Vibration Characteristics ofUltrasonic Transducer inThermosonic FlipChipBonding

Thermosonic flip chipbonding hasbeenwidely usedin fine pitch ICpackaging foritsunique features. Byusing thermosonic flip chip bonding atanaluminum wirebonder, lmmxlmmchipwith8goldbumpsisbonded successfully toAgsubstrate, andthebonding strength reaches ashighas about 30gf/bump. Dynamical characteristics ofultrasonic transducer areinvestigated byfinite element methodand experiments using impedance analysis andlaser Doppler measurement. TheFEM analysis showsthat, ultrasonic transducer system vibrates incoupling ofall excited modes, which results incomplicated vibrations during bonding. The third axial vibration mode,whichincludes 1.5wavelengths and3nodes, isthedominant working mode.However, the dominant vibration isdisturbed significantly byundesirable non-axial modessuchasflexural vibration. Moreover, there aresomeother un-wanted modesparasitizing closely to dominant mode.Velocities oftransducer hornsampled by LaserDoppler Vibrometer showthesystem vibrates with several modessimultaneously. Theimpedance results using impedance analyzer prove there aresomeother undesirable frequencies close totheworking mode.Allnon-working modesofultrasonic transducer willdisturb thebonding process anddegrade bondquality, sotheymustbewell controlled toobtain unique vibration modeandstable vibration forthermosonic flip chip bonding.