| Rigid-flex PCB bothly has the characters of rigid PCB and flexible PCB, with excellent heat resistance ability, dielectric properties and electrical properties. It can bend, torsion and move, also has a high assembly reliability. Rigid-flex PCB is developing with the future trend towards the direction of light, thin, short, small, and has a broad prospects for development.The key manufacturing technology for flexible area of rigid-flex PCB was researched including fine lines produce process, black hole process, plasma cleaning process and pads nickel plating process. The results are as follows.By copper thinning process, the copper foil was thinned from 12 μm to 3.5 μm. Then the developing speed, developing pressure, etching speed and etching pressure of four factors were optimized by optimize experimental design. According to range analysis, line width uniformity analysis and etching factor analysis, the optimum parameters for semi-additive process to produce 30 μm fine line was obtained: the speed of developing is 3.2 m/min, the above and below pressure of developing is respectively 1.4 kg/cm2 and 1.3 kg/cm2. The speed of etching is 4.5 m/min, and the above and below pressure of etching is respectively 1.6 kg/cm2 and 1.5 kg/cm2.Through producing flexible PCBs with four different hole morphology, the metallographic section analysis were all conducted after black hole process, board electroplating and thermal shock test. It found that flexible PCBs with different hole morphology had a big influence on black hole process, selecting a new drilling tool and plasma cleaning the hole can improve the black hole process obviously; Through producing rigid-flex PCBs with different thickness and different aperture, we had analyzed the copper thickness after electroplating. It proved that different thickness and different aperture rigid-flex PCBs have different black hole effect, and there was an interaction between the conductive carbon-black/graphite layer and subsequent electroplating liquid exchange when it is electroplating.By plasma cleaning univariate analysis, the impact trend of plasma gas from CF4 flow, O2 flow, processing power and processing time on test indicators were determined. Then the four factors of CF4 flow, O2 flow, processing power and processing time were optimized, and the optimum parameters for cleaning the hole were obtained: CF4 flow 100 cc/min, O2 flow 250 cc/min, processing power 4000 W, processing time 35 min. At last, choosing the best cleaning parameters and combined with secondary black hole process of 10 minutes, it proved that it can be applied to the produce of six layer rigid-flex PCB holes metallization.By combining different parameters between current density and time, we made sure that the most suitable nickel plating current density ranges from 2.5 A/dm2 to 3 A/dm2. NiCl2、Ni(NH2SO3)2、H3BO3 and pH four factors were optimized to obtain the best nickel plating parameters: the concentration of NiCl2 was 16 g/L, the concentration of Ni(NH2SO3)2 was 400 mL/L, the concentration of H3BO3 was 48 g/L, and pH was 4.2. By nonlinear regression analysis, we got the quadratic regression equation of nickel plating uniformity δ and nickel plating average thickness I. Applying the equation to actual production, it greatly reduce the defect rate of PCB caused by uneven nickel plating thickness. |
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