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PCB007-Aug2020

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70 PCB007 MAGAZINE I AUGUST 2020 All these constraints make traditional me- chanical PCB depaneling methods—including routers, saws, die-cutting, punching, scoring, and pizza-cutting, etc.—less practical and less cost-effective. This impels a move toward la- ser cutting, which offers substantial benefits in virtually every one of the areas previously mentioned, although usually at the expense of reduced cutting speed. Why UV Laser Cutting? Laser depaneling has, of course, been in use for some time. But it's important to understand and differentiate the various technologies re- ferred to by this terminology. The original im- plementations used CO 2 lasers that emit in the far infrared. This technology cuts by heating the bulk material, which results in a signifi- cant charring and heat-affected zone (HAZ). Also, compared with shorter, ultraviolet (UV) wavelengths, this long wavelength cannot be focused to a small spot size, meaning it pro- duces a larger kerf width. More than a decade ago, the diode-pumped solid-state (DPSS), nanosecond pulse width, frequency-tripled laser emerged as a viable source for PCB depaneling. It offers ultravio- let (355 nm) output with sufficient pulse en- ergy to enable material removal through a rel- atively "cold" ablation process—that is, one with a much smaller (but still noticeable) HAZ than the CO 2 laser, and also substantially less production of debris and recast material. The pulse energy and repetition rate of commer- cially available sources enable cutting at eco- nomically viable feed rates, although not as fast as the CO 2 laser. The primary benefits of UV technology are summarized in Table 1. Table 1: Primary benefits of UV technology.

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