What Should Buyers Compare in a Hermetic Cable Assembly?

There is no universal leak-rate value suitable for every application. The buyer should define the internal volume, pressure differential, operating temperature, acceptable permeation, and required service life before setting a limit. Helium mass-spectrometer testing is commonly used for sensitive leak detection, while gross-leak and fine-leak methods address different failure sizes. MIL-STD-883 Method 1014 is frequently referenced for hermeticity testing, but its applicability and acceptance criteria must be agreed in the procurement specification. Ask for the measured result, test pressure, tracer gas, stabilization time, equipment method, and calibration evidence rather than accepting the phrase hermetic as a performance value.

Compare the sealing medium against temperature cycling, pressure differential, moisture exposure, mechanical loading, chemical contact, and electrical insulation needs. Glass-to-metal and ceramic-to-metal constructions can provide a rigid inorganic barrier, but their coefficient of thermal expansion and assembly stress must match the surrounding materials. Epoxy systems may be useful for particular cable geometries or cost targets, yet cure profile, moisture uptake, outgassing, chemical resistance, and ageing data deserve close review. Material names alone do not establish hermeticity. Buyers should request the qualified construction drawing, material designations, cure or firing controls, and test data from production-representative samples.

Continuity and insulation resistance identify basic open, short, and insulation defects, but they do not fully validate a sealed interconnect. Depending on the application, specify dielectric withstand, contact resistance, current-temperature rise, shielding effectiveness, signal integrity, impedance, insertion loss, or high-speed performance. Test voltage, duration, ambient conditions, conductor configuration, and pass-fail limits must be documented. Electrical validation should also consider derating: current capacity changes with conductor size, contact design, ambient temperature, bundle arrangement, and allowable temperature rise. A connector that passes a bench test may still be unsuitable if the installed cable system creates excessive heat or signal degradation.

The cable jacket is not automatically the pressure barrier. The critical interface is where the cable, insulation, braid, filler, and seal material enter the connector or feedthrough. Jacket hardness, diameter tolerance, surface energy, water absorption, thermal expansion, chemical resistance, and flex life can influence bonding, compression, strain transfer, and leak stability. Polymeric materials can also release absorbed moisture or volatile compounds under vacuum and temperature. Compare the complete cable-and-termination construction, not just the jacket label. Qualification should include thermal cycling, mechanical loading, pressure exposure, and post-test leak measurement using production-representative cable lots.

A responsible technical package normally includes an approved drawing, revision-controlled specification, materials or bill of materials, electrical ratings, environmental limits, inspection plan, and defined leak-test method. Request representative test reports showing actual conditions and measured results, not only a certificate of conformity. For regulated or safety-critical programs, clarify lot traceability, calibration records, change-notification rules, nonconformance handling, and sample retention. If the assembly is part of a larger vehicle, medical, energy, or automation system, the buyer should map supplier evidence to the end-product approval process. Certifications such as IATF 16949 or IRIS describe applicable management systems; they do not replace product-specific hermeticity evidence.

The lowest unit quotation can conceal tooling, engineering, test-fixture, cable preparation, inspection, packaging, and requalification costs. Compare total delivered cost across the expected annual volume and include MOQ, setup charges, spare requirements, warranty provisions, and the effect of a supplier change on system validation. Lead time should be separated into design review, sample manufacture, testing, approval, and repeat production. Ask what events reset the schedule, such as material substitutions or drawing changes. Lifecycle risk is better assessed through documented process controls, component availability, change management, traceability, and service support than through price alone. A controlled comparison matrix makes commercial and technical trade-offs visible.