Research And Application On Laser Direct Via Formation Technology For HDI Printed Circuit Board

With the increasing demand for miniaturization,multifunction and portability of electronic products,high density interconnection?HDI?printed circuit board?PCB?employed as the high-speed signal transmission is indispensable.The difficulty of the HDI board lies in the fabrication and metallization of the blind via in the interlayer.The blind via is the necessary technology to obtain high-density interconnection between different conductive layers of PCB.In this paper,a copper induced direct CO₂ laser drilling blind via was studied to simplify the working process and enhance blind via alignment with the aid of copper brown oxidation.The surface-treated copper holding a roughened surface to extend the laser route in its surface and with a high laser absorptivity were confirmed by scanning electron microscopy?SEM?,3D microscope,X-ray photoelectron spectroscopy?XPS?,infrared thermal camera,and metallographic microscopy.It therefore breaks the limitation of pure copper ablated by CO₂ laser.Copper clad laminate?CCL?of copper with thickness of 18?m and dielectric layer with thickness of 80?m was treated in the brown oxidation solution of 45 mL/L MS800 for 90 s to produce qualified ?100?m blind vias by laser drilling technology.In the research of via metallization by direct electroplating technology of organic conductive film,the principle of organic conductive film were introduced.Taking the direct metallization system E?DMSE?developed by Enthone as an example,the process is elaborated.The effects of polymerization agent concentration,acid strength?pH value?,temperature and treatment time on the resistance and copper plating rate of the organic conductive film were discussed by single factor experiments.The optimal conditions for the catalytic formation of the organic conductive film by orthogonal test were as follows:25 mL/L 7388A polymerization agent,45 mL/L 7388B polymerization agent.Temperature is 14? and pH is 2.0.The average copper plating rate of the organic conductive film obtained under the optimal catalytic conditions was 3.72mm/min.The PCBs with blind via fabricated under this condition passed the reliability test required by IPC-TM650.The above research results were applied to the fabrication of 8-layers'free via stacked up structure?FVSS?HDI board.The influence of the brown oxide layer on the core layer lines during the production process,the influence of the manufacturing technology on the expansion and contraction,and the method for increasing the productivity of CO₂ laser processing machine were studied deeply.Firstly,it is determined that the brown oxide layer is the cause of a large amount of residual copper,short circuit and notch in the core layer.Then the problem was improved by chemically removing the brown oxide layer.The core layer set yield was increased from 12.8%to80%and after repair was 95%.It was subsequently determined that the lamination process had the most significant effect on the expansion and contraction.From one lamination to four laminations,the expansion and contraction varied by up to 0.1%.Summarize the control range of the engineering pre-release coefficient with different pressing times,so that the expansion and contraction batch control could be carried out simply and efficiently.At the same time,a remedy for abnormal expansion and contraction was proposed in order to obtain PCB with a controllable size.Subsequently,it was found that the production efficiency of the CO₂ laser processing machine could be improved by changing the shape of the laser beam and reducing the number of pulses,and the quality of the processed blind via was qualified,which saved the cost of purchasing equipment.Finally,8-layers'free via stacked up structure HDI board was successfully fabricated,and the production yield rate was up to 76%.