CT adds depth to x-ray inspection

Computed tomography imaging provides multiple x-ray images of an object captured at different angles.

Ann R. Thryft, Contributing Technical Editor -- Test & Measurement World, 12/16/2011 10:34:20 AM

Thorsten Achterkirchen VP and GM Teledyne Rad-icon Imaging

Traditional x-ray cameras are often used in nondestructive electronics testing, such as during PCB (printed-circuit board) inspection, or in quality assurance when engineers need to gather quantitative data for specification drawings. CT (computed tomography) imaging takes the technology a step further, as it provides multiple x-ray images of an object captured at different angles, thereby increasing the available data, said Thorsten Achterkirchen, VP and GM for Teledyne Dalsa’s Rad-icon Imaging division.

Q: How does CT imaging improve on traditional x-ray imaging?
A: Traditional x-ray cameras take a single projection view of an object, while CT x-ray cameras take as many as 100 or 200 images, each of which is a slightly different projection. Using sophisticated software algorithms, these can be reassembled into a three-dimensional model of the part, allowing the inspection of complex manufactured shapes, such as PCBs.

For many industrial CT applications, including electronics inspection, you need to acquire a lot of images in a short period of time, and you must have high sensitivity since each image only uses a small dose of radiation. But each image must also contain a signal-to-noise ratio that’s high enough so the software can analyze the images for defects. Therefore, CT imaging provides a huge leap forward in capturing defects compared with traditional single-shot x-ray imaging.

Q: What are some difficulties in adapting CT imaging to inspection?
A: In electronics inspection, when you need to check every high-value part that comes through, you need very high throughput. Historically, this type of CT x-ray application has been hampered by lower processing power, causing lower throughput. Another limitation has been frame rate, or how quickly you can acquire all of those images. Next, many traditional x-ray detectors take a long time to process images.

The latest generation in digital x-ray imaging technology leverages CMOS sensors. These offer a much higher-performing active element and better sensitivity. They also provide much better sensitivity, which enables the detection of features at very low image “noise” levels.

Q: What improvements have you made to your CMOS CT sensors ?
A: The Shad-o-Box product family started out with the 1024, a 2-in. by 2-in. camera running at 1 to 2 fps. Over the years, our customers have asked for products with larger active areas and higher frame rates to be able to do real-time inspection and CT imaging of larger objects. Therefore, in June 2011, Rad-icon released the Shad-o-Box 1280 HS to address these requirements.

In this new camera, the CMOS sensor’s frame rate is 30 fps, which is faster than the previous generation sensor by nearly an order of magnitude. This is, therefore, our first truly real-time product, since 30 fps is the acquisition speed needed for use in electronics production lines. The camera also has 1.6-Mpixel resolution at that frame rate. We’ve almost completely eliminated image artifacts.

Q: What are other feature improvements?
A: The 1280 HS has 14-bit digital image quality and a real-time GigE interface. The camera’s active area is 5 in. by 5 in., and pixel size is 100 microns, making it the ideal image size and resolution for PCB inspection, as well as for dimensional verification and failure analysis. T&MW