Can Zhou

New Applications of an Automated System for High-Power LEDs

An automatic system based on thermoelectric cooler (TEC), a microfan, and microcontroller is first applied to thermal management of high-power light-emitting diodes (LEDs). Its hardware is composed of microcontroller as a control core, K-type thermocouples as acquisition devices, and TEC and a microfan with heatsink as cooling vehicles. The experiment confirms that the LEDs substrate temperature can be controlled effectively, and indicates that the LED chips are operating reliably. Specifically, in high-temperature environments of 43 °C, the system can automatically drop to the low set temperature (30 °C) due to thermoelectric effect driven by TEC. Heat transfer analysis shows that maximum LED power cooled by the system is 106.7 W, and the total power consumption of the automatic cooling system is only 8.85 W. The automatic cooling system has a high cooling efficiency.

A Novel High-Speed Jet Dispenser Driven by Double Piezoelectric Stacks

A novel bi-piezoelectric jet dispenser with a zoom mechanism is proposed to distribute adhesives rapidly. The work frequency of the new jet dispenser can reach 500 Hz. The volume of the minimum dot is about 25 nL, and the volume error among dots is not more than ±10%. The dot size can be controlled by adjusting the driving voltage of the piezoelectric stack, filling pressure, and the opening time of the valve. Subsystem physical models of the jet valve are presented on the basis of the bi-piezoelectric principle and the zoom mechanism, which involves an electromechanical model, dynamic model, and fluid-solid coupling model. Based on these physical models, a coupled mechanical-electrical fluid simulation model is established, which can be simulated. The simulation results of the multiphysics-coupled model are in accordance with the experiment. The coupling model will develop a reliable simulating platform for high-speed fluid jet. The effectiveness of the bi-piezoelectric method and models is confirmed, and it will provide a new technology for microelectronics packaging.

Control and Jetting Characteristics of an Innovative Jet Valve With Zoom Mechanism and Opening Electromagnetic Drive

In order to develop jetting technology in LED and microelectronics packaging, an innovative electromagnetic jet valve with zoom mechanism and opening electromagnetic coil is suggested, and an improved method of double voltage drive is applied in the electromagnetic control. It is found that the needle stroke of the new jet valve is increased to 1.3 times, and the needle velocity is raised to 1.8 times, and the temperature of opening electromagnetic coil is lowered to 6.7 °C. The jet valve can successfully jet 4 Pa·s high-viscosity adhesives at room temperature due to the improvement of dynamic characteristics. It will provide a new method for jetting high-viscosity adhesives.

The Mathematical Model and Novel Final Test System for Wafer-Level Packaging

To develop integrated circuit (IC) test of wafer-level packaging, the electromechanical model of microprobe testing process and the IC final test system of wafer-level packaging based on microprobe arrays are first proposed. An electromechanical model of the process of microprobe testing is derived, which is based on the analysis of the collected real-time force and electrical data using designed force sensing system, voltage measuring circuit and loading system. It is found that the contact resistance is a quartic function with respect to the loading force, and the loading force has nonlinear hysteretic damping characteristics with respect to the displacement and speed of the microprobe. The real-time contact resistance is approximately an exponential function of the damping force. Finally, the effectiveness of the proposed electromechanical model on wafer-level packaging testing using our designed new microprobe arrays testing system is confirmed. It will provide models and methods for developing IC final test of wafer-level packaging.

An Electromechanical Model and Simulation for Test Process of the Wafer Probe

With the fast development of IC (integrated circuit) packaging industry, IC test is becoming more and more important, especially the probe test of the wafer packaging. Based on experimental data and theoretical analysis, an electromechanical model is first proposed to describe the characteristics of the testing process of wafer probe to understand the behavior of micro-probe testing process, and to simulate the whole physical process. The model consists of a dynamic mechanical model, a dc electro-mechanical coupling model and an ac impedance model, which is used to analyze the overall physical properties of the probe test process and has a good agreement with the experimental data. Based on the electromechanical model, a simulation platform is established first, which will provide a simulation tool for the design of the microprobe and setting of multiparameters.

Copper Pulse-Reverse Current Electrodeposition to Fill Blind Vias for 3-D TSV Integration

The through-silicon-via (TSV) interconnection in 3-D integration is one solution being explored to solve current 2-D interconnect problems in the semiconductor industry. In this paper, TSV fillings by pulse-reverse current electrodeposition of Cu with various parameters were carried out to improve the via filling performance. Especially, the influence of current density and electrodepositing time on the TSV filling property was studied. The high aspect ratio reaching 6:1 in via filling was achieved by applying the pulse-reverse current form, which was mainly caused by effective adsorption and redistribution of additives inside via.

SiO2-coated Cu nanoparticle/epoxy resin composite and its application in the chip packaging field:

A silicon dioxide–copper (SiO2-Cu) epoxy resin composite material for chip packaging was made by a mechanical mixing method with epoxy resin as the base glue and SiO2 coated with nano-Cu (SiO2-Cu) particles as the filler. The dispersion of SiO2-Cu nanoparticles in epoxy resin was studied using scanning electron microscopy and transmission electron microscopy. Meanwhile, the effects of the filler on the coefficient of thermal conductivity, the coefficient of thermal expansion (CTE), and the mechanical properties of the composite material were also studied. The results show that SiO2-Cu nanoparticles disperse well in the epoxy resin, the coefficient of thermal conductivity of SiO2-Cu epoxy resin composites increases with an increase in the SiO2-Cu filler amount, the coefficient of thermal conductivity begins to decline when the filling volume is over 25%, and the suitable amount of SiO2-Cu is 25% of the total volume. With the increase in the filler, the CTE of the composite decreases; when the SiO2-Cu filling amount is 25%, the material has good impact resistance and a long electromigration failure time for chip packaging materials.