An Automated Single HBLED Test Station
HBLED tests using different types of test sequences in the various stages of production, such as during the study design and development, on-wafer measurements during production and testing of the package. Testing “recipe” is associated with many steps, but this article focuses on the “factual basis” for this important test recipes that describe how to probe the characteristics of LEDs and sample test. The emphasis is on the characterization of electrical equipment, but also a technique in which light metering appropriate.Instruments by applying a new test technology, test times and costs can be reduced.
Basic experiments in which electrical current voltage (IV) measurements to the functional properties of the LED to obtain. IV curves generated looks pretty much like an ordinary diode. Testing complete, many points versus voltage of the existing activities to cover, but limited sample points are generally sufficient to probe the figures of merit LED.
Some tests require the application of DC source to the LED, and then measuring the voltage produced, other tests require the implementation and measurement of DC electric current through the LED. A source-measure unit (SMU Source Meter instrument or ®) is ideal for this kind of testing because it combines a precision power supplies with a high accuracy of measurement comparable to that achieved with a precision digital multimeter (DMM). Simply put, this tool can act as a power source to DC voltage or power supply, and the size of each type of signal.
Forward Voltage (VF) and optical test. VF control test of the LED forward voltage operation. VF testing performed by a voltage drop when the source is known and measurements generated in the diode. When forward current is applied to the diode, it started to do. During the initial value of the source of low current, voltage drop on the diode will increase rapidly, but the slope began to flatten as the drive current increases. diodes are usually operated in this region are relatively constant voltage, therefore it is useful to the diode to be tested under these conditions. Typical flow test ranged from a few tens of milliamps to amps, while the resulting voltage measurement usually ranges between a few volts. These results are usually used by manufacturers for binning purposes as a forward voltage is directly related to the chromaticity (color characteristics) of the LED.
Forward biasing is also used for testing optical, because the flow of electric current is closely related to the size of the light emitted. optical power measurement can be made using the integrating sphere or the place near the LED diode will be tested to the emitted photons to catch. light is then converted into flows, which can be measured by the ammeter or a single channel Source Meter instruments.
In many applications to test, the diode voltage and light output measured simultaneously using a stable source of current value. In addition, data such as the spectral output are obtained using the same drive current value and a spectrometer.
Reverse breakdown voltage (VR) and leakage current (IL) test. Applying a negative bias current to the LEDs will be possible to investigate what is called reverse breakdown voltage (VR). Testing should now be set at a level where an increase in the measured voltage is no longer significant when the flow is a bit stronger. At a higher level than this voltage, a large increase in reverse bias current as a result of significant changes in the voltage reversed. The specifications for these parameters are usually the minimum value. The test is performed by low-level source of reverse bias current for a certain time, then measuring the voltage drop across the LED. The measurement results are usually in the range of tens of volts.
Typically, the voltage (volts to tens of volts) is used for the leakage current (IL measure). IL test for measuring the low-level leakage currents in the LED with a reverse voltage is lower than defective. It is customary to measure leakage, and more generally to measure the insulation, to ensure production does not exceed certain limits. There are two reasons for this. First, the low current measurements require more time controlling, so they take longer to complete. Secondly, the influence of environmental and electrical interference noise in the environment to exert a greater test signals at a low level, so extra care is needed in the shield. This complicates testing device for extra protection and can interfere with automatic component handlers.
Single LED test system. A single LED automatic test station usually consists of a PC, components and dual-channel controller Source Meter instruments such as the Keithley Model 2602A. If the test is performed on the stage of production wafers, a wafer probe station will also be involved.
In the test system, the main goal is to save the computer data in a database for documentation. Secondary objective is to recreate the sequence of tests on Source Meter instruments for the various components. However, the actual Model 2602A independently of the controller PC. After a test Script Processor (TSP), which supports write a complete test plan to operate on the instrument itself. In other words, the user can write a complete PASS / FAIL test scripts and sequentially those of the front panel of the unit to be established without reprogramming of the instrument.
In production-oriented setting, the LED controller components transport persons with a test setup in which the electrical contacts Source Meter establishment. was shielded from light fixtures and home room photo detector for measuring light. In this configuration can Dual-Channel Single Source Meter used for both source and measure the connection. Channel A, a test signal to the LED and measuring the electrical response, while Channel B monitor photodetector in optical measurement.
Test sequences can be programmed to begin using digital signal lines from the controller component, an early “test it” (Sot) signals. When the instrument detects the signal source Meter Sot, characterization tests for the LED starts. After all the electrical and optical test is completed, the digital line of instruments for measuring Source Meter sending “complete” signal to the handler component. Moreover, the instrument built all source intelligence can gauge the pass / fail operation and sends a command via a digital I / O port to instruct the controller component to the trash based on the LED pass / fail criteria. Usually two further action took place simultaneously: the transfer of data to a PC for Statistical Process Control (SPC), and the installation of new mechanical LED in the test setup.
LED Measurement System for Multiple Devices / Arrays. Large-scale production of test and some may involve the LED array LED combustion process. In this test, some sections measured over a certain period. A continuous flow is usually required to drive LED, but perhaps a few meters from the light detectors for active plywood through the Switch system. Appropriate instruments and switching systems and will be determined by different dynamics of the electrical currents in the study, and the number of tested devices, successively, respectively.
For example, Keithley’s Model 3706 System Switch / Multimeter offers six-card slots that can handle up to 576 or 2688 channels multiplexed switch matrix cross points. He also has the ability of TSP, which makes it a good friend for the company Source Meter instruments. TSP-Link ® offers it, the two tools to quickly and easily integrated into a tight synchronization operations, and both can be controlled from a single test script to the test to maximize.
Speed Test Programming with TSP. With a variety of instruments, the computer control over all aspects of the exam. If so, in order to test each element of the instrument must be configured for each test and then enter the desired action, and then restore the data on the PC monitor. Control of your PC and then to assess the pass / fail criteria and take appropriate action for binning LEDs. Each order is sent out and consume valuable production time and lower throughput.
Clearly, most of the time sequence of tests taken by the communication of information to and from your PC. Instruments with the possibility of the amount of TSP traffic dramatically reduce the communication bus, and thus the system throughput for complex test sequences
With TSP, the majority of the test cycle embedded in the instrument. TPS is a full-featured test engine that the control sequence of the test sequence may, with the single pass / fail criteria, mathematics, computation, and control of digital I / O. TSP can store user-defined test sequences in memory and execute it on command. This reduces the setup and configuration time for each step in the sequence of test and increase throughput by reducing the number of communications to and from the instrument and PC
Using the TSP process consists of three simple steps: 1) Create a script. 2) Download the script for the instrument. 3) Phone to scripts work. The test script can be written using the software equipped with Test Script Builder respective Source Meter instrument, or can be downloaded to the instrument using another program, such as Visual Basic or LabVIEW.
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