Journal of SMT Article


Author: Dr. Udo E. Frank
Date Published: 1/1/2005   Volume: 18-1

Abstract: Conventional inspection technologies - namely optical, machine vision (CCD cameras), and laser systems - are commonly used to examine solder bumps on wafers. They are limited, however, in determining such characteristics as diameter, height, and roundness of the ball, and to the detection of directly viewable defects, such as pits, cracks, and bridging. However, defects within the bumps are undetectable with these systems. While traditional X-ray imaging equipment can look within the solder bumps and thus determine the existence of sub-surface voids, such systems are not designed to perform automatic analyses of voids within a bump and provide a means of establishing parameters for automatically accepting or rejecting area array components during inspection.

X-ray imaging technology can now detect and measure voids within solder bumps on chips, and determine the viability of the component based on pre-set threshold values. The X-ray inspection system converts 3D voids to measurable 2D images, enabling the system to calculate the ratio of the size of the void(s) within a solder bump to the total mass of the ball. The system can also determine the largest linear distance between two points in the void and compare the result with the diameter of the ball. Depending on the parameters pre-established by the operator, the solder bump is deemed acceptable (capable of providing a reliable and sufficient interconnect) or unacceptable. Either method of analysis can be employed and used as criteria for determining the expected performance of the ball.

This new inspection technology ensures solder bump integrity while reducing the scrapping of viable components due to minor voids. The X-ray system employs an efficient inspection process, as once a solder bump is deemed defective, no further inspection of the component is necessary.

This report describes inspection of wafer bumps using a specialized high-resolution X-ray inspection system, compares the technology with traditional X-ray imaging, and provides details pertaining to wafer handling, operation of the equipment, software, configuration options, data analysis, and generation of reports.

Key words: X-ray inspection, wafer bump inspection, solder bumps.

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