Abstract Structural components such as printed circuit boards (PCBs) are critical in the thermomechanical reliability assessment of electronic packages. Previous studies have shown that geometric parameters such as thickness and mechanical properties like elastic modulus of PCBs have direct influence on the reliability of electronic packages. Elastic material properties of PCBs are commonly characterized using equipment such as tensile testers and used in computational studies. However, in certain applications viscoelastic material properties are important. Viscoelastic influence on materials is evident when one exceeds the glass transition temperature of materials. Operating conditions or manufacturing conditions such as lamination and soldering may expose components to temperatures that exceed the glass transition temperatures. Knowing the viscoelastic behavior of the different components of electronic packages is important in order to perform accurate reliability assessment and design components such as printed circuit boards (PCBs) that will remain dimensionally stable after the manufacturing process. Previous researchers have used creep and stress relaxation test data to obtain the Prony series terms that represent the viscoelastic behavior and perform analysis. Others have used dynamic mechanical analysis in order to obtain frequency domain master curves that were converted to time domain before obtaining the Prony series terms. In this paper, nonlinear solvers were used on frequency domain master curve results from dynamic mechanical analysis to obtain Prony series terms and perform finite element analysis on the impact of adding viscoelastic properties when performing reliability assessment. The computational study results were used to perform comparative assessment to understand the impact of including viscoelastic behavior in reliability analysis under thermal cycling and drop testing for Wafer Level Chip Scale Packages.
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From lab to lamp: Understanding downconverter degradation in LED packages
Downconverters, primarily inorganic phosphors, are critical components in white solid-state LED-based lighting and liquid crystal display backlights. Research efforts have led to a fundamental understanding of a downconverter's absorption, photoluminescence, and efficiency as a function of composition, structure, and processing conditions. However, considerably less work has focused on the reliability of phosphors once they are incorporated into LED packages. Solving these issues is often the final step before the commercialization of new materials, but the significant resources and time required to evaluate and mitigate materials failure are rarely discussed in the literature. In this Perspective, we discuss the need for conducting downconverter reliability testing and the potential of accelerating, screening, and understanding downconverter failure modes. Our focus highlights the mechanisms of failure and discusses how this influences materials selection and the design of different LED packages. We also stress the potential for accelerated reliability testing protocols and note the potential role first-principles calculations and data-driven models could play in establishing the compositional-processing trends for different aspects of downconverter reliability. We close with possible research directions that could improve downconverter reliability and emphasize the importance of assessing a material's (chemical) stability where multiple manufacturing and processing steps can dictate system performance.
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- Award ID(s):
- 1911311
- NSF-PAR ID:
- 10422388
- Date Published:
- Journal Name:
- Journal of Applied Physics
- Volume:
- 132
- Issue:
- 19
- ISSN:
- 0021-8979
- Page Range / eLocation ID:
- 190901
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0122735
