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58 The PCB Magazine • June 2015 ensuring maximum productivity. A must-have for any UV laser micromachining tool is a tel- ecentric lens. As shown in Figure 5, a telecentric lens ensures that the laser beam always strikes the material at a 90-degree angle, thereby cre- ating a perpendicular via or cut anywhere the machine processes the material. Typical UV laser tools use a combination of linear stages and galvanometers (motor- ized mirrors) to position the laser beam on the part being processed. Many manufacturers use a move-then-process method to cut the full panel area—moving the stage to an area on the panel within the galvanometer field, process- ing that area, stopping the laser, moving to the next area, processing, stopping, etc. This results in a lot of non-value-add time since the laser is off during each long move. In addition, due to small galvanometer and linear stage errors, as well as due to optics aberrations, that method can result in incongruous cut lines where one galvanometer field touches the next. The method of compound beam position- ing resolves both of these issues by moving all beam positioning devices at the same time in a manner similar to hand-writing. For a stage- plus-galvanometer beam positioning system, one can think of the stage as the arm mak- ing the large and slow motions to cover the entire page at the same time as the galvanom- eter acts as the wrist and hand, making the small, precise, and fast motions to form the words. This method ensures high productivity given that very little time is wasted with the laser not processing, as well as avoiding qual- ity problems caused by galvo field incongrui- ties since the laser is continuously processing while moving. Accurate High-Speed Beam Positioning Precise beam positioning at high velocities is more difficult. It is crucial to maintain adher- ence to part dimensional toler- ances, as well as to avoid local- ized heating quality issues by moving the beam fast enough to spread out laser pulses even at high laser pulse repetition rates. Accurate high-speed beam positioning becomes also becomes important as feature sizes shrink, and thinner and more heat-sensitive materials are used. Here, good tools set them- selves apart. It becomes much more difficult to maintain pre- cise beam positioning at high velocities for small features and tight curves given the high accelerations that the beam positioning components must overcome. One method of overcoming these challenges is to include a solid-state device as part of the beam positioning mechanism since such solid- Figure 5: a telecentric lens restores the laser beam to vertical no matter the galvanometer angle. FeAtuRe STAYING CURRENT continues