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INSPECTION, MEASUREMENT, AND TEST

INSPECTION, MEASUREMENT, AND TEST 19.15

Power supplies will be required to provide power to the device for testing. Power supply consid-
erations include the number of supplies and their voltage and current specifications. All traces, wires,
and fixtures must withstand the maximum expected voltage and current. Some tests can be danger-
ous to humans or even the test equipment. For example, testing the breakdown voltage of the DUT
exposes it to a very high voltage (hundreds of volts) to ensure compliance to specification. Safety
considerations must be adhered to as defined in Sec. 19.4. Often a pulsed high-current source will
be used to keep the test equipment to a reasonable size and to prevent destroying the DUT, particu-
larly in wafer form when no heat sinks can be attached to the device. Even at a package test, any kind
of heat sinking capability would be minimal.
Digital logic input and output pins may be used as digital control pins needed to access the DUT
or configure it for certain test modes. Control, signal lines, or identification pins may be used to con-
trol relays or switches on the DUT fixturing. Different devices require different fixturing and often
the test program will electronically check the identification information of the fixture to ensure it is
the correct one.
The prober/handler interface will allow indexing to the next die or package as well as sending
category or binning information that allows the sorting of devices into different grades. Often the
interface will also integrate equipment for temperature testing. The integration of a prober or han-
dler into a tester is often more time consuming than expected due to the mixing of mechanical and
electrical issues. There is a standard set of signals expected for this interface that can be provided
with simple transistor-transistor logic (TTL) logic or via a standard interface like the general pur-
pose instrument bus (GPIB).
System controllers are required to run and coordinate all the operations for the test cell.
Considerations for the system controller include the operating system used, networking capabilities,
processing power or speed, upgradeability, the testing language(s) supported, and whether the oper-
ating system language is an industry standard or a proprietary.
A final factor to be considered is that often test systems are installed in clean areas or areas with
limited access. Since it is inconvenient to carry out test development in these limited-access areas, it
is important to find a way to do remote development.
Basic Test Setup for Linear Devices. The test setup for a linear device is dependent on its func-
tion and the level of testing required. For instance, testing a simple diode will require a programma-
ble voltage and a current source, in addition to a voltage and current measuring device (typically
called a parametric measurement unit, or PMU). An oscilloscope or programmable threshold counter
will also be required to measure its ac switching characteristics. The architectural decisions on the
tester will depend upon how much automation is needed and what level of accuracy is desired. For
example, to test a small batch of diodes, a human operator can manually test with a power supply, a
voltmeter, a pulse generator, an analog oscilloscope, a pencil and notepad. For a large quantity of
diodes, with the requirements of data logging and temperature testing, one would need to add an
automation—comprising a system controller, computer controllable PMU, signal generator,
scope/counter, a temperature controllable device handler, and some form of device-marking system
to allow the data log to track the device.
Future Trends in Linear Devices. In the future, more and more of these linear devices will be inte-
grated into the higher-level assemblies of the final product as manufacturers strive to add value and
reduce cost.

19.2.4 Testing Digital Devices
Digital Market Segments. Digital devices provide logic and computing capabilities for low-end
gadgets all the way up to the most complex systems. Some examples of this are appliances, printers,
calculators, cars, and computers. The major types of digital logic devices include processors, appli-
cation specific integrated circuits (ASICs), and programmable logic. Processors can be programmed
to do multiple tasks. ASICs are designed and optimized with only one application in mind, for exam-
ple, controlling a printer, or monitoring an automobile’s performance. Because of this, ASICs are
much simpler and cheaper to design. The cost and time to market are the major reasons why

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