Due to the TCE(thermal coefficient of expansion) mismatch, power semiconductor suffers from bonding crack and delamination due to large temperature swing. For verification of power semiconductor reliability, power cycling test is conducted. Junction temperature evaluation is most important factor which determines validity of the acceleration life test. In this paper, conceptual methodology how to evaluate the real-time junction temperature during the power cycling acceleration test was introduced. Junction temperature is evaluated by forward voltage drop measurement, and the junction temperature is real-time monitored during the power cycling test. Proposed real-time junction temperature monitoring technology was effective for the power cycling test control, and it is expected to be very effective for various applications.
A ceramic substrate must not only have an excellent thermal performance but also be thin, since the electronic devices have to become thin and small in the electronics industry of the next generation. In this manuscript, a thin ceramic substrate (thickness: 30-70 µm) is reported for the next generation ceramic substrate. It is fabricated by a new process [granule spray in vacuum (GSV)] which is a room temperature process. For the thin ceramic substrates, AlN GSV films are deposited on Al substrates and their electric/thermal properties are compared to those of the commercial ceramic substrates. The thermal resistance is significantly reduced by using AlN GSV films instead of AlN bulk-ceramics in thermal management systems. It is due to the removal of a thermal interface material which has low thermal conductivity. In particular, the dielectric strengths of AlN GSV films are much higher than those of AlN bulk-ceramics which are commercialized, approximately 5 times. Therefore, it can be expected that this GSV film is a next generation substrate in thermal management systems for the high power application.
To estimate influence of silicone encapsulant for ceramic LED package, we prepared silicone samples and ceramic LED packages used encapsulant as the same silicone with neither bonding adhesive nor phosphor. Also, a test jig was designed for high temperature operational life (HTOL) test on ceramic LED packages. The test jig made ceramic LED packages luminous, and was able to guide the light from ceramic LED packages to silicone samples. And then, thermal and optical stress tests on silicone samples were performed with HTOL test on ceramic LED packages in three different temperatures to compare the transmittance of the silicone samples according to the thermal and optical stress from ceramic LED packages. Transmittance of silicone sample and luminous flux of ceramic LED package were measured every 250 hours by UV-VIS spectrophotometer and integrating sphere, respectively. As results, more transmittance variations at 300~400 nm were inspected in silicone samples tested by thermal and optical stresses than by only thermal stress. And, the difference of transmittance characteristics was analyzed to find out how the silicone samples had changed during thermal and optical stress test with Raman analysis. In addition, the luminous flux of ceramic LED package was also changed during HTOL test according to transmittance variations in silicone samples.
A precise monitoring on the junction temperature of the light-emitting diode (LED) packages during a lifetime tests is very helpful to make a diagnosis of their quality change and to analyse the optical degradation. We proposed a new model for internal quantum efficiency (IQE) of the LED packages as a function of the junction temperature and developed an in-situ IQE measurement system for an investigation of the optical degradation mechanism in the LED packages. A lifetime test for 2,500 hours had been carried out with in-situ monitoring on the relative optical power and the sub-threshold leakage current. In addition, we had measured the junction temperature and the IQE as a tool for the degradation analysis of the LED packages. No change in the IQE and the leakage current throughout the lifetime test has been observed although there was a 10% optical degradation of the LED package.
We achieved the junction to air thermal resistance as low as 13 [K/W] and the enhanced lifetime (MTTF) estimated over 50,000 hours using a thermal-via structure in LTCC-based LED packages. Exponential decay of brightness in the LED packages was assumed and Arrehenius model as a life-stress model was used to analyze the lifetime of the LED packages.
We present 660-nm GaInP-AlGaInP ridge multiple-quantum-well laser diodes (LDs) reliably operating at high output power over 200 mW at 70/spl deg/C not showing unstable higher order lateral modes owing to an adoption of a dry etching method instead of a conventional chemical wet etching for realizing steep ridge sidewalls. Employing an optimized two-step n-cladding layer LDs produced very narrow horizontal and vertical beam divergence angles of 8.6/spl deg/ and 15.3/spl deg/, respectively. To the best of our knowledge, this vertical beam divergence angle is the lowest value ever reported in high-power 660-nm LDs operating over 200 mW and is expected to play an important role in minimizing the coupling loss between LD and passive optical components in digital versatile disc system.
Generally, reliability concerns of LED lighting system were focused on the degradation of GaN LED chips. But in actual applications, some other types of degradation are occasionally reported. One of the major reliability issues is sulfur originated corrosion of lead frame. Influence by corrosion, mechanism of corrosion, corrosive tendency and methodology to evaluate quantitative corrosion was considered during the study.
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