AMD is gearing up to introduce a significant enhancement for its next generation of Zen 6 processors through a groundbreaking D2D (Die-to-Die, chip-to-chip) interconnect technology. Interestingly, the foundational elements of this evolution have already been integrated into the Strix Halo APU. Over recent years, AMD has advanced its process and architecture level innovations, but the interconnection approach between the CCDs and I/O chips has remained largely unchanged since the Zen 2 era. The introduction seen in Strix Halo signals a major evolution anticipated for Zen 6.

Existing Ryzen processors rely on the SERDES PHY module located at the CCD's edge. SERDES (Serializer/Deserializer) functions to translate parallel signals within the CCD into a fast serial bitstream for transportation through the organic substrate, before being deserialized on the receiving end. While viable for conventional packaging, this method naturally incurs additional power consumption and latency: the process of serialization demands encoding, equalization, and clock recovery, with deserialization reversing these processes, rendering the operation energy-intensive and time-consuming. With the inclusion of NPUs and other heterogeneous units, the traditional SERDES channel no longer suffices for current bandwidth and latency requirements.

Strix Halo's methodology diverges from tradition. It utilizes TSMC's InFO-oS (Integrated Fan-Out on Substrate) along with Redistribution Layer (RDL) technologies to facilitate direct chip-to-chip communication through compact, dense parallel lines. At the packaging level, InFO-oS permits the addition of further wiring layers between the silicon and organic substrate, while RDL aids in signal redistribution into these wiring layers. This allows for direct interconnection between the CCD and SoC chip via expansive parallel ports, bypassing reliance on the SERDES module. Visual evidence of the "fan-out" structure can already be discerned in Strix Halo's chip photomicrographs: an organized arrangement of micro-pad areas supplanting the expansive SERDES circuits.

The advantages of this strategy are palpable. Power consumption drops markedly and latency improves as the need for intricate serial-to-parallel conversions is obviated. The parallel bus offers increased instantaneous bandwidth and facilitates more interconnect ports within the CPU, thereby augmenting communication capabilities. For APUs, this means smoother data exchanges between GPUs, NPUs, and CPUs, supporting AI insights and high-bandwidth graphical tasks. For the forthcoming Zen 6 CPUs, it promises enhanced efficiency in multi-CCD interconnections, particularly in expansive server and HPC contexts.

Naturally, fan-out packaging isn't without hurdles, given the high design complexity RDLs present, which involves the stacking and prioritization of multiple wiring layers. Concurrently, balancing packaging yield and cost is crucial, especially in mass production settings where consistency is a pivotal concern. Nonetheless, considering TSMC's well-established utilization of the InFO series process in high-end mobile SoCs, AMD's decision to implement it within PC and server platforms seems to be more about design and validation than technical achievability.

Strategically, this development underscores AMD's continual strides toward a die-based architecture, with Zen 6 set to pioneer the fully integrated D2D parallel interconnect. This advancement not only refines power and performance but also lays the foundation for integrating more heterogeneous units down the line, with Strix Halo providing a glimpse into the future. Strix Halo has served as a "preview" of the new interconnect on APUs, reflecting some of the "DNA" present in Zen 6. As we approach the official unveiling, this detail is anticipated to be a pivotal point in Zen 6 architecture's promotional narrative.

In conclusion, AMD's resort to advanced packaging and interconnect technologies marks a pivotal step in overcoming the limitations of traditional approaches. Refining inter-chip communications is just as crucial as process advancements focused on reducing transistor size. The transformation evident in Strix Halo heralds a new dimension in multichip interconnects for future Zen 6's, elevating expectations for AMD's competitive stance in the realms of high-performance computing and AI.