Fine Line Multi-layer Rigid-flex Printed Circuit Board, Key Technology Research And Application

The development trends of electronic products require PCB (printed circuit board) along the development direction of "light, thin, short and small" and multifunction. Multi-layer Rigid-flex PCB with its small size, light weight, avoiding connection errors, the increasing of assembly flexibility and three-dimensional assembling, will be an important development direction of PCB.The fabricating of through-hole in Rigid-flex zone of multi-layer Rigid-flex PCB is one of the crucial processes. In this paper, the drilling and plasma desmear process were researched by integrating the practice and theory. In the research of drilling process, the optimal cutting parameters of through-hole in Rigid-flex zone of two common multi-layer Rigid-flex PCB were obtained by orthogonal experimental design method; By determining the relation between hole drilling number and cutting wear, the cutting life of 0.25mm diameter hit for different multi-layer Rigid-flex PCB was defined; the emerged cause and emerged law of long nail head for copper and polyimide were also researched to provide the production guidance of reliable high multi-layer Rigid-flex PCB.In plasma desmear experiments, plasma etching uniformity in different plate areas of plasma machine body and different working times were designed to provide a stable experimental environment for the later quantitative research. Based on a stable experimental environment, the nonlinear regression equations between etched rate of polyimide, epoxy resin and acrylic plastic in multi-layer Rigid-flex PCB and plasma etching parameters were fitted by minitab software through Uniform design method. In the latter of the paper, by assuming that the reaction mechanism between plasma and organic materials in multi-layer Rigid-flex PCB and employing the knowledge of chemical kinetics, the plasma etching rate relation with different organic material in Rigid-flex PCB was successfully deduced, thereby the mechanism of CF4 and O2 plasma etching with organic materials in multi-layer Rigid-flex PCB was theoretically confirmed.For fabricating high ratio of depth to diameter, flatness holes in multi-layer Rigid-flex, the penetration of plasma in through hole, and the influence of high ratio of CF4 amount to O2 amount to the roughness of through-hole wall were also studied. Experimental results show that in the high layers of Rigid-flex PCB, plasma cleaning should be divided into two stages, the first desmear is carried with the experimental results of "uniformity study of Plasma etching to different materials", the second desmear is carried with the plasma gas of large CF4 to O2 proportion.The paper also studied based on the Rigid-flex PCB's development trends to fine lines. The impact of spraying pressure to fine copper conductive lines was analyzed theoretically. Theoretical results show that when the spraying pressure is increased, on the one hand, it can enhance etching uniformity and increase the etching factor, On the other hand, it will cause more serious wallside copper eroded. Therefore, in the fine-line production process, the spraying pressure must be controlled in an appropriate range.The commonly used cupric chloride etching solution is difficult to meet future deveploment of fine lines in multi-layer Rigid-flex. In this paper, a novel nitric acid etching solution was prepared. The roles of each component in solution, the reasons that the nitric acid etching solution can improve the etching factor and waste gas and solution recovery system in exhausted solution were described. Compared with the acid cupric chloride etching solution, the nitric acid etching solution highlights its application prospects in the future.Finally, to verify the application effect of experimental results in Rigid-flex PCB, a six-layer Rigid-flex PCB containing of 100μm width fine lines was designed. The final product showed that the experiment results from drilling and plasma desmear through-hole in rigid-flex zone greatly improved the reliability of metallized through-holes. The fine lines in the product also show that the spraying pressure must be an appropriate value.