Running scan test on three pins: yes we can!

Imagers are pretty little objects nowadays, their size is always shrinking and having only three standard digital pins available on their package is a most common thing. Looking back in 2006, only three years ago, people asked for a solution to run industrial structural test on such complex devices could though only reply ¿impossible¿ or ¿Do It Yourself¿. STMicroelectronics did not escape the rule. An internal development and a partnered development were thus successively launched to address this issue. This article proposes to examine all the why and how of these developments along with the good results obtained during that time, in terms of test cost improvement, area overhead in silicon, design flow updates and industrialization process. Getting all sensors designed today equipped and test data volume (and time) improvements in the range of 25X to 30X just took that three years time. Now that the solution is industrially available, it's also time to share and look at the future of industrial scan test on three pins...