Researchers from the U.S. National Institute of Standards and Technology (NIST), the University of California, San Diego (UCSD), and other institutions published a study examining how to predict the cure evolution of a highly filled epoxy and its ability to withstand thermal degradation when used in advanced semiconductor packaging.
These materials are known as underfill and are used in applications such as fine-pitch interconnects and flip-chip technology. Their function is to enhance mechanical durability, redistribute thermomechanical stresses, and improve the reliability of solder joints. However, their performance depends not only on their composition; it is also affected by the degree of cure achieved during processing and by their thermal stability during operation.
What did the researchers measure?
The team used differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), along with a kinetic model incorporating diffusion effects. The analysis showed that the apparent activation energy changes as the reaction progresses and rises sharply at high conversion rates. This indicates that curing is not a single-step process but involves multistage behavior affected by diffusion control.
To address this characteristic, the researchers used a modified two-step Kamal–Sourour model, incorporating diffusion effects in the second stage. According to the published abstract, the model improved the ability to predict the degree of conversion after reaching the vitrification stage and was also used to simulate curing according to a thermal-processing schedule in an oven.
What changes in practice?
The results indicate that designing a thermal-processing schedule can be based on a quantitative model that tracks the later stages of curing, rather than relying solely on a fixed duration or temperature. According to the study, the predicted processing schedule achieved an almost complete degree of cure. This provides engineers with a means of assessing whether the material has completed its required transformation before moving on to production or testing stages.
The researchers also tested the effect of cryomilling on TGA measurements and found that it improved the repeatability of the results without causing detectable chemical changes. The study also addressed thermal-lifetime estimation according to the ASTM E1641/E1877 protocols, using a 5% mass-loss criterion in a nitrogen environment. The results showed a strong dependence of the estimate on temperature.
Why does this news matter?
The study provides a framework for linking material behavior during curing with thermal-reliability assessment, which is important in advanced packaging, where fine-pitch interconnects and multiple materials affect a package’s ability to withstand operating cycles. However, the results do not constitute comprehensive industrial qualification of any particular material or process; they are based on a highly filled epoxy and specific measurement conditions, while the thermal-endurance estimates relied on mass loss in nitrogen. Therefore, how these estimates translate to actual operating conditions and different commercial materials remains a question requiring additional validation.
The paper is titled “Predicting Cure Evolution and Thermal Endurance of a Highly Filled Epoxy Underfill for Advanced Packaging” and was published in the Journal of Polymer Science in 2026, with DOI: 10.1002/pola.70283. The source gives the news publication date as September 11, 2026, while indicating that the paper dates to August 2026.