The final level, Level 4, has evolved within the past five to seven years. For monolithic microwave ICs, higher-density integration results in fewer square millimeters of gallium arsenide substrate material and hence lower cost. For the U.S. Department of Defense, the motive for focusing and strengthening the nation's investment in electronic packaging technology is the potential for significant advancements in system performance and affordability. It is needed in military applications such as radar, electronic warfare, communications and smart munitions, and commercial applications such as telecommunications, direct broadcast satellite, cellular radio, personal communication systems and intelligent transportation systems. These technologies offer the reduction or elimination of wirebonds, increased reliability, improved yield and lowered fabrication costs.
Multilayer substrates enable dense packaging of components and modules.
And for experimental purposes the front-end tooling costs tend to be uneconomical. Maximum operating frequency is limited to about 10 GHz because of dielectric losses, but emerging developments promise to reduce those losses and improve performance. Multilayer substrates have been developed for a variety of complex microwave circuit designs and interconnection techniques, but attachment of active devices or chips must be surface-mounted or inserted in cavity cutouts with exposed conductors within the sublayers. The Hughes team's approach focused on development of multilayer tiles fabricated from aluminum nitride, which exhibits a good thermal match to both silicon and gallium arsenide. And Westinghouse, teamed with IBM and TRW, used MMIC and digital ICs in a flip-chip configuration.