Multi-jet atmospheric glow plasma for PCB desmear process

Summary form only given. The plasma desmear process is widely used in the printed circuit board industry. During drilling, drill bits become heated resulting in the melting and smearing of the epoxy-resin base material across the inner-layer copper surfaces within the hole barrel to which subsequent through-hole plating must connect. If not corrected, the smear would constitute a dielectric layer between the inner-layer copper surfaces and the plated copper, and the circuit would be defective. In order to effectively remove the residual smear like epoxy resin base material commonly found on the micro-via blind holes after drilling. We invented the multi-jet atmospheric glow plasma system and have compared the effect of micro-via blind holes desmearing at low pressure with that of a multi-jet atmospheric glow plasma source at atmospheric pressure. A multi-jet atmospheric glow plasma system with the radio frequency generated hollow cathodes was used for the PCB desmear process which operated in atmospheric pressure. The size of the proto-type system is 180 by 60 mm. The electrode comprises 100 hollow cathodes with flowing gas and the distance of both electrodes is adjustable between 1 and 10 mm. However, the construction perfectly enables further scaling up. The forward RF-power to sustain the discharge at atmospheric pressure can be as low as 12 W. Using this multi-jet atmospheric glow plasma source, we have successfully verified a possibility to ignite and maintain an atmospheric pressure discharge in He and He + O/sub 2/ in the RF powered multi-cylindrical hollow cathodes with inner diameter of 500 /spl mu/m. The discharge is stable, volume filling, silent, with no streamer. Our results show that residual smear can be effectively removed by a He + O/sub 2/ plasma, If it is performed under optimum process condition. The optimum process conditions for the removal of residual smear existing on the micro-via blind holes are the plasma exposure time of I min and the RF- power of 80 W. On the other hand, the highest efficiency of the residual smear clearing was achieved for a low-pressure plasma exposure time of 1 min and RF-power of 40 W. In both experiments, the higher O/sub 2/ content in the He plasma, the residual smear of micro-via blind holes effectively removed. As a result, the multi-jet atmospheric glow plasma source may substantially save coats by avoiding investment of the vacuum equipment and may bring a number of interesting applications in large area cold atmospheric plasma processing.