PCB007 Magazine

PCB-Nov2016

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36 The PCB Magazine • November 2016 FEATURE by Jim Bovatsek SPECTRA-PHYSICS Introduction For more than 30 years, lasers have played a significant role in the manufacturing of PCBs. It is not a coincidence that electronic devices have, at the same time, become increasingly minia - turized. The ability to tightly focus a laser beam much smaller than a mechanical tool has been an enabler of such dense, compact circuitry; and the elimination of consumables such as drilling and routing bits has reduced manufacturing costs. The workhorse laser technology over the years has been the carbon dioxide (CO2) laser, which has provided manufacturers with reliable, cost-effective power for various applications. The most identifiable laser process in PCB manufac - turing is what is referred to as via drilling, which involves laser drilling a hole through an electri- cally insulating dielectric layer on a copper sub- strate. Generally, if the substrate is left intact, the hole is a blind via; if it is also drilled through, it is a through via. Very small holes having di- ameters below about 150 micrometers are com- monly referred to as microvias. After a subse- quent copper plating step, an electrical intercon- nection through the dielectric layer is formed. By arranging these vias in various two-dimensional configurations and by implementing additional build-up, drilling, and plating steps to introduce a third dimension, the high-density inter connect (HDI) and packaging needs of today's powerful yet compact electronic devices are satisfied. Making it Smaller As always there is a mandate for smaller: small - er mobile devices, smaller microchips, smaller electronics packages, and smaller interconnect vias. Vias drilled with CO2 lasers are generally limited to diameters of 60–80 µm or larger due to the long (~10 µm) wavelength of the light, which has a direct bearing on how small the beam can be focused. While smaller via sizes can technical- ly be achieved, the business case quickly vanish- es due to higher overall process complexity (and therefore cost). Here is where shorter-wavelength pulsed ul- traviolet (UV) diode-pumped solid-state (DPSS) laser technology enters the picture. The short UV wavelength—about 30 times shorter compared to CO2 wavelengths—can easily be focused to Advanced UV Lasers for Fast, High-Precision PCB Manufacturing

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