21 February 2011 Reliable laser micro-welding of copper
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The reliability of copper welds is still a problem today concerning the high demands of spot or contact welding for the electronic or medical industry. Due to the low absorptivity at wavelengths of 1 micron and the very high thermal conductivity of copper, even small surface contaminations lead to drastic variations in weld quality. The wavelength of 532 nm (frequency-doubled Nd:YAG laser) is much better absorbed by copper at room temperature. Combining the two wavelengths and using the drastic increase in absorption with increasing temperature leads to an efficient spot welding solution. By the use of intelligent pulse forming with the thermal pulses of a Nd:YAG laser the spot weld reliability is improved significantly. This paper discusses a solution where Nd:YAG laser pulses composed of 85 - 90% of 1 micron and 10 - 15% of 532 nm radiation are used for spot welding of 80 - 300 micron thick copper ribbons. A weld spot diameter variation below 6% combined with 100% full penetration welding is achieved. The process efficiency is improved by more than a factor of two compared to conventional spot welding with 1 micron radiation.
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Christoph Rüttimann, Christoph Rüttimann, Ulrich Dürr, Ulrich Dürr, Anas Moalem, Anas Moalem, Marc Priehs, Marc Priehs, } "Reliable laser micro-welding of copper", Proc. SPIE 7920, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XVI, 792007 (21 February 2011); doi: 10.1117/12.875033; https://doi.org/10.1117/12.875033


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