Issue link: https://iconnect007.uberflip.com/i/1330321
JANUARY 2021 I PCB007 MAGAZINE 91 guide material. After the copper is etched from the backside, the top side is circuitized with copper pads. The Terabus project wants to create a dense, hybrid packaging structure made up of "Opto- chips," "Optomodules" connected with flexi- ble waveguides to create the "Optocard" with additional waveguides in a backplane between Optocards. This is shown in Figure 14. The fu- ture vision is for an "optically-enabled MCM" as seen in Figure 3d (~2020 Roadmap figure) with performance projected into the 2014 to 2016 era [9] . Other flex optical cabling is ThunderBolt from Apple. Similar to Intel's LightPeak, Thun- derbolt is a combined electrical/optical con- nection standard. Figures 14a, b, and c show these flex poly- mer waveguides in the Optocard. A frame is employed to address the need of flat working surfaces that are required during optical fab- rication, as seen in Figure 14a. The flex as- sembly is aligned to the Optomodule and Py- ralux and is used to laminate them together. The entire assembly is then baked under pres- sure to cure the Pyralux. The fully assembled structure is shown in Figure 14b. The attach- ment process is repeated at the other end of the waveguide flex to complete the Optocard, as seen in Figure 14c. EIT also employed ink- jet printing of the waveguides successfully [11] . The Terabus Structure consists of the Op- tomodule connected to the HDI PCB (Opto- card seen in Figures 15 and 16a), with inte- gral or flex waveguides (Figure 16b), patterned by the process in Figure 16c and showing its cross-section seen in Figure 16d, e, f, and g. The Optomodule is an organic HDI chip carrier (known in IBM as SLC) with the Optochip con- taining optical VCSEL and PD chips aligned by Optochip lens array to waveguide lens array on the Optoboard. Figure 13: IBM opto packaging strategy: a 2011 strategy of grouped waveguide cables to CPU Modules, CPUs processor package and Modules that individual MicroPOD optical connectors rack with 16 Processor Modules: 4 racks per system. (Source: IBM) [17]