Key Engineering Materials Vols. 645-646

Abstract: Micro electroforming technology is widely used in fabrication of multilayer or moveable metal micro devices. The fabrication of these devices is usually suffered from high internal stress in micro-electroformed layers which seriously restricts the application and development of micro electroforming technology. Therefore, to control the internal stress is very important for improving the quality and performance of micro-electroformed layer. However, published studies on internal stress in the electroforming layer were mostly based on additive-free solution. According to additive solution, the effect of ultrasonic and current density on compressive stress occurring in the electroforming layer is investigated in this paper. The results indicate that the compressive stress keeps increasing with current density within range from 0.2 to 2 A/dm². Meanwhile, the compressive stress in ultrasonic solution decreases by 73.4 MPa averagely comparing to that in ultrasonic-free solution, and the compressive stress also keeps decreasing with the ultrasonic power which gets the lowest value at 200W. Moreover, the mechanisms of additive-induced compressive stress and ultrasonic relieving compressive stress are discussed. This research work will complement the ultrasonic-stress reduction theory and may contribute to the development of micro electroforming technology.

Abstract: Considering the safety of the charge filled in the chambers and the operational reliability, a low temperature eutectic alloy bonding was preferred for the final assembling process of MEMS-based solid propellant microthrusters (SPM) array with top-side igniters. The optimum conditions of the alloy coating are the pH value of the solution is 0.5, the base metal layer is composed of Ti (60nm)/Cu (500nm) deposited by magnetron sputtering. The bonding process was conducted in an oven with air and the bonding temperature is 70°C. To predict the performance of bonding layer, the temperature distributions of eutectic alloy layer were simulated by ANSYS software when the chamber is full of high temperature reactants. The simulation results demonstrated the bonding strength wouldn’t cut down since the heat transfer induced by the combustion of charge. The assembled MEMS-SPM array was tested under constant voltage, the results indicated that the eutectic solder bonding procedure meet the requirements of the MEMS-SPM assembling.

Abstract: The failure mechanism of through silicon vias impacted by large current pulse is reported. A theoretical model has been built to describe how TSVs fails when impacted by large current pulse. The theoretical model is then solved by applying COMSOL Multiphysics and the weak points of the TSV have been pointed out. By applying the large current pulse generating and testing system, an experiment has been done to verify the theoretical model. The results show that although the TSVs may be broken down when impacted by large current pulse, it can still be function by using several TSVs in parallel.

Abstract: In order to gain strongly hydrophobic film with large area and flexibility conveniently and effectively, how to prepare film with combination of technologies including micro fabrication, chemical grafting and micro molding is discussed. Firstly, micro channel arrays that the width is 5μm on the silicon wafer are prepared by micro fabrication. Then after spraying PVDF (Polyvinylidene Fluoride) lotion and pouring PDMS (Polydimethylsiloxane) glue solution onto the silicon wafer as the mould successively, the mixture need to be precured, which constructs rough structures in micro and nanoscale on the low surface energy film. Finally chemical grafting for film is carried out under the condition of O₂ and 130°C so that the modification layer easy to adhesive on the boundary between PVDF and PDMS can be formed. Through the above technical routes, the strongly hydrophobic film that the general contact angle exceeds above 145o, the area is 180mm×64mm, the thickness is 0.9mm and the composite layer is firmly combined is gained. Compared to other hydrophobic materials the film is available in large area and has an advantage of flexibility. Meanwhile, the way that the film prepared by micro molding and in virtue of the silicon wafer with micro channel arrays as the mould contributes to large scale production.

Abstract: TiO₂ nanofilms with different morphology were prepared by anodic oxidation method by changing the electrolyte concentration, anodization voltage, anodization time and anode-cathode distance. The surface of the nanofilm was modified by a kind of solution which consists of lauric acid and hexadecane. And this article find a proper electrolytic time, a medium voltage, a proper anode-cathode distance and a lower electrolyte concentration are beneficial to the hydrophobicity of the nanofilm.

Abstract: With the excellent thermal conductivity and the compatibility to micro electromechanical systems technology, silicon is widely used in micro heat pipes (MHPs). Copper shows higher heat transfer capability and capillary traction than silicon. Copper pillars modified microgrooves were fabricated on the silicon wafer using electroforming technique in this paper. Water contact angle measurements and thermal behavior tests were employed to the fabricated microgrooves and MHPs. Under the input power of 4 W, how the working fluid flowed in the microgrooves and steam chamber was easily observed by digital camera. The experiments demonstrated the working fluid flowed via copper pillars instead of the silicon microgrooves due to the adhesive force between working fluid and copper pillars were larger than that between working fluid and silicon microgrooves. This work showed copper pillars had a better capillary traction than the silicon microgrooves, and could make the MHP work as a vapor chamber.

Abstract: TSV is a new technology to make interconnections between chips by creating vertical wafer-to-wafer vias. The application of ICP ( inductively coupled plasma ) dry etching to make TSV is discussed in this paper. Starting with hardware conditions of the equipment, a large number of experiments were conducted to test the process parameters combining with the fundamentals of dry etching. By constantly modifying the parameters to optimize the process, a final result of TSV with the width of 2.62um, depth of 63.5um, verticality of 89.8°and scallop of 70.3nm was realized in this paper.

Abstract: High-Cr cast-penetrated layer contained nanometer ceramic particles was formed on the surface of the medium carbon steel ZG250-470 by adding nanoTiN intermediate alloy powder to cast-penetrated agent. Microstructure and wear resistance of the strengthened cast-penetrated layer were studied. The results showed that: compared with not adding intermediate alloy, there were finer and more uniform microstructure and better high temperature and high speed wear performance of strengthened cast-penetrated layer strengthened by nanoTiN intermediate alloy. Strengthening effect would be best by adding the intermediate alloy containing rare earth. By adding intermediate alloy containing Ni, the best high temperature wear resistance of cast-penetrated layer could be obtained.

Abstract: Due to the application of lead-free solders, the quality and reliability of plastic packaging device are influenced by the increase of reflow temperature. In this paper, a low-profile quad flat package (LQFP) is chosen to illustrate the interface deformation during reflow soldering. The stress analysis theory and the finite element analysis (FEM) simulation are introduced in this paper. By means of finite element software, the distribution of hygrostress, thermal stress and the deformation of device on the printed circuit board (PCB) are analyzed and calculated under different temperature. The relationship between delamination length and deformation is given. The simulation results show that the warping phenomenon is found at the apex angle of the device; delamination is easily produced in the interfaces between different materials by thermal stress, and possibly leads to the device failure.

Abstract: The hematite α-Fe₂O₃ is considered as low cost-effective semiconductor for photo-catalysis recently. We have prepared high quality α-Fe₂O₃ nanopowder by sol-gel method, as shown by XRD diffraction, we could find that the powder are as small as 5-10nm. We also characterize the photo-catalysis properties on such magnets, which show unique photo-induced catalysis capacity.