Miniaturized SAW filters using a flip-chip technique

This paper describes a miniature surface acoustic wave (SAW) filter, 3.2×2.5×0.9 mm³, which is applicable for radio frequency (RF) stage filters in mobile phones. The SAW filter is reduced in size by using 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 of gold bumps on the SAW chip, with gold metallized pads, on a ceramic package at a temperature below 200°C. This bonding ensures that the SAW chip is fixed mechanically, and connected electrically, with the package. Frequency responses of a 950-MHz flip-chip SAW filter are compared with responses of a SAW filter with a conventional package. The results of reliability tests for flip-chip SAW filters are shown