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74 PCB007 MAGAZINE I AUGUST 2020 and kerf width. This reduces production costs by enabling downstream production processes to achieve higher yields (Figure 4). Finally, the reduced HAZ and increased throughput possible with the Coherent pulsing method, but with lower pulse energy when pro- cessing a flex PCB, are illustrated in Figure 5. Practical, High-Pulse Energy DPSS UV Lasers For traditional, thick PCB materials, imple- menting the Coherent pulse control method in practice requires a UV DPSS laser source having higher pulse energy than previously commer- cially available. To meet this need, Coherent de- veloped the AVIA LX, a 20 W (at 355 nm), solid- state, nanosecond pulse width laser, which can produce a pulse energy of up to 500 µJ. This laser was specifically designed to enable high throughput, high-quality PCB depaneling. It combines several technological advances in design and manufacturing to deliver this high energy output along with an unmatched com- bination of high reliability, superior perfor- mance, and low cost of ownership. In particular, this product leverages the ex- tensive experience at Coherent in producing reliable, long-lifetime lasers with UV output. The non-linear (frequency tripling) crystals used in it are produced within Coherent, pro- Figure 4: Top view of a 100-µm polyimide foil shows a cutting result achieved with a competitor's UV DPSS laser on the left, having a wide cut kerf and a sizeable HAZ. The cutting result on the right was achieved with the Avia LX UV DPSS laser. This delivers a narrower trench channel and smaller HAZ. Figure 5: Top view of 0.13-mm FPCB cut using a (left) a competitor's UV DPSS laser and (right) a high-pulse energy UV DPSS laser (AVIA LX). This produced a much smaller HAZ and achieved this at a higher cutting speed (13 mm/s compared to 11mm/s).