Yunna Sun

Design, fabrication and measurement of a microchannel heat sink with a pin-fin array and optimal inlet position for alleviating the hot spot effect

A microchannel heat sink with an inlet near the midpoint of the diagonal and high aspect ratio micro pin-fin array was designed, fabricated and measured. The heat transfer performance of the microchannel heat sink was simulated by a computational fluid dynamics (CFD) method. The inlet near the midpoint of the diagonal was proposed to alleviate the hot spot effect. The maximum temperature of the chip was reduced by up to 26.7% at a dissipation power of 72?W compared with other reference inlet/outlet configurations. Other parameters of the micro pin fins, such as the height, the spacing distance and the edge length, were optimized for improving heat transfer capacity. The microchannel heat sink prototype sample was fabricated and tested through UV-LIGA technology and an infrared thermal imaging system, respectively. The convective heat transfer increased at high flow rates (40?ml?min?1~90?ml?min?1), which resulted in a gradually increasing deviation between simulation and experiment. The measurement results show that the maximum dissipation heat flux can reach 209?W?cm?2 when the chip maximum temperature is under 85??C at a flow rate of 90?ml?min?1. It is shown that the optimization of inlet position and micro pin-fin geometrical topology give the microchannel heat sink the potential to remove high heat flux.

A complex reinforced polymer interposer with ordered Ni grid and SiC nano-whiskers polyimide composite based on micromachining technology

A complex reinforced polymer interposer comprised with conductive Ni cylinders, ordered Ni grid and SiC nano-whiskers/Polyimide (PI) composite was proposed. The conductive Ni cylinders distributing in the middle of each Ni grid unite designed as the supporting structure were used as electric connecting component for the interposer and were insulated by the SiC nano-whiskers/PI composite. The comprehensive properties of the complex reinforced polymer interposer were improved by a complex reinforced mechanism: the improved thermal conductivity and mechanical strength by the Ni supporting structure and the reduced metal/polymer interfacial mismatch due to the SiC nano-whiskers/PI composite with the optimized mixture ratio. The above complex reinforced polymer interposer and a traditional reinforced polymer interposer only with Ni grid were fabricated using micro-machining technology for comparative analysis. The comprehensive properties of these two polymer interposers were analyzed respectively. Compared with the traditional design, the comprehensive properties of the proposed complex reinforced polymer interposer were improved further, such as, 21.3% increase for the Young modulus, 10.1% decrease for the coefficient of thermal expansion (CTE) and 54.9% increase for the thermal conductivity. Such complex reinforced mechanism based on the metal ordered grid and random nano-whiskers has potential to expand the applications of the polymer interposer.

Thermal effects of TSV (through silicon via) with void

Duo to the TSV fabrication process, the void or stream often exists in the TSV. As we all know the void and stream cannot easily being avoided, the thermal mechanical reliability of TSV integrated circuit (IC) shall be studied deeply for evaluating the fatigue life of the IC products and rearranging the location of TSVs to relieving thermal issues. In addition, the thermal mechanism of void model is different from the vertical TSV. Therefore, it is meaningful and significant to study the thermal stability of void model. This paper evaluates the thermal mechanical stability during the change of the void location and size by finite element method (FEM). The interfacial lines of void TSV suffer different thermal stress and strain induced by the unbalanced deformation of the void, and the interaction of void and TSV.

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.

The thermal mechanical reliability induced by the integrated circuits fabrication process

This work mainly focuses on the thermal mechanical stability issues on the three dimensional thought silicon vias in the fabrication stage. The fabrication processes, including redistribution layer fabrication, baking glue and reflowing soldering, and filling under-fill are analyzed. With distinct thermal mismatches of the thought silicon vias Cu and SiO2, stress concentration induced by discontinuity of the model structure, and the high thermal gradient, the thought silicon vias Cu suffers sever thermal management problems and even the thermal failure. The fabrication processes not only lead high tensile press on some local area but also bring high compressive press in some region. Moreover, the compressive press in X direction (σx = -100 MPa) and tensile press in Y direction (σy = 109 MPa) work together at the inflection point of the TSVs and SiO2. The interaction of the two forms the normal stress is very interesting, and the thermal stability of the singularities has great different changing mechanism.

Design and Optimization of a Stationary Electrode in a Vertically-Driven MEMS Inertial Switch for Extending Contact Duration

A novel micro-electro-mechanical systems (MEMS) inertial microswitch with a flexible contact-enhanced structure to extend the contact duration has been proposed in the present work. In order to investigate the stiffness k of the stationary electrodes, the stationary electrodes with different shapes, thickness h, width b, and length l were designed, analyzed, and simulated using ANSYS software. Both the analytical and the simulated results indicate that the stiffness k increases with thickness h and width b, while decreasing with an increase of length l, and it is related to the shape. The inertial micro-switches with different kinds of stationary electrodes were simulated using ANSYS software and fabricated using surface micromachining technology. The dynamic simulation indicates that the contact time will decrease with the increase of thickness h and width b, but increase with the length l, and it is related to the shape. As a result, the contact time decreases with the stiffness k of the stationary electrode. Furthermore, the simulated results reveal that the stiffness k changes more rapidly with h and l compared to b. However, overlarge dimension of the whole microswitch is contradicted with small footprint area expectation in the structure design. Therefore, it is unreasonable to extend the contact duration by increasing the length l excessively. Thus, the best and most convenient way to prolong the contact time is to reduce the thickness h of the stationary electrode while keeping the plane geometric structure of the inertial micro-switch unchanged. Finally, the fabricated micro-switches with different shapes of stationary electrodes have been evaluated by a standard dropping hammer system. The test maximum contact time under 288 g acceleration can reach 125 µs. It is shown that the test results are in accordance with the simulated results. The conclusions obtained in this work can provide guidance for the future design and fabrication of inertial microswitches.

Thermomechanical reliability of a Cu-TSV integration model based on 3D fabrication processes

In the 3D integration stages, the structure of the TSV is changed with the development of the procedure. The 3D though silicon via (TSV) integration models with the new updated structure depended on the integration processes (fabricating redistribution layer (RDL), reflowing solders and filling underfill) were analytically studied in this work. The equivalent stress, von Mises stress, was used to describe and evaluate the change rule and trend of the 3D TSV integration models during the integration integrations. The changing mechanism of thermal stress and strain on the updated models was varied for the free-form deformation space was substituted by the new fabricating structure. The thermal mechanical stability of the updated 3D TSV integration model is analyzed by the steady-state solver finite element method (FEM). The maximal von Mises stress of the updated models decreased with the procedures carried on. The thermal mechanical reliability of final 3D TSV integration model during the operating stage was simulated by the time-dependent solver of FEM. After 3 cycles the maximal thermal stress and strain at the maximal temperature (MT) dropped to near the yield stress of Cu, nevertheless, in the 6 cycles the maximum of the MT raised up but still less than the maximum of the past three cycles may result from the reshaped structure and strain harness processes. The tearing and cracks might be induced for the tensile stress in both X and Y directions are all enlarged greatly. However, the shear stress got into a stable value about 105 MPa after 2 cycles.

A fast response breath detection system based on bridge tied CNT sensor fabricated by micromachining

This paper reports on a novel implanting micromachining technology. By using this method, for the first time, we could implant both ends of nano-scale materials into micro-scale metal materials at room temperature. Micro gas sensor with CNT bridging a pair of Au electrodes was fabricated. Direct contact and strong interactions between CNTs and the electrods contribute to its stable electronic performance (8,000 s for 1% fluctuation of resistance change exposed to nitrogen). The micro sensors also exhibit high resistance response, fast response time, rapid recovery and good reproducibility to dimethyl methylphosphonate vapor.

A novel inertial microswitch with synchronous follow-up compliant electrodes for extending output switch-on pulse width

This paper reports a novel inertial microswitch with synchronous follow-up compliant electrodes for extending output switch-on pulse width. The flexible movable electrode and stationary electrode are proposed to keep a continuous duration contact by double-stair and spring-shape structures, which can not only extend the output switch-on pulse width but also reduce the impact bounces. Then the inertial microswitch has been fabricated using surface micromachining and multilayer electroplating technology. The comparison testing results show that there is no contact bouncing behavior can be observed under ∼466g half sine-wave shock acceleration and the test output switch-on pulse width can reach 390μs, which is longer than that in the traditional design.

A MEMS inertial switch with electrostatic force assistance and multi-step pull-in for eliminating bounce and prolonging contact time

A novel MEMS inertial switch with electrostatic force assistance and multi-step pull-in behavior has been designed, which can help the electrodes weaken the bounce and keep a long contact in the inertial switch before the leakage of electricity ends compared with the traditional rigid contact between electrodes. The dynamic switching and pull-in performance is simulated by finite element method. The designed structure is completed by multi-layer metal electroplating based on Surface micromachining technology. Finally, the fabricated device is tested by dropping hammer system. Its indicated that compared to the inertial switch with electrostatic force assistance has no bounce behavior, and realizes ∼512μs long stable contact compared to that without the applied electrostatic force.