Shozui Takeno

Laser Drilling of Epoxy-Glass Printed Circuit Boards

Nagoya Works,Mitsubishi Electric Corporation, 1-14, Yada-minami 5-chome, Higashi-ku, Nagoya, Aichi 461-8670, Japan E-mail: Takeno.Shozui@aj.MitsubishiElectric.co.jp Manufacturing Engineering Center, Advanced Technology R&D Center, Mitsubishi Electric Corporation, 1-1, Tsukaguchi-honmachi 8-chome, Amagasaki, Hyogo 661-8661, Japan **** Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan

Laser drilling by high peak pulsed CO2 laser (LDHPCL)

Control of input heat to reduce the incidence of recast layers and cracks formed during laser processing of non-metallic materials was studied.Suitable ranges of pulse parameters including peak power, pulse duration, and frequency for non-metallic materials were determined using theoretical investigations. Based on the results of this experiment, a high peak pulsed CO2 laser which output pulses of tens of microseconds using the TEMoo beam mode and 5kW of peak power, was developed. This high peak pulsed CO2 laser was used to study the fundamentals of laser drilling of ceramics and printed wiring boards (PWBs).In the case of ceramics, recast layers including microcracks on the side walls of drilled holes were caused by conventional CO2 lasers. Use of the high peak pulsed CO2 laser reduced the size of recast layers. Furthermore, the effect of the beam-plasma interaction on the hole shape was examined. The results revealed that in air, plasma plume induced beam scattering increased hole diameter. It was also found that decreasing the pulse duration could limit the effects of beam scattering.Conventional laser drilling of PWBs results in glass fiber protrusions. The high peak pulsed CO2 laser was found to decrease the amount of glass fiber protrusions. It was discovered that lowering the pulse frequency successfully reduced heat accumulation; a major cause of glass fiber protrusions. It was possible to fabricate high aspect ratio (=10) holes in epoxy-glass PWBs without glass fiber protrusions using the high peak pulsed CO2 laser set a short pulse durations and low frequencies.Control of input heat to reduce the incidence of recast layers and cracks formed during laser processing of non-metallic materials was studied.Suitable ranges of pulse parameters including peak power, pulse duration, and frequency for non-metallic materials were determined using theoretical investigations. Based on the results of this experiment, a high peak pulsed CO2 laser which output pulses of tens of microseconds using the TEMoo beam mode and 5kW of peak power, was developed. This high peak pulsed CO2 laser was used to study the fundamentals of laser drilling of ceramics and printed wiring boards (PWBs).In the case of ceramics, recast layers including microcracks on the side walls of drilled holes were caused by conventional CO2 lasers. Use of the high peak pulsed CO2 laser reduced the size of recast layers. Furthermore, the effect of the beam-plasma interaction on the hole shape was examined. The results revealed that in air, plasma plume induced beam scattering increased hole diameter. It was also ...