Height measurement of microbumps using a white-light triangulation method

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 5256 ms to 3184 ms 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.

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Hybrid Bright-Dark-Field Microscopic Fringe Projection System for Cu Pillar Height Measurement in Wafer-Level Package

Wang,

Zhou,

Zhang

et al. 2024

Sensors

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Cu pillars serve as interconnecting structures for 3D chip stacking in heterogeneous integration, whose height uniformity directly impacts chip yield. Compared to typical methods such as white-light interferometry and confocal microscopy for measuring Cu pillars, microscopic fringe projection profilometry (MFPP) offers obvious advantages in throughput, which has great application value in on-line bump height measurement in wafer-level packages. However, Cu pillars with large curvature and smooth surfaces pose challenges for signal detection. To enable the MFPP system to measure both the top region of the Cu pillar and the substrate, which are necessary for bump height measurement, we utilized rigorous surface scattering theory to solve the bidirectional reflective distribution function of the Cu pillar surface. Subsequently, leveraging the scattering distribution properties, we propose a hybrid bright-dark-field MFPP system concept capable of detecting weakly scattered signals from the top of the Cu pillar and reflected signals from the substrate. Experimental results demonstrate that the proposed MFPP system can measure the height of Cu pillars with an effective field of view of 15.2 mm × 8.9 mm and a maximum measurement error of less than 0.65 μm.

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Height measurement of microbumps using a white-light triangulation method

Cited by 3 publications

References 19 publications

An enhanced centerline extraction algorithm for complex stripes in linear laser scanning measurement

An enhanced centerline extraction algorithm for complex stripes in linear laser scanning measurement

Image processing method in bump height measurement in chip packaging

Hybrid Bright-Dark-Field Microscopic Fringe Projection System for Cu Pillar Height Measurement in Wafer-Level Package

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