Presto Engineering tests CMOS image sensors up to 12-inch in diameter
Testing CMOS image sensors on a wafer-size scale can be problematic as creating uniform illumination over a large area is a challenge. Presto Engineering has developed a custom, computer-controlled solution that illuminates sections of the wafer in turn. Integrating the results enables the whole wafer to be tested automatically for an array of large sensors or even sensors that can be up to the size of a 12-inch wafer.
“An entire wafer can be tested in a laboratory using a similar method,” explained Martin Kingdon, Presto Engineering’s VP of sales. “However laboratories are not geared up for fast commercial testing so we designed our own solution to test any size wafer. Importantly, we can do this in small to medium sized test runs here in Europe at our Class 10K cleanroom facility in Meyreuil, France. . . We believe that we are probably the only such commercial test service to be available in Europe.”
Small image sensors can be illuminated with a controlled, uniform test pattern, due to the small size. As area increases, it is harder to maintain the uniformity across the test area of an individual sensor due to the limitation of the optics. By illuminating sections of the wafer in turn, Presto Engineering is able to merge the results together to test the functionality of the image sensors on the wafer.
Large sensors are driven by applications in medical imaging, aerospace, security and military equipment that require whole wafer-sized, image sensors and are transitioning from CCD to CMOS solutions. They also require larger sensors to provide the resolution required to provide clear sharp images, as well as other 4K resolution cameras. The tester is located in Presto’s EAL 5/6+ facilities so that it meets the security needs of sensitive applications.
Presto’s Teradyne IP750Ex based test solution provides a large, 80 x 100mm, uniform (± two per cent), high-intensity illumination field up to 10K lux at a range of colour temperatures. Built-in IR filtering prevents sensor damage. It can create a customised test for complex devices (as large as 32M pixels at speeds up to 200MHz) on up to 12-inch wafers.