In 1994 HP (now Agilent Technologies)   bought Four Pi, the people who invented the method. Agilent is now marketing their SBL X-ray inspection system as the 5DX.

An SBL X-ray machine consists of five main components; a low power X-ray, a high-speed digitizing imager, a precision XYZ locator, powerful image processing hardware and software and statistical algorithms for analysis.

A small area of a printed circuit assembly (PCA) is positioned beneath the X-ray source, the imager beneath the PCA digitizes the information and passes it to the image processors. Another area of the PCA is positioned and the process repeats until the entire PCA has been 'viewed'.

At the same time, the image processing software is creating high-resolution three-dimensional representations of every solder joint on the PCA based on several images of the same area taken from slightly different angles, much the same way images are created from satellites in space.

Those three-dimensional representations are then processed by algorithms using heuristics and statistical methods to analyze the quality of each solder joint and to detect solder balls and shorts caused by errant solder flow. An image of the entire PCA is generated and printed. All solder joints which fall below any acceptable criteria are indicated in the printed image.

Amazingly, all of this takes place in only seconds. An SBL machine can 'inspect' hundreds of solder joints each second. For us at GE, a typical PCA could be inspected in 20 seconds including the time it took to print the report image. One of the great side effects of the statistical analysis of the images is that the attribute information related to the 'goodness' of every single solder joint was now converted to variables data where 'goodness' can be measured and tracked

This picture is an X-ray image of solder joints along one side of a Quad Flat Pack (QFP). The software I created converts the X-ray image into solder profiles along the X and Y axes of the cross hair and displays the solder joint profiles in gray at the left and bottom.

We used this software to help mere mortals like ourselves visualize the X-ray images and to tune the statistical inspection algorithms we were writing. Since the machine was used for a Navy project and access was limited to the area where the machine was located, the software also allowed us to document and demonstrate the inspection capabilities of the machine to others.

I created this software at the time when a 50MHz '486 was the hottest machine