High-speed microvia formation with UV solid-state lasers

Laser drilling has emerged in the last five years as the most widely accepted method of creating microvias in high-density electronic interconnect and chip packaging devices. Most commercially available laser drilling tools are currently based on one of two laser types: far-IR CO₂ lasers and UV solid-state lasers at 355 nm. While CO₂ lasers are recognized for their high average power and drilling throughput, UV lasers are known for high-precision material removal and their ability to drill the smallest vias, with diameters down to about 25-30 μm now achievable in production. This paper presents an historical overview of techniques for drilling microvias with UV solid-state lasers. Blind and through via formation by percussion drilling, trepanning, spiralling, and image projection with a shaped beam are discussed. Advantages and range of applicability of each technique are summarized. Drivers of throughput scaling over the last five years are outlined, and representative current-generation performance is presented.