How do I select between a hermetic and a non-hermetic package for an RF module?
Hermetic vs Non-Hermetic RF Module Packaging
The hermetic versus non-hermetic decision has major implications for module cost, size, weight, and supply chain. Hermetic packages require specialized materials, processes, and test equipment that add significant cost and lead time.
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
Frequently Asked Questions
Can I make a non-hermetic package work in a harsh environment?
Yes, with mitigation. Apply conformal coating (parylene C provides excellent moisture barrier), use die passivation (silicon nitride over the MMIC surface), select moisture-resistant materials (gold wire bonds instead of aluminum, which is susceptible to corrosion), and control the operating environment (sealed enclosure at the system level with desiccant). These techniques can extend the service life of non-hermetic modules to 10-20 years in moderate environments.
How much more does a hermetic package cost?
Hermetic packages typically cost 2-10x more than non-hermetic equivalents: a QFN package costs $0.10-0.50, while an equivalent ceramic hermetic package costs $5-50. The cost depends on material (Kovar, LTCC, alumina), size, pin count, and volume. Assembly in a cleanroom environment with seam welding or solder sealing adds $10-50 per unit in labor and test costs. For military/space programs, the total packaging cost can be 50-80% of the module's total production cost.
What testing verifies hermeticity?
Fine leak test: the package is pressurized with helium tracer gas, then placed in a mass spectrometer leak detector chamber. Leak rates above 1x10^-8 atm-cc/sec indicate a seal failure. Gross leak test: the package is immersed in a heated fluorocarbon bath; bubbles indicate a large leak. PIND test (Particle Impact Noise Detection): detects loose particles inside the sealed package that could cause circuit failures. Moisture content test: packages opened and internal atmosphere analyzed by mass spectrometer to verify moisture < 5000 ppm.