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.
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.
