Even today laser spot welding of copper is a challenging application in the micro-electronic industry. Requirements for yield, strength and process stability are high and still increasing. Typical applications are bonding and contacting. In general laser welding is considered as a process with high reliability. But copper alloys especially have characteristic properties like high heat conduction, inconstant absorption level depending on surface conditions and material temperature, abruptly changing physical state between solid and liquid condition etc. There are existing strategies like pulse forming and beam shaping as well as adaptation of the laser wavelength which can be used to increase the process reliability of the spot welding of highly reflective materials. Moreover a closed loop control was developed which is able to set up the process parameters even inside of the working pulse based on the process signals feedback. The paper contains a survey of the existing methods of increasing the process reliability and will show advantages and disadvantages of the single strategies. The initial results of using closed loop feedback control systems for copper welding under industrial conditions will be presented, as well as a novel method where IR and green wavelength mixing is used to achieve reproducible and energy-efficient copper welds.
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