Test:

Electrical Test

Electrical testingis 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 anautomatic (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.

Figure 1.Example of an IC Tester (Left) and

Three (3) Examples of Test Handlers (Right)

The

testing process executed by the tester is controlled by the

test

programor 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.

There are

usually two versions of the test program.  One is a

productionversion and the other is a

quality

assuranceversion.  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.

The test

program usually consists of two types of test blocks, namely,

parametric and functional.

Functionaltesting checks if the device is able to perform its basic

operation.

Parametrictesting 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

othertemperatures 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.