In this study, we introduced a hybrid Potts-phase field model to simulate the co-evolution of grain growth and pores migration in sintered silver layers. The Potts model is good at capture the grain growth dynamics, while the phase field model describes the evolution of the porous network. These models are coupled via a hybrid free energy function to achieve a realistic representation of the microstructure evolution. This study further extends the hybrid model by incorporating (a) a flexible exchange interaction matrix to model the crystal anisotropy in grain growth, (b) Glauber or Kawasaki dynamics to describe different diffusion mechanisms, and (c) the effect of pinning sites, representing impurity-driven grain boundary stabilization. The computational framework is implemented using Taichi Lang, which allows for efficient parallel simulations. Results show that the model effectively captures the long-term evolution of the sintered silver microstructure in good agreement with experimental observations. This hybrid model is a powerful tool to predict microstructural reliability of sintered silver die attach layers, supporting material design and process optimization for high-power electronic applications.

Phosphor-converted white light-emitting diodes (pc-white LEDs) have attracted considerable attention as a new generation light source since the first commercial GaN chip was invented in 1990s. A pc-white LED can be regarded as a sophisticated system including a number of components made of a variety of materials. An understanding of the behavior of its component parts is helpful to gain a comprehensive insight of the failure of the pc-white LED itself. For this reason, issues related to materials and reliabilities of the LED key components such as LED chip, phosphor, encapsulant, lead frame, and interface are discussed in this chapter.

The color coordinate shift of light-emitting diode (LED) lamps is investigated by running three stress-loaded testing methods, namely step-up stress accelerated degradation testing, step-down stress accelerated degradation testing, and constant stress accelerated degradation testing. A power model is proposed as the statistical model of the color shift (CS) process of LED products. Consequently, a CS mechanism constant is obtained for detecting the consistency of CS mechanisms among various stress-loaded conditions. A statistical procedure with the proposed power model is then derived for the CS paths of LED lamps in step-loaded stress testing. Two types of commercial LED lamps with different capabilities of heat dissipation (CHDs) are investigated. Results show that the color coordinates of lamps are easily modified in various stress-loaded conditions, and different CHDs of lamps may play a crucial role in the various CS processes. Furthermore, the proposed statistic power model is adequate for the CS process of LED lamps. The consistency of CS mechanisms in step-loaded stress testing can also be detected effectively by applying the proposed statistic procedure with the power model. Moreover, the constant assumption in the model is useful for judging the consistency of CS mechanisms under various stress-loaded conditions.

In this paper, lumen degradation is described by using a modified Brownian motion process for mid-power white-light LED packages, which were aged under step stress accelerated degradation test (SSADT). First, a SSADT model has been established based on the theory of equivalent accumulative damage. Then, a method was proposed to improve the accuracy of the parameter estimation by carefully modifying the estimator, which was proposed in the previous research. Experimental data show that parameters estimated by using SSADT model are very close to those estimated by using constant stress accelerated degradation test (CSADT) model, indicating the feasibility of the SSADT model. The experiment also indicates that SSADT can be used as an alternative to CSADT, as it enables comparable estimation accuracy, while using less testing time, a smaller sample size and less test capacity.

A degradation mechanism analysis methodology is proposed for the mid-power white-light LED packages in this paper. Based on the degradation data obtained from a series of aging tests that are performed on the individual packaging material, the degradation kinetics of lumen output and spectral power distribution of the LED packages are investigated using optical simulation. As a result, although the reflectivity of the packaging materials decreased severely for the blue lights (i.e., 450 nm), the simulation showed that lights at this wavelength were little absorbed in the LED package. More specifically, it is found that: 1) the degradation of the blue lights is mainly due to blue chip deterioration, while rarely affected by the degradation of the silicone encapsulant and other packaging materials; 2) the degradation of the down-converted lights is significantly attributed to the degradation of the blue chips, the phosphors, the lead frames, and the package housing; and 3) the degradation of the silicone encapsulant contributes about 1.35% to the total lumen degradation within 168 h, while has no more contribution to the lumen degradation with further aging duration. The simulation results have been validated by experiments and successfully applied to the degradation mechanism analysis of LED packages in LM-80-08 tests.