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Geng(SMH)_CH19.qxd 04/04/2005 20:00 Page 19.14

INSPECTION, MEASUREMENT, AND TEST

19.14 FINAL MANUFACTURING

Supply currents (I , I ): Each supply draws a predetermined amount of current when set to the
cc dd
correct voltage. This can be tested with the device in a static condition or while running in a typical
operation.
Input voltage/currents (Iih, Iil, Vih, Vil): Each input pin has a valid range of voltage and current that
will be judged correctly by the DUT. This applies to digital pins at two levels, logic “0” and “1”.
Output voltage/current (Voh, Vol, Ioh, Iol): Each output pin has a specified voltage and current
specification representing logic “0” and “1” levels.

Common Test Challenges. Noise in a test setup can cause failure and erode performance. Proper
grounding techniques—decoupling capacitors at the power supplies and DUT and if a certain
resource is noisy, isolating it and coupling the resource to other quieter ones through a radio fre-
quency (RF) ferrite bead or inductor—are important. Also the overall noise floor (in dB or volts per
root hertz) needs to be compared against the device requirements. It is difficult and time consuming
to improve an overall test solution’s noise floor if it is worse than the device requirements.
The DUT interface can be a challenge in several ways. The pin count of an IC may be in thou-
sands with very small pitch distances between pins. This increases the complexity because of the
physical limitations of trace routing and typically will increase the number of layers required on the
load board to isolate the signal traces going to these types of devices. Typically the test source and
measure resources go through a pogo pin to a DUT printed circuit board that has a special socket
called a contactor to physically interface with the actual device. Another challenge is noise transfer-
ence and the inductive coupling of ac waveforms on top of each other.
A wafer probe card interface has much the same problems as the DUT board. Some options are
blade or needle-type connections or membrane probes. Other new technologies are being developed
to accommodate more complex pad geometries.

19.2.3 Testing Linear Devices
Linear Device Market Segments. Linear markets could have a very wide definition. For this hand-
book, linear devices will be defined as power products such as power supplies, voltage regulators, and
power switches; communications products such as signal amplifiers, switches, filters; and other cate-
gories such as light emitting diodes (LEDs) for brake lights, stop lights, and optical mouse devices.
Definition of a Linear Device. A linear device is one in which the output is linearly proportional
to the input, within a given range. Linear devices are sometimes also called analog devices. As
opposed to digital devices, linear devices have a continuously variable output that is theoretically
capable of taking on an infinite number of states. Some common linear devices include operational
amplifiers (OP AMPs), filters, voltage regulators, analog switches, diodes/LEDs, transistors, triacs/
silicon controlled rectifiers (SCRs), and optical couplers.
Linear devices are the building blocks or the “analog glue” that manufacturers of higher-level
products use to complete their product. For instance, a cell phone will combine a microcontroller,
Flash memory, static random access memory (SRAM), digital signal processing (DSP), and many
linear components such as RF amplifiers, filters and switches, and LEDs.
Architecture of a Linear Device Tester. The architecture of a linear device test system is very
dependent on the type and variety of linear device that will be tested. Often the first choice to be
made in selecting a tester for linear devices is between automated test equipment (ATE) and “rack
and stack,” i.e., a combination of individual instruments. This is discussed more in Sec. 19.3. Since
the architecture of a test system for linear devices is highly dependent on device functionality and
these devices require a very low COT, many times the architecture is custom tailored to a specific
family of devices and is not a general purpose one. However some of the typical tester building
blocks that are needed include the following:
A switching matrix provides a method of connecting the source and measurement devices to the
different pins of the DUT. The number of pins, their function, and parameter specifications must be
considered when specifying (or designing) the switching matrix requirements.

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