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Has LED lamps and lanterns reliability testing method and cost control - (AddTime - 2013-01-22)

In recent years, due to the rapid development of LED technology, the main performance indicators are greatly improved, at present, the LED device hair efficacy of more than 200 lm/W, industrialization level of 110 ~ 120 lm/W, can be used as a light source in the lighting field application, at present has entered the outdoor landscape lighting, functional lighting, commercial lighting

In recent years, due to the rapid development of LED technology, the main performance indicators are greatly improved, at present, the LED device hair efficacy of more than 200 lm/W, industrialization level of 110 ~ 120 lm/W, can be used as a light source in the lighting field application, at present has entered the outdoor landscape lighting, functional lighting, commercial lighting, etc. In the application process, there are several main technical and cost problems, such as the 200W led Flood light lamps and lanterns of energy efficiency is not high, the led white light color in some lighting situation is not appropriate, the reliability of the led lamps and lanterns is not high, some product life is very short, and the price of led lamps and lanterns at present slant generally higher, these problems to solve and improve further. Industry peers to LED light source reliability and cost problem is more attention, all trying to solve in. This paper will focus on the two problems are relatively detailed description and analysis.

A, 200W led Flood light and lanterns reliability
The 200W led Flood light and lanterns of the classification, performance and reliability, the United States "energy star" has a specific provision [1], reliability indicators, the main provisions 200W led Flood light lamps and lanterns life 35000 hours, in the whole life period colour changes in CIE1976 (u, v) within 0.007. The United States SSL plan specified in the life of white LED devices in the 2010-2015 years for 50000 hours. In 200W led Flood light lamps and lanterns for the life of the general also mentioned 3 ~ 35000 hours.
The above mentioned 200W led Flood light and lanterns life and color keep degree index, from the current view is very high, in fact, a lot of 200W led Flood light and lanterns also can not reach the requirement, because 200W led Flood light and lanterns is the technology involved of the many problems, is very complicated, mainly system reliability problems, including LED chip, packaging device, driving power module, heat dissipation and the reliability of the lamps and lanterns. The following for these problems are analyzed:

1, 200W led Flood light and lanterns reliability related content is introduced
On the analysis of the reliability of 200W led Flood light and lanterns, before LED to the reliability of the basic content, make some introduction to the reliability of the 200W led Flood light and lanterns thorough analysis help.
1) essence failure, dependent failure
LED device failure generally can be divided into two kinds: essential failure and dependent failure. Essential failure refers to the LED chip failure, and divided into electric drift and ion thermal diffusion failure. Dependent failure is composed of encapsulation structure material, process cause, namely encapsulation structure and use of epoxy, silica gel, conductive rubber, phosphor, welding, lead, process, temperature of the factors.

(2) ten degrees law
Some electronic devices in a certain temperature range, the temperature rise every 10 ℃, its main technical indicators down half (or fall quarter). Practice has proved, LED device heat sink temperature in fifty ℃ to 80 ℃, LED life value basic conform to the law of ten degrees. Recently, media reports: LED device temperature every rise by 2 ℃, its life fell by 10%, when the temperature from 63 ℃ to 74 ℃ rise, the average life down 3/4. Because device packaging process different, completely may appear this kind of phenomenon.

(3) the meaning of life
LED life refers to the provisions under the working conditions, the light output power or light attenuation to the initial value of the 70% of working time, and at the same time, color change is kept within 0.007.
LED life meaning is LED products before the failure of the average of the working time, with MTTF to say, it is the most common electronic device reliability parameters.
Reliability test content including reliability screening, environmental test and life test (long-term or short-term). We have discussed here is life test, other project temporary not consider.

(4) long life test
In order to confirm whether the LED lamps and lanterns life 35000 hours, the need for long-term life test, the current practice of basically formed consensus as follows: because GaN base LED device began to output optical power is not stable, so according to the United States ASSIST league rules need electrical aging, 1000 hours after the measured light power or light for the initial value. After 3000 hours and rated current, light measurement (or light power) attenuation to less than 4%, plus current 3000 hours, the light attenuation wants to be less than 8%, again electrify 4000 hours, a total of 10000 hours, the measured light attenuation to less than 14%, namely to light more than 86% of the initial value. Only at this time to prove that ensure LED life up to 35000 hours.

(5) accelerated life test (short-term)
Electronic devices accelerated life test can increase stress (electric power or temperature) test, here is to discuss the way of measuring the temperature stress, calculation of the life is LED average life, namely failure before the average working time. Using this method will greatly shorten the testing time LED life, to prompt improvement, improve the reliability of LED. And temperature stress of the life test method in this paper [2] has been discussed, mainly quotes "amarr Kathy" (yamakoshi) luminous GuanGuang power slow degradation formula, through the degradation coefficient for different accelerated stress temperature LED life test data, then use "Arrhenius" (Arrhenius) equation numerical analytical method to get the normal stress (room temperature) LED the average life span, referred to as "degradation coefficient analysis method", this method USES three different stress temperature is 165 ℃, 175 ℃ and 185 ℃, the measured data to calculate the average life at room temperature consistency. This test method is reliable, at present already in this research, drafting "semiconductor light-emitting diode life test method" standard, the domestic some enterprise also development accelerated life test equipment instrument.

2, LED device reliability
LED device reliability depends mainly on two parts: epitaxial chip and device packaging performance quality, these two failure mechanism is completely different, are discussed.

(1) epitaxial chip failure
Influence epitaxial chip performance and quality, mainly and epitaxial layer especially p-n junction part of the dislocation and deficiencies of the number and distribution of metal and semiconductor layer quality, and epitaxial layer and the chip surface and surrounding contamination caused by ion number and related conditions. Chip in the heating power up conditions, will gradually cause dislocation, defect, surface and surrounding produce electric drift and ion thermal diffusion, make the chip failure, it is the essence of what is said above failure. To improve epitaxial chip reliability index, fundamentally to reduce epitaxial growth process of dislocation and defect and epitaxial layer surface and surrounding contamination, improve the metal and semiconductor quality, so as to improve the service life of the time. There are reports of bare chip for accelerated life test and calculate, general life 100000 hours, or even hundreds of thousands of hours.

(2) the device package failure
Reports say: LED device failure about 70% above is caused by the package, so packaging technology for LED device is the key technology. The LED device packaging technology in this paper [3], [4] in detail, so in this paper not only a brief analysis about LED device package reliability problems. LED package failure is dependent failure, its reason is very complicated, main source has three parts:

First, packaging material not beautiful causes, such as epoxy, silica gel, phosphor, base, conductive rubber, solid crystal materials etc. Second, the packaging structure design is not reasonable, such as material not matching, produce stress, cause fracture, open circuit, etc. Thirdly, encapsulation process not appropriate, such as loading piece, bonding, dispensing technology, curing temperature and time, etc. In order to improve the device package reliability, first in material selection to strictly control the quality of materials, in the packaging structure in addition to consider the efficiency of light and heat outside, consider a variety of materials together ReZhang when matching problem. In the packaging process, want to strictly control each procedure of the process, as far as possible the automation equipment, ensure the process consistency and repeatability, ensure the LED device performance and reliability.