Embedded RDL formation in Non-Photo Polymers using Excimer Laser Ablation

Abstract

Abstract The continuous trend towards miniaturization, increasing performance and mobility of electronic devices drives interconnect density and integration, not only at the chip level, but also at interposer and package level. Silicon interposers coming from wafer foundries using back end of line (BEOL) redistribution layer (RDL) processes have been introduced successfully. However, there is a continuing need for low cost interposers based on large organic or glass panels. While traditional organic flip-chip substrates using semi-additive processes (SAP) have not been able to scale to ultra-fine RDL pitches, photo-sensitive spin-on dielectrics and RDL processes used for wafer level packaging do not sufficiently address the cost reduction need, This paper presents the latest results from cost effective and innovative package RDL processes using excimer laser ablation, to meet the market's most stringent requirements. To enable panel and wafer based interposers to reduce RDL cost and scale interconnect pitch to 40um and below, excimer laser ablation is introduced as a direct patterning process that uses proven industrialized excimer laser sources to emit high-energy pulses at short wavelengths to remove polymer materials with high precision and high throughput. The combination of a high-power excimer laser source, large-field laser mask and precision projection optics enables the accurate replication and placement of fine resolution circuit patterns without the need for any wet-processing. In addition, with excimer laser patterning technology the industry gains a much wider choice of dielectric materials (photo and non-photo) to help achieve further reductions in manufacturing costs as well as enhancements in interposer and package performance. In this paper, we propose new process that uses excimer laser ablation to integrate via and RDL traces in one patterning process step, followed by seed layer deposition, plating and planarization steps. A new integration process flow is proposed, and its technical robustness and commercial advantages have been demonstrated. The capability of this excimer laser process to extend the current material portfolio to non-photo materials will be discussed, and its commercial benefits as compared to the current process of record (POR) will be highlighted.