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100 I-CONNECT007 MAGAZINE I APRIL 2026 of the light is the second main parameter making the choice of the correct laser source important. Laser sources have discrete wavelengths, which have a huge impact on the desired application. The wavelength, i.e., the "color" of the light, deter- mines the absorption behavior of each material. We've learned this from our daily lives: If materials absorbed different wavelengths homogeneously, our visual impression of the world would be a greyscale between black and white. However, for most of us, the world is colorful. Due to the reddish appearance of copper, we see that red is predominantly reflected at the surface while the other colors of our spectral eyesight are absorbed more strongly. From the perspective of a laser application, we prefer to use wavelengths outside the red spectrum to deposit laser energy for removal purposes, such as green or blue light. On the other hand, we can use the reddish spec- trum to prevent copper from absorbing the laser energy and being damaged by it. By selecting the appropriate laser wavelengths, we can directly influence the targeted removal and protection of different materials. The most common laser wave- lengths utilized in the PCB industry are: • 355 nm (UV) • 532 nm (Green) • 1064 nm (IR) • 9600 nm (IR/CO 2 ) For each application that requires laser process- ing, selecting the laser wavelength is important. This makes it mandatory to consider the entire ap- plication spectrum of current and future materials before deciding the laser wavelength. Drilling Methods: Navigating the Possibilities Laser drilling involves several distinct methods for creating holes. The choice depends on the target diameter, the material stackup, and the required pulse diameter. • Trepanning: The laser beam follows a spiral path to cut out the hole. This is used when the desired hole is larger than the beam diameter (Figure 2). • Pulsing: Also known as "percussion drill- ing," where the beam diameter matches the desired hole diameter, allowing the via to be created in one or more pulses without mov- ing the beam (Figure 3) • The Combi Method (Figure 4): A multi-step process typically involving: 1. UV-nano or pico- green to trepan (ablate) the top copper layer. 2. CO 2 to pulse and remove the di- electric material. 3. Optional: A de-focused UV or pico-green pass for "bot- tom cleaning" to ensure a reliable connection to the inner layer. There are two methods of direct CO 2 drilling, which differ from one another only in the first step. • Direct copper pulsing: Uses only a CO 2 laser. Since CO 2 cannot ablate shiny copper, the copper surface is chemically treated (black- ened or browned) to increase absorption Figure 2: Trepanning process. Figure 3: Pulsing process. Figure 4: Combi process. D R I V I N G I N N OVAT I O N