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40 The PCB Magazine • November 2016 ADVANCED UV LASERS FOR FAST, HIGH-PRECISION PCB MANUFACTURING countered, resulting in the most efficient process- ing and maximum throughput. As an example, consider the case where this optimal combina- tion happens to occur at 200 kHz for a laser hav- ing PRFnom of 100 kHz. Both the average power and pulse energy are lower than at PRFnom, but the same number of pulses are emitted in half the time; and although the pulse energy is lower and the per-pulse ablation rate will therefore be lower, the data in Figure 2 indicate it will not be lower by a factor of 2. Hence, a net improvement in the process throughput will be realized. In this fairly common scenario—a mismatch between the design point of a laser and the needs of a specific application—lasers with elevated power levels for an extended range of PRFs are highly advantageous. There are other ways to maximize the poten - tial of today's higher-power UV lasers. If the opti- mal energy for efficient processing is significantly lower than the energy at the designed PRFnom for maximum laser average power , then it may make sense to split the beam into multiple lower energy beams and route them to multiple pro - cessing heads (as shown in Figure 4a). Using such a configuration, the effective throughput of the processing laser can be further improved com- pared to the above described approach of simply increasing the PRF. The throughput advantage is greater for smaller vias since they require lower energy and therefore a larger number of beam splits can be made. As an example, Figure 4b con- tains a table demonstrating the effective via drill- ing rate for the case of a single beam/high PRF vs. a split beam configuration for drilling ABF blind vias of diameters 50 and 100 µm which using a 15 W UV laser system. With the latest 30 W ver- sion of the laser, the throughputs would be about double that of the 15 W model. Laser Processing for Flex PCB Manufacturing Not only is packaging becoming smaller, it is by necessity becoming increasingly flexible. De - vice miniaturization has reached the point where modules can be integrated into very thin items— credit cards, passports, clothing (wearables), even paper—and interconnection and packaging schemes must accommodate the same. In addi - tion, the flex PCBs allow for more versatile and compact arrangements within portable devices, leading to reduced form factors, increased func- tionality, and design flexibility. With such driv- ing forces, manufacturing of flex PCBs has expe- rienced rapid growth for several years and this is likely to continue. Figure 4: Splitting a laser's high-power beam (a) allows higher overall drilling rates (b), especially for smaller diameter vias which require less pulse energy. (a) (b)