determination on the coefficient of thermal expansion in high-power ingan-based light-emitting diodes by optical coherence tomography

by:Getian     2020-08-07
Coefficient of thermal expansion (CTE)
Is a physical quantity indicating the thermal expansion value of the material at the time of heating.
For advanced thermal management, accurate and immediate determination of CTE of packaging materials becomes more and more important because of the highpower lighting-
LEDs (LEDs)
An increase is currently under way.
In this study, we used optical coherent tomography (OCT)
InGaN of the measured CTE-based (λu2009=u2009450u2009nm)high-
Power LED packaged in polystyrene resin.
The distance between the various interfaces of the October image was observed and recorded to derive the instantaneous CTE of the packaged LED under different injection currents.
The LED junction temperature under different injection current is established by the forward voltage method.
Therefore, the instantaneous CTE of the measured polystyrene resin is from 5.
The status quo of the 86 u2009 × u2009 10−5 u2009 °C −1 pair.
At 10 × 10-5 CC-1 at 25-25 °c in the junction temperature range, and present an even distribution in the scan area 200 u2009 × 200 μm on October.
Most importantly, this work validates the assumption that October could provide an alternative approach to directly and non-destructive determination of the spatial resolution of CTE for encapsulated LED devices, which is better than conventional CTE Measurement techniquesThe lighting-LEDs (LED)
Is a revolutionary, compact, and energy-
Saving light sources.
It can directly convert current into radiation emission through the luminous effect, which is widely used in many commercial applications such as LCD panel backlight, optical communication and ordinary lighting.
In recent years, with the rapid growth of the lighting market, people\'s demand for lighting equipment is getting higher and higher.
The Power led is higher than ever before.
Generally speaking, high
Power LED devices include LED chips mounted on a ceramic base for mechanical stability and low thermal resistance for lead connections or electrical interconnect layers that connect the anode/cathode on the LED chip, as well as the packaging resin to protect the LED chip below.
In a high-
One of the most challenging issues with power LED devices is finding the right packaging material for reliable thermal management.
The large amount of heat generated around the LED chip connection area is transferred to the entire device, resulting in thermal expansion of packaging materials, especially the filling glue resin.
This will inevitably lead to strain due to the large difference in the degree of expansion between the LED chip and the filling glue resin, resulting in reliability problems and hindering high-
Automotive forward lighting, color sequential projection display and power LED devices in urban environmental engineering.
Therefore, proper heat pipe management and reliable inspection of packaging materials must be carried out to ensure high optical output and high maintenance time
Power LED equipment.
Coefficient of thermal expansion (CTE)
Is a physical quantity indicating the thermal expansion value of the material at the time of heating.
When the LED works at a high level
Temperature stress has become a key problem under current conditions.
Thermal stress caused by CTE mismatch between packaging materials and LED chips (
Or between substrate material and ceramic base)
Causes lead and solder ball fatigue on the LED chip and causes the encapsulated LED device to strip or crack.
These problems limit the reliability and stability of LED devices.
Therefore, accurate and immediate determination of CTE for high CTE in advanced thermal management
Power LED equipment is very important. The time-domain OCT (TD-OCT)
Technology was first invented by D. Huang .
It was used in biomedical applications in 1991.
Based on the interference structure with optical path modulation, the depth-
Resolved information.
However, the system sensitivity and imaging speed of TD-Limited in October. Hence, Fourier-domain OCT (FD-OCT)
Including spectrumdomain OCT (SD-OCT)and swept-source OCT (SS-OCT)
Developed to overcome the limitations of TD-OCT. Compared to TD-OCT, FD-
October can find the depth-
In the absence of optical path modulation, the information is distinguished in the interferometer.
Currently, SD-OCT and SS-
In October, the system can provide frame rates of up to hundreds of frames per second, and the system sensitivity is greater than 100db.
In the past decade, October has served as a provider of non-invasive, high-speed anddimensional (3D)
The construction is mainly in the field of biological specimens, such as digestive medicine, heart disease, dermatology, oral mucosa, ophthalmology, etc.
Usually, the high resolution of 1-10 μm can be provided in the axial and transverse direction in October, and can be reached ~ Penetration depth of 2mm.
Although widely used in the above areas in October
When it comes to biomedical applications, few studies have used October as an inspection tool for the semiconductor industry.
Through the inspection of the October 3D image, the spatial distribution and changes of the sample structure can be identified, so that optical inspection can be carried out on a variety of industrial products.
In this study, we studied the temperature.
Dependency and depth
Determine the October resolution image of InGaN-instant CTE for packaging materialsbased (λu2009=u2009450u2009nm)high-power LEDs.
Typically, CTE of the material is measured using a thermal mechanical analyzer (TMA)
, It provides a single value of CTE based on a specific material experiencing a uniform temperature change.
After cooling to room temperature, the change of material length is measured to determine the CTE.
However, it is difficult for CTE that encapsulates LED devices to be determined by the traditional method of using TMA, because it contains many different components (materials)
This must be measured at the same time.
Therefore, it is important to develop an inspection tool that can provide the filling glue material to measure the spatial distribution of CTE, as it may have a strong connection with the stability and reliability of LED equipment.
As revealed in this paper, October can not only check the changes in CTE of packaged LED devices, but also reconstruct the measured CTE value into two-dimensional (2D)
Spatial distribution on a given chip area (200u2009×u2009200u2009μm).
The distance between the various interfaces in the October image was observed and recorded to derive the instantaneous CTE of packaged LED devices with different injection currents.
The relationship between junction temperature and injection current is established by the forward voltage method.
The results show that the instantaneous CTE of the measured polystyrene resin is from 5.
The status quo of the situation of 86 u2009 × u2009 10 u2009 C pairs.
In the October scan area of 10 × 200 μm at 25-25 °c in the junction temperature range, a uniform distribution is shown.
Most importantly, this work validates the assumption that October could provide an alternative approach to directly and non-destructive determination of the spatial resolution of CTE for encapsulated LED devices, which is better than conventional CTE Measurement techniques
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