High quality and process stability for welding copper

Hannover, Germany - A newly developed "laser pre-pulse module" can be used to initiate the copper welding process and provide a 100% welding guarantee. The laser is small, inexpensive, and the result of process developments at the Laser Zentrum Hannover e.V. (LZH). The pre-pulse is decisive for automating micro-processing or for connecting surface mounted devices to printed circuit boards.

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Welded contacts on an IC (TSOP 0.5mm pitch) on a printed circuit board (Ilfa) using a laser pre-pulse and IR laser main pulse.

Copper alloys are often found in electronics, sensors, and precision engineering applications. Here, high demands are placed on the heat and mechanical stress resistance of spot welds, and laser micro-welding has shown very good weld qualities. However, non-ferrous metals are difficult to weld due to high reflectivity and a sudden jump in energy absorption when the melting temperature is reached. It is difficult to repeat good welding results and retain process stability. Up to now lasers have only been used following complex surface treatment or for manual applications.

Researchers at the Department of Production and System Technology at the LZH have developed a new process, which uses a laser pre-pulse with a peak output of no more than 1 MW and a pulse length of only a few nanoseconds to initiate the welding process. This short-pulsed, solid-state, frequency converted laser produces a beam with a high degree of absorption, and the conventional IR laser provides stable conditions for the subsequent high-output welding. The welding energy can be easily controlled after pre-pulsing.
Experiments using the pre-pulse prototype of the company’s neoLASE were carried out on an 80 µm thick, 2 mm wide copper band. After 200 repetitions, the welding results were constant, implying that the welds were 100% good.

"This result is already a great success," says engineer Anas Moalem, who is responsible for the development of the process.

Apart from improved precision and quality, the process window for the laser parameters could be expanded considerably. Depending on the weld spot diameter, the laser output power could be reduced by up to 40%, meaning that using the compact pre-pulse module (13 x 9 x 4 cm) could result in energy savings in the kilowatt range for IR welding lasers.
Developments took place within the framework of the SME-innovation project "Supreme," which was financed by the BMBF (German Federal Ministry of Education and Research) under supervision of the PTKA-Project Management Agency Karlsruhe. Support was also given by the companies Arteos GmbH and Ilfa GmbH.

For more information, email m.botts@lzh.de

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