Piezoelectric Micro-jet Research Articles

Suppression of the height deviation on metal bumps manufacturing by an ultrasonic vibration control

On-demand droplet printing based on piezoelectric micro-jet device (PMJD) is considered a flexible and high-precision method to generate metal droplets directly for flip-chip bonding in industrial electronics. However, the quality of flip-chip bonding is closely related to the height deviation of the solidified droplets (the metal bumps), which is influenced by the complicated hydrodynamics of impacting and oscillation of the droplet with oxide film. Here, the numerical and experimental investigations are first conducted to study the effect of the liquid bridge and deposition parameters on the height deviation of the solidified droplets. The rapid oxidation of the liquid bridge and under-oscillation during the deposition process are the main reasons for height deviation. In addition, the undamped oscillation with high-speed impact and instantaneous solidification also deteriorates the height deviation. To this end, an oscillation control strategy based on ultrasonic-assisted metal droplet deposition (UAMDD) is proposed and verified to be a reliable regulation strategy to suppress the height deviation of the printed bumps. The effective regulating range of height deviation is studied experimentally by changing the ultrasonic vibration amplitude. Finally, a 10 × 10 array composed of 100 solidified metal droplets is printed with the UAMDD, which has the height deviation of 554 ± 6 μm. And the dimensionless height deviation (Δh/h) of solidified bumps is stayed below 2.1 %.

Flow and thermal coupling analysis in metal droplet-based 3D printing: Evolution mechanism and regulation strategy under ultrasonic vibration

Formation of uniform pileup morphology and excellent bonding strength between two adjacent metal droplets are essential in droplet-based 3D printing. However, due to the unstable included angle (“gap”) of the pileup droplets generated by the complex coupling effect between the fluid flow and thermal deformation during the printing process, the successive pileup droplets tend to form poor accuracy morphologies, non-uniform properties, and low-quality bonding strength of the formed microstructure. Since the unstable flow and thermal deformation of the liquid metal is inherent properties in droplet-based 3D printing technique with the same parameter conditions, the morphological deterioration or even instability pileup process still remain common challenge in this technique. Here, the effects of velocity and thermal behaviors on the morphology and size of the pileup droplets were revealed. To accomplish this, a droplet pileup numerical model based on the volume of fluid (VOF) was developed to analyze the spreading and solidification mechanism of the pileup process. In addition, a series of printing experiments with the successive pileup of Sn droplets, generated by a self-developed piezoelectric micro-jet device (PMJD), were conducted to demonstrate the effects of impacting velocity and solidified temperature on the pileup morphology. The evolution mechanisms of impacting velocity and heat accumulation effect and its influence on the dimensional accuracy were revealed. Finally, the originality of this work is an ultrasonic-assisted metal droplet pileup (UAMDP) method was first proposed and applied to effectively regulate the pileup morphology and improve the bonding strength. The evolutions of the influence of the velocity field, temperature field, and pileup behaviors during the spreading process were analyzed thoroughly. A surface morphology analysis further showed the effect of ultrasonic vibration on the contact region between two pileup droplets. And experiments showed that such UAMDP (under voltage of VP-P = 15 V) has 5.9 times enhancement in the adhesion tangential force between two pileup metal droplets. This study provides a foundation for further development of metal droplet-based 3D printing technology.

Injection of Viscous Micro-Droplet via Nozzle-Driven Piezoelectric Micro-Jet and Its Performance Control Method.

The inkjet printing technology based on piezoelectric micro-jets can effectively realize the efficient and high-precision processing of special-shaped structures. In this work, a nozzle-driven piezoelectric micro-jet device is proposed, and its structure and micro-jet process are described. ANSYS two-phase, two-way fluid-structure coupling simulation analysis is carried out, and the mechanism of the piezoelectric micro-jet is described in detail. The effects of voltage amplitude, input signal frequency, nozzle diameter and oil viscosity on the injection performance of the proposed device are studied, and a set of effective control methods is summarized. The correctness of the piezoelectric micro-jet mechanism and the feasibility of the proposed nozzle-driven piezoelectric micro-jet device are proved by experiments, and an injection performance test is carried out. The experimental results are consistent with the ANSYS simulation results, which confirms the correctness of the experiment. Finally, the stability and superiority of the proposed device are verified via comparation experiments.

Investigations into wetting and spreading behaviors of impacting metal droplet under ultrasonic vibration control

Ultrasonic-assisted metal droplet deposition (UAMDD) is currently considered a promising technology in droplet-based 3D printing due to its capability to change the wetting and spreading behaviors at the droplet-substrate interface. However, the involved contact dynamics during impacting droplet deposition, particularly the complex physical interaction and metallurgical reaction of induced wetting-spreading-solidification by the external energy, remain unclear to date, which hinders the quantitative prediction and regulation of the microstructures and bonding property of the UAMDD bumps. Here, the wettability of the impacting metal droplet ejected by a piezoelectric micro-jet device (PMJD) on non-wetting and wetting ultrasonic vibration substrates is studied, and the corresponding spreading diameter, contact angle, and bonding strength are also discussed. For the non-wetting substrate, the wettability of the droplet can be significantly increased due to the extrusion of the vibration substrate and the momentum transfer layer at the droplet-substrate interface. And the wettability of the droplet on a wetting substrate is increased at a lower vibration amplitude, which is driven by the momentum transfer layer and the capillary waves at the liquid–vapor interface. Moreover, the effects of the ultrasonic amplitude on the droplet spreading are studied under the resonant frequency of 18.2–18.4 kHz. Compared to deposit droplets on a static substrate, such UAMDD has 31% and 2.1% increments in the spreading diameters for the non-wetting and wetting systems, and the corresponding adhesion tangential forces are increased by 3.85 and 5.59 times.

On-demand preparation of calcium alginate microspheres via piezoelectric microfluidics

Calcium alginate microspheres (CAMs) have attracted extensive attention as a novel drug carrier due to their cheapness, biodegradability, biocompatibility and nontoxicity. The existing preparation technologies of CAMs require complex process steps and involve multiple types of equipment, which are difficult to achieve the real-time and on-demand supply of microspheres in micro-reaction experiments. In this work, CAMs for prolonged drug release are prepared by the designed piezoelectric microfluidic devices using sodium alginate (NaAlg) and calcium chloride (CaCl 2 ). Specifically, the on-demand CAMs are synthesized timely by piezoelectric micro-jet followed by the transportation of piezoelectric micro-pump. Furthermore, various solution concentrations, main parameters of excitation signal and different nozzle diameters are evaluated in terms of size, morphology and drug release rate. The control method of CAMs’ size is obtained based on the multi-physics coupling analysis. Experimental results show that the doxorubicin hydrochloride loaded CAMs (DOX-CAMs) which can be prepared on demand, have excellent uniformity and dispersion, and the minimum average particle size is about 81.9 µm. The controlled drug release rate of DOX-CAMs reaches 83.2 % after 24 h. Moreover, the piezoelectric microfluidic devices and corresponding control methods may have potentials to be adapted for synthesizing other inorganic composite microspheres. • Piezoelectric microfluidics realize the timely supply of microspheres on demand. • The control strategy of microspheres was obtained by simulation analysis. • Preparation of high-quality microspheres with uniformity and dispersion. • Microspheres have excellent drug release performance.

Deposition behavior optimization of on-demand tin droplet with gravity based on piezoelectric micro-jet

Metal droplet ejection has a wide application prospect in the field of additive manufacturing in recent years. Dispensing the droplet along the gravitational direction has been invested by many studies and offers favorable performances in applications. However, the oblique impact and asymmetric deposition process of metal droplets caused by gravity are still unclear which might limit the applications, such as the processing of metal components in space and the irregular 3D surface repair. In this work, the deposition behaviors of molten tin droplets under different process parameters are studied, and the optimization of process parameters under the effect of gravity is proposed for the deposition of on-demand droplet based on a piezoelectric micro-jet device (PMJD). To accomplish this, the theoretical models are established to build the mapping relationships among the process parameters, impact dynamic and solidification process of the droplet. Meanwhile, the temperature effects of the droplet and substrate on the dynamic contact line and maximum diameter are simulated; the asymmetric deposition behaviors of the droplet under different impact velocities and solidification time are also analyzed. Moreover, the final solidification shapes of the droplet corresponding to the process parameters are measured. The results indicate that the effect of gravity on the deposition behavior is restrained by increasing the impact velocity and solidification time; and the reliability of the theoretical models and simulation results is also validated

On-demand direct printing of tin microdots by a piezoelectric microjet: design, simulation, and experimental evaluation

Metal microdot precision printing is widely applied in flexible circuit manufacturing, ball grid array and additive manufacturing, etc. Compared with indirect metal microdot printing, direct printing can realize high efficiency printing by directly ejecting hot-melt metal droplets. While, due to the compressibility of the driving gas, uniform printed microdots are hardly to be obtained by using the existing direct printing method. In this work, a piezoelectric microjet, which can print tin microdots directly by the drive of piezoelectric actuator without complex pneumatic system, is designed. Optimization analyses of the displacement amplifier are carried out to obtain high amplification efficiency for realizing hot-melt droplet ejection and effective heat insulation. The forming, spreading, and solidification processes of the ejected hot-melt tin droplets are discussed, and the printing mechanism is revealed. Based on experimental research, the influences of the excitation parameters and the target surface characteristics on the morphology and size of the printed tin microdots are studied, and the methods to meet different printing requirements are proposed. Tin microdot diameter of 340 μm can be printed on the surface with temperature of 120 °C when voltage pulse with amplitude of only 16 V is applied on the designed piezoelectric microjet with the nozzle diameter of 200 μm. The feasibility and controllability of the tin microdot printing methods are verified by two-dimensional printing and three-dimensional deposition printing test. This work can provide important reference for on-demand printing of metal microdots.

Waveform Optimization of Piezoelectric Micro-Jet for the Control of Metal Micro-Droplet Ejection

On-demand metal droplet ejection is a critical technical branch in industrial electronics. Among them, high temperature and surface tension are the mainly limited factors affecting the single droplet ejection of hot-melt metal. To this end, this article proposed a waveform optimization scheme based on a piezoelectric micro-jet device (PMJD) actuated by a piezoelectric stack and a flexible hinge amplifier for liquid metal. The structure and operation principle of the PMJD is presented and analyzed. The numerical simulation model for hot-melt metal is established; the ejection mechanism and boundary condition of metal droplet are analyzed in detail by a direct fluid-thermal-structure interactions numerical method, which reveals two operation modes of metal droplet ejection under trapezoidal driving waveform. The driving waveform for the PMJD is designed and optimized to allow metal droplets to be ejected, and the variation of the initial velocity and shape of droplets are also analyzed based on the designed waveform. Furthermore, the critical value of satellite droplets generation with fracture of liquid bridge is discussed by simulation, and the optimized waveforms can also be used to suppress satellite droplets.

Study on the Performance of a Designed Annular Piezoelectric Microjet for Active Lubrication of Space Bearing

Lubrication failure of bearing is one of the important factors that limit the service life of the space shafting system. Due to the strict restrictions on the volume and weight, the traditional oil supply devices are difficult to meet the requirements of space active lubrication. In this article, we propose a piezoelectric microjet, which can achieve active lubricating for bearings of space equipment serving in a harsh environment. A constant pressure oil storage system, with a storage capacity of more than 4 g and can achieve vacuum oil storage, is proposed. Control accuracy of 0.012 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> L per pulse is obtained and a theoretical service life of more than 20 years can be achieved. The whole active lubricating system is embedded in the bearing system, which has no effect on the normal operating of the original bearing system and almost creates no mass increment of the bearing system. The methods of controlling the characteristics of the ejected oil droplet are proposed to meet different lubrication requirements. Combined with the monitoring of bearing temperature and friction torque, active lubrication on demand can be realized. This work can provide important references for prolonging the service life of space bearing.

Influence of input signal on injection performance for needle driven piezoelectric micro-jet device

Due to the fast response, high precision and high working frequency, needle driven piezoelectric micro-jet devices have been applied in various industrial fields. The injection performance is important for the applications. The jetting velocity of the micro-droplets has a great influence on the ligament length and satellites. In this paper, the Fluent stimulation model of dynamic mesh motion has been established to simulate the jetting process. Meanwhile, the dependences of volume and jetting velocity of micro-droplets on input signal, including voltage, falling time, and fluid pressure, have been studied. The results show that the jetting velocity of micro-droplets can be changed and the volume is invariant by adjusting falling time, which can be used to guide the control of the needle driven piezoelectric micro-jet devices. Furthermore, the experimental system has been designed and the experiments show that the average minimum jetting velocity is about 0.724 m/s. The ligament length increases almost linearly with jetting velocity of the micro-droplets. And the optimal jetting velocity is less than 2.745 m/s, which cannot generate satellites.

Development of a resonant piezoelectric micro-jet for high-viscosity liquid using a longitudinal transducer

A resonant piezoelectric micro-jet (RPMJ) using a longitudinal transducer (LT) is proposed for achieving high-speed jetting of high-viscosity liquid. The continuous droplets are realized by the pressure change of micro-jet element (MJE) which can be generated by the high frequency vibration of the LT. The RPMJ is designed and its driving principle is simulated to reveal the pressure change and the jetting status. The modal and harmonic response analyses are performed to determine the resonant frequency of the LT. The transient and two-phase coupling analyses are launched to optimize the parameters of the MJE; and the jetting performances under the various viscosities of silicone oils are analyzed. A prototype of the RPMJ is fabricated and its tested system is established. The jetting of the silicone oil with the viscosity of 150 cps is achieved under the voltage of 300 Vp-p and frequency of 19.4 kHz, and the average flowrate is about 0.07 ml/s. The maximum average flowrate can reach to 0.51 ml/s when the viscosity is 2 cps. In a word, the viscosity range of operable liquid has been broadened using the proposed RPMJ.

A Trace Redundant Lubrication Piezoelectric Microjet for Bearing System

A piezoelectric microjet, which can achieve lubrication on demand, is designed to realize the trace redundant lubrication for bearings. The volume of the ejected oil droplet can reach 0.0147 μ L with the velocity of the droplet as 0.91 m/s. A coupling analysis method is proposed to analyze the influences of excitation and oil properties on the dynamic characteristics of droplets. Based on the theory of central oil film thickness, an oil volume prediction model for the trace redundant lubrication of deep groove ball bearings is given. Experiments are carried out, the proposed coupling analysis method is verified by comparing the analysis results with experimental data, and the relative errors are given. The designed microjet is proved to be effective for redundant lubrication by testing its actual lubricating performance. The numbers of voltage pulses, which are required to achieve trace redundant lubrication under different excitations and operating conditions, are given. The validity of the proposed oil volume prediction model is proved by comparing results obtained from experiments and theoretical calculations, and the relative errors are given.

Influences of fluid characteristics on piezoelectric micro-jet based on direct coupling method

ABSTRACTThe piezoelectric micro-jet technology, which can achieve the drop-on-demand requirement, is based on the piezoelectric ink-jet technology. The injection performance of the micro-jet is influenced by the liquid properties as well as the applied pulse voltages. A direct coupling simulation method for analyzing the injection performance of a kind of micro-jet is proposed here. The forming processes of droplets inside the cavity at different time are given. The effects of the density, surface tension and viscosity of the lubrication oil on the molding time, molding length and velocity of the droplet are analyzed. Based on the comparisons between the simulation results and the experimental data, the direct coupling simulation method is proved to be an effective method to analyze the injection performance of the micro-jet quantitatively.

Influences of Excitation on Droplet Spreading Characteristics Ejected by Piezoelectric Micro-Jet

Thanks to its quick response, high precision and simple structure, piezoelectric micro-jet has been applied in various industrial fields. Especially in 3-D printing and surface coating whose accuracy has an important relationship with the spreading characteristics of the ejected droplets. A piezoelectric micro-jet, which can be used for 3-D printing and coating, is presented in this paper. The influences of excitation parameters on the spreading characteristics of ejected droplets are analyzed by a proposed tree dimension multi-physical coupling analysis method, in order to improve the ejection accuracy of the piezoelectric micro-jet. The spreading processes from the initial forming to the complete spreading of droplets are given. Based on the obtained results, the recommended adjustment schemes of excitation for improving the droplet spreading precision are given. Besides, the adjustment methods of ejecting distance and height are given to avoid the mutual interference during the process of droplet spreading. Experiments are carried out, the proposed coupling method and analysis results are proved to be effective.

Research on the Acoustic-Structure Coupling Characteristics of a Piezoelectric Micro-Jet Used for Lubricating

The injection performance of the piezoelectric micro-jet is mainly determined by the acoustic characteristics created in the cavity by the vibration of the piezoelectric vibrator. As sensors are difficult to be placed into the cavity of the piezoelectric micro-jet, the inside acoustic characteristics are hard to be tested by experiments. Thus, an acoustic-structure coupling model is given, and simulation analyses are carried out in this paper to study a piezoelectric micro-jet used for lubricating. The suitable working frequency for getting better lubricating performance is obtained by the frequency response characteristics analyses. The driving mechanism is revealed by comparing with the injection results. The influences of excitations on the acoustic pressure at the nozzle part are analyzed, and the methods for adjusting the working performance are obtained. The acoustic structure coupling model and results are verified by comparing with the experiment results.

Influences of Excitation on Dynamic Characteristics of Piezoelectric Micro-Jets.

Piezoelectric micro-jets are based on piezoelectric ink-jet technology and can achieve the drop-on demand requirements. A piezoelectric micro-jet which is designed for bearing lubrication is presented in this paper. In order to analyze the fluid dynamic characteristics of the piezoelectric micro-jet so as to obtain good injection performance, a direct coupling simulation method is proposed in this paper. The effects of inlet and viscous losses in the cavity are taken into account, which are close to the actual conditions in the direct coupling method. The effects of the pulse excitation parameters on the pinch-off time, tail length, velocity, and volume of the droplet are analyzed by the proposed direct coupling method. The pressure distribution inside the cavity of the micro-jet and the status of the droplet formation at different times are also given. In addition, the method is proved to be effective in predicting and analyzing the fluid dynamic characteristics of piezoelectric micro-jets by comparing the simulation results with the experimental results.

The numerical and experimental research on injection performance of piezoelectric micro-jet

Abstract The injection characteristics of a piezoelectric micro-jet are analyzed in this paper by numerical simulations and experiments. The effect of acoustic-structure interaction on the working frequency of the vibrator are analyzed by simulations and experiments. The vibration statuses of the vibrator are given when the cavity is filled with liquid or air. A simulation method for analyzing the frequency response characteristics of micro-jet is proposed, and the influences of the shell materials on the nozzle pressure are analyzed. In order to improve the injection performance, the recommended working frequency and adjustment methods of the excitations are given when selecting different shell materials. Experiments are carried out and the actual injection performance is obtained which prove the numerical simulation method can be effective.

Comparative Influences of Fluid and Shell on Modeled Ejection Performance of a Piezoelectric Micro-Jet

The piezoelectric micro-jet, which can achieve the drop-on-demand requirement, is based on ink-jet technology and small droplets can be ejected out by precise control. The droplets are driven out of the nozzle by the acoustic pressure waves which are generated by the piezoelectric vibrator. The propagation processes of the acoustic pressure waves are affected by the acoustic properties of the fluid and the shell material of the micro-jet, as well as the excitations and the structure sizes. The influences of the fluid density and acoustic velocity in the fluid on the nozzle pressure and support reaction force of the vibrator are analyzed in this paper. The effects of the shell material on the ejection performance are studied as well. In order to improve the ejection performance of the micro-jet, for ejecting a given fluid, the recommended methods of selecting the shell material and adjusting excitations are provided based on the results, and the influences of the factors on working frequencies are obtained as well.

Effects of Structural Sizes on the Injection Performances of Piezoelectric Micro-jet

Effects of Structural Sizes on the Injection Performances of Piezoelectric Micro-jet

Effects of pulse voltage on piezoelectric micro-jet for lubrication

A novel piezoelectric micro-jet for bearing lubrication is presented in this paper, and the micro-jet is working at the slapping mode. The micro-jet is embedded in the bearing system, and add little mass or volume of the system. In order to meet the different requirements for different applications and to improve the injection performance of the micro-jet, the trapezoidal wave is selected as the pulse voltage by analyzing the Fourier expansion of different pulse forms. And the influences of the parameters of the trapezoidal wave are analyzed by experiments. The injection status of the micro-jet and the mass of the droplet under single pulse voltage are obtained. The recommended exciting method for different requirements are given by analyzing the results.