Laser drilling of blind holes in FR4/glass

In the last two years, laser drilled microvias have become the dominant method for producing blind vias smaller than 150 mm, with over 100 laser drilling machines with a variety of laser types installed worldwide. Only a few of these systems have been qualified for drilling blind holes in standard glass reinforced FR4. Details a production line at Siemens AUT LP in Karlsruhe, Germany, involving the successful evaluation, introduction, and full production of laser drilling of FR4/glass. An ESI 5100 with Ultraviolet Nd:YAG laser operating at 355nm was chosen for all copper structuring and all microvias less than 150 mm in diameter in thin materials, and a TEA CO2 laser was chosen for thicker constructions, where at least 250 mm holes were required. Production has been running since November 1996. Details the process modifications, design rules, qualified materials, reliability tests, and production experiences.