21 GHz fT — what it buys the front end
The NXP BFU660F,115 is a silicon NPN RF transistor with a 21 GHz transition frequency, making it suited for low-noise amplification up through the 5.8 GHz ISM band. The 0.6 dB to 1.2 dB noise figure across 1.5 GHz to 5.8 GHz tells you this part can sit in the first LNA stage without burying the signal in its own noise — a common failure point when a cheaper wideband transistor gets substituted. Collector current is rated 60 mA max and collector-emitter breakdown at 5.5 V, so keep it in the small-signal role; it is not built for power stages.
SOT-343F footprint — what the rework bench needs to know
Package is SOT-343F, a 4-lead leadless plastic package with the supplier device code 4-DFP. The leads are flush with the body — no visible gull-wing to inspect with a loupe.
Product status is Active, so this transistor is still in normal production. No last-time-buy notice, no end-of-life clock ticking.