Artificial intelligence (AI) applications have gradually entered people's daily lives. Since AI must rely on complex computing and represent a strong computing and data processing center behind it, improving the operational effectiveness of data centers has also become an important technology development issue. This paper discusses the development of the Open Computing Project (OCP) and the uniqueness of the Mirror Mezz connector introduced by Molex, as well as the role it plays in the OCP.
The OCP Creates a Collaborative Open-Source Environment for Computer Hardware
The world is experiencing explosive growth in new AI applications, ranging from multiplayer games to cybersecurity protection, disease detection, and supply chain optimization, which have improved our daily lives in many ways. Rapid development of AI is generating a large number of new hardware accelerators for machine learning (ML) and deep learning (DL). Common requirements for flexibility, robustness, serviceability, configuration management, power, and cooling have emerged due to the need to enable multiple computational accelerators within the data center and to establish an open accelerator module infrastructure, making open mezzanine modules a sensible design option.
To improve the development of computing accelerators, the establishment of an open platform in conjunction with the technology industry is urgently needed, hence the advent of the OCP. The OCP originated in 2009 with Facebook (now known as Meta), and as the Facebook platform became more popular, Facebook began to optimize its data centers to better meet consumer needs. The company formed a team to create the world's most efficient data center, which increased energy efficiency by 38% while reducing operating costs by 24%.
In 2011, Facebook released the designs and helped launch the OCP program in collaboration with companies such as Intel and Goldman Sachs. Over the past decade, the OCP has worked to replicate collaborative open-source software environments for computer hardware, where cross-functional engineering teams can create reference designs that accelerate the pace of innovation in data centers.
Today, more than 200 companies, including Molex, have joined the OCP community to address difficult and unique challenges, to innovate rapidly from a broader perspective and ultimately to make hyperscale infrastructure more efficient, flexible, and scalable.
The Open Accelerator Infrastructure (OAI) group is a subgroup of the OCP server group that defines open standards for accelerator infrastructure systems consisting of accelerator modules, a baseboard, tray, and chassis to handle these intense workloads. In 2019, the organization released the Open Accelerator Module (OAM) v1.0 standard containing the Molex Mirror Mezz mezzanine connector, a design specification that requires high-density board-to-board connections between GPU modules and the baseboard capable of handling 56 Gbps. This connection must be small enough to allow space for other key components, achieve high differential pair count, and maintain extremely low levels of crosstalk.
Mirror Mezz connector with maximum design flexibility
Mirror Mezz connector, introduced by Molex, is a footprint-compatible hermaphroditic connector, which is compatible in length and width, regardless of male and female terminations. The application cost is reduced by stackable mating, which means that the connector can mate to itself, thus reducing the number of parts, simplifying the bill of materials and consolidating the supply chain efforts. The connector has a very high density of 107 to 115 differential pairs (DP)/in² and a signal integrity requirement of 56G-PAM4, which supports data rates of up to 56 Gbps per differential pair and is designed to handle data requirements for intensive AI applications and is suitable for telecommunications, networking, and other applications.
Self-mating or cross-mating (where different stack heights are required) of Mirror Mezz, a hermaphroditic connector, easily achieves the required mating height to meet application requirements and provides maximum design flexibility with the least tools. When combined for mating, a 2.50 mm high connector and a 5.50 mm high connector can achieve stack heights of 5.00mm, 8.00mm and 11.00mm. When two mezzanine connectors stacked 5.00 mm high and 10.00 mm flat flexible cable (FFC) are used, they can be stacked 20.00 mm high, with the highest stacking height of 120.00 mm.
The Mirror Mezz connector with open pin field rows, supporting differential signals up to 17 GHz, and offset GSSG pinout. Nine signal pins can be set in a pitch of 8.10mm. The combination of signals and grounding in the Mirror Mezz connector pin area is accurately arranged to maximize high-speed performance and clear wiring in the connector space.
The Mirror Mezz connector has an intricate terminal structure, provides a variety of mechanical strength versions for user choice, and features cutting-edge electrical functions. It provides two electrically tuned signal contacts to transmit high-speed signals cleanly for maximum signal integrity (SI). The bending direction of terminal contacts is different between rows. This design reduces crosstalk between rows, meets industry requirements for higher speed, has wider grounding pins, balances electric fields, and shields the difference from surrounding transmission lines.
Mirror Mezz connectors are mated with contact beams to prevent poor contact caused by vibration or terminal lifting and to ensure constant double contact points for electrical reliability. The geometry of the contact beam provides a reliable forward force to cope with harsh environments, and a 1.50-mm nominal contact wipe ensures that sufficient engagement surfaces can also be formed with strong vibration or inadequate mating.
Mirror Mezz connectors have signal integrity up to 56 Gbps NRZ, 112 Gbps PAM-4, support resonance-free, 0-35 GHz, use 92 ohms nominal impedance design, have high pin counts of up to 271 differential pairs, and dense connector pin fields up to 107-115 differential pairs per square inch.
Mirror Mezz connectors can be applied to data/computing devices such as networking devices, servers, memory, and infrastructure and networking devices in the telecommunications/network field.
Connectors that meet strict OAM (Open Accelerator Module) infrastructure requirements and restrictions
To support the strict requirements and limitations of the OAM infrastructure, Molex launched the Mirror Mezz 15×11 OCP connector solution, which is the only connector interface specifically developed between modules and base board. This connector provides excellent signal integrity and density to enable customers to achieve the mechanical and electrical goals required for the next generation of high-speed systems. In addition to all the necessary signals, the 15×11 Mirror Mezz connector for OAM also transmits the necessary power to the module, thus creating an all-in-one solution for mezzanine connectivity.
Mirror Mezz 15×11 OCP connectors provide 165 differential pairs per square inch by stacking and mating them to reduce application costs, while providing maximum design flexibility, allowing users to pair connector versions at different heights and achieving the stacking heights required for their applications.
The Mirror Mezz 15×11 OCP connector has a robust housing design, with the pin area packaged to protect the pin and provide blind-mate guidance, thereby eliminating any mis-mating possibilities, and can use mezzanine-flexible cable links to save costs and provide excellent signal integrity through controlled channels and pinned grounds, with relaxed tolerances to accommodate offsets between circuit boards and between flexible architectures.
The Mirror Mezz 15×11 OCP connector has a fit and combined contact beam structure that prevents vibration and terminal lifting to ensure constant 2-point contact for electrical reliability. The geometric structure of the beam provides reliable forward force and 1.50 mm nominal contact wipe for harsh environments to ensure adequate connection.
The Mirror Mezz 15×11 OCP connector is designed with a stitched ball grid array (BGA), allowing more cost savings than insert-molded BGA attachments. The stitched contact structure reduces lead-times and the connector design allows for simplified product matrix.
Higher data rate improvement version facing new challenges
The innovative features of the Mirror Mezz connector helped drive the design of the first-generation OAM, but the OCP is continuing to make more efforts. The OAI (Open Accelerator Infrastructure) team of the OCP is working to improve accelerator functionality and aims to develop new specifications that support 112 Gbps or higher.
The current Mirror Mezz connector still falls short of the 112 Gbps specification, but Molex has created a new, improved version, the Mirror Mezz Pro, that specifically addresses the challenges posed by the 112 G-PAM4. Mirror Mezz Pro, designed by Molex, improves performance and signal integrity at twice the maximum data rate of 112 Gbps PAM-4, while suiting the original compact PCB footprint. The BGA size of the new connector has been reduced to minimize return loss at high frequencies, and the terminals and housings have been adjusted to minimize impedance variation, thus achieving 112 Gbps performance and the same mechanical and electrical robustness acceptable to customers.
Mirror Mezz Pro Connectors
The Mirror Mezz Pro Connector has now been selected by the OAI team of the OCP as OAM v1.5's board-to-board mezzanine connector standard, which will have the opportunity to break through the next generation of hyperscale infrastructure. The Mirror Mezz Pro version is the latest in a series of innovative products launched by Molex in cooperation with the OCP.
Mirror Mezz Pro Application
Conclusion
The OCP, supported by many technology practitioners, is an important standard specification for data center equipment, and fewer matching parts are required for high-speed, high-density server applications to reduce costs, improve operational efficiency, and improve design flexibility. The Mirror Mezz connector, introduced by Molex, will be the best option for the relevant applications without separate matching parts and extra costs.