Huiying Wang

Monitoring and intelligent control of electrode wear based on a measured electrode displacement curve in resistance spot welding

Advanced high strength steels are being increasingly used in the automotive industry to reduce weight and improve fuel economy. However, due to increased physical properties and chemistry of high strength steels, it is difficult to directly substitute these materials into production processes currently designed for mild steels. New process parameters and process-related issues must be developed and understood for high strength steels. Among all issues, endurance of the electrode cap is the most important. In this paper, electrode wear characteristics of hot-dipped galvanized dual-phase (DP600) steels and the effect on weld quality are firstly analysed. An electrode displacement curve which can monitor electrode wear was measured by a developing experimental system using a servo gun. A neuro-fuzzy inference system based on the electrode displacement curve is developed for minimizing the effect of a worn electrode on weld quality by adaptively adjusting input variables based on the measured electrode displacement curve when electrode wear occurs. A modified current curve is implemented to reduce the effects of electrode wear on weld quality using a developed neuro-fuzzy system.

Simulation and characterization of a laterally-driven inertial micro-switch

A laterally-driven inertial micro-switch was designed and fabricated using surface micromachining technology. The dynamic response process was simulated by ANSYS software, which revealed the vibration process of movable electrode when the proof mass is shocked by acceleration in sensitive direction. The test results of fabricated inertial micro-switches with and without anti-shock beams indicated that the contact process of micro-switch with anti-shock beams is more reliable than the one without anti-shock beams. The test results indicated that three contact signals had been observed in the contact process of the inertial switch without anti-shock beams, and only one contact signal in the inertial switch with anti-shock beams, which demonstrated that the anti-shock beams can effectively constrain the vibration in non-sensitive direction.

Development of a shock acceleration microswitch with enhanced-contact and low off-axis sensitivity

In the present work, microswitches with different shapes have been fabricated by low-cost and convenient multi-layer electroplating in order to develop a shock acceleration microswitch with enhanced-contact and low off-axis sensitivity. Modal analysis based on FEM shows that the three kinds of new designed microswitches have lower off-axis sensitivity than our previous device, i.e., type I. The packaged microswitches were tested by the drop hammer system. The generated half-sine-like shocking acceleration with amplitude of 80g, lager than the threshold, was applied to the microswitches. The test contact time of the microswitch IV is about 55µs, whose contact effect is much better than conventional. A shock acceleration microswitch IV with a movable contact point utilizes the double spring-mass system to realize an enhanced-contact effect and is considered as a better selection for long duration contact and relatively low off-axis sensitivity.

High-g MEMS shock threshold sensor integrated on a copper filling through-glass-via (TGV) substrate for surface mount application

This paper presents the fabrication of a through-glass-via (TGV) substrate with an integrated high-g MEMS shock threshold sensor on it, which will minimize the die size of the whole sensor, avoid lead-wire bonding and facilitate the surface mount. Moreover, smaller volume could also improve the anti-shock capability of the sensor. The TGV substrate is fabricated by developed composite-mask powder blasting and copper filling technology. The jet trace and distribution of the particles with different sizes during the powder blasting has been simulated by ANSYS finite-element method. The relationship of etching depth and blasting time under different mask opening sizes is evaluated. Fabricated via holes are filled successfully by periodic pulse reveres (PPR) electroplating copper. Finally, the all-metal shock threshold sensor is integrated on the TGV substrate by surface micromachining. And the integrated sensor has a reliable switch-on signal when 1000g shock acceleration is applied.

A multidirectional-sensitive inertial microswitch with electrophoretic polymer-metal composite fixed electrode for flexible contact

A multidirectional-sensitive inertial microswitch with polymer-metal composite fixed electrode has been designed and fabricated based on non-silicon surface micromachining in the present work. The microswitch can sense the applied accelerations from any directions in xoy plane and positive z-axis. Its vertical composite fixed electrode is completed by electroplating and electrophoretic deposition, which can realize a flexible contact between the electrodes and eliminate the bouncing phenomenon and prolong the contact time. As a result, the stability and reliability of the inertial switch could be greatly improved. The test results show that the threshold acceleration of the fabricated prototype is generally uniform (~70g) in different sensitive directions in xoy plane and z-axis. The contact time of the microswitch with composite fixed electrode is ~110μs in vertical direction, which is longer than that (~65μs) of one without polymer.

Mechanical property evaluation of TSV-Cu micropillar by compression method

A micro-compression test method was presented to evaluate the mechanical property of the TSV-Cu micropillar in this paper. Firstly, the test sample containing TSV-Cu micropillar was prepared by MEMS micromachining technology. Then, the mechanical property of TSV-Cu micropillar was measured by a self-made micro-compression system. Finally, the effect of thermal treatment on the mechanical property of TSV-Cu micropillar was studied. The experimental results showed that the average yield strength (σ0.2) of the TSV-Cu micropillar was 167 MPa. But it decreased to 137 MPa after being thermally treated at 400°C for 1 hour, which was probably due to the increased grain size of Cu.

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.

A vertical driven inertial micro-switch with dual spring to prolong holding time

In this paper, a new model has been proposed for the design of inertial micro-switch. Compared with the traditional model consisted by movable-fixed electrode, the electrodes are designed as two movable springs. The dynamic response processes of electrodes can be controlled via the structure parameters. The simulation results indicated that the elastic contact can effectively prolong the holding time. The fabricated prototypes were tested by drop hammer system. The test results demonstrated that the holding time of improved inertial micro-switch much longer than the traditional designed one with the same threshold acceleration.

Study of mechanical properties of Cu through-silicon-vias (TSV) specimen using electrodeposition bath

The Cu specimens were fabricated by the UV-LIGA process using the electrodeposition bath for through-silicon-via (TSV) filling. Mechanical property of th e Cu specimens was investigated by a uniaxial tensile test. The elastic modulus, yield strength, breaking stre ngth and ultimate strain are 95GPa, 314MPa, 367MPa and 12.4%, respectively. The results indicated that the yield strength and breaking strength of as-deposited Cu specimens were higher than that of the bulk Cu, while the elastic modulus was lower than that of the bulk Cu. The elastic modulus of C u thin film in surface and section are 115.7GPa and 105.4GPa measured by nanoindentation, respectively. This difference is caused by the difference of the grain orientation between the surface and section of Cu thin film.

Design and fabrication of Cu-TSV free-standing specimen for uniaxial micro-tensile test

A novel test sample with a micro scale free-standing specimen of Cu-TSV used for uniaxial micro-tensile test is presented in this paper. Design of a deformation-buffer reticular supporting frame of the test sample effectively reduces the deformation of Cu-TSV thin film during clamping operation. The stress resulting from electrodepositon process is minimized by fabricating Cu-TSV thin film on surface-treated titanium seed layer. The process of titanium seed layer avoids alkali corrosion and simplifies fabrication procedure compared with that of the traditional Cr/Cu seed layer. Both finite-element method (FEM) simulation and experimental results indicates the advantages of this new design. The test sample fabricated by the optimized process well coordinates with our micro-tensile system. The Youngs modulus and the ultimate tensile strength of tested Cu-TSV thin film measured by our micro-tensile system are 25.4∼32.9GPa and 574∼764MPa, respectively.