Thermal Analysis of Reflow Process for PIC-Embedded Package Substrate with 2.3D RDL Interposer for Co-Packaged Optics

Toward a next generation co-packaged optics (CPO), we have worked on a novel package substrate in which photonics integrated circuits (PICs) are embedded. The substrate can be provided as known good package substrate with optoelectronic conversion function and can be assembled in the same condition as conventional package substrates. In addition, the substrate realizes high-density optical assembly by optical redistribution layer (RDL). In this paper, we show design of the test vehicle using 2.3D electrical RDL interposer and provide its thermal analysis results for a reflow process.

I. Introduction

Co-packaged optics (CPO) has attracted much attention from many applications requiring very high bandwidth for data transfer, such as data center switch application-specific integrated circuits (ASICs), artificial intelligence (AI) and disaggregated computing [1]. Recently, first generation CPO was released from Broadcom which supports total bandwidth of 51.2 Tbps for a switch ASIC [2], and many research groups have worked on next generation CPO technologies [3]–[5]. We have worked on active optical package (AOP) substrate for next generation CPO [6]. AOP substrate is a novel package substrate in which photonics integrated circuits (PICs) are embedded. It provides all required photonics functions to realize CPO, such as optoelectronic conversion function, optical redistribution layer (ORDL) function and detachable optical connector. Compared to other works (CPO using photonics dies or sub-modules on interposer or package substrate), the AOP substrate can be provided as known good package substrate with optoelectronic conversion function and can be assembled in the same condition as conventional package substrates. We demonstrated key technologies for the AOP substrate, such as PIC die embedding, micro mirror optical coupling, polymer-waveguide ORDL and self-aligned optical connector [7]–[9]. Recently, we are fabricating the first active demonstration sample as the test vehicle. In this paper, we show its design and thermal analysis results for reflow process.