Study On Joining Piezoelectric Ceramics To Copper Stator Elastic-bodies For Ultrasonic Motor

One of the key technologies of ultrasonic motor manufacturing process is the technology to integrate stators. At present, the organic adhesives have been widely used to bond the piezoelectric ceramics to the copper stator elastic-bodies across the world. However, some problems in the bonding process have not been solved, such as having difficulty in selecting the appropriate adhesives, high requirements for solidification, instability of the performance, hard for mechanizing production and aging of the adhesive layers. Therefore, it will become one of the important directions for promoting the development of ultrasonic motors to research and develop new connecting technologies. In this paper, the piezoelectric ceramics and the copper stator elastic-bodies were successfully joined by soldering process. The solders of Sn-40 Pb, Sn-3.5Ag and Sn-52 In were respectively adopted to join,which matched with different kinds of flux. Through carrying out the vibration finite element analysis of the soldered stators and studying on the reflow soldering process about the three solders deeply, the optimal solder, flux and process parameters for joining the piezoelectric ceramics to the copper stator elastic-bodies were determined.Firstly, by the vibration finite element analysis of the soldered stators, some results have been obtained that all the three kinds of soldered stators could generate the B09 mode shape which was consistent with the pre-calculated design. When the excitation frequencies were respectively 39.41 kHz, 39.77 kHz and 39.32 kHz, the amplitudes of the three kinds of soldered stators reached the maximum values, which were 2.79 ?m, 2.79 ?m and 3.30 ?m under the excitation voltage of 80 Vpp.The results clearly indicate that all the three kinds of soldered stators can meet the requirements of ultrasonic motors for the vibration performance of stators. Because of the stress concentration, the maximum in-plane shear stress of the connecting layers were all located in the intersections of the gap and the edge. And the maximum in-plane shear stress were 2.07 MPa, 3.04 MPa and 2.91 MPa,respectively, which were all less than the required minimum shear strength of the connecting layers.After that, the three kinds of solders were respectively used to join. The optimal reflow parameters were determined and the effects of peak temperature, time above liquidus and joining pressure on the vibration performance of soldered stators were studied. It can be concluded that the optimal reflow parameters for joining with Sn-3.5Ag solder were 250 ?, 60 s and 180 N pressure. The amplitude of the soldered stators could reach 2.0 ?m and the consistency of the two phase modal frequencies of the stators was good. This is to say that the vibration performance of the stators joined with Sn-3.5Agsolder can basically meet the requirements of ultrasonic motors. The optimal reflow parameters for joining with Sn-52 In solder were 140 ?, 115 s and 100 N pressure. The amplitude of the soldered stators was up to 2.5 ?m and the consistency of the two phase modal frequencies of the stators was great. This is to say that the vibration performance of the stators joined with Sn-52 In solder can fully meet the requirements of ultrasonic motors. However, the vibration performance of the stators joined with Sn-40 Pb solder was poor, so the Sn-40 Pb solder was not suitable for stators joining.In addition, based on the study on the soldering performance and the corrosive property of the several matching fluxes, we found that the rosin organic flux exhibited so many advantages of weak corrosive property, suitable viscosity, good effect and the convenience of use, which was the best choice.Further studies on the performance of the stators joined with Sn-52 In solder found that the piezoelectric constant d33 of the PZT8 piezoelectric ceramics did not change a lot during the heating process. So it can be drawn that the soldering process will not affect the piezoelectric property of the piezoelectric ceramics. The shear tests of the Sn-52 In solder joints showed that the fracture was located at the interface of the solder and the copper substrate, and the shear strength reached up to 6.9MPa, which could meet the requirement of stators for the mechanical property of connecting layers.When the stator joined with Sn-52 In solder was used to assemble in an ultrasonic motor, the locked-rotor torque and the no-load speed of the ultrasonic motor were 0.7 N · m and 120 r / min,respectively, which could basically meet the requirements of ultrasonic motors for the load characteristics.