10.2 The LED Aging Test and an Aging Mechanism
217
chaos. There are five major mechanical vibration tests: sweep vibration, fixed vibration, resonance, vibration fatigue, and random vibration. According to International
Electro-technical Commission (IEC) standards, the full amplitude is 1.5 mm under
the test frequency of 20 ~ 100 Hz. The peak value of the acceleration is about 50 g
under the test frequency of 100 ~ 2 kHz. The experiment can be performed according
to JESD22 B-103. Performance test is required before and after the VVF test.
(2) Salt spray aging test
The salt spray test is performed to evaluate the corrosion resistance of exposed parts
of the component under salt spray, humidity and hot environment. The salt spray
test includes natural environment exposure test and artificial accelerated salt spray
environment test. The artificial salt spray test includes neutral salt spray, acetate salt
spray, copper-salt-accelerated acetate spray, and alternating salt spray. The condition
and method of the salt spray test is described in more detail in the GB/T 10,125–1997
national standard.
(3) Gas environment accelerated test
The atmosphere contains corrosive components and corrosive factors such as oxygen,
humidity, temperature changes and pollutants. Therefore, under the influence of the
atmosphere, free radicals and peroxides will be generated in the polymerized organics
of packaged LEDs, which may destroy the organics. Under a certain temperature and
humidity, an accelerated corrosion of packaged LEDs or packaging materials by H 2 S,
SO 2 , NO 2 , Cl 2 and other harmful gases can be used to evaluate the resistance to gas
corrosion of the device. The condition and method of the gas environment accelerated
test and mixed gas test are described in more detail in the IEC 60,068 standard.
(4) Temperature and light exposure (TL) test
Organic decomposition reactions like photo-oxidation and photo-hydrolysis can be
caused by sunlight, short wavelength radiation from the device itself, or other random
light sources. Thus, the polymer of packaged LEDs will be destroyed. The light
conversion efficiency and transparency of the resin-based polymer commonly used
in packaged LEDs will be reduced by short wavelength irradiation, which is the result
of the aging of high-molecular materials. After aging, the high-molecular materials
often suffer from surface chalking, discoloration, blistering, cracking, and shedding.
Therefore, a basis for improving device reliability can be provided by the aging test of
light conversion materials and light transmitting materials by performing temperature
and light tests on LEDs. An alternative wavelength of 445 ± 5 nm is used in the TL
test, while the irradiation level is 350 ~ 1000 mW/cm
2 . The test period is 1000 h
if the test temperature is higher than 20 °C of the operating temperature and 10 °C
below the glass transition temperature. If the operating temperature is 20 °C above
the temperature of 10 °C below the glass transition temperature, the temperature of
10 °C below the glass transition temperature should be chosen as the test temperature.
The material is considered to be failed when the light transmission efficiency or light
conversion efficiency is reduced by 10%.
217
chaos. There are five major mechanical vibration tests: sweep vibration, fixed vibration, resonance, vibration fatigue, and random vibration. According to International
Electro-technical Commission (IEC) standards, the full amplitude is 1.5 mm under
the test frequency of 20 ~ 100 Hz. The peak value of the acceleration is about 50 g
under the test frequency of 100 ~ 2 kHz. The experiment can be performed according
to JESD22 B-103. Performance test is required before and after the VVF test.
(2) Salt spray aging test
The salt spray test is performed to evaluate the corrosion resistance of exposed parts
of the component under salt spray, humidity and hot environment. The salt spray
test includes natural environment exposure test and artificial accelerated salt spray
environment test. The artificial salt spray test includes neutral salt spray, acetate salt
spray, copper-salt-accelerated acetate spray, and alternating salt spray. The condition
and method of the salt spray test is described in more detail in the GB/T 10,125–1997
national standard.
(3) Gas environment accelerated test
The atmosphere contains corrosive components and corrosive factors such as oxygen,
humidity, temperature changes and pollutants. Therefore, under the influence of the
atmosphere, free radicals and peroxides will be generated in the polymerized organics
of packaged LEDs, which may destroy the organics. Under a certain temperature and
humidity, an accelerated corrosion of packaged LEDs or packaging materials by H 2 S,
SO 2 , NO 2 , Cl 2 and other harmful gases can be used to evaluate the resistance to gas
corrosion of the device. The condition and method of the gas environment accelerated
test and mixed gas test are described in more detail in the IEC 60,068 standard.
(4) Temperature and light exposure (TL) test
Organic decomposition reactions like photo-oxidation and photo-hydrolysis can be
caused by sunlight, short wavelength radiation from the device itself, or other random
light sources. Thus, the polymer of packaged LEDs will be destroyed. The light
conversion efficiency and transparency of the resin-based polymer commonly used
in packaged LEDs will be reduced by short wavelength irradiation, which is the result
of the aging of high-molecular materials. After aging, the high-molecular materials
often suffer from surface chalking, discoloration, blistering, cracking, and shedding.
Therefore, a basis for improving device reliability can be provided by the aging test of
light conversion materials and light transmitting materials by performing temperature
and light tests on LEDs. An alternative wavelength of 445 ± 5 nm is used in the TL
test, while the irradiation level is 350 ~ 1000 mW/cm
2 . The test period is 1000 h
if the test temperature is higher than 20 °C of the operating temperature and 10 °C
below the glass transition temperature. If the operating temperature is 20 °C above
the temperature of 10 °C below the glass transition temperature, the temperature of
10 °C below the glass transition temperature should be chosen as the test temperature.
The material is considered to be failed when the light transmission efficiency or light
conversion efficiency is reduced by 10%.