Advances in Package Microvia Interconnects: Breakthroughs With Picosecond UV Laser Ablation

Downscaling of microvias to approach the critical dimension (CD) of routing half-line pitch is crucial for advanced packaging but presents significant challenges. The state-of-the-art (SotA), achieved with nanosecond (ns) pulsed UV laser, results in via diameters of 20 μm. By employing a 5- picosecond (ps) pulsed UV laser, microvias of 5 μm were achieved in a 5 μm thick Ajinomoto build-up film (ABF) through conventional laser ablation and could be reduced to 3 μm by adding a thin copper layer on top of the ABF as a buffer. With thinner and filler-free materials, the minimum demonstrated microvia size was further down to 1.26 μm on a 2 μm thick JSR dielectric film. A via matrix of 26x33 (858) was presented. The heat affected zone (HAZ) and defects were around 0.5 μm. The landing accuracy within 16x16 (256) with via pitch of 5 μm matrix was analyzed which was ±0.34 μm. Considerations for next-generation system designs for one micron and submicron microvias are discussed.