MINIATURIZED SAW FILTERS USING A FLIP-CHIP TECHNIQUE

This paper describes a miniature surface acoustic wave (SAW) filter, 3 .2 x 2.5 x 0.9 mm(3), which is applicable for radio frequency (RF) sta ge filters in mobile phones. The SAW filter is reduced in size by usin g a flip-chip assembly technique. The technique uses gold bumps on the SAW chip and gold-gold thermosonic face-down bonding. The gold bumps are formed onto the wafer by a conventional wire bonding machine using gold wire. The thermosonic face-down bonding enables the connection o f gold bumps on the SAW chip, with gold metallized pads, on a ceramic package at a temperature below 200 degrees C. This bonding ensures tha t the SAW chip is fixed mechanically, and connected electrically, with the package. Frequency responses of a 950-MHz flip-chip SAW filter ar e compared with responses of a SAW filter with a conventional package. The results of reliability tests for flip-chip SAW filters are shown.