Tin/Silane Modification Technology For Surface Roughness Reduction In Printed Circuit Board Interlayer Copper

The printed circuit board is a basic carrier for signal transmission in electronic products.In the communication domain,the skin effect of high-frequency signal transmission poses a serious challenge to the signal integrity of the fifth-generation mobile communication technology.Control over the surface roughness of the inner surface of the printed circuit board is one of the technical means to control the interlayer bonding strength of the multilayer printed circuit board.The rough surface benefits the uplift of the interlayer bonding strength,but affects the high-frequency signal transmission on the printed circuit board under the skin effect.Therefore,research on the copper surface treatment technology of the interlayer of the printed circuit board to fit the high-frequency signal transmission is one of the industrial concerns.This has important application value for the development of a new generation of electronic products.At present,brown oxide is the mainstream technology for copper surface treatment in printed circuit board manufacturing.However,this technology corrodes the copper surface,and the roughness is out of control,so the signal integrity of high-frequency signal transmission cannot be ensured.This paper,focusing on the treatment technology for the inner copper surface,aims to obtain better interlayer bonding strength and less surface roughness.On the basis of the existing copper surface treatment technology,the plasma surface modification was combined with the brown oxide technology,the single-factor experiment was employed to determine the modification ability of the plasma on the copper surface,and afterwards the orthogonal experiment method was adopted to study the effect of the combination,yielding the optimal plasma/brown oxide surface treatment method for the FR-4 material.Furthermore,the silane film was also introduced to the surface of the existing brown oxide layer,forming a brown oxide/silane composite intermediate layer.The intermediate layer can increase the interlayer bonding strength between HVLP copper foil and M4 and M6 G materials by57.5% and 90.6%,respectively,compared with that treated just with brown oxide.The tin/silane compound modification method to treat the copper surface of the printed circuit inner layer was investigated as well.This method is a competent candidate for the next generation of copper surface treatment technology because of the fact that it can alleviate the problem of copper surface corrosion by obtaining an intermediate tin/silane layer on the copper surface through chemical means.The technical process is as: reductive tin plating?surface activation?coating with the silane coupling agent.The optimal formula and processing conditions of the reductive tin plating/silane treatment solution were obtained through optimization.Based on the optimized formula and processing conditions,a six-layer high-frequency test board was made with the independently developed plated through hole copper-plated device.The results of the 3D microscope,the tensile tester,and the insertion loss test of the test board showed that the inner layer copper treated with tin/KH550 has surface roughness Ra of0.91?m and Rsar of 133.1%,lower than that treated with brown oxide of 0.95?m and135.2%,and has the interlayer bonding strength of 0.772N/mm,higher than that treated with brown oxide of 0.672N/mm.In the 20 GHz environment,the test board has an insertion loss of-103.95 d B/m,lower than that subject to brown oxide of-106.4d B/m.The compatibility of several common high-frequency/high-speed materials in industrial production with tin/KH550 surface treatment technology was tested,showing the interlayer bonding strength is greater than 0.7N/mm.The intermediate layer obtained with this method can form a stable combination with these common high-frequency/high-speed materials,so this method has remarkable application prospects in future.