Dependence of a hybrid 125W S-band switch-limiter receiver protector's performance on packaging technique: Plastic/leadframe QFN vs. ceramic/air-cavity SMT
A hybrid assembled switch-limiter function in a leadframe-based plastic QFN package (in a “stacked-die” approach where P-I-N diode chips are die-attached to a ceramic interposer), is compared with the same function in a high-performance all-ceramic air-cavity package. In both cases, the ceramic offers electrical isolation of components, the ability to customize microstrip printed elements, and high thermal conductivity for high power handling. The QFN offers the ability to mount die on the ceramic or directly on the leadframe, but with lower placement accuracy with attendant large tolerance allowances. The QFN can only be assembled with single-diameter gold wirebonds, while the ceramic package can be assembled with a mix of multiple size gold wirebonds and ribbonbonds. The design goals were to provide 125W power handling through one arm of the switch to a termination load, and allow up to 2W power handling through the other switch arm to a reflective limiter that will allow no more than 20mW through to an LNA, across an operating range of -55° through +85°C. P-I-N, limiter and Schottky diodes were employed in the design, together with discrete silicon blocking capacitors and bias components.
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