Piezoelectric Ceramics and Flexible Printed Circuits’ Interconnection Using Sn58Bi Solder Anisotropic Conductive Films for Flexible Ultrasound Transducer Assembly

Interconnection technology using Sn58Bi solder anisotropic conductive films (ACFs) has been chosen to assemble piezoelectric ceramics on flexible printed circuits for ultrasound imaging applications. The bonding and dicing processes were performed, and the bending of test samples was evaluated. The results showed excellent integrity of solder ACFs' interconnects compared with other Ni-/Au-coated polymer ball and Ni ball-based ACFs' interconnects. The metallurgical interconnects of the solder ACFs produce lower electrical resistances after pressure cooker and bending reliability tests. Moreover, the solder ACFs with a high-speed bonding process resulted in more electrically conductive, more reliable, and finer-pitch bonding for producing higher process yield and higher density ultrasound transducer arrays.