Service Manuals, User Guides, Schematic Diagrams or docs for : Keithley Appnotes 2519 HBLED Test
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A G R E AT E R M E A S U R E O F C O N F I D E N C E even been significant strides towards replac-
ing fluorescent and incandescent lighting for
general illumination. This expansion of ap-
plications and widespread implementation
of LED-based lighting systems has created
a tenuous situation for manufacturers. There
is a strong need to decrease the unit costs
of these devices by dialing in manufactur-
ing process and increasing throughput while
maintaining innovation and a technological
foothold through continued R&D.
In order to simultaneously achieve these
High Value
goals, the device characterization becomes
all the more important. Test engineers must
build systems that maintain the thorough na-
HBLED Testing
ture of R&D testing with increased through-
put for effective production. This carry-
through of high accuracy testing is critical
for refining processes and improving yields
Jason Chonko, Keithley Instruments, Inc., as new technology is commercialized, while
implementation of automated measurement
and handling techniques help to increase the
production throughput without compromis-
High brightness LEDs (HBLEDs) offer much HBLEDs used in illumination, where incan- ing high precision and sensitivity. These re-
higher performance than traditional LEDs, descent and fluorescent lamps currently have quirements must be met in the testing of in-
but come with significantly higher cost. a significant unit price advantage. dividual devices (for example, with handler
These two factors drive the way HBLEDs Effective electrical measurements must systems testing chips or packaged parts), and
are tested in both R&D and Production. be carried through R&D into production, during initial upstream screening with on-
and this often takes place while technical is- wafer testing of many devices in parallel.
Testing Needs sues are still being worked out. Meticulous
The demand for High Brightness Light production testing is critical for refining pro- LED Attributes Define Testing
Emitting Diodes (HBLEDs) is growing rap- cesses and improving yields as new technol- In their simplest form, traditional LEDs
idly because of their high efficiency, long ogy is commercialized. Nevertheless, rapid have homogeneous structures that use the
life, and wide range of available colors. automated measurements are also crucial for same type of material for the P and N junc-
These characteristics are driving their use in high production throughput, while maintain- tion. This minimizes lattice matching dif-
applications such as architectural lighting, ing high precision and sensitivity over wide ficulties and simplifies processing, which
automotive lighting, medical equipment, parameter ranges. These requirements must makes them inexpensive but not especially
military systems, and even general illumina- be met in testing individual devices (for ex- efficient at light generation. A typical operat-
tion. The demand for these devices will grow ample, with handler systems testing chips ing condition is a drive current of 20mA at a
even faster with lower prices and increased or packaged parts) and when doing initial forward bias of 2V. Depending on the range
efficiency, but these two steps require refined upstream screening with on-wafer testing of of products and drive currents, luminous in-
testing methodology and instrumentation. many devices in parallel. tensity could range from 1 to 100mcd. One
To take advantage of the new opportu- of these LEDs, designed for use as an indica-
nities that HBLEDs bring, manufacturers Alternate Testing Needs tor lamp, might cost $0.30.
are looking for ways to increase production Recent advances in High Brightness HBLEDs have more complicated semi-
volumes and reduce unit costs of existing Light Emitting Diodes (HBLEDs) have conductor structures (Figure 1) created us-
HBLED designs. In R&D labs, new III-V caused demand to increase significantly. The ing multiple materials. These heterogeneous
materials and phosphors (for white light) are higher efficiencies, longer lifetimes, and an junctions, or heterojunctions, are constructed
being investigated to find those that allow increased assortment of colors available with with multiple III-V materials such as AlGaN.
HBLEDs to be produced cheaply and with this new breed of LED have allowed the de- These structures are designed to optimize
better performance. Major objectives in- vice to expand on its old role as an indicator the generation of photons from the recombi-
clude higher efficiency, more colors, higher lamp and move into more widespread ap- nation of charge. By combining these struc-
current density and optical output, and better plications. Today, LEDs are being used for tures with better light extraction techniques,
packaging with increased cooling capabili- specialty and automotive lighting, medical luminous outputs can range from one hun-
ties. These aims are especially important for equipment, and military systems. There have dred to several thousand mcd.
High Value HBLED Testing April 2004 1
tested still remains small and the test time has a relatively small im-
pact on production throughput.
Test Methodologies
HBLEDs applications and increased processing require a meld-
ing of test strategies and instrumentation. The basic measurement
methodology in most component testing is to apply a current or volt-
age source to the device under test (DUT), and then measure its re-
sponse to that stimulus.
In the case of HBLEDs, the following tests are typically per-
formed:
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