Morphology Control and Mechanism of Different Bath Systems in Cu/SiCw Composite Electroplating.

With the rapid development of electronic technology and large-scale integrated circuit devices, it is very important to develop thermal management materials with high thermal conductivity. Silicon carbide whisker-reinforced copper matrix (Cu/SiCw) composites are considered to be one of the best candidates for future electronic device radiators. However, at present, most of these materials are produced by high-temperature and high-pressure processes, which are expensive and prone to interfacial reactions. To explore the plating solution system suitable for SiCw and Cu composite electroplating, we tried two different Cu-based plating solutions, namely a Systek UVF 100 plating solution of the copper sulfate (CuSO4) system and a Through Silicon Via (TSV) plating solution of the copper methanesulfonate (Cu(CH3SO3)2) system. In this paper, Cu/SiCw composites were prepared by composite electrodeposition. The morphology of the coating under two different plating liquid systems was compared, and the mechanism of formation of the different morphologies was analyzed. The results show that when the concentration of SiCw in the bath is 1.2 g/L, the surface of the Cu/SiCw composite coating prepared by the CuSO4 bath has more whiskers with irregular distribution and the coating is very smooth, but there are pores at the junction of the whiskers and Cu. There are a large number of irregularly distributed whiskers on the surface of the Cu/SiCw composite coating prepared with the copper methanesulfonate (Cu(CH3SO3)2) system. The surface of the composite is flat, and Cu grows along the whisker structure. The whisker and Cu form a good combination, and there is no pore in the cross-section of the coating. The observation at the cross-section also reveals some characteristics of the toughening mechanism of SiCw, including crack deflection, bridging and whisker pull-out. The existence of these mechanisms indicates that SiCw plays a toughening role in the composites. A suitable plating solution system was selected for the preparation of high-performance Cu/SiCw thermal management materials with the composite electrodeposition process.

Application of Ni/SiCw Composite Material in MEMS Microspring.

The microspring is a typical type of device in MEMS devices, with a wide range of application scenarios and demands, among which a popular one is the microelectroformed nickel-based planar microspring prepared by the UV-LIGA technology based on the SU-8 adhesive. It is worth noting that the yield strength of the electrodeposited nickel microstructure is low, and the toughness of the structure is not high, which is unbeneficial for the enduring and stable operation of the spring. The paper mainly presents the methods of preparing high-aspect-ratio Ni/SiCw microstructures for MEMS devices based on UV-LIGA technology, developing Ni/SiCw-based microspring samples with a thickness of 300 µm, and applying a DMA tensile tester for mechanical property tests and characterization. In addition, the paper explores the influence of heat treatment at 300 °C and 600 °C on the tensile properties and microstructure of composite coatings. The results show that the W-form microspring prepared from Ni/SiCw composites not only has a wider linear range (about 1.2 times wider) than that of pure nickel material but also has a stronger resistance capacity to plastic deformation, which is competent for MEMS device applications in environments below 300 °C. The research provides a frame of reference and guidance for improving the stable cyclic operating life of such flat springs.

Advancements in SiC-Reinforced Metal Matrix Composites for High-Performance Electronic Packaging: A Review of Thermo-Mechanical Properties and Future Trends.

With the advancement of semiconductor technology, chip cooling has become a major obstacle to enhancing the capabilities of power electronic systems. Traditional electronic packaging materials are no longer able to meet the heat dissipation requirements of high-performance chips. High thermal conductivity (TC), low coefficient of thermal expansion (CTE), good mechanical properties, and a rich foundation in microfabrication techniques are the fundamental requirements for the next generation of electronic packaging materials. Currently, metal matrix composites (MMCs) composed of high TC matrix metals and reinforcing phase materials have become the mainstream direction for the development and application of high-performance packaging materials. Silicon carbide (SiC) is the optimal choice for the reinforcing phase due to its high TC, low CTE, and high hardness. This paper reviews the research status of SiC-reinforced aluminum (Al) and copper (Cu) electronic packaging materials, along with the factors influencing their thermo-mechanical properties and improvement measures. Finally, the current research status and limitations of conventional manufacturing methods for SiC-reinforced MMCs are summarized, and an outlook on the future development trends of electronic packaging materials is provided.

Process improvement of high aspect ratio nano-gratings based on synchrotron x-ray.

To achieve better structural accuracy and aspect ratio, nano-gratings with a vertical angle close to 90° and a depth-to-width ratio of about 8 were prepared by synchrotron radiation. The optimal exposure dose and development time were determined to be 0.006 (A·h) and 6 min, respectively, by observing the surface loss and roughness of the gratings with slit widths of 150 nm and 250 nm under different conditions. To obtain the desired rectangular grating structure, the experimental conditions were optimized with the help of controlled variables experimental method. With the mask-to-photoresist pitch and the development and drying temperatures of 20µm and 23 °C, the optimized depth-to-width ratio of the nano-gratings with a slit width of 250 nm can reach 8.28. The cone angle can reach 88.4°. The aspect ratio of the nano-gratings with a slit width of 150 nm is 7.18, and its cone angle is 87.1°.

Design, Manufacture and Test of Piezoelectric Cantilever-Beam Energy Harvesters with Hollow Structures.

This article presents a single-crystal piezoelectric energy harvester (PEH) with a trapezoidal hollow hole that can obtain high energy density at low frequency. Harvesters with a hollow structure were fabricated through a series of manufacturing processes such as thermocompression bonding, screen printing and laser cutting. Finite element analysis (FEA) and experimental results showed that using low modulus brass instead of stainless steel as the PEH substrate enhances the voltage output of the device, and the hollow design greatly increases the overall stress level and power density. In addition, the developed PEH with a trapezoidal hole obtained the best output performance; when the acceleration, resonance frequency and matched load resistance were 0.5 g, 56.3 Hz and 114 kΩ, respectively, the peak voltage was 17 V and the power density was 2.52 mW/cm3. Meanwhile, compared with the unhollowed device, the peak voltage and maximum power density of the proposed PEH were increased by 30.7% and 24.4%, respectively, and the resonance frequency was reduced by 7%. This study verified the feasibility of the optimized design through simulation and experimental comparison.

Preparation of Microneedle Array Mold Based on MEMS Lithography Technology.

As a transdermal drug delivery technology, microneedle array (MNA) has the characteristics of painless, minimally invasive, and precise dosage. This work discusses and compares the new MNA mold prepared by our group using MEMS technology. First, we introduced the planar pattern-to-cross-section technology (PCT) method using LIGA (Photolithography, Galvanogormung, Abformung) technology to obtain a three-dimensional structure similar to an X-ray mask pattern. On this basis, combined with polydimethylsiloxane (PDMS) transfer technology and electroplating process, metal MNA can be prepared. The second method is to use silicon wet etching combined with the SU-8 process to obtain a PDMS quadrangular pyramid MNA using PDMS transfer technology. Third method is to use the tilting rotary lithography process to obtain PDMS conical MNA on SU-8 photoresist through PDMS transfer technology. All three processes utilize parallel subtractive manufacturing methods, and the error range of reproducibility and accuracy is 2-11%. LIGA technology produces hollow MNA with an aspect ratio of up to 30, which is used for blood extraction and drug injection. The height of the MNA prepared by the engraving process is about 600 µm, which can achieve a sustained release effect together with a potential systemic delivery. The height of the MNA prepared by the ultraviolet exposure process is about 150 µm, which is used to stimulate the subcutaneous tissue.

Shock-Resistibility of MEMS-Based Inertial Microswitch under Reverse Directional Ultra-High g Acceleration for IoT Applications.

This paper presents a novel MEMS-based inertial microswitch design with multi-directional compact constraint structures for improving the shock-resistibility. Its shock-resistibility in the reverse-sensitive direction to ultra-high g acceleration (~hunderds of thousands) is simulated and analyzed. The dynamic response process indicates that in the designed inertial microswitch the proof mass weight G, the whole system's stiffness k and the gap x2 between the proof mass and reverse constraint blocks have significant effect on the shock-resistibility. The MEMS inertial microswitch micro-fabricated by surface micromachining has been evaluated using the drop hammer test. The maximum allowable reverse acceleration, which does not cause the spurious trigger, is defined as the reverse acceleration threshold (athr). Test results show that athr increases with the decrease of the gap x2, and the proposed microswitch tends to have a better shock-resistibility under smaller gap. The measured responses of the microswitches with and without constraint structure indicates that the device without constraint structure is prone to spurious trigger, while the designed constraint structures can effectively improve the shock-resistibility. In this paper, the method for improving the shock-resistibility and reducing the spurious trigger has been discussed.