Study On Process Technology And Application Of Embedded-flex Printed Circuit Board

E-flex PCB is a kind of PCB that the small flexible circuits unit is embedded in the intermediate rigid board and built up by the Build-up method, of which the electronic interconnection between flexible circuit and rigid circuit is the blind hole between inner-outer layers, but not the same layer. E-flex PCB incorporates almost all the merits of rigid-flex PCB and HDI PCB, which will be a new direction of the development of the printed circuit board.This thesis described and showed the special structure and process of E-flex PCB, and researched on the specifications design and process technology of E-flex PCB, including E-flex flexible capability research, inter-layer adhesion research, and the depth control of UV laser milling research. Finally, then produced 10-layer-E-flex PCB products successfully.The results of critical processes were:(1) E-flex PCB flexible capability researchEstablish the structural model and flexural stress analysis model of E-flex PCB, Analysis showed that the embedded dimension d E and the dimension of blind hole to the rigid-flex edge d H were playing important roles on the flexible capability and electrical interconnection of E-flex PCB. The fitting polynomial was found after analyzing the relationship between the deflection number and d E, d H, which was showed below:Y =- 34.2 + 22.7d E + 16.3d HFitting polynomial showed that it was linear growth relationship between Y and d E, d H to some degree; the analysis of variance showed d E was much more significant than d H, d E impacted on the flexing and electrical interconnection of E-flex PCB significantly; Finally, the parameters d E = 2.0cm, d H = 1.8cm was the minimum critical parameters of E-flex PCB and met to the flexibility testing standard; Then, design the verification experiments, analysis showed that the ability to control the process of flexible capability test was capable under the these optimal parameters, and the design parameters were acceptable.(2) E-flex PCB inter-layer adhesion researchPlasma treatment for PI cover film was applied for manufacturing Rigid-flex PCB to improve the lamination adhesion and avoided delamination in rigid-flex PCB,especially in E-flex PCB. A L9(34) orthogonal array experiments were designed to characterize the optimized plasma parameters for treating PI cover film, with roughness and contact angle as indicators. Through range and variance analysis of contact angle, the optimized plasma parameters were obtained, which were Gas proportion as CF4:VO2=0.1, RF power at 11 k W, Time at 10 min, Gas flow rate at 1500ml/min. Linear correlation relationship was found from the results of surface roughness and water contact angle of in a certain rang, and the the roughness Ra increased and the contact angle decreased significantly after PI cover film treated by plasma; PI cover film treated by the optimized plasma parameters had a good agreement in binding force with the increase of 0.88N/mm through peel strength test. Delamination was avoided after thermal stress test. PI cover film treated under optimized plasma parameters could effectively prevent delamination of Rigid-flex PCB, and improve the reliability of E-flex PCB.(3) The depth control of UV laser milling researchDesign orthogonal experiment, study on the ability of the UV laser on controlling milling depth, and optimize the fine parameters in E-flex PCB. Analyze the factors of UV laser, the factors in priority order were laser power- laser frequency- height of Z axis- spot diameter; When the cutting depth goal was the maximum depth, the factors’ optimal levels were laser power 9W, spot diameter 0.1 mm, laser frequency 80 k Hz, Z axis height 0.1 mm; When the cutting depth goal was quantitative requirements 98.4μm, through the analysis of the probability graph, the optimal parameters’ level group was laser power 9W, spot diameter 30μm, laser frequency 60 k Hz, Z axis height 0.1mm.Based on the theory and practical operation above, 10 E-flex PCB process and experiment scheme were designed, then produced 10 layers 3+4+3 E-flex PCB successfully, the yield of which was up to 81.25%, and meet to the relevant technical standards perfectly.