Modeling Study Of Via Hole Interconnection Structure In Multilayer LCP Circuit

With the accelerated improvement of 5G communication technology standards,modern electronic systems continue to develop in the direction of high frequency and high density integration.Liquid Crystal Polymer（LCP）is widely used in high frequency multilayer circuit boards with excellent microwave and millimeter wave characteristics.In the multilayer circuit board structure,it is particularly important to design a via hole interconnection structure with excellent electrical characteristics in order to achieve efficient interconnection of different layers of electronic devices and transmission line structures.As the discontinuity of the via hole interconnection structure is one of the root causes of many electromagnetic compatibility problems,high precision modeling and simulation can greatly improve the design efficiency of microwave and millimeter wave circuits.Based on the multilayer LCP circuit board,this paper designs and realizes a broadband via hole interconnection structure,and uses two modeling methods to analyze the via hole interconnection structure equivalently,and the main work content is as follows:（1）The preparation process of multilayer LCP circuit boards is systematically studied.By cooperating with enterprises,a four layer LCP substrate preparation process is realized by using a mixed lamination method of single-sided and double-sided copper-clad substrates.The multilayer LCP substrate with 1 to 3 blind hole and 1 to 4 via hole structures are prepared by mechanical and laser drilling technology,and the samples are sliced and characterized by scanning electron microscopy.The results show that the metal plating on the the surface of the via hole is uniformly distributed,which could be used for microwave circuit design.（2）A Grounded Co-planar Waveguide to Stripline to Grounded Co-planar Waveguide（GCPW-SL-GCPW）via hole interconnection structure based on multilayer LCP technology is designed and fabricated.The influence law of physical parameters of the interconnection structure on the microwave transmission characteristics is analyzed in detail.The results show that the insertion loss S₂₁is better than 2.45 d B and the return loss S₁₁is better than 10 d B when the blind hole radius is 0.07 mm,the pad radius is 0.17 mm,and the anti pad radius is 0.26 mm.In order to suppress crosstalk from higher harmonics,the interconnection structure is optimally design using electromagnetic shielding via holes.It is found that when multiple electromagnetic shielding via holes with 0.05 mm radius and0.2 mm hole spacing are introduced around the signal via hole,the insertion loss S₂₁is better than 0.6 d B and the return loss S₁₁is better than 15.7 d B in the wide frequency range of 0.1 GHz～40 GHz,and the interconnect structure achieves the best performance.The interconnection structure is prepared and tested based on the four layer LCP substrate.The results showed that the test and simulation results are in good agreement.（3）To solve the problems of time-consuming and high cost in the traditional interconnection structure modeling methods,this topic introduces the fast convergence algorithm into the GCPW-SL-GCPW via hole interconnection structure modeling,and constructs a fast convergence equivalent circuit model.In the solution of the model parameters,the quotient term with two Hankel functions in the inter-layer capacitance C_bis reasonably truncated,which accelerates the convergence speed and simulates it’s convergence.The study shows that the introduction of the fast convergence resolution reduces the truncation number N₁of C_b1from 200 to 1 and the truncation number N₂of C_b2from 200 to 2,which greatly improves the computational efficiency.The final results of the equivalent circuit model show that the model simulation results are consistent with the overall trend of the full wave simulation and the measured values in the frequency range of0.1 GHz～40 GHz.All simulations are run on a computer configured with an Intel（R）Core（TM）i5-1035 G1,and the model take only 2 min to build and run,which can be used for preliminary modelling of the interconnection structure.（4）In order to further improve the modelling accuracy and extend the modelling bandwidth,the fast converging equivalent circuit model is improved and a high accuracy equivalent circuit model for the GCPW-SL-GCPW via hole interconnection structure is proposed.By simulating the current distribution in a metal plate under three boundary conditions,PML,PEC and PMC,the inter plate impedance Z_ppis introduced to describe the effect of the power/ground plane on the via hole transmission characteristics.By reclassifying the via hole structure,the parasitic parameters arising from high-order attenuation modes,parallel plate effects and electromagnetic mode conversion effects are analyzed and calculated,so as to improve the model network parameters.The final solution of the optimized equivalent circuit model shows that the model simulation results are in high agreement with the full wave simulation and the measured values in the frequency range of 0.1 GHz～40 GHz.The model has high accuracy and fast solution speed,and can be used for high frequency modelling of broadband interconnection structures.