Material property, compatibility, and reliability issues in diamond-enhanced, GaAs-based plastic packages

The mechanical performance and reliability of various Al₂O₃ ceramics were evaluated with intended applications as insulator frames for radio frequency/microwave power packages. Considering variations in base-flange material properties (CuW, CuMoCu), base-flange thickness (0.040 in., 0.020 in.), assembly process material (AgCu, Cu) assembly process temperature (860°C, 1080°C), and Al₂O₃ insulator material (96%, 99%, 20% ZrO₂/Al₂O₃, ZTA), finite element analysis (FEA) spatially resolved the fabrication-induced stresses during the assembly of CuW/Al₂O₃ and CuMoCu/Al₂O₃ structures and showed the critical regions to be the frame corners at the metal base-flange/Al₂O₃ interface. Bend strengths (four-point) and Weibull distributions were determined for each Al₂O₃ material and coupled with the FEA-predicted stresses for the various package configurations and assembly processes, the failure probabilities (P_f ) for the various CuW/Al₂O₃ and CuMoCu/Al₂O₃ structures were calculated. The CuMoCu-based structures exhibited the greatest warp deformation (concave upward, +), and highest stress and failure probability for all Al₂O₃ insulator varieties. The CuW-based structures exhibited an order-of-magnitude lower warp deformation (concave downward, −), an order-of-magnitude lower stress in the Al₂O₃, and in excess of seven orders-of-magnitude lower failure probability than CuMoCu-based structures, for all Al₂O₃ insulator varieties. Confirmational experiments were conducted using AgCu and direct-bond copper (DBC) assembly processes for selected varieties of CuW/Al₂O₃ and CuMoCu/Al₂O₃ structures. Al₂O₃ failure sites were identified using radiographic, ultrasonic and optical techniques and were in good agreement with model predictions of suspect structures and failure location. The strength and reliability data were considered in conjunction with relative cost for the Al₂O₃ ceramics to select an optimum frame insulator for the application.