Low heat input welding by continuous-wave Nd:YAG laser processing

Abstract

Low-power applications of laser technology include the manufacture of fuel injectors, pacemakers, and electronic assemblies. For many electronic packages, the final sealing operation can expose the heat-sensitive glass-to-metal seals, semiconductors, and any plastics to severe thermal extremes. Traditional methods of hermetically sealing enclosures use pulsed Nd:YAG. Pulsed processing is used with the theory that the high peak pulse energy will allow adequate penetration, and the low average power will keep the total heat input to a minimum. This approach, however, does not always account for the need of 75-80% overlap of the pulses needed to achieve hermeticity. This requirement for overlap fixes the table feedrate and dictates a finite time of laser illumination on the device. Hence, the effective heat input is a strong function of the time of laser illumination, not just average power. In this work, we demonstrate that the total time of laser illumination on the part is critical, and that high brightness continuous-low divergence continuous wave (CW) laser processing can achieve thermal inputs equal to or less than pulsed processes. From this work, it will be shown that 0.25-mm penetration welds can be made in Ti6AI4V at feed-rates of 85 ipm with maximum temperatures below 300°C.Low-power applications of laser technology include the manufacture of fuel injectors, pacemakers, and electronic assemblies. For many electronic packages, the final sealing operation can expose the heat-sensitive glass-to-metal seals, semiconductors, and any plastics to severe thermal extremes. Traditional methods of hermetically sealing enclosures use pulsed Nd:YAG. Pulsed processing is used with the theory that the high peak pulse energy will allow adequate penetration, and the low average power will keep the total heat input to a minimum. This approach, however, does not always account for the need of 75-80% overlap of the pulses needed to achieve hermeticity. This requirement for overlap fixes the table feedrate and dictates a finite time of laser illumination on the device. Hence, the effective heat input is a strong function of the time of laser illumination, not just average power. In this work, we demonstrate that the total time of laser illumination on the part is critical, and that high brightne...