Printed Circuit Design & Fab - June 2008 - (Page 40)

drill DrIllIng oF PCBs — an overview Engineering advances have increase throughput and enabled smaller via sizes with increased process reliability. by TODD LIZOTTE, GABOR KARDOS and RONALD D. SCHAEFFER As a laser processing service provider, our shop has worked with many industries and seen many applications over the last decade. Laser drills are well established in the field of microvia formation, having taken over for mechanical drills as via diameters have gotten smaller. The drilling of vias in printed circuit boards has been a topic of discussion for many years. Mechanical drilling has been done since the start of the PCB industry, and in the last ten years, lasers have taken over in a number of the high end applications, although mechanical drilling technology has also advanced during that time. As little as eight years ago, you could still go on the IPC show and find at least a dozen companies promoting laser FiGurE 1. 50 micron mechanically drilled vias on 200 micron centers drilled at 200 holes per minute. 40 microvia and mechanical drills. At present, at least in the U.S. market, the field has largely been narrowed down to just a few players, with only Excellon and Hitachi offering both mechanical and laser (CO2 and UV based) Hitachi leads the market in both the U.S. and abroad, so most of the specifications and examples shown are taken from Hitachi. To keep a leadership position within the marketplace requires the continuous development of new product lines, as well as enhancements to existing products, as the microelectronics packaging and PCB markets shift to continuously higher densities and precise tolerances. The latest products entering the U.S. marketplace include flexible modular systems that allow for simultaneous drilling of different jobs using a single CNC controller, which provides flexibility in high precision and small lot PCB production. Current models offer industry leading accuracy and speed, outfitted with vision systems, and so are capable of achieving high aspect ratio drilling with front to back alignment. For high volume applications, there are six spindle drilling platforms designed for high throughput production that maintain high accuracy and reliability in multi-shift operations. Depending on process requirements, the customer can select their drilling systems to be outfit- ted with spindle speeds ranging from 125,000 to 300,000 RPM, with higher speeds targeted towards micro-hole drilling down to 0.100 mm. In general, mechanical drills are the choice for any vias over 0.250 mm, and while they can be used down to 0.100 mm, (actually, we have seen mechanical drills that can create 0.050 mm vias!), in this range, lasers may be a better choice depending on the application. For vias smaller than 0.100 mm, better results are obtained using laser drills. It should also be noted that mechanical drilling technology has advanced in the area of blind hole drilling. FiGurE 1 shows 0.050 mm mechanically drilled holes using 250,000 RPM spindles in BT material. The holes are on 200-micron pitch and the photograph was taken after 2000 holes had been drilled. Within the U.S., the retooling of production drilling equipment has demonstrated significant increased production capacity. Specifically, at a recent install of an ND-6N series system, the first production run averaged in excess of 300 holes/ minute including tool changes. Further efficiency has been gained by the ability of systems to be seamlessly integrated into existing drill and job setup automation and networking software. Because customers require increased precision and throughput, industry leadJUNE 2008 printEd circuit dESign & fAB

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Printed Circuit Design & Fab - June 2008 Contents Our Line Market Watch Around the World Happenings ROI Tip Jar Interconnect Strategies Final Finish Forum DFA/DFT Signal Integrity From the Field DFA Fab Basics Drill Off the Shelf Marketplace Ad Index BGA Bulletin

Printed Circuit Design & Fab - June 2008

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