| As a kernel for the transmission of various components and circuit signals,printed circuit board(PCB)has become a vital part of electronic information products.In recent years,researches and development of flexible printed circuits(FPC)is in full swing,and has a good application prospect in consumer electronics,intelligent transportation and other industries.The quality and reliability of the flexible circuit determine the quality and reliability of the entire equipment.Conventional preparation methods,such as nano-silver paste coating,could achieve high resolution and conductivity,but the cost of nanosilver(<100 nm)remains high;and electrochemical or chemical plating,although the low cost and convenient,long-term immersion in the solution will damage the quality of substrate and film,so there needs a new preparation method to broaden ideas.At the same time,bonding strength between films substrate can not meet the thousands of bending requirements only by methods such as physical adsorption.Thus,molecular grafting becomes a new research hotspot.In terms of raw materials,silver,which is more economical than gold,is suitable as a matrix film layer for flexible circuits because of its highly conductive material.The extraordinary mechanical and electrical properties of carbon nanotubes(CNTs),as well as the excellent dielectric property and surface activity of nanodiamonds(NDs),make a great promotion of composites performance.In this paper,CNTs and NDs were used as the additive phase to prepare a highly conductive,anti-corrosion and flexible Ag-based composite film.And in molecular grafting method,the bonding strength between flexible substrate and composite film was enhanced.In addition,the effects of two-component spraying,spin coating and spin-spray coating on the deposition and dispersibility of CNTs in Ag matrix were investigated,and the influence of CNTs before and after modification on the conductivity of films was also investigated.Then,NDs were further added to the Ag/CNTs composite to investigate the relationship between the doping amount of CNTs and NDs and the corrosion resistance of the coatings.Finally,a flexible circuit was prepared by mask method and an electronic component was integrated to prepare a functional LED light-emitting device to illustrate its usability.The main contents are as follows:(1)Influencing factors of film-substrate bonding strength included mechanical interlocking,molecular grafting and substrate heat treatment.The mechanical interlocking was formed by chemical etching to form micro-nano pits,which will generate pinning effect during the peeling process to enhance the force.Molecular grafting formed a stable chemical bond between Ag matrix and substrate,which had excellent bonding strength;As for substrate heat treatment,the peel force increased due to the cracking of the cracks in the PET when crystallizes.In general,mechanical chimerism,molecular grafting and substrate heat treatment can all affect the bonding strength,and the effect of molecular grafting was significantly better.Ultimately,the strength between film and substrate reinforced by molecular-grafting reached 12 N/cm,providing a stable prerequisite for the usability of flexible devices.(2)As for preparation method,it is difficult to deposit CNTs by two-component spraying method,and the Ag/CNTs composite film prepared by two-component spin coating has better uniformity and deposition amount.Two-component spin-spray method combines advantages of spraying and spin-coating to enable the preparation of Ag/CNTs and Ag/CNTs/NDs composite films with large deposition and excellent dispersibility.For layer assembly,CNTs and NDs acted as heterogeneous nucleation and reinforcement phases of Ag,and Ag encapsulated CNTs and NDs in its matrix and determines the basic properties of the films.The surface of the composite film was smooth,with a surface roughness value of 10-20 nm and a minimum value of 10.9 nm.The grain size was about 200 nm.(3)CNTs reduced the sheet resistance by 77% at most,while NDs increase the film resistance by 51.4% at most,but NDs can effectively improve the dispersion of CNTs and NDs in the dispersion of silver ammonia solution and the corrosion resistance of the composite film,as well as its environmental stability.It is found that contact voids of the ordered circular grains were significantly larger than ordered polygonal grains.The increase of the grain boundary contact surface can increase the mean free path of electrons to improve the conductivity of the film.Therefore,the conductivity of the film prepared by spin-spray coating is better than that of the same sized nano-hybrid film.(4)The grafting of TES molecules successfully thiolated CNTs because of “—SH” bonding and retained the intrinsic structure of CNTs.The pre-plated Ag nanoparticles on the surface of CNTs are approximately 30 nm in diameter and uniformly distributed.At 5 g/L doping,the composite pre-plated CNTs exhibited a 64.5% reduction in sheet resistance compared to the pristine CNTs.This is mainly due to the chemical bonds between the pre-plated nanosilver and the carbon nanotubes via "S-Ag",which improves the interfacial wettability between Ag and CNTs.(5)CNTs aggravate the corrosion tendency of Ag/CNTs composite film and accelerate the corrosion rate.The addition of NDs increased the corrosion potential and reduced the corrosion current density.The more NDs doping in the experimental range are,the better the corrosion resistance is,which was consistent with the results of polarization curve and electrochemical impedance spectroscopy.(6)For the practicability of composite film.In the bending test,CNTs can stabilize the change trend of the sheet resistance,while NDs tended to destabilize the resistance change under the premise of maintaining high conductivity,but the weather resistance was enhanced.The self-made LED lamp bead device maintained a long and unblinking appearance in the case of bending,folding and twisting at 90°.Further,the integrated circuit was further made as an alternately flashing state of two LEDs,illustrating the applicability of the flexible circuit. |
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