AC_scan compare with traditional dc_scan has more advantage. Actually, more times we use scan for transitor defect detecting. For smaller gate and complex circuits. We cannot generate enough pattern vectors to coverage all logic. Although, we generate large vectors. The speed is the bottle necking for this also.
AC_scan can run very fast and save test time. The scan_shift can detect more accurate location. Past 5-years IC testing, I found the more useful function is time delay detecting. For example, the IC when work under 100MHz, all function's are acceptable. When frequency goes high and high, some parts will unstable or fail. Why? Does the circuit design has problem,maybe? Manufacture issue, maybe? Or test method need improve,maybe? Test hardware need optimize, maybe?
So many factors will affect this. But, fortunately some chips passed. And we can remove test environment & design issues. We think over to find some ways to compare the pass and fail chips. At end , we found why frenquency affect?
AC_scan with step compare, it is good way for this. Generate diffrent vectors and run with different frequencies, we can detect the fail location. After PFA, the fail should manufacture issue. Some bridge need improve.
At present, many test engineers will use AC_scan for defect detecting. It is not end. Do we have more good ways for this? Yes.. let's discuss for next page.
Blog Make a Frequency Plan Tom Burke 17 comments When designing a printed circuit board, you should develop a frequency plan, something that can be easily overlooked. A frequency plan should be one of your first steps ...