A Low Cost Wafer Scale Package Technology for mm-wave Applications
The availability of low-cost, high performance amplifiers is crucial to the continued development of mm-wave commercial applications from 17 to 40 GHz. Typical applications include wireless data links such as Local Multipoint Distribution Service (LMDS) and point-to-point microwave radio as well as automotive 24GHz, instrumentation, and VSAT satellite ground stations. Recent industries’ technical trend for mm-wave MMICs is using surface mount packages for assembly cost reduction. Typical high frequency packages are Rogers 4003 material for SMT packages , plastic material for QFN packages  and liquid crystal polymer material for SMT packages .
No matter what packaging techniques are used, conventional packages require assembling processes such as die attaching, wire-bonding, and lid attaching. Those assembly processes are key bottlenecks for the cost reduction. To realize radical manufacturing cost reduction, we propose a wafer scale packaging technique for mm-wave MMIC manufacturing. There are some technical challenges to realize wafer scale package for mm-wave MMIC applications. RF interface must be optimally designed to obtain good 50-Ohm matching.
MMIC design must be considered for the proximity effect from a capping wafer. The amplifier shown in this paper was carefully designed to realize optimum performances in wafer scale package environment.
In this paper, wafer scale packaging information is shown including factors that make it low cost. RF I/O design and tested performance for the wafer scale package are shown. After the discussion of the wafer scale package design, the design and performance of a broadband driver amplifier is described. The MMIC broadband amplifier technique is explained for resistively matched amplifier design. A 17 to 33GHz broadband driver MMIC amplifier was designed and fabricated by Avago technology’s in-house 6” GaAs wafer scale package process. Finally, full measured data is shown for the amplifier in the low cost 4x4mm QFN compatible wafer scale SMT package.