Hans Krüger

Recent advances in SAW packaging

Continuous size reduction of todays mobile telephones in parallel with enhanced functionality demands for higher integration of components as well as for significantly reduced device and component size. Since modern surface acoustic wave (SAW) components combine superior filter functionality with small size, they play an important role in mobile phone evolution. Increasing the levels of functional integration and permanent miniaturization are therefore the major driving forces in current SAW filter development. Conventional wire-bonded ceramic, metal or plastic packages are to an increasing degree being replaced by space efficient flip-chip or chip-scale packages. EPCOS proprietary packaging technology chip sized SAW package (CSSP) combines consequent package size reduction, filter application-specific technological features and outstanding internal electromagnetic performance made possible by the flip-chip technology. Specific CSSP technologies - each offering an optimum ratio between active chip space and package size - were developed for lower frequency (e.g. CDMA-IF) filters as well as for extremely frequency-precise IF-filters (e.g. GSM-IF), 1 GHz and 2 GHz RF filters, respectively. As functional integration like balun functionality or impedance transformation becomes more and more important for RF SAW filters, an integral design approach including acoustical and 3-D electromagnetic effects has to be used. The influence of sophisticated electromagnetic package design will be illustrated by examples resulting e.g. in superior amplitude and phase symmetry of balanced RF filters. Further size reduction will be obtained by integrating SAW filters with active as well as passive components in the frontend of cellular terminals.