Low-cost E-band flip-chip assembly and materials

By extending the wireless backhaul network to higher frequencies, more bandwidth is available, enabling the higher capacity microwave radio links, to accommodate the increase in traffic from, for example, data use in smartphones. Products for the E-band (specifically 71-76, 81-86, and 92-95 GHz) are now on the market, and, as always, there is a drive for reducing cost, both in manufacturing and sourcing, while maintaining high performance. This paper describes in detail the incoming material and assembly process for E-band GaAs flip chips with lead-free solder, using high volume manufacturing equipment. The choice of incoming materials such as chips, chip carriers, flux and underfill is discussed, and future paths indicated. The target is to take manufacturing processes and materials typically used in consumer products and employ them in millimeter wave products as far as possible. A first assembly round using daisy chain and transmission line test chips mounted on hardback boards with teflon top layer has proven successful, with very high yield in assembly but some problems remaining related to printed circuit board quality.