What is the difference between a bed of nails test fixture and a flying probe for RF PCB testing?

Bed-of-nails and flying probe are two approaches for PCB-level electrical testing, each with different strengths for RF applications: (1) Bed of nails (BON): a custom fixture with an array of spring-loaded test probes (pogo pins) arranged to contact specific test pads on the PCB. All probes contact the board simultaneously when the board is pressed onto the fixture. Test time: 1-10 seconds per board (all points tested in parallel). Pros: very fast (high throughput for production), tests all points simultaneously, and can include RF probes for coaxial or GSG contact. Cons: expensive fixture ($5,000-50,000 depending on complexity), fixture is specific to one board design (not reusable), requires test pads on the PCB (adds area), and fixture modification for design changes is costly. RF capability: limited. Standard pogo pins have significant inductance (> 1 nH), limiting useful frequency to < 1-3 GHz. Specialized RF pogo pins: designed for controlled impedance (50 Ω, coaxial structure). Useful to 6-10 GHz. Cost: $50-200 per RF probe point. GSG probes in a BON fixture: useful to 18-40 GHz (expensive and fragile). (2) Flying probe: a machine with 2-8 motorized probe arms that move to each test point sequentially. Each arm has a probe tip that contacts one pad at a time. Test time: 30 seconds to 10 minutes per board (sequential testing of each point). Pros: no custom fixture (the machine is programmed, not physically rebuilt for each design), quick setup (hours vs weeks for BON), cost-effective for prototypes and low-volume (< 1000 boards), and flexible (easy to add or change test points). Cons: slow (sequential testing, not parallel), limited number of simultaneous contact points (2-8), and RF capability limited by probe arm mechanics (practical limit: 1-3 GHz for standard flying probes). (3) For RF PCB testing: BON is preferred for production volumes > 1000 boards at frequencies < 10 GHz. Flying probe is preferred for prototyping and low-volume at frequencies < 3 GHz. For frequencies > 10 GHz: neither standard BON nor flying probe is suitable. Use VNA-based testing with precision connectors or GSG probes (manual or automated probe station).