*As Featured on NI.com
Original Authors: Shun-Chung, Shiao, Shining Technologies Co. Ltd.
Edited by Cyth Systems
The Challenge
Falling price forces LED manufacturers to look for a higher-yield, lower-cost tester but need to be able to cover the same test plan and to maintain the measurement accuracy.
The Solution
Use NI PXIe-4137 to test faster with SourceAdapt technology, to measure breakdown voltage and test high power LED with its pulse and 200 V range capability, and to get rid of the use of oscilloscope in thyristor testing with its 1.8 MS/s digitizing feature.
Today, LEDs can be seen in all facets of life—they are used in lighting, tablets, mobile phones, and as a light source for vehicles and panels. Quality tests for LEDs are becoming more and more significant and satisfying market demand remains an important issue. Therefore, increasing LED test speeds have become key to enhancing production capacity.
Shining Technology Co. Ltd. has been working on the design, construction, and optimization of LED testers for many years, creating LED testers with high precision and speed. The single-site tester previously used for the semiconductor LED wafer, which is small in size and difficult to test, was often the bottleneck for production capacity. In response, Shining Technologies has been dedicated to the research and development of exclusive multi-site optoelectronic test technology, aiming to create an easily maintained multi-site LED tester (Figure 1.) that can improve production capacity and reduce costs.
High-speed SMU Reduces Hardware Procurement Costs
Thermal resistance is a key aspect in LED tests and is usually examined after an LED is encapsulated to detect problems such as insufficient heat dissipation or overly fast LED luminous decay. When testing an LED’s thermal resistance, a low but constant current is applied and thermal curve graphs prior to and after forward voltage application are created. However, due to the insufficient sampling rate of the previous SMU, an additional oscilloscope was often required when testing which increases the cost of hardware procurement.
Now, Shining Technologies uses NI SMU with sampling rate of 1.8 MS/s, the highest in the industry. The SMU is able to simultaneously measure with high precision voltage and current traveling in the same channel. This not only lowers the cost of hardware procurement, but also simplifies the complexity of the test system, eliminating problems such as having to work with the low sample resolution of oscilloscopes.
The Trend of Using Multi-site LED Testers for Production Line Tests
The electrical properties test of an LED often includes examining I-V curves. Poor I-V characteristics can directly affect the color and brightness of an LED-backlit LCD, resulting in poor display quality. Through I-V curve measurements, we can determine whether overshooting occurs when the LED lights up, ensuring the quality of the LED.
Due to the LED’s small size, it is difficult to design tester mechanisms. Moreover, the previously used single-channel LED tester has become insufficient due to increasing market demands and price reductions. Therefore, it is essential to equip production lines with the Multi-site LED Tester.
The exclusive multi-site optoelectronic test technology (Figure 2.) provided by Shining Technologies helped overcome many of the mechanical difficulties in a multi-site prober. Using an NI Single-Board RIO as the core controlling system for automated machines and adopting the automated testing PXI platform as its basic architecture, the prober and the tester can be integrated into a single PXI system. Apart from providing an electric current range (pulse) of 10 A and a voltage range of 200 V, NI SMU’s high resolution (100 fA or 100nV) also helps to enhance test precision, allowing it to detect optoelectronic currents between 10 pA and 100 mA. Not only does its voltage range of 200 V support the breakdown voltage measurement, the pulse mode can also avoid damages to a high-power LED caused by continuous heating.
Compared to the LED tester constructed using box instruments, the Multi-site LED Tester developed using PXI and NI SMU can greatly increase test speeds without compromising measuring specifications and precision, completing tests for 40 LEDs per second. This is 5 times faster than a traditional LED tester. (Figure 3.)
The Advantages Brought About by NI SMU
NI SMU’s unique SourceAdapt technology can also assist in LED testing. Due to different LED designs and loads, transient responses in each LED test differ as well. NI SMU offers fast, normal, and slow transient response modes to suit DUTs (device under test) with different loading characteristics. Transient response parameters can also be adjusted through SourceAdapt to fit with the DUT, avoiding inaccurate results due to overshooting or undershooting and achieving a reliable and precise testing method.
Integrating its exclusive simultaneous multi-site optoelectronic testing technology with the PXI system and NI SMU, Shining Technologies successfully increased its production capacity by 5 times, and is able to test more than 40 LEDs per second. Shining Technologies also created an easy operating interface for the testing system using the graphical programming language LabVIEW. Compared to traditional box instruments, the PXI platform takes up less space, provides simultaneous multi-site testing, and efficiently reduces the cost of hardware procurement for an LED testing company. Most importantly, the Multi-site LED Tester provides precise measurements of electrical and optical properties, significantly increasing production capacity and shortening time to market to satisfy market demand.
Original Authors:
Shun-Chung, Shiao, Shining Technologies Co. Ltd.
Edited by Cyth Systems
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