Flexible Copper Circuit Laser Direct Writing Semi-additive Process Research

The microelectronics industry’s increasing demand for miniature size and integration of devices is promoting the development of flexible circuit processes.Flexible circuits,which attach conductive lines to flexible insulating substrates,are widely used in military,defense,automotive and electronics fields because they are thin,portable,bendable and stretchable.Based on the requirements of conductivity,bendability and line width refinement of flexible circuits,this paper proposes two processes for the preparation of flexible circuits,namely,element-doped precursor film preparation process combined with UV laser direct writing process and microwave ECR film preparation process combined with femtosecond laser direct writing process.With the goal of enhancing the ductility of flexible circuits,the first process uses the molecular precursor method to prepare a copper salt precursor solution containing metal Ti or Al doped elements.Selects copper acetate monohydrate as the copper salt,spin-coats the precursor film on the flexible substrate by using a homogenizer,and direct-writes the conductive copper lines on the surface of the copper salt film by using a UV laser;The reaction mechanism was under investigated of the UV laser direct-writes copper by TGA and XRD;Multiple comparison tests were conducted to explore the relationship between the direct writing of copper conductive lines in terms of line width and resistance value and various laser parameters including defocusing amount,laser repetition frequency and scanning speed to optimize the process parameters.The results show that the optimal parameters for the preparation of Ti element-doped flexible circuits are pulse width 1ns,defocusing volume0.6mm,laser scanning speed 3mm/s,laser repetition frequency 70 KHz,and the width of Ti element-doped copper line is 102.32μm with a square resistance of12.943Ω;The optimal parameters for the preparation of flexible circuits with Al element doping are pulse width 1ns,defocusing volume 0.8mm,laser scanning speed 2mm/s,laser repetition frequency 70 KHz,the width of Al element doped copper wire is 70.254μm,and the square resistance is 2.536Ω.To investigate the effect of different element doping concentrations on the bending performance of flexible circuits,the fol lowing conclusions were reached: Ti and Al elements can effectively improve the bending performance of flexible circuits,and will further improve with the increase of doping concentration in the range of 5% solution concentration.Based on the above flexible circuit preparation process,flexible circuit devices such as electric heating film,electric heating lugs and flexible keyboard were prepared.With the goal of improving the line width refinement of flexible circuits,the second process sputtered copper nitride films on PI substrates by building a microwave ECR platform with microwave ECR sputter coating.Building a femtosecond laser platform to obtain copper conductive structures by direct femtosecond laser writing of copper nitride preparation.The s tudy investigated the reaction mechanism of femtosecond laser direct-written copper nitride,and analyzed the influence of femtosecond laser parameters on the direct-written copper line width by comparing several sets of experimental results,and obtained the following optimal numbers: pulse width 228 fs,laser power 0.2W,laser repetition frequency 200 KHz,and scanning speed 25mm/s.The copper line width prepared under this parameter was 8.14μm.