Product Code: ICA10_303

Reliable Laser Micro-Welding of Copper
Authors:
Christoph Ruettimann, LASAG AG, C.F.L.; Thun Switzerland
Ulrich Duerr, LASAG AG, C.F.L.; Thun
Anas Moalem, Laserzentrum Hannover e.V; - Germany
Presented at ICALEO 2010

The reliability of copper (spot) welds is still a problem today concerning the high demands of e.g. spot or contact welding for the electronic or medical industry. Two aspects characterising this reliability are tackled: the reproducibility of the weld geometry and the reduction of thermally induced side effects, like sputtering.
One problem in copper welding is the low absorption on a clean polished surface which is about 5% at room temperature at the 1 micron emission of standard industrial lasers. This low absorption in combination with the unique thermal properties of copper lead to the fact that even small surface contaminations lead to drastic variations in weld quality. The frequency doubled Nd:YAG at a wavelength of 532 nm is much better absorbed by the copper surface at room temperature.
Combining these two wavelengths and using the drastic increase in absorption even at 1 micron at higher temperature leads to an efficient spot welding solution by using pulse forming with the thermal pulses of a Nd:YAG laser. At the beginning of the pulse the high intensity 1 micron radiation is partly converted to 532 nm radiation which preheats the surface to a level where the absorption for 1 micron radiation is high enough. From this point on the pulse power is reduced and the welding is finished by the 1 micron radiation. The total pulse length is typically less than 5 ms. The increase in weld reliability - which is significant - will be demonstrated.

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