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The traditional cup-shaped LED packaged with epoxy molding compound materials (EMC-LED) and chip-scale packaged LED (CSP-LED) were prepared and analyzed in this article. It is found that high temperature can result in the spectrum red shift and the photoelectric performance degradation for these LEDs due to the degradation of chip and packaging materials. Compared with EMC-LED, the CSP-LED device has a lower thermal resistance of 3.31 °C/W due to the shorter thermal dissipation path and has better stability under the different temperature and drive current conditions. All the simulation results agree well with experimental and theoretical results, indicating that the photoelectric and thermal properties of the CSP-LED can be improved by introducing ceramic substrate and optimizing the material of the interconnected surface and the size of the conduction area. These results have guiding significance for the future CSP-LED design and application. [ABSTRACT FROM AUTHOR]

In this study, the influence of moisture on the elastic modulus of a no-flow underfill is characterized over a wide range of accelerated testing environments, and the permanent changes are evaluated upon fully redrying. Moisture saturation is reached in all environments prior to testing, thus the inherent wet modulus of the underfill is identified for each respective level of moisture preconditioning. The change in the elastic modulus as a function of moisture concentration is measured, as well as the reversible and irreversible effects from moisture uptake in the underfill upon redrying. Thermal aging from the temperature component of the accelerated testing environment is found to have no effect on the elastic modulus, while the moisture uptake is found to notably decrease the modulus at higher humidity levels. Recovery experiments demonstrate that most of the loss in the elastic modulus from moisture exposure is recoverable, although more irreversible damage did occur at higher humidity levels. Hydrolysis contributed to the irreversible loss in the modulus, while the reversible component is attributed to plasticization of the underfill from moisture uptake. [ABSTRACT FROM AUTHOR]