Thermomechanical and Compression Analyses for Large-Scale Co-Packaged Optics (CPO) Assembly

With the development of artificial intelligence (AI) and other high-performance computing, the data transmission bandwidth in data centers has increased to 51.2 Tbps and will double every two years. The traditional pluggable optical modules have difficulty in satisfying the requirements. Co-packaged optics (CPO) integrates ASICs and optical engines (OEs) on the same substrate, providing a low energy loss and high throughput solution. However, the CPO structure is complicated and the package size is large. Therefore, the assembly-induced mechanical stresses and warpage of CPO are serious issues. In this article, assembly feasibility based on a $200\times 200$ mm2 51.2-Tbps CPO was analyzed by a cross-scale simulation methodology with multiple mechanical stresses. First, the ASIC structure optimization of the CPO was carried out, and the CPO substrate was determined. Then, based on the above-optimized structure, the thermal reflow simulations of ASIC and mechanical compression simulations of OEs were conducted by the birth and death element method. The results showed that the stiffener ring in the ASIC package was optimized to be 3 mm in height and 15 mm in width. The 5-mm PCB was determined for the CPO substrate. The CPO substrate warpage under the socket after the thermal reflow was less than 0.05 mm and the maximum equivalent stresses of the ball grid array (BGA) in the whole assembly process were less than the yield strength of the SAC305 by submodel structure analysis. The socket terminal forces after mechanical compression were greater than 0.1 N. The analyzed results meet the process targets during the assembly of the CPO.