless deposition,are two kinds of conventional process in the fabrication of flexible electronics.Although they can successfully manufacture metal circuit on polymer substrate,they can't meet the needs of low cost,high resolution,maskless and rapid manufacturing simultaneously.Laser direct writing technology is a non-contact processing method that integrates optics,precision machinery,electronic technology and computer technology,having many advantages such as low operation difficulty,fast processing speed and customized processing.At present,nanosecond continuous lasers are usually used as heat source for the manufacture of flexible circuits,but the circuit resolution is limited by thermal diffusion and light diffraction limit.Therefore,a method which can efficiently complete the preparation of high-quality and high-resolution flexible circuits has become the focus of attention.In this paper,the technology of femtosecond laser-induced reduction and sintering of copper oxide(CuO)nano-ink was used to conduct theoretical and experimental research on the preparation of copper(Cu)circuit array on polyimide.The influence of laser processing parameters on the quality of Cu circuits was determined and the high-purity and high-resolution Cu circuits were obtained eventually by optimizing nano-ink formulations as well as processing parameters.In addition,this paper successfully prepared high porosity Cu circuit array by adjusting laser processing parameters,and verified its feasibility as a liquid wick of flexible micro-heat pipe through quality characterization,providing new ideas for practical application of this technology.The main research methods and conclusions are as follows:(1)A single factor experiment method was used to study the influence of different composition and ratio of CuO nano-ink on its stability and reduction.The results show that the most suitable mass ratio of polyvinyl pyrrolidone(PVP)as a solid dispersant is m CuO nanoparticleCuO NP</sub>:m PVP=3.08.Ethylene Glycol(EG),a liquid phase reducing agent,also acts as a viscosity modifier,the most suitable mass ratio of which is m CuO NP:m EG=1.48.All in all,the best formulation for CuO nano ink is made up of three components:50wt%CuO NP,16.25wt%PVP and 33.75wt%EG.(2)The processing research of femtosecond laser-induced reduction and sintering of CuO nano-inks to prepare Cu circuits was conducted.It is found that oxygen plasma treatment can activate the polyimide surface and make the surface hydrophilic,which is beneficial to improve the adhesion of Cu circuits to flexible substrates.The single-factor experimental method was used to study the effects of CuO nano-coating thickness,pulsed laser energy,scanning speed and scanning times on the quality of Cu circuit.By optimizing the process parameters,a high-purity and high-resolution Cu circuit with width of 11?m,height of 7.1?m,Cu content of 91.416%,porosity of 9.89%,and resistivity of 130.9??cm was finally obtained to meet the application requirements of high-quality electronic devices.(3)A flexible Cu circuit array with porosity of 30.22%was obtained by adjusting laser processing parameters,and the average capillary suction rate in anti-gravity direction was calculated to be 1.26mm/s when that in horizontal direction was 1.67mm/s(deionized water was used as working fluid).In the view of that,the feasibility of this processing method in the application of flexible micro heat pipes can be verified through the analysis of infiltration,which also known as permeability. |
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