Research On Laser Processing Technology For Surface Metallization Of Polymeric Materials

In recent years,with the increasing demand for integration and lightweight of electronic modules,3D molded interconnect devices have attracted wide attention.In the manufacturing technology of 3D molded interconnect devices,the surface metallization of polymer is the key step to form circuit pattern.There are some problems in the current technology,such as the complexity of equipment process and the limitation of material system.In this paper,the selective metallization of polyimide surface was studied by laser-induced selective activation method.Firstly,a set of dynamic focusing laser modification equipment and high-throughput testing equipment were built for sample preparation and batch characterization respectively.Secondly,starting from the two-dimensional surface,the laser surface modification process and the formation mechanism of surface porous microstructure were studied.Further,the influencing factors of laser modification process of three-dimensional curved surface polymer were studied.Finally,by this process,the surface mounted circuit and flexible electromagnetic shielding film was prepared as demonstration.The main contents of this paper are followed.(1)In the aspect of equipment development,in order to realize the preparation of selective metallized surface,a set of dynamic focusing surface laser modification system is developed and built,which realizes the on-line tracking of beam focal plane(dynamic focal length ± 15 mm,external servo slide expansion ± 50 mm)in the process of laser scanning.Furthermore,in order to meet the requirements of high-throughput characterization of the prepared samples,a high-throughput material testing and analysis system based on hybrid method was developed,and the resistance of the sample array was measured by four probe digital source meter and spectrometer The maximum detection efficiency is 256/batch,the sheet resistance test range is100 μΩ/sq ～ 211 mΩ/sq,and the transmittance response band is 200 ～ 1100 nm.(2)In the research of metallization process of 2D polymer surface,polyimide was taken as the research object,and the laser modification process parameters were optimized.Under the parameters of power 2W,repetition rate 60 k Hz and scanning speed 1500 mm/ s,the metallized surface with sheet resistance less than 400 m Ω/sq was successfully prepared.SEM analysis shows that the laser modified surface with high quality has micron scale porous structure.The coupling model of heat transfer and fluid movement between laser and polymer surface in liquid phase based on phase field method is established.It is proposed that the impact of bubbles and micro jet in nucleate boiling process may be an important factor to produce the porous structure of polyimide.Through ASTM-D3359 test method,the adhesion between the metallized surface and the substrate is verified to be 5B;through repeated bending test,the bending fatigue resistance of the metallized surface is verified to be more than 500 times.Finally,the process is successfully applied to the manufacturing of SMD circuit and flexible electromagnetic shielding film of LED,and the electromagnetic shielding effectiveness is up to 140 d B in the band of 8.2 ～ 12.4GHz.(3)In the research of metallization process of 3D polymer surface,the numerical model of laser energy density distribution is established by MATLAB,and the influence of depth,defocusing amount and tilt angle on the energy density distribution is analyzed.It is proved that the defocusing tolerance of 500 μm can be extended to effective focusing range within 30 mm after the introduction of dynamic focusing;at the same time,the tilt angle should be controlled within 30° in order to improve the accuracy,and then the distortion of light spot is reduced and the effective modified surface is obtained.Through experiments,it is verified that the deflection angle caused by transverse and longitudinal deviation is the main factor leading to the rise of sheet resistance.Through the transverse and longitudinal motion compensation method of external XY axis,the metallized surface with thin layer resistance stable below 30mΩ/sq is prepared.The influence of deflection angle introduced by three-dimensional surface slope on the sheet resistance of metallized surface is further studied,and the effective deflection angle limit is obtained.It is about 30° which is consistent with the predicted results.Finally,the beam distortion caused by the deflection angle is effectively reduced by using the step-by-step laser surface modification technology strategy,and the metallized surface manufacturing of threedimensional ladder structure and semi-cylindrical structure is realized.