Practical optical waveform probing of flip-chip CMOS devices

Internal node waveforms are recovered through the backside of flip-chip CMOS devices under real test conditions using a commercially available tool. A novel noise reduction scheme significantly reduces acquisition times by canceling environmental and laser noise. Long test loops can be examined with 10 GHz bandwidth using a 35 ps pulse width mode-locked laser source and equivalent-time-sampling. Other system issues, including phase locking the fixed 100 MHz laser clock to a variable frequency tester clock, will also be discussed.