Excimer Laser Ablation for Microvia and Fine RDL Routings for Advanced Packaging
Excimer laser ablation is a direct etching process using high-energy pulses at short wavelengths that allows patterning of most polymers at minimal thermal impact through bond breaking. Metal layers of >1μm in thickness serve as a stop layer, so underlying circuits are not affected by the excimer laser ablation. With this type of patterning technology, the advanced packaging industry gets access to materials that do not require photo patterning and allow a wider range of options for coefficient of thermal expansion (CTE) matching in the package. A tool, consisting of a high-power excimer laser source, a reticle-sized laser mask, and reduction projection optics on top of a state-of-the-art wafer stepping stage enables the accurate and cost-effective replication and placement of high-resolution circuit patterns. We will explain the excimer laser technology and its application for drilling microvias and trenches that are used in different packaging applications.