Experimental investigation of a PCM-HP heat sink on its thermal performance and anti-thermal-shock capacity for high-power LEDs

A new type application specific light emitting diode(LED) package(ASLP) with freeform polycarbonate lens for street lighting is developed,whose manufacturing processes are compatible with a typical LED packaging processThe reliability test methods and failure criterions from different vendors are reviewed and comparedIt is found that test methods and failure criterions are quite differentThe rapid reliability assessment standards are urgently needed for the LED industry85℃/85 RH with 700 mA is used to test our LED modules with three other vendors for 1000 h,showing no visible degradation in optical performance for our modules,with two other vendors showing significant degradationSome failure analysis methods such as C-SAM,Nano X-ray CT and optical microscope are used for LED packagesSome failure mechanisms such as delaminations and cracks are detected in the LED packages after the accelerated reliability testingThe finite element simulation method is helpful for the failure analysis and design of the reliability of the LED packagingOne example is used to show one currently used module in industry is vulnerable and may not easily pass the harsh thermal cycle testing

Reliability test and failure analysis of high power LED packages

Surface-mount device light emitting diode (SMD-LED) is characterized by small size, wide viewing angle and light weight It becomes the main package type of LED gradually The traditional visual inspection is likely to cause misrecognition due to personal subjectivity and different defect recognition standards Therefore, this study develops an automatic SMD-LED defect detection system, which is characterized by non-contact inspection, defect recognition standardization and upgrading product quality It detects the common and important defects in LED package components, including missing component, no chip, wire shift and foreign material In this study the gray scale characteristic of histogram is used as the rapid sieving analysis indicator of missing component defect, and then the component and solder joint are positioned by using fast normalized cross-correlation, and the maximum correlation coefficient value is used as judgment indicator of no chip defect In order to overcome the difficult identification as the weld line is subject to light rays, the improved Michelson-like contrast (MLC) enhancement is proposed, and the segmentation threshold is selected by entropy information to segment the weld line successfully Furthermore, in order to overcome the effect of the tolerance of component size and internal electrode and unfixed weld line position resulted from lead frame process on foreign material detection result, the multiscale adaptive Fourier analysis (MAFA) is proposed in the concept of texture anomaly detection for foreign material defect detection The result proves that the proposed method can segment the defect effectively and correctly compared with the phase-only transform (PHOT) and multiscale phase-only transform (MPHOT), and it can be used in other fields of texture anomaly detection The overall recognition rate of this system is 9825%, contributing to the large market demand and high component quality of LED industry

Automated optical inspection system for surface mount device light emitting diodes

Light-emitting diodes (LEDs) are considered an ideal substitute for low-efficiency traditional light sources with broad applications in all scientific disciplines. For the past recent years, several developments and innovations have been reported that strengthen the reliability and thermal efficiency of speeding up the LED packaging process. This paper reviews and summarizes various changes and improvements made to die attachment, wire bonding, phosphor coating, encapsulation processes, and thermal management. It also covers the reasons for choosing the materials at every stage of LED packaging. Moreover, the review reveals a broad scope for future research, particularly on thermal management by nanoparticles and improved light intensity by different synthesized phosphors.

Die attachment, wire bonding, and encapsulation process in LED packaging: A review

Reliability is essential for large-scale applications of high-power light-emitting diode (LED) devices, modules, and systems for general illumination. In this paper, the reliability of a novel application-specific LED package (ASLP) is investigated by thermal shock testing, failure analysis, and fluid-solid coupling thermo-mechanical simulation. The reliability of the ASLP modules was validated with a dual-bath liquid thermal shock testing from 233 to 398 K. The non-destructive failure analysis was conducted to the catastrophic failure ASLP samples by fluorescent penetrant inspection. The delaminations at the interfaces within the ASLP module were detected. The failure mechanisms were identified by digital optical microscopy and field emission scanning electron microscope inspection after the decapsulation. The experimental results show that fracture failure occurs at the wedge joint of the bonding wire, which leads to the catastrophic failure of the ASLP module. The stress and strain behaviors of the ASLP module, especially the bonding wire under thermal shock loading, were analyzed through thermo-mechanical modeling with the nonlinear time- and temperature-dependent material properties. Significant thermal gradient within the ASLP module during the thermal shock testing was taken into consideration by the fluid-solid coupling transient thermal transfer analysis. The effects of the delaminations detected by the fluorescent penetrant inspection on the reliability of the bonding wire were also examined. It is found the delaminations existing at the interfaces within the ASLP module induce significant plastic strain to the wedge joint and results in fracture failure. The results from the numerical simulation can make a good prediction of the failure mechanism of the ASLP modules under thermal shock loading.

Study on the Reliability of Application-Specific LED Package by Thermal Shock Testing, Failure Analysis, and Fluid–Solid Coupling Thermo-Mechanical Simulation

High power light emitting diodes (LEDs) have begun to play an important role in many illumination applications due to their excellent performance in terms of high efficiency, low power consumption, high reliability and long life. With the rapid development of the LED industry, the reliability is becoming essential for the large scale applications of LED devices, modules and systems. Generally the thermal cycling and thermal shock test are conducted for validation the reliability performance and exposure the potential design problems during the new packaging development. In this paper, the reliability performance of the typically LED package is evaluated by the accelerated stress test under thermal cycling and thermal shock conditions. The optical degradation and electrical parameters variation of the LED package are monitored during the experiments. The thermo-mechanical responses of the LED package under thermal cycling and thermal shock loadings are investigated by sequential coupling thermo-mechanical finite element modeling interoperated with nonlinear time and temperature dependence materials properties. The stress and strain behavior of the LED package especially of the gold wire is examined. The effects of thermal gradient in the LED package during the thermal cycling and thermal shock tests and the time and temperature dependent materials property of the silicone on the reliability performance of the LED package are investigated. The physical mechanisms of failure of LED package samples are analyzed by decapulation and optical microscopic detection method. These efforts are helpful for design of reliability for the high power LED packaging development.

Comparison of LED package reliability under thermal cycling and thermal shock conditions by experimental testing and finite element simulation

As the most promising candidate for the realization of high-efficiency light sources for general lighting, the high power lighting emitting diodes(HP-LEDs) still have reliability issues that hinder the large scale application of LED devices. Nowadays, the reliability is becoming an essential barrier for LED devices to substitute the traditional light sources. Failure analysis is one of the key approaches to improving the reliability of LED products. In this paper, three techniques, namely fluorescent penetrant inspection (FPI), chemical decapsulation and Nano-CT scanning, which are usually applied in other fields, are proposed as major failure analysis tools. Both of their advantages and disadvantages are also recommended, and then combining fluorescent penetrant inspection (FPI) and chemical decapsulation with field scanning electron microscope (FSEM) to analyze the failure modes of one LED sample undergoing 200 thermal shock cycles, and find the fracture of gold wire is attributed to excessive tensile stress of shrink of silicone encapsulations.

Feng Jiao

Papers

Study on the Reliability of Application-Specific LED Package by Thermal Shock Testing, Failure Analysis, and Fluid–Solid Coupling Thermo-Mechanical Simulation

Comparison of LED package reliability under thermal cycling and thermal shock conditions by experimental testing and finite element simulation

Failure analysis techniques for high power light emitting diodes