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Investigation to increase the welding joint area with modulated laser beam welding over gap

: Chung, W.; Häusler, A.; Olowinsky, A.; Gillner, A.; Poprawe, R.


Journal of Laser Micro/Nanoengineering. Online journal 13 (2018), No.2, pp.117-125
ISSN: 1880-0688
Journal Article
Fraunhofer ILT ()

Due to the increasing power level of semiconductor components such as LEDs and IGBTs, larger connection areas are required in the near future, which should be also stable at high temperatures. However, these requirements cannot be realized by conventional joining processes such as ribbon bonding and soldering for contacting semiconductor components. Traditional welding methods, such as laser beam welding, are not used because the conventional process approaches induce thermal stress beyond the destruction threshold of sensitive substrate materials. The Laser Impulse Metal Bonding (LIMBO) realizes a laser-gap welding process between a 200 μm thick copper sheet and a 105 μm thick copper plating board without damaging the underlying PCB. The central approach of the LIMBO process is the modulation of the focus diameter to adjust the laser beam intensity on the workpiece. This results in melting, deflection and contacting the upper joining partner with the lower one. However, this method is currently only limited to spot welding. The aim of this paper is to expand the LIMBO process to increase reproducibility by using pre-pulsing method and the process stability with controlling the energy input and the beam modulation. Based on this expansion, the spot welding process is transferred to a linear connection between the two joining partners with overlap pulsed welding method over a weld joint length over a l = 1 mm without destructing the underlying thermal sensitive substrate.