X-Ray Radiography

All FA Techniques

See Also:

Failure Analysis

Optical Inspection

X-Ray Radiography

X-Ray Radiography is a nondestructive semiconductor failure analysis technique used to examine the interior details of the package. It operates on the principle of dissimilar transmission of X-Rays through different materials. The ability of a material to block X-Rays increases with its density. It is this dissimilar transmission of X-rays through different materials that is utilized to create an image of various contrasts. X-Ray imaging may be accomplished on film, by fluoroscopy, or by using image intensifying video systems.

A typical modern X-Ray inspection equipment has a filament that produces an electron beam used to excite a target into producing X-Rays. The X-Ray emissions are then directed to and transmitted through the specimen. The transmitted X-Rays are collected by a detector, translated into electric signals, amplified, and transformed into an X-Ray image.

The varying densities of the various materials comprising the specimen allow different amounts of X-Rays to pass through, resulting in varying grayscale levels on the X-Ray image. The quality of the X-Ray image formed therefore depends not only on the proper operation of the X-Ray equipment used, but on the composition of the specimen as well. Some materials used in semiconductor assembly, such as aluminum wires, are transparent to X-Ray, and are therefore invisible in X-Ray images.

Fig. 1. Example of a Top View X-ray Photo of an IC

X-Ray radiography is commonly used to inspect for wiresweeping and other wirebond problems, die attach voids, package voids and cracks. It is excellent for determining leadframe outlines as well. Traditional x-ray systems use photosensitive films to record the x-ray image. Since X-Rays are not easy to focus, this method produces low-resolution images, which greatly limits its usefulness.

Today, X-Ray systems use a microspot source, real-time detection and automated manipulation of the sample to achieve higher resolution and throughput. These systems are capable of detecting much finer package details and defects.

Fig. 2. Example of an X-ray Inspection System

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