See also the Cassini Reference Guide, CH 3: Care & Maintenance, Electrostatic Discharge (ESD) Control for additional information.

Electrical Over Stress:

Electrical Over Stress (EOS) is a nebulous term that, in general, means one item damaging another item. In order to provide some clarity to the term EOS with regards to the RI8546 DC TIM, we will define that EOS means potential DUT damage from one of three possibilities:
1) Voltage output when none is expected
2) Power supply static over-voltage
3) Power supply overshoot during voltage changes

1) Voltage output when none is expected:

All TIM contacts are either tied resistively to ground or are open when the tester is in its idle state. A properly working tester will have no voltage on its outputs when none is expected.

If the disconnect circuitry on any output is not operating properly, the tester's diagnostics (run from the 'Diagnose' panel using a diag plate) will find the error and flag a failure.

Note that the tester has a smart compiler to minimize test time. One technique that the compiler can use, if the test engineer allows it, is to not reset to the tester's complete idle state between parts. For example, if a relay is switched from its idle state, it is better both in time and durability to not switch the relay when cycling between parts. The compiler will know to only switch at the start of a test run. With this in mind, the test engineer can choose to leave some supplies on between parts or turn them off. Typically a test engineer would turn off all supplies. However if they choose to leave one or more on, then you would expect to see voltage on that supply when cycling between parts. If that voltage is a concern, the test engineer should modify the test plan accordingly.

2) Power supply static over-voltage:

The power supplies are all guaranteed accurate to the data sheet specs.

If any power supply is not accurate, the tester's diagnostics (run from the 'Diagnose' panel using a diag plate) will find the error and flag a failure.

3) Power supply overshoot during voltage changes:

All supply bandwidths are properly equalized to ensure that voltage changes are flat with no overshoot or ringing.

 

Power supply bandwidth is guaranteed by design.

Note that all the Roos supplies are significantly faster (higher bandwidth) than other testers, or bench supplies. Voltage switching time is approximately 5 uS for the PowerVI and static digital, and switching time is about 50 uS for the VCCs. While proper TIM design prevents these supplies from ringing or overshooting into a resistive load, physics dictate that it is possible, with improper Fixture or Device Interface Board (DIB) design to induce overshoot at the DUT. Long wires combined with DIB board capacitance will form a tank circuit that induces ringing on a fast voltage step. If the Fixture and DIB are designed to minimize line inductance and minimize stray (or deliberate) capacitance, then the DUT will not experience overshoot with Roos supplies.

EOS Conclusion

When the Fixture, DIB, and test plan are designed using proper engineering techniques, the Cassini tester, and specifically the RI8546 DC TIM, do not generate any EOS.

ESD

For the purposes of this discussion, ESD is defined as statically generated electricity causing damage to a DUT.

The Roos testers are ESD protected. The chassis and all TIMs are aluminum shells. All TIMs are grounded to earth through the chassis, which is grounded through the mains ground.

Note that this assumes the facility's mains contain a proper earth ground for both the handler and tester. Also note Roos recommends that the ground wire and clip provided with all Roos testers is connected to the handler chassis to tie the tester and handler chassis together. This will keep the handler and tester at the same potential regardless of the quality of the facility's mains ground.

ESD Conclusion

When properly earth grounded, the Roos tester is not subject to ESD and will not discharge into a properly grounded handler.