One-sentence answer: 5G filter cavities are mostly die-cast aluminum structures, where sand holes and cover screw surfaces are hidden leak sources, and cavities interconnected through coupling windows mean whole-cavity testing can only determine total leakage. Using the CTS Sentinel C28WE (C28) leak detector to perform cavity air tightness testing via pressure decay or vacuum decay is a common interception method on filter production lines.
Sand holes may only be exposed after machining or plating, invisible to the naked eye, yet they form stable micro-leaks; sand holes at different positions in the same mold follow no pattern, making it difficult to intercept them by visual inspection upstream.
The cavity consists of multiple resonant cavities connected through coupling windows; after a leak is found in whole-cavity testing, segmented re-testing is still required to locate the specific cavity.
Cover screw holes, tuning screw holes, and connector mounting surfaces constitute a large number of potential leak paths, and each opening must be plugged or guaranteed to be sealed.
Sealing locations: die-cast cavity body (sand holes, shrinkage porosity), cover-to-cavity mating surface, tuning screw threads, connector mounting surface, cavity-to-housing mating surface.Consequences of leakage: moisture intrusion causes corrosion of the internal plating of the cavity, deterioration of insertion loss and out-of-band rejection indicators, and degraded base station coverage performance; after corrosion, the indicators are irreversible and the entire unit must be replaced, resulting in high maintenance costs.
Rely on resolution and consistency, not visual inspection. Leak rate resolution 0.0005 scc/min (a resolution specification, not equal to the minimum leak rate the instrument can detect), combined with built-in calibrated leak automatic calibration, can stably identify the persistent micro-leaks formed by sand holes; at the same time, it is recommended to move testing forward to after machining is completed and before assembly begins.
Test the whole cavity first, then perform segmented re-testing. Whole-cavity testing serves as the gatekeeper for the assembly and is highly efficient; after a defect is identified, use the segmented plugging method to localize cavity by cavity. Only the combination of the two can provide usable process feedback while ensuring cycle time.
Use the local plugging method to vacuum or pressurize the connector mounting surface alone, and compare with the whole-cavity result to determine whether the leak comes from that location. This type of re-test should be solidified as a fixed step in defect analysis.
Divert by defect morphology. Sand holes are defects of the casting body itself, with fixed positions that recur with mold locations; channels caused by machining are mostly related to tool marks, threaded pilot holes, or mating surface flatness, and their positions change with the machining datum. Only by collecting segmented re-test results together with casting batches and machining parameters can credible process feedback be provided.
The key to 5G filter cavity air tightness is to intercept sand hole micro-leaks, combine whole-cavity and segmented testing, and provide feedback to the process. The CTS C28WE, with dual methods, ambient drift correction, and 32 programs, adapts to shared-line testing of multi-band cavities, forming front-end assurance for filter reliability.
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