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72 PCB007 MAGAZINE I AUGUST 2020 fluence for ablation even well out of perfect fo- cus for the laser. The benefits are faster cutting and reduced system complexity. An example of the improvements achieved are shown in Figure 1, which compares cuts in a 1.6-mm PCB with copper traces, made us- ing the type of UV DPSS laser currently com- mercially available for this application versus the same material processed using this new approach. The board processed with this tech- nique shows a cleaner cut edge and substantial improvement in the cut edges of the copper traces. Figure 2 demonstrates the reduction in kerf width achieved utilizing this method. Figure 3 shows how it enables cutting of multilayer PCBs (with glass fiber layers) with minimal debris, narrow trench width, and sub- stantially reduced HAZ. In the past, laser cutting of polyimide and EMI shield foil produced some delamination at the cut line due to the wide HAZ. In this case, it's necessary to use lower pulse energy to avoid damaging the material. But the same pulsing approach is utilized to eliminate heat buildup and delivers the same benefits of reduced HAZ Figure 2: Top views of a 0.95-mm PCB cut using (left) a competitor's UV DPSS laser and (right) a high-pulse energy UV DPSS laser (AVIA LX), which yields a narrower and more consistent kerf. Figure 3: Cross-sections of a 1.6-mm, multilayer PCB (with glass fiber layers) cut using a (left) a competitor's UV DPSS laser and (right) a high-pulse energy UV DPSS laser (AVIA LX) the new Coherent method. This delivers a more narrow trench channel and smaller HAZ.