Green Laser Welder produces consistent joints in copper and gold

Paul Boughton
Miyachi Europe is introducing the ML-8150C SHG Green Laser Welder, which is specifically designed to produce consistent and reliable welds in gold and copper. The ML-8150C is therefore suited to many applications in, for example, the semiconductor and electronics manufacturing sector, including welding gold and copper wires to substrates.
Gold and copper are known to be difficult metals to laser weld; they have high surface reflectance - exactly the same property that gives gold its lustrous appearance and makes it attractive as a jewellery metal - which makes it difficult for laser energy to penetrate below the surface. However, both gold and copper absorb more strongly in some parts of the light spectrum than in others (indicated by the fact that both are coloured metals) and, in particular they exhibit increased absorbance of green light (a gold foil beaten so thin that it becomes transparent appears green when held to the light).
Miyachi's ML-8150C exploits this property by delivering laser energy with a wavelength of 532nm, which is green light. The unit employs an SHG - second-harmonic generation - architecture in which laser light is first produced at 1064nm. Although this is in the infrared spectrum, it is not well-absorbed by gold and copper. Miyachi's SHG design doubles the frequency of the light, halving the wavelength to 532nm and increasing by a factor of between 4.5 and 20 the energy absorbed by the metals to be joined. Improved beam definition, coupled with higher power, raises the energy-density of the laser by some nine times compared to Miyachi's earlier product in the sector.
In practice, the ML-8150C has produced high-quality and repeatable welds when joining multiple different metal forms and materials. These include welding gold wires to integrated-circuit lead frames and copper wires to PCB substrates. Equally good results are obtained with spot-welding of copper sheet, joining of bus bars for low joint resistance and in solderless assembly of surface-mount components to PCB. In trials, laser penetration into three thicknesses of 0.5mm, non-coated CuSn6 (copper alloyed with 6 per cent tin) was measured at 1.26mm, effectively welding together all three sheets.
The Miyachi ML-8150C has a maximum rated output of 5W, with energy of 4J/pulse in pulses 0.2-5ms wide, a repetition rate of one to 30 pulses/s. Peak power output is 1.5kW. Miyachi says the new system is easily integrated into a manufacturing environment, occupying an outline that measures just 822 (H) x 430 (W) x 869 (D) mm; it operates from a single-phase, standard 200-240V AC supply.
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