Small-sized dual-band SAW filters using flip-chip bonding technology

New small-sized dual-band SAW filters have been developed. The filter has the dimension of 3.0×3.0×1.0 mm³ and the weight of 30 mg. In order to realize such compact packaging, 62% of surface mount area and 45% of weight of the conventional dual-band SAW filters, we adopt flip-chip bonding technology with Au-bumps. The dual-band filter, for Japanese PDC (Personal Digital Cellular) mobile phones, has been realized on a single chip. Two cascaded IIDT (Interdigitated Interdigital Transducer) resonator filters with numerous electrical connections between chip and package are easily assembled. To improve mechanical reliability, Al-Cu/Ta-Al/Al-Cu multiple layer film applied to the bump bonding pads on the chip surface. The developed filter successfully achieves high rejection level of 55 dB at image frequency as well as low insertion loss of 2.3 dB in the pass-band of around 900 MHz. A two-chip dual-band SAW filter with 1.8 GHz and 940 MHz band, with low loss of 2.7 dB, is also developed for DCS (Digital Cellular System) and EGSM (Extended Global System for Mobile communication) dual-band phones.