Power Short Test Flashcards
Why we do Power Short Test/ Objective of Power Short Test
FVMI.
To detect presence of short in power pins.
For good device, impedance between VCC/VDD to GND pin would be high.
For bad device (defect present in DUT), impedance between VCC/VDD to GND pin would be low/short.
Also to detect short present in test hardware (DIB, PIB, Probe card) in between power and ground plane.
Why Force Voltage? Why not Force Current?
Forcing current in power pin could lead to hit clamp voltage for good device. If we forget to set clamp voltage carefully (lower than allowed voltage at power pin), it can damage power pin.
Why do we force low voltage?
If there is any short, path resistance between VCC & GND pin will be very low. If forcing high voltage, power dissipation in shorted pat will go high and can cause heat generation which can caused damage to tester hardware/sockets.
How much current you expect to measure for DUT to PASS the test ?
Current should be very low (in nA).
Do you require to setup clamp? If yes, then how much you should setup?
Yes, 1mA current clamp to detect short without damaging DUT & tester resource.
What will happen if you do not setup a clamp ?
If short present, high current will cause high power dissipation which cause more heat generation. Thus, cause damage to DUT or test hardware component (socket, caps)
Will you be able to detect an open condition in DIB using PS test?
No, if open condition present, low current will still be measured (in nA) because of instrumental internal leakage & power caps leakage.
I could see some device has multiple VCC pins. How should we do the PS test for that device?
Join all power pins together to force small voltage and measure current. If power pins are mapped with different channel, then we will configure individual channel to force voltage.
Can we use Source Measurement Unit (SMU) to run PS test?
SMU is a bench instrument to force voltage/current. Yes.
Can we use Power Measurement Unit (PMU) to run PS test?
Generally, no. PMU is present inside of digital card to do DC parametric test. It is not used to power up DUT.
But technically, PMU can be used for FVMI mode, so PS test is possible with PMU.
What are the debugging steps if you measure zero current?
If zero current, maybe there is an open connection present. To detect open connection:
1. Remove DUT from socket. Put wire between VCC and GND to make short.
2. Run PS test to see if hitting clamp. This is to understand that test hardware and instrument is okay. Thus probably, DUT pin might not touch socket.
3. If still zero current, remove socket and try force voltage at VCC pin. Measure voltage at socket to see if voltage present. TRY to search at which connection voltage is lost (whether socket problem or traces problem).
What could be the debugging steps if measure clamp current?
If hit clamp current, the short connection is present. (When hitting current clamp, voltage will be zero)
1. Remove DUT from socket and run to see if still hitting current clamp. Remove peripheral one by one to see where short connection comes from. Or just check resistance using multimeter.
