Laser surface texturing of copper metal
Laser polishing of copper metal to form contrast is a relatively well known method, but because of the high reflectivity inherent in such metals, it is often more difficult to obtain dark markings. The IPG Photonics Silicon Valley Technology Center (SVTC) has developed such a technology to produce a dark surface with a L* value <30 on the surface of copper.
As shown in Fig. 5, the difference in roughness of the laser-treated surface (<1 μm Ra) can be seen by comparison with the surface roughness before polishing. However, the surface structure is more complicated and the surface area is greatly improved, thereby forming a highly absorbent surface.
Figure 5: Copper metal treated with 150 picosecond pulses
The rightmost part of Figure 5 is the laser-free polished area and the left side is the laser-treated area. These features are an order of magnitude smaller than those formed on aluminum materials (Figure 3). The resulting surface structure supports the assumption of a nonlinear, plasma-controlled process rather than the traditional heat removal process. Further relevant evidence is that the same laser parameters can be used to process 20 μm thick copper foil without material distortion, despite the use of sub-nanosecond lasers with an average power of 28.5 W.