•Defects detection using active thermography is proposed.•Temperature distribution is acquired by the infrared imager.•The results in thermograph between defects and reference are very different.•The results in temperature history between them are very different.•Different kinds of chips with different sizes are tested.With the development of electronics towards smaller, more compact, and increasingly complex, flip chip technology has been used extensively in microelectronic packaging, and disadvantages occur in traditional detection methods. It is indispensable to explore new methods for flip chip solder joint inspection. In this paper we investigate an approach for solder joint inspection based on the active thermography. The basic principle of the active thermography method is described, and the experimental investigation is carried out using the method. The test flip chip is heated by a non-contact heating source. The thermal distribution on two kinds of chips is captured by an infrared thermal imager. With median filter and segmentation processes, positions of the bumps are segmented. For chips with smaller bumps, principal component thermography is introduced to enhance the segmentation process. The analysis results demonstrate that missing bumps in flip chips can be discerned obviously, which proves the feasibility of the proposed method for defects inspection of flip chips.

•We set up a reflective optical system for detecting the reflectance spectra.•The reflectance spectra of ethanol/methanol vapor are higher than that of nitrogen.•The three PCs capture 97.93% of the total variance in the reflectance spectra.•The higher the concentration is, the thicker the liquid films are.•As the concentration increases, there appears red shifting.We have demonstrated the application of the hierarchical micro/nanostructures of Morpho didius butterfly scales for gas sensing. A reflective optical system was set up to detect the reflectance spectra of butterfly wing samples in a specific gas environment. Principle component analysis method was employed to discriminate and identify nitrogen, methanol and ethanol vapors according to the distribution of the projection points. Meanwhile, we constructed an appropriate 2D optical model of the butterfly scales with Rsoft software and theoretically simulated the gas sensing performance by rigorous coupled wave analysis technique. In the theoretical study, exposing the structures to vapors was modeled as vapor adsorption, resulting in the formation of nanometre-thick liquid films onto the structures, where the thickness of the film increased with the vapor concentration increasing. The experimental and simulation results match well, confirming that the butterfly scales indeed have the sensitivity and selectivity for vapors sensing. As such, we believe an optimized artificial structure mimicking Morpho butterfly scales can be used as gas sensors for sensitive and selective detection of closely related vapors.

We investigated the deformation behaviors of Zr65Cu17.5Ni10Al7.5 in superplastic forming in silicon mould via numerical modeling and experiments. The data needed for the constitutive formulation were obtained from compressive tests to establish a material library for finite-element simulation using a DEFORM 3D software. A constant speed forming process of a micro gear was modeled where the loading force, feature size and amount of deformation in the micro gear in silicon mould were analyzed in detail for the optimal requirements of micro gear forming and the protection of silicon mould. Guided by the modeling parameters, an amorphous metal micro gear was successfully obtained by our home-made superplastic forming system with the optimized parameters (temperature of 683 K, top speed of 0.003 mm/s until the load force reaching limiting value at 1960 N, and a gradually decelerating process for holding the force to the end). Our work gives a good example for optimization of superplastic forming and fabrication of BMGs in microparts.

•We investigate the laser welding of annealed Zr55Cu30Al10Ni5 bulk metallic glass.•We analyze the effect of welding speed and annealing on the laser welding.•The high speed facilitates better joint based on the penetration bead.•Annealing can suppress crystal growth and hence leads to nanocrystallization.•Annealing of BMG samples prior to welding can improve the properties of the joints.Laser welding is one of the promising ways for manufacturing metallic glass products with complicated shape and geometry. In this work we focus on the effect of annealing treatment and welding parameters on laser welding of annealed Zr55Cu30Ni5Al10 bulk metallic glass as intended and unintended heat treatment occurs in the process. We find that laser welding can produce well welded specimen plates with no obvious welding defects in the joints and high welding speed may lead to better joints. Although higher annealing temperature or longer annealing time leads crystallization, bulk metallic glass material still remains largely amorphous in the heat affected zone. Compared with the welded joint without annealing, the micro-hardness and bending strength are enhanced due to the presence of the nanocrystals occurred in annealed welding joint. Therefore, appropriate annealing treatment with the annealing temperature near the glass transition temperature and annealing time as long as that in hot embossing of BMG parts may play a beneficial role in laser welding of metallic glasses.

Flip chips are widely used in microelectronics packaging owing to the high demand of integration in IC fabrication. Solder bump defects on flip chips are difficult to detect, because the solder bumps are obscured by the chip and substrate. In this paper a nondestructive detection method combining ultrasonic excitation with vibration analysis is presented for detecting missing solder bumps, which is a typical defect in flip chip packaging. The flip chip analytical model is revised by considering the influence of spring mass on mechanical energy of the system. This revised model is then applied to estimate the flip chip resonance frequencies. We use an integrated signal generator and power amplifier together with an air-coupled ultrasonic transducer to excite the flip chips. The vibrations are measured by a laser scanning vibrometer to detect the resonance frequencies. A sensitivity coefficient is proposed to select the sensitive resonance frequency order for defect detection. Finite element simulation is also implemented for further investigation. The results of analytical computation, experiment, and simulation prove the efficacy of the revised flip chip analytical model and verify the effectiveness of this detection method. Therefore, it may provide a guide for the improvement and innovation of the flip chip on-line inspection systems.

Flip chip technology is an attractive choice for high-density packaging and complex microsystem architectures. A critical element in the successful application of flip chip technology is the reliability of solder bumps. In this paper a nondestructive detection method is presented for the flip-chip solder bump inspection using ultrasonic excitation and vibration analysis. Simulations are implemented to explore the feasibility of this method, and experimental investigations are also performed, where the flip chips are excited by continuous ultrasonic waves and their vibration velocities are measured by a laser scanning vibrometer for further analysis. The results reveal that the defective chips can be distinguished from the good chips by the chip vibration velocities with the feature coefficient α, which proves the effectiveness of this method. Therefore, it may provide a new path for the improvement and innovation of flip chip on-line inspection systems.

Morpho butterfly wings show brilliant blue color, which has a close relationship with the hierarchical micro/nano structures on the surface of scales. When liquids such as methanol, ethanol and isopropanol with different refractive indexes drop onto the scales, the reflectance of wings would decrease. The main peaks of reflectance shift to the right and the scales turn to yellow-green. After the liquids volatilizes completely, the scales revert to the original blue color. The typical micro/nano structures of Morpho butterfly wing scales are modeled, and the reflectance variation in the course of dropping liquids is simulated. Furthermore, the principal component analysis (PCA) method is employed to analyze the experimental and simulation reflectance data, extract principal components and reduce dimensions. As a result, the curves mapping the reflectance variation are clearly shown in the coordinate system consisting of three principal components. The typical color variation of scales during the dropping process could be monitored, and different kinds of liquids could be obviously distinguished according to the distributed regions of mapping points. This study provides guidance to environmental media detecting as well as data processing, and enhances the fabrication and application of the mimic Morpho butterfly wings micro/nano structures.

Voids at the bonding interface of adhesive bonding are often generated due to incomplete flowing of the polymer. Gas residues from the adjacent polymer may fill these voids to form gas bubbles. Although the empirical method had been applied for a long time to eliminate the bubbles, theoretic analysis considering the bubble behavior during bonding process is more preferable because of the better universality. The interrelationships between processing parameters and bubble deformation were investigated. A theoretic model describing those interrelationships was developed reasonably using gas diffusion theory to predict the bubble behavior. The mathematic equations of this model were deduced and the solution was obtained with some proper simplifications. Experiments under different conditions were carried out and the experimental results were contrasted with the theoretical predictions. The model errors were then analyzed. It indicated that when choosing temperatures and pressures carefully, the model could predict the bubble behavior accurately.

In this work, the hierarchical micro/nanostructures of Morpho butterfly scales were employed for chemical sensing purposes. We observed that the color and the brightness of the butterfly wings change obviously when the surrounding medium was altered. With an optical system setup, we quantified the shift of the major reflection peak and the change in peak intensity, which corresponds to the observed change of color and brightness. In order to guiding the engineering design of artificial butterfly scales as a new platform for chemical sensors, we further constructed two-dimensional optical models with three different geometrical designs. Rigorous coupled wave analysis technique was employed to analyze the models. By comparing the modeling results with experiments, we identified the key characteristics of the butterfly scales that were relevant to chemical sensing applications. These characteristics should be implemented and optimized in designing and fabricating the bio-inspired sensors for sensitive and selective detection of closely related chemicals.

The process of patterned wafer bonding using ultraviolet (UV) adhesive as the intermediate layer was studied. By presetting the UV adhesive guide-layer, controlling the thickness of the intermediate layer (1–1.5 μm), appropriate pre-drying temperature (60°C), and predrying time (6 min), we obtained the intermediate layer bonding of patterned quartz/quartz. Experimental results indicate that patterned wafer bonding using UV adhesive is achieved under room temperature. The process also has advantages of easy operation, low cost, and no plugging or leakage in the patterned area after bonding. Using the process, a microfluidic chip for red blood cell counting was designed and fabricated. Patterned wafer bonding using UV adhesive will have great potential in the fabrication of microfluidic chips.

The uniaxial compressive behavior of the Zr65Cu17.5Ni10Al7.5 bulk metallic glass has been studied at temperatures ranging from 673 to 723 K with a strain rate range between 5.0 × 10−4 s−1 and 1.0 × 10−1 s−1. The results indicate that the flow stress is below 50 MPa at temperatures above 683 K under strain rates below 1.0 × 10−3 s−1. Then the bulk metallic glass filling in the silicon mold with hot embossing technology has been investigated, and the appropriate superplastic forming conditions for micropart fabrication are explored experimentally. Mechanical grinding is put forward to remove the flash of the micropart accurately, then the silicon mold is dissolved in potassium hydroxide solution, and a good dimensional accuracy for a micro-spur gear with 0.1 module, 20 teeth and a spline structure in the core is obtained. It follows from the results that the superplastic micro-forming of Zr65Cu17.5Ni10Al7.5 bulk metallic glass with silicon mold is promising for manufacturing the high-performance complex micro amorphous components for micro electro-mechanical systems.

Surface mount components have been extensively used in microelectronic packaging. However, it brings great challenge for defect inspection with the development of solder bumps towards ultra-fine pitch and high density. Traditional nondestructive detection methods are insufficient for solder joint assessment due to their own disadvantages. Therefore, it is necessary to explore new methods for solder joint inspection. A novel approach based on the pulsed phase thermography was investigated for identifying the defects of solder joints. In this approach, the test chip was stimulated by a thermal pulse, and the consequent transient response was captured by a commercial thermal imager. The spacial and temporal filtering techniques were adopted to improve the signal to noise ratio. The recorded thermograms were input to an improved median filter with a 5×5 mask, and the temperature evolution of each pixel was extracted and smoothed by the moving average operation. Then the temperature–time curve was fitted with an exponential function. To eliminate emissivity variations and heating non-uniformity, we converted the fitted temperature values in time domain to the phase information in frequency domain using the fast Fourier transform. In low frequency range, the phase–frequency curve of the defect area was differentiated from that of the sound area. The results demonstrate that this approach is effective for identification of the missing bumps, and can be used in the solder joint inspection in high density packaging.

Solder bump inspection of flip chip has gained more attention with the widely use of flip chip package technologies in microelectronics packaging industry. A non-destructive testing method using ultrasonic excitation and modal analysis was presented for the detection of solder bump missing, a typical defect occurred in flip chip. The flip chip with arrayed solder bumps is modelled, and the effect of solder bump missing on the modal frequencies is investigated. The shifting of the natural frequencies of the reference flip chips and defect flip chips are simulated and measured in the experiments. The analysis results of the theoretical calculation, simulation and experiments all reveal that the natural frequencies of defective chips are smaller than the ones of non-defective chips, which can be used for defective flip chips detection. Therefore, the modal analysis can be a useful tool for fault diagnosis of flip chip.