Alibaba Cloud Server R&D Team Publishes Three Papers on High‑Density PCIe 6.0, 100G‑PAM4 Ethernet, and Immersion‑Cooling PCB Materials at IEEE EPEPS 2024 and PCB West 2024

Recently, three papers from Alibaba Cloud's server R&D team were accepted at the top international conferences IEEE EPEPS 2024 (Electronic Packaging, Interconnect, and System) and PCB West 2024, focusing on high‑density PCIe 6.0 channel optimization, 100G‑PAM4 Ethernet performance in air and immersion cooling, and new low‑cost sustainable PCB materials for immersion‑cooled systems.

With the rapid growth of AI applications, the required compute infrastructure has expanded dramatically, demanding higher data‑transfer rates and bandwidth. PCIe 6.0 doubles the data‑transfer speed to 64 Gb/s, while 100G‑PAM4 Ethernet provides even greater throughput, both essential for accelerating deep‑learning training and inference. However, achieving these speeds introduces signal‑integrity challenges such as loss, reflection, and crosstalk.

Paper 1: Fan‑out Region Crosstalk Optimization of High‑Density PCIe 6.0 SMT Connectors (EPEPS 2024)

Background: Modular hardware designs in data centers favor compact PCB layouts, leading to dense SMT connectors with limited spacing for shielding. PCIe 6.0’s PAM4 signaling is especially sensitive to noise, making crosstalk mitigation critical.

Results: The study analyzes various fan‑out routing strategies, compares simulation and measurement data, and demonstrates that optimizing the fan‑out region significantly reduces crosstalk, improving PCIe 6.0 signal integrity for system designers.

Paper 2: Comparative Evaluation of 100G‑PAM4 Ethernet Link Performance in Air and Immersion Cooling Conditions (EPEPS 2024)

Background: Data‑center cooling consumes a large portion of total power, and immersion cooling offers higher energy efficiency but introduces dielectric changes that affect high‑speed Ethernet signal integrity.

Results: Simulations and lab measurements reveal that immersion cooling reduces link margin by ~2 dB and degrades BER by about two orders of magnitude compared with air cooling. The authors recommend DOE‑based simulation and the development of immersion‑optimized QSFP connectors to mitigate these effects.

Paper 3: A Case Study on the Performance and Reliability of New Low‑Cost and Sustainable PCB Materials for Immersion‑Cooling Computer Systems (PCB West 2024)

Background: As cloud providers shift from air‑cooled to immersion‑cooled data centers, there is a need for PCB materials that perform reliably in liquid environments.

Results: The study introduces new CCL materials with lower and more stable operating temperatures (30‑50 °C), reduced hygroscopicity, and non‑flammable properties by decreasing PPO, Br, and Cl content. Comprehensive electrical and reliability testing confirms that the new materials meet or exceed performance targets, offering cost‑effective, environmentally friendly solutions for immersion‑cooled servers.

These findings provide valuable guidance for the design of high‑speed interconnect architectures and cooling strategies in Alibaba Cloud’s AI Infra 2.0 servers, enhancing both performance and energy efficiency.