Bumps are important structures used to connect chiplets to the interposer or package substrate in advanced chip packaging. Bump-height inconsistency will lead to problems in chip interconnection. Thus bump height detection plays a significant role in chip package quality inspection. The optical triangulation measurement system is preferably used to measure bump height in industry due to its high accuracy and high efficiency which meets the need of on-line inspection. In the system, the speed of image processing is one of the key factors which influence the measurement efficiency. Traditional means of bump height measurement often sacrifice speed to achieve high-precision measurement which leads to low efficiency. In this paper, a fast optical stripe feature extraction method is proposed which combines the gray centroid method with the Steger method in laser strip image processing in the optical triangulation system. This method can effectively reduces the number of iterations in image processing so as to accelerate the measurement speed. Firstly, the method uses the grey centroid method to calculate the center point coordinates of the light strip. Secondly, the coordinates derived are used as the initial point selection range for Steger method. Finally, the center points of the laser strip are obtained using the Steer method. The experimental results show that the proposed method reduces the time to extract the centroid of light strip from 5256ms to 3184ms under the same hardware conditions without compromising the accuracy compared to the conventional Steger method. To demonstrate the effectiveness in practical application, the centroid for 10 stripes was measured using the proposed method. Experimental results show that the proposed method significantly reduces the extraction time for centroid coordinates by about 40% without notable accuracy degradation.
The modern industry has higher precision demand for micro-angle measurement, the measurement methods and measurement techniques are constantly progressing. A micro-angle measurement method based on the interference imaging principle of F-P etalon was proposed, and the micro-angle measurement can be achieved in conjunction with an effective data processing technique. This paper performs error analysis and experimental study on the measurement system. Theory analyzes the effect of temperature change, nonlinearity of focal length calculation model, focusing error, and F-P etalon interval on micro-angle measurement results, and proposes possible solutions. A micro-angle measurement experiment with different F-P etalon intervals (2 mm, 3 mm, 5 mm) were performed using existing experimental devices. The experimental results show that the uncertainty of the micro-angle measurement results at interval d = 3 mm is optimal; under the current test conditions, the angle measurement uncertainty in the 300" measurement range is not greater than 0.08".
FBG is a kind of promising high precision strain sensor, and it can not only detect the homogeneous strain, but also identify non-uniform strain distribution. In the application of FBG in inhomogeneous strain sensing, genetic algorithm is an important method to reconstruct the non-uniform strain from reflection spectra of FBG. However, the practical reconstruction of genetic algorithm demonstrates its shortcomings such as low computational efficiency, easily falling into local optimal solution, etc , and it is well known that there is a great relationship between computational efficiency and population initialization of genetic algorithm. In general genetic algorithm employed in FBG strain reconstruction, the initialized population is randomly distributed strain along FBG axial direction, which ignores the continuity between neighbor strains. To reduce the number of population parameters and make the original population more close to the real strain distribution, a new method of population initialization is proposed here, that is using polynomial function parameters to be the initialized population instead of the randomly distributed strain, supposed that the FBG axial strains can be described as a polynomial function with independent variable of axial position. In simulation experiments, the reflection spectrums of a 10mm-long FBG are obtained from T-Matrix method in four cases of strain-free, linear-distributed strain, parabola-distributed strain and exponential –distributed strain, and then the general genetic algorithm and the new genetic algorithm with simplified population initialization were applied to reconstruct the strain distribution from the reflection spectrums respectively. The experiment results verify the supposition of the polynomial function of the FBG, and show clearly that the new method can improve the computational efficiency of genetic algorithm in FBG inhomogeneous strain demodulation greatly. From the results, it is found that with the same calculation accuracy, the computing time of the new population initialization method is reduced to about 1/5 of the general on average.
As a sensing cell, Fiber Bragg grating (FBG) can transduce physical quantities like strain, temperature, etc, having
attractive merits of being small and light, resistance to corrosion and immunity to electromagnetic interference, etc.
Commercial FBG strain sensor has a sensing range of no more than 9000 με (0.9%), however, larger-range strain sensor
is demanded in industry such as heavy structural distortion and crack-happening. A new kind of large strain sensor based
on FBG is studied here. The sensing element has a metal trapezoidal frame. The two feet of the frame can sense a large
strain of the body, which is converted to a small strain on the surface of the frame' beam. The attached FBG senses this
small strain, and then the body's strain can be known from the FBG's wavelength shift. The trapezoidal frame is taken
theoretically analysis adopting the 'unit load method' and numerical simulation by finite element method. The
sensitivity model of the sensor between the body's strain and the FBG's wavelength shift is deduced and verified. Real
large strain sensors are homemade, with verifying sizes. The large strain is controlled by a motorized translation stage,
and the FBG's wavelength shift is interrogated by MOI sm125 interrogator. The experimental results show an
outstanding large-strain sensing ability of the sensors, having the sensing range of -20~40%, with the linearity of less
than 1%, the hysterisis error of less than 1% and the repeatability of less than 0.9%.
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