Electrical Test


Electrical testing is the identification and segregation of electrical failures from a population of devices.  An electrical failure is any unit that does not meet the electrical specifications defined for the device. 

In simplified terms, electrical testing consists of providing a series of electrical excitation to the device under test (DUT) and measuring the response of the DUT.


For every set of electrical stimuli, the measured response is compared to the expected response, which is usually defined in terms of a lower and an upper limit.  Any DUT that exhibits a response outside of the expected range of response is considered a failure.


In production mode, electrical testing is usually performed using a test system or platform, consisting of a tester (see Fig. 1) and a handler (see Fig. 2).  Such a test system is also referred to as an automatic (or automated) test equipment, or ATE.  The tester performs the electrical testing itself, while the handler takes care of transferring the unit to the test site and positioning it for proper testing, as well as reloading it back into another tube after the testing process is completed.         


The testing process executed by the tester is controlled by the test program or test software.  The test program is usually written in a high level language such as  C++ or Pascal.  It consists of a series of several test blocks, each of which tests the DUT for a certain parameter. Every test block sets up the DUT fixtures for proper testing  of the DUT for the corresponding parameter.  It also tells the tester what electrical excitation needs to be applied  to the DUT, as well as the correct timing of applying them. 


Figure 1.  Example of an IC Tester


There are usually two versions of the test program.  One is a production version and the other is a quality assurance version.  The production version has stricter limits compared to the QA version, while the QA version more or less tests the DUT to the datasheet specification limits. The differences in production and QA limits, or the guardbands, should be large enough to take into account errors attributed to over-all testing variability and noise, but not large enough to result in over-rejection.  If the guardband is chosen properly, any unit passing the production test is almost sure to pass the datasheet limits, regardless of which test equipment on the floor is used.


Figure 2.  Three (3) Examples of Test Handlers (Right)


The test program usually consists of two types of test blocks, namely, parametric and functional.  Functional testing checks if the device is able to perform its basic operation.  Parametric testing checks if the device exhibits the correct voltage, current, or power characteristics, regardless of whether the unit is functional or not. Parametric testing usually consists of forcing a constant voltage at a node and measuring the current response (force-voltage-measure-current, or FVMC) at that node, or forcing a constant current at a node and measuring the voltage response (force-current-measure-voltage, or FCMV).


Electrical testing is normally done at ambient temperature, but testing at other temperatures is also being done depending on the screening requirements.  For instance, latch-up problems have better chances of being detected at an elevated temperature while hot carrier failures are easier detected at low temperatures.  Aside from 25C, other standard test temperatures include -40C, 0C, 70C, 85C, 100C, and 125C.


Test Links:  Electrical Test Burn-in Marking Tape and Reel Dry Packing  Boxing and Labeling

See Also:  Test Glossary Test Confidence Strip TestingIC Manufacturing;  Test EquipmentTest Accessories




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