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Yang S.-C.,National Chiao Tung University | Lin P.,National Chiao Tung University | Wang C.-P.,Electronics and Optoelectronics Research Laboratories | Huang S.B.,Electronics and Optoelectronics Research Laboratories | And 4 more authors.
Microelectronics Reliability | Year: 2010

The investigation explores the factors that influence the long-term performance of high-power 1 W white light emitting diodes (LEDs). LEDs underwent an aging test in which they were exposed to various temperatures and electrical currents, to identify both their degradation mechanisms and the limitations of the LED chip and package materials. The degradation rates of luminous flux increased with electrical and thermal stresses. High electric stress induced surface and bulk defects in the LED chip during short-term aging, which rapidly increased the leakage current. Yellowing and cracking of the encapsulating lens were also important in package degradation at 0.7 A/85 °C and 0.7 A/55 °C. This degradation reduced the light extraction efficiency to an extent that is strongly related to junction temperature and the period of aging. Junction temperatures were measured at various stresses to determine the thermal contribution and the degradation mechanisms. The results provided a complete understanding of the degradation mechanisms of both chip and package, which is useful in designing highly reliable and long-lifetime LEDs. © 2010 Elsevier Ltd. All rights reserved.


Yang S.C.,National Chiao Tung University | Pang L.,National Chiao Tung University | Fu H.K.,Electronics and Optoelectronics Research Laboratories | Wang C.P.,Electronics and Optoelectronics Research Laboratories | And 4 more authors.
Japanese Journal of Applied Physics | Year: 2010

The capability of high-power nitride-based light-emitting diodes (HPLED) to withstand electrostatic discharge (ESD) is very important key index due to the horizontal structure of the insulating property of the sapphire substrate. Accordingly, the investigation of ESD failure mechanisms is a beneficial topic. However, it is difficult to real-time monitor the damage caused by the ESD stress because it occurred in a very short period. Before the series ESD stress, atomic force microcopy (AFM) and conductive AFM (C-AFM) were applied to explore the correlation between surface morphology and electrical properties of LED chips. Furthermore, after the series ESD stress, transmission electron microscopy (TEM) was used to investigate the failure modes and compare to the distribution of the surface current observed by C-AFM. These findings suggest that the V-shaped defect and surface morphology are strong correlate to the endurance of ESD stress. © 2010 The Japan Society of Applied Physics.


Chen T.T.,Electronics and Optoelectronics Research Laboratories | Wang C.P.,Electronics and Optoelectronics Research Laboratories | Fu H.K.,Electronics and Optoelectronics Research Laboratories | Chou P.T.,Electronics and Optoelectronics Research Laboratories | And 2 more authors.
Optics Express | Year: 2014

This study of the optoelectronic properties of blue light-emitting diodes under direct current stress. It is found that the electroluminescence intensity increases with duration of stress, and the efficiency droop curves illustrated that the peak-efficiency and the peak-efficiency-current increases and decreases, respectively. We hypothesize that these behaviors mainly result from the increased internal quantum efficiency. © 2014 Optical Society of America.


Wang C.-P.,Electronics and Optoelectronics Research Laboratories | Chen T.-T.,Electronics and Optoelectronics Research Laboratories | Fu H.-K.,Electronics and Optoelectronics Research Laboratories | Chang T.-L.,National Taiwan Normal University | And 2 more authors.
Microelectronics Reliability | Year: 2012

The purpose of this study is to investigate the thermal behavior at the die-attached interfaces of flip-chip GaN high-power light emitting diodes (LEDs) using a combination of theoretical and experimental analyses. The results indicate that contact thermal resistance increased dramatically at the die-attached interfaces with aging time and stress, degrading the luminous flux. The junction temperature and thermal uniformity of the flip-chip structure both strongly depend on the arrangement of gold bumps. Local hot spots effectively reduce light output under high electric and thermal stress, influencing the long-term performance of the LED device. The results were validated using finite element analysis and in experiments using an infrared and an emission microscope. A two-step thermal transient degradation mode was identified under various aging stresses. A simulation further optimized the bump configuration that was associated to yield a low junction temperature and high temperature uniformity of the LED chip. Accordingly, the results are helpful in enhancing the performance and reliability of high-power LEDs. © 2011 Elsevier Ltd. All rights reserved.


Lu S.-T.,Electronics and Optoelectronics Research Laboratories | Lu S.-T.,National Tsing Hua University | Lin Y.-M.,Electronics and Optoelectronics Research Laboratories | Chuang C.-C.,Electronics and Optoelectronics Research Laboratories | And 3 more authors.
IEEE Transactions on Components, Packaging and Manufacturing Technology | Year: 2011

The demand for high-density electronic applications is growing. This work develops a novel chip-on-flex (COF) package with sidewall-insulated Au-coated polyimide (PI) compliant-bumps. A double-layer anisotropic conductive adhesive (ACA) material that meets the assembly requirement is adopted for the ultra-fine pitch interconnects. A process for manufacturing 20-μm pitch compliant-bumps is proposed for ACA-bonded COF packages. The double-layer ACA consists of an ACA layer with a diameter of 2.8 μm conductive particles and an NCA layer as an interlayer to bind a silicon chip with a flexible substrate. The bonding accuracy for ultra-fine pitch is determined using X-rays. To evaluate the quality of bonding, the electrical insulation is tested and the contact resistance of the daisy chain with 606 input/output (I/O) around the periphery of the chip is measured. The double-layer ACA material is assembled at different bonding temperatures to study the effects of bonding temperature on the interface adhesion using differential scanning calorimetry (DSC) and a 90° peeling test. The reliability of the fabricated COF interconnects is also evaluated by performing an 85°C/85% relative humidity thermal humidity storage test (RH THST) for 1000 h and a-55°C ~ 125°C thermal cycling test (TCT) for 1000 cycles. The interfaces between the silicon chip and the substrate of the failed samples in the reliability tests are then observed using the cross-sectional scanning electron microscopy (SEM). The compliant-bump-bonded samples with the double-layer ACA provide their excellent electrical insulation performance even at a joint space of 5 μm whereas the Au-bump samples have a short-circuiting rate of more than 50%. Notably, the contact resistance also remains stable and varies by under 3% in both the RH THST for 1000 h and the TCT for 1000 cycles. The presented results show the reliable bonding quality and stable contact resistance of the COF package that is bonded with the compliant-bump structure using the double-layer ACA, indicating its great potential for use in ultra-fine pitch applications. © 2011-2012 IEEE.


Lu S.-T.,National Tsing Hua University | Lu S.-T.,Electronics and Optoelectronics Research Laboratories | Chen W.-H.,National Tsing Hua University | Chen W.-H.,National Applied Research Laboratories
IEEE Transactions on Advanced Packaging | Year: 2010

The need for flexible interconnects in advanced applications in consumer electronic products is increasing rapidly. The reliability and flexibility of ultra-thin chip-on-flex (UTCOF) interconnects formed using anisotropic conductive adhesive (ACA) are thus investigated. Two films of ACA materials, namely ACA-P and ACA-F, are assembled at different bonding temperatures to study the effect of temperature on the adhesion at the substrate-adhesive and adhesive-chip interfaces using differential scanning calorimetry (DSC) and a 90° peeling test. The contact resistance of a daisy chain with 188 input/output (I/O) is measured to examine the quality of bonding through dummy test samples with an 80-μm pitch. The reliability of the fabricated UTCOF interconnects bonded via selected ACA joints is evaluated by performing an 85 °C/85% RH thermal humidity storage test (THST) for 1000 h, and their flexibility is evaluated in static bending and four-point bending tests. The interfaces between the ultra-thin silicon chip and the substrate of failed samples in the THST and four-point bending testing are then investigated by scanning electron microscopy (SEM), which is utilized to obtain cross-sectional images. Finite element analysis is also conducted to elucidate the failure mechanism of the UTCOF interconnects in the four-point bending test. The averaged maximum allowable deflections of the fabricated UTCOF interconnects with ACA-P and ACA-F materials are 26% and 168%, respectively, higher than those of the COF interconnects with a chip thickness of 670 μm. Moreover, the contact resistance remains stable, varying by less than 10%, in the static bending test with a bending radius of 30 mm. According to the results thus obtained, give the appropriate choice of an ACA material and the optimal curing conditions, the UTCOF interconnects with ACA joints reliably serve as flexible interconnects for use in consumer electronic products. © 2006 IEEE.


Cheng T.-H.,National Tsing Hua University | Cheng H.-C.,Feng Chia University | Chen W.-H.,National Tsing Hua University | Huang H.-Y.,Electronics and Optoelectronics Research Laboratories | Chang T.-C.,Electronics and Optoelectronics Research Laboratories
2014 International Conference on Electronics Packaging, ICEP 2014 | Year: 2014

In the study, the lead-free solder joint reliability and fatigue failure mechanism of an ultra-fine-pitch 2.5D multi-chip module (MCM) on board is predicted under board-level drop impact test according to JEDEC board-level test specification. To achieve the goal, the Input-G method incorporated with finite element (FE) analysis is applied to predict the transient dynamic responses of the 2.5D MCM on board. To demonstrate the effectiveness of the proposed FE model, the calculated results are compared with those obtained from experimental testing. The experimental drop test is performed on the 2.5D MCM on board with or without underfill using a JEDEC-compliant drop tester, and the associated failure mechanism is examined by way of an optical microscope. At last, the dependences of the allowed shock pulse tolerances in JEDEC drop test standard and also underfill are assessed on the dynamic behavior of the solder joints under drop impact.


Hsiao T.-C.,Electronics and Optoelectronics Research Laboratories | Hsiao T.-C.,National Tsing Hua University | Wang P.-H.,National Tsing Hua University | Fan C.-T.,National Tsing Hua University | And 2 more authors.
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2011

Recently, photoacoustic imaging has been intensively studied for blood vessel imaging, and shown its capability of revealing vascular features suggestive of malignancy of breast cancer. In this study, we explore the feasibility of visualization of micro-calcifications using photoacoustic imaging. Breast micro-calcification is also known as one of the most important indicators for early breast cancer detection. The non-ionizing radiation and speckle free nature of photoacoustic imaging overcomes the drawbacks of current diagnostic tools - X-ray mammography and ultrasound imaging, respectively. We employed a 10-MHz photoacoustic imaging system to verify our idea. A sliced chicken breast phantom with granulated calcium hydroxyapatite (HA) - major chemical composition of the breast calcification associated with malignant breast cancers - embedded was imaged. With the near infared (NIR) laser excitation, it is shown that the distribution of ∼ 500 μm HAs can be clearly imaged. In addition, photoacoustic signals from HAs rivals those of blood given an optimal NIR wavelength. In summary, photoacoustic imaging shows its promise for breast micro-calcification detection. Moreover, fusion of the photoacoustic and ultrasound images can reveal the location and distribution of micro-calcifications within anatomical landmarks of the breast tissue, which is clinically useful for biopsy and diagnosis of breast cancer staging. © 2011 SPIE.


Fu H.-K.,Electronics and Optoelectronics Research Laboratories | Lin C.-W.,Electronics and Optoelectronics Research Laboratories | Chen T.-T.,Electronics and Optoelectronics Research Laboratories | Chen C.-L.,Electronics and Optoelectronics Research Laboratories | And 2 more authors.
Microelectronics Reliability | Year: 2012

Environmental concerns have led to the popularity of solid stating lighting, in which a high quality white light source depends on the stable property of light emitting diode. This study examines a white-light high-power light-emitting diode composed of a blue chip and yellow phosphor. A white-light light-emitting diode can be divided into four parts - a blue chip, yellow phosphor, transparent silicone, and reflector. In a transient experiment, the wavelength shift of the blue chip markedly affects the conversion efficiency of yellow phosphor, causing white-light deviation, especially in the sharp variation region of absorption of yellow phosphor. A series of short-term experiments was conducted to identify the mechanisms of color deviation between yellow phosphor and transparent silicone. The robustness of commercial phosphor and silicone was much stronger than expected. In addition to a yellowed reflector and blue chip degradation, several combinations of degradation mechanisms between yellow phosphor and transparent silicone. In a long-term experiment, damaged silicon confines blue light resulting in warm white light. Two suggestions are provided to obtain white-light light-emitting diodes with high color reliability. © 2011 Elsevier Ltd. All rights reserved.


Fu H.-K.,Electronics and Optoelectronics Research Laboratories | Wang C.-P.,Electronics and Optoelectronics Research Laboratories | Chiang H.-C.,Electronics and Optoelectronics Research Laboratories | Chen T.-T.,Electronics and Optoelectronics Research Laboratories | And 2 more authors.
Microelectronics Reliability | Year: 2013

For high-power light-emitting diodes, heat management and reliability are important issues. The reliability and long lifetime of solid state lighting are especially essential in the high temperature applications, such as street lighting and automotive lighting. Because of the characteristics of semiconductor, the electrical property of light-emitting diodes is varying with operating temperature. Then, the alternation of electrical property changes the heating power and operating temperature of light-emitting diodes. This is a mutual interaction between electrical property and operating temperature, until they reach the steady state. In this paper, we designed experiments and calculation to optimize the simulation of temperature distribution of light-emitting diode module. With forward voltage measurement and thermal transient testing of light-emitting diodes, we obtained the initial values of simulations. The infrared camera captured the thermal images to verify the simulation results. With this method, we can effectively evaluate the temperature distribution of light-emitting diode module. © 2012 Elsevier Ltd. All rights reserved.

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