A hermetic surface-mount ball grid array (BGA) LTCC package for multi-function T/R MMICs up to Ku-band

This paper presents the design aspects of a hermetic SMT package for multi-function ICs up to Ku-band. With the goal to release the first off-the-shelf packaged core-chip product on the market, a custom ceramic package has been specifically designed for M/A-COM Tech Asia X-band XZ1002 T/R core-chip MMIC. The design and process trade-offs to address RF performance, thermal aspects, SMT assembly and hermeticity, lead to the choice of a multi-layer LTCC substrate coupled to a collective hermetic lid approach and balling process developed with the substrate manufacturer and the assembly house. The final package consists of a 12×12-mm² 3-layer LTCC substrate, hermetically sealed with an AuSn preformed Kovar lid, and a backside ball grid array having 1-mm pitch and 0.6-mm nominal ball diameter. Extensive 3D electromagnetic simulations were carried out to optimize the package RF transitions and isolation, leading to a Board-to-MMIC transition having less than 0.5 dB insertion loss, and >; 25 dB return loss at 10 GHz. The functionality of this first pass package has been demonstrated with the evaluation of a packaged X-band core-chip: In Transmit or Receive modes, the circuit exhibits an average gain of 25- and 20 dB respectively, with full amplitude and phase control.