Research On Back Drilling Technology And Signal Integrity Of Through-hole In 5G Communication PCB

The requirements of high density,high heat dissipation,and high reliability of signal transmission in the fifth generation（5G）communication field have brought opportunities and challenges to the existing printed circuit manufacturing technology.Improving system signal integrity,innovating Fine-Line and interconnection structure manufacturing technology,and solving the high-density problem of the printed circuit board（PCB）have become the research hotspot in the industry.According to the technical requirements of through-hole interconnection for 5G communication PCB,this work studied the through-hole back drilling technology using hole structure electromagnetic simulation and process optimization.5G communication technology is one of the foundations of realizing the "Internet of Everything",and PCB is the basic component supporting 5G communication technology.Therefore,the research on the manufacturing technology of PCB for 5G communication has important value and application prospects.Adopting a multi-layer structure to deal with the high density of PCB is the main way in the industry at present.Hole metallization is a technical means to realize the electrical interconnection between layers.The quality of interconnection holes of PCB directly affects the quality of transmission signal and the reliability of the system.A through-hole is one of the three interconnection holes in PCB.For through-hole with a diameter greater than 100 μm,mechanical drilling has the advantages of convenient processing and cost.Due to the interaction between the drills and the PCB material,hole deformation and stub have become important factors affecting the through-hole quality.The electromagnetic simulation method was used to establish the simulation model of multi-layer PCB via structure.According to the simulation results,the effects of via pad radius,anti-pad radius,and differential via spacing on impedance were analyzed,and the variation law between stub length and signal integrity was obtained,which provided theoretical support for the application of mechanical through-hole back drilling technology in 5G communication PCB.Using the simulation conclusion to make the test board,the S parameter showed that the change law of the signal integrity of the test board was consistent with the simulation results,which verified the correctness of the simulation.The shortest stub length was 141 μm,and its signal integrity was the best.When the frequency was 20 GHz and the line length was 50.8 mm,the insertion loss was-2.26 d B.And the return loss was less than-15 d B in the range of 0-20 GHz.The depth control accuracy of PCB back drilling technology is affected by many process parameters,such as rotation speed,feed speed,and retract speed of drills.In this thesis,the relationship between back drilling process parameters was studied by using the orthogonal experimental design method.The experimental results showed that the feed speed was the main factor affecting the depth control accuracy.Using the best drilling parameters and appropriate plate thickness measurement method,the average stub length of the whole plate could be 133.7 μm.Using 3D back drilling technology,the stub length tolerance was controlled within 50-200 μm,and the Ppk was 3.09.Even if the tolerance was reduced within 50-150 μm,the Ppk could reach 1.90.