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LED Production Test Using the
Agilent B2900A Series of SMUs

Technical Overview


Agilent B2901/02/11/12A Precision Source/Measure Unit
Agilent B2901A Precision SMU, 1ch, 100 fA resolution, 210 V, 3 A DC/10.5 A pulse
Agilent B2902A Precision SMU, 2ch, 100 fA resolution, 210 V, 3 A DC/10.5 A pulse
Agilent B2911A Precision SMU, 1ch, 10 fA resolution, 210 V, 3 A DC/10.5 A pulse
Agilent B2912A Precision SMU. 2ch, 10 fA resolution, 210 V, 3 A DC/10.5 A pulse




Introduction both voltage and current. They cover
currents from 10 fA to 3 A (DC)/10.5 A
Numerous emerging light emitting (pulse) and voltages from 100 nV to
diode (LED) applications have created 210 V. In addition to these compre-
a demand for LEDs with higher quality hensive measurement capabilities,
and reliability. Testing that is both the B2900A Series of SMUs pos-
more accurate and faster and that sesses high throughput that reduces
permits quicker sorting is therefore test times. The B2900A Series of
required for both on-wafer devices SMUs also has many features that
during fabrication and for packaged make it well-adapted for production
devices during final test. test, such as pass/fail binning, a
digital I/O interface for handler
Both electrical and optical tests are control, and code compatibility with
typically performed on LEDs. The standard single and dual channel
Agilent B2901/02/11/12A Precision SMU products.
Source/Measure Unit is the best
solution for all electric tests such as This technical overview focuses on
a forward voltage test (VF), a leakage the electrical testing of LEDs in pro-
current test (IR) and a breakdown duction. If you need to perform optical
voltage test (VBR). In addition, it can tests in addition to electric tests, then
be used to provide forward current dual-channel models of the B2900A
bias during optical test. Series of SMUs can be used. The
dual-channel models of the B2900A
The B2900A Series of SMUs is a Series of SMUs permit one channel
compact and cost-effective benchtop to measure photo diode current while
Source/Measure Unit (SMU) with the other channel drives the LED.
the capability to source and measure
Easy production test Program memory For tests that utilize lots of repeated
code (such as subroutines), program
system configuration improves throughput memory can dramatically reduce test
Figure 1 shows a conceptual diagram Fast test times are essential to times. Of course, programs can be
of a system based on the B2900A maximize throughput and maintain saved to or loaded from any attached
Series of SMUs for production LED high levels of factory productivity. USB flash memory device (please see
electric test. The widely available Besides possessing fast intrinsic Figure 2).
banana style terminals of the B2900A measurement speed, the B2900A
Series of SMUs greatly simplify the Series of SMUs has a program The B2900A Series of SMUs also has
test system configuration. As will be memory function that can be used to a data buffer on each SMU channel
discussed later, in most production improve production test throughput. that can hold up to 100,000 data
testing measurement results are Program memory allows you to store points. This enables you to transfer
compared with pre-defined limits and long strings of SCPI command lines all the data in the buffer at once after
pass/fail judgments are made. Output once into the volatile memory of the a series of measurements have com-
signals from the GPIO port of the B2900A Series of SMUs and then pleted instead of having to transfer
B2900A Series of SMUs can be used recall those strings multiple times data after every measurement. One
to communicate with the component while the program is executing using way to use this to improve throughput
handler to sort devices based on the a single SCPI command. By storing would be to have the B2900A Series
pass/fail criteria. the command strings in memory, the of SMUs send measurement data to a
time that would have been spent PC while a component handler places
The B2900A Series of SMUs supports sending those same commands over a new device on a DUT interface.
several communication protocols, a communication bus is eliminated.
GPIB, USB and LAN, and these can
be used with both SCPI and IVI-COM
drivers. SCPI is an industry-standard High force DUT interface
command set for basic instruments
with a uniform structure that supports Test
leads
a common set of commands. The
SCPI command set of the B2900A GPIB
Series of SMUs not only supports its LAN Low force
advanced features but also general- USB GPIO Mechanical
purpose SMU commands (such as connection
those used by the Keithley 2400) to
simplify test program migration. In Component handler
addition, the IVI-COM drivers for the
B2900A Series of SMUs work in a
variety of programming environments Figure 1. Example test system configuration for a packaged device using the B2900A
and languages, so you can develop Series of SMUs
programs without having to use
low-level commands.
Store Breakdown voltage test
Leakage current test
Forward voltage test

Store/Load
Program memory
SCPI command line strings




Figure 2. Program memory allows strings of SCPI commands to be stored for later execution


2
Multiple pass/fail Characteristics of
judgment modes forward direction LEDs
In production test, a limit test func-
IF Characteristics of
tion is generally used to eliminate
reverse direction LEDs
defective devices through a pass/fail
judgment based on pre-defined limits. SMU reaches compliance status
Recognizing that there are a variety of
pass/fail limit scenarios, the B2900A
VF VComp
Series of SMUs supports two modes: PASS FAIL
Compliance mode and Limit mode
Figure 3. Example showing how the Compliance mode's pass/fail test capability can be
(up to 12 binning limits possible).
used to determine LED polarity

Compliance mode utilizes the intrinsic
compliance feature of the B2900A
Series of SMUs that allows a limit Characteristics of the device
to be placed on voltage or current which passes in Limit Test
IF
output to prevent device damage.
Characteristics of the device
When the SMU's output reaches the
which fails in Limit Test
limit value during a measurement it is
in compliance status. If Compliance VLow VF VHigh VF FAIL
mode is enabled, then the test fails
when the SMU reaches compliance PASS
status. One possible use of this
Figure 4. Example showing how the Limit mode's pass/fail test capability can be applied
feature is to determine the polarity
to an LED forward voltage test
of LEDs (please see Figure 3).

Limit mode is usually used to deter-
mine if a device parameter is within PASS
specified low and high limits. When FAIL Low1 Low2 High2 High1
Limit mode is enabled the B2900A A B C D E
Series of SMUs makes a Pass/Fail Limit 1 Measurement
judgment based on whether or not parameter
the measured value is within speci- Limit 2
fied low and high limits (please see Bit pattern 100 010 000 001 011
Figure 4). A typical use of this mode
is to perform grading and sorting. For If a device fails the Limit 1 tests, it will be sorted into bins A or E.
For devices that pass the Limit 1 tests, the Limit 2 tests will be performed.
example, using two binning limits If a device then fails the Limit 2 tests, it will be sorted into bins B or D.
in Limit mode it is possible to sort Devices that pass all of these tests will be sorted into bin C.
devices into five classes (please see
Figure 5). Figure 5. Example showing how to sort devices into five classes using two limit tests

After performing pass/fail testing
with these modes, you can view
the results on the wide QVGA LCD
display of the B2900A Series of
SMUs. In addition, you can program
the B2900A Series of SMUs to output
specified Pass/Fail bit patterns
through the GPIO port to other
equipment such as handlers for
component binning.


3
Production LED test Start Summary
flow example The Agilent B2901/02/11/12A
Store SCPI command line strings
Figure 6 shows a simplified flow for Precision Source/Measure Unit is
to the program memory
production LED testing. Before begin- the best solution for the production
ning the actual testing, it is good Forward voltage test testing of LEDs and other devices.
practice to store repeated operations The B2900A Series of SMUs pos-
into the program memory of the IF 1. Force current IF sesses high throughput, which
B2900A Series of SMUs (such as the
2. Measure voltage VF greatly reduces test times. In addi-
forward voltage test in this example). VF
tion, the program memory function
After this test pre-loading has been of the B2900A Series of SMUs allows
performed and the stored program the test throughput to be improved
has been run, the B2900A Series of RUN stored program even more. The B2900A Series of
SMUs waits for a Start of Test (SOT) SMUs also provides useful features
Wait for SOT for production test such as pass/fail
trigger from the component handler.
Once the LED is in-place, the handler Measurement
decision-making, a digital I/O inter-
sends an SOT trigger signal to the face for handler control, and program
B2900A Series of SMUs to inform it Output pass/Fail pattern compatibility with standard single and
that testing can begin. The B2900A dual channel SMU products.
Output EOT
Series of SMUs first makes a mea-
surement using the programs stored The B2900A Series of SMUs is
Yes Another equipped with popular banana
in program memory and displays device?
the Pass/Fail testing result. Then, style terminals that make it easy to
No connect to other instruments in a
the B2900A Series of SMUs sends a
End production test system. Both SCPI
specified Pass/Fail bit pattern and
an End of Test (EOT) signal to the commands and IVI-COM drivers are
Figure 6. LED production test flow example available for the B2900A Series of
component handler and stores the using the B2900A Series of SMUs
test data to the PC. This procedure is SMUs for remote control using the
then repeated until all of the devices GPIB, USB or LAN communication
have been tested. protocols.

Its wide current and voltage measure-
ment ranges (from 10 fA/100 nV to
10.5 A/210 V) provide superior
measurement performance and allow
you to test devices more accurately
and easily than ever before.

For more detailed information on the
various models of the B2900A Series
of SMUs, please refer to the data
sheet of the B2900A Series of SMUs
(5990-7009EN).




4
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