OAM Accelerator Module PCBA

16–26 Layer OCP OAM 2.0 GPU/NPU Mezzanine Module with 112 Gbps PAM4

Product Overview

The OAM (Open Accelerator Module) PCBA is the OCP-standardized mezzanine form factor carrying GPU or NPU silicon in modular, hot-swappable AI server architectures. Unlike proprietary SXM modules, OAM delivers an open ecosystem with standardized 7-row high-density mezzanine connectors and 112 Gbps PAM4 signaling per lane. Our assembly process handles large BGA ASICs with 6,000+ pins, advanced thermal interface material (TIM) application, and stiffener ring attachment for warpage control. The board routes 32× SerDes lanes per edge for north-south and east-west connectivity, enabling flexible scale-up and scale-out topologies. Deployed in Baidu Kunlun, Intel Habana Gaudi, and AMD Instinct MI300 OAM platforms for hyperscale AI training and inference.

Key Specifications

PCBA Assembly Challenges

Assembling the OAM module places extreme demands on SMT precision and thermal management. The centerpiece is a large GPU/NPU ASIC BGA — typically 6,000+ balls at 0.8 mm pitch — with coplanarity requirements held to 0.08 mm across the entire package to prevent head-in-pillow defects. A stainless steel stiffener ring is adhesively bonded around the ASIC perimeter before reflow to counteract PCB warpage during the high-temperature profile; ring height tolerance and adhesive cure must be precisely controlled to avoid interfering with heatsink mounting. Thermal interface material (TIM) is dispensed onto the ASIC lid post-reflow with automated thickness control (±25 µm) to ensure uniform thermal conductivity across the 400–700 W thermal design power. The 7-row mezzanine connectors along all four edges require co-planarity below 0.10 mm and are inspected by 3D SPI before paste and 3D AOI after placement. Double-sided assembly may be used for voltage regulator modules (VRMs) on the reverse side, demanding staged reflow to protect the primary-side ASIC and HBM packages. Post-reflow, 3D X-ray inspection verifies every BGA joint under the ASIC and HBM stacks, with void rates held below 10% on power and ground balls per IPC Class 3.

Test Strategy

Each OAM module undergoes a rigorous multi-stage test sequence. Flying probe ICT verifies passive component values, power-to-ground resistance (checking for shorts across the multi-rail VRM domain), and continuity on all mezzanine connector pins. Boundary scan (JTAG 1149.1/1149.6) tests interconnects between the ASIC, HBM memory, and peripheral controllers, covering over 95% of nets without physical probe access. High-speed SerDes testing runs PRBS31 patterns at 112 Gbps PAM4 on all 32 lanes per edge, measuring eye height, eye width, and bit error rate (BER < 1E-15) across voltage and temperature corners. Thermal validation operates the module at maximum TDP for 8 hours in a controlled chamber, monitoring ASIC junction temperature, VRM hotspot, and mezzanine connector temperature rise. Final system-level integration testing plugs the module into an OAM-compliant baseboard, validating full link training, memory channel integrity, and sustained inference throughput before shipment.

PCB Manufacturing Difficulty

Fabricating the OAM module PCB is an elite manufacturing challenge. At 16–26 layers of Megtron 7 or IT-988G ultra-low-loss laminate, layer-to-layer registration must be held to ±2 mil across the full 102×165 mm panel — a single misregistered via can short a SerDes differential pair. Backdrilling is applied to all high-speed via transitions to remove stubs that cause signal degradation above 28 GHz, with stub length controlled to under 6 mil. The aspect ratio of plated through-holes exceeds 10:1 in 26-layer boards, requiring advanced pulse plating for uniform copper deposition. Impedance is modeled layer by layer with 3D field solvers and verified by TDR on every panel; differential pairs targeting 85 Ω or 100 Ω are held to ±8% tolerance. The dense BGA breakout region under the ASIC requires laser-drilled microvias with 1:1 aspect ratio and stacked via structures. ENEPIG surface finish is applied uniformly across all pads to support both wire-bondable and solderable surfaces. Every finished board undergoes 100% automated optical inspection and impedance coupon testing prior to assembly release.

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