FEC200 SOPK Test
This describes the SOPK test in most FEC diode testers.
SOPK tests some properties of the tester, fixture, and fixture wiring, as well as some properties of the diode under test.
The Kelvin contact part of SOPK checks to be sure that on both sides of the diode under test the "force" contact and the "sense" contact are connected together. Ideally (but not always) the contacts should be connected together only by being in contact with the device under test. 1
A test is also made of the diode under test to see that it is neither "shorted" nor "open." These tests are made at moderate currents and low voltage, so a "short" means that the diode has a substantially non-existent reverse characteristic. An "open" likewise indicates (for a single junction diode) an extremely poor forward characteristic.
If the diode is connected to the test contacts and is neither open nor shorted then a determination is made of the orientation of the diode in the contacts. Some of our testers can reverse the diode electrically should it be found that it is presented "reversed." Others merely detect the occurrence of the reversed diode and report it for "binning" purposes.
Once the hardware test is performed the software or firmware translates the results into a number from 1-5 which has the following meanings:
"1" means that one (or more) of the four test probes is not in contact with the diode. Nothing is to be implied about the condition of the diode itself.
"2" means that the diode is in contact with the probes1 but that it is "shorted."
"3" means that the diode is in contact with the probes1 but that it is "open." 2
"4" means that the diode is in contact. It is not shorted or open but is in the "reversed" orientation.
"5" is usually the expected result. The diode is not shorted or open and is correctly oriented and connected to the fixture.
The number 1-5 is reported as a test result which may be displayed, logged, and/or used for "binning" purposes.
In FEC testers, test limits are "inclusive" so if the SOPK test has a limit of >2 then any result from 2-5 is considered "passed." In this case only "1" (bad contact) would fail.
1There are many types of test clips and fixtures. The ideal fixture would have no connection from force to sense probes except when a diode was present and connected to them. Unfortunately not all fixtures are ideal, so the user must be aware of this distinction.
2Multifunction or Bipolar devices may indicate 'open' even if they are not. The 'contact' and 'short' tests still work correctly in this case.