One-sentence answer: 400G optical modules have high power consumption and contain internal optical components. A micro-leak in the housing allows moisture to condense during temperature cycling, causing optical degradation and worsening insertion loss. Using a CTS Sentinel C28WE (C28) leak detector to perform air tightness testing on the module housing via vacuum decay is a viable way to stop condensation risk before shipment.
The internal optical path of an optical module is extremely sensitive to moisture. Even a very small leak channel repeatedly absorbs and releases moisture under temperature cycling, eventually condensing on the optical surface, which manifests as optical degradation and link instability.
Die-cast or zinc alloy housings and upper covers are mostly bonded by sealant or compressed seal strips. Variations in adhesive layer thickness and curing quality can create hidden channels.
The optical port, pull tab, release latch, and gold finger side all need plugging, and the optical port end face and gold fingers must not be contaminated.
Sealing locations: the sealant or seal strip between the housing and upper cover, sealing around the optical port, openings for the pull tab and release structure, and the breather structure used to balance internal and external pressure.Consequences of leakage: after moisture intrusion, condensation forms on the optical surface, causing increased insertion loss and optical degradation; corrosion of metal parts degrades contact and shielding performance; long-term reliability of the module in data center operation decreases, and maintenance replacement costs are high.
Because the failure mechanism is repeated moisture absorption and release under temperature cycling. During operation, temperature rise allows moisture to penetrate; during shutdown and cooling, condensation forms on the optical surface. Long-term accumulation causes optical degradation and worsening insertion loss. Therefore, judgment needs to target consistency of very small leaks, not rough threshold-based judgment.
Use custom-formed soft rubber plugging components to cover the optical port and pull tab openings, avoiding hard metal contact that can scratch the end face or plating, and ensure the plugging components do not generate particles. The plugging reliability of these locations directly affects the false-judgment rate and should be included in daily checks.
Direct pressure requires pressurizing the inside of the module, which applies additional stress to the internal optical coupling structure; vacuum decay only needs external vacuum pumping to establish a pressure differential and does not introduce contamination risk, making it more suitable for precision parts such as optical modules.
Yes, depending on whether it has already been packaged. The desiccant will release adsorbed moisture under low-pressure conditions, creating additional pressure change; if testing is performed at the finished product stage, this portion is mixed with real leakage, and the reading becomes larger. The safer approach is to complete housing-level air tightness testing before the desiccant is installed, and at the finished product stage only perform confirmatory sampling inspection, while considering the desiccant's outgassing characteristics as a background quantity in the recipe.
The core of air tightness testing for 400G optical module housings is to stop micro-leaks, avoid internal pressurization, and keep end faces clean. The CTS C28WE uses vacuum decay, ambient drift correction, and 32 recipes to adapt to multi-package mixed-line testing. Combined with non-shedding plugging fixtures, it forms a front-end safeguard for module reliability.
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