A landmark perspective published by the National Institute of Standards and Technology (NIST) and collaborators identifies critical measurement and materials gaps in polymer-based semiconductor packaging-deficiencies that directly threaten the long-term reliability of automotive sensors and engine control units (ECUs). The paper, titled "Material Needs and Measurement Challenges for Advanced Semiconductor Packaging: Understanding the Soft Side of Science," appeared in IEEE Transactions on Components, Packaging and Manufacturing Technology in August 2025. It grew from a NIST-organized workshop held at the 35th Annual Electronics Packaging Symposium in Binghamton, New York, on September 5, 2024.
Background
As transistor scaling reaches its physical limits, packaging challenges compound-from mechanical stress and distortion to electrical interference, environmental degradation, and failure mechanisms. Polymer-based packaging materials, once viewed as little more than adhesives or encasements for chips, have emerged as critical factors in reliability, performance, and cost.
Polymers such as epoxies, silicones, and polyimides encapsulate chips, connect them to circuit boards, and sustain long-term operation. As the industry shifts toward 3D heterogeneous integration-where multiple chips are stacked or linked in three dimensions-the demands on these materials are escalating rapidly.
ISO 26262, the international standard for functional safety in road vehicles, was originally published in 2011 and revised in 2018. It applies to all vehicle elements, including hardware, software, and human interactions, ensuring safety is addressed from concept through decommissioning. Automotive-grade packaging polymers must therefore satisfy both long-service-life reliability requirements and the stringent safety classifications governing ECU and sensor assemblies.
Details
The core problem, as the NIST-led authors document, lies in the physicochemical behavior of polymer packaging under real-world automotive operating conditions. Unlike metals or ceramics, polymers are time- and temperature-sensitive, absorbing moisture and changing shape under stress, according to NIST. These behaviors can cause chips to warp, signals to degrade, or connections to fail over years of operation.
For automotive applications, the stakes are particularly acute. Cars typically last 10 to 15 years, so chip designers must demonstrate that autonomous and driver-assistance systems maintain a zero-failure rate throughout the vehicle's lifespan. This service-life requirement collides with the documented instability of thermoset resins, underfill materials, and epoxy molding compounds when subjected to thermal cycling, humidity ingress, and mechanical vibration-all common in under-hood and chassis-mounted sensor or ECU installations.
The NIST CHIPS team addresses these issues through three interconnected workstreams. First, the initiative outlines critical challenges and opportunities related to polymer-based "soft" materials in advanced semiconductor packaging, with emphasis on polymer science, measurement science (metrology), and the strategic development of research-grade test materials (RGTMs). These efforts aim to advance fundamental understanding of structure-property-processing relationships, promote standardized guidelines and innovative characterization methods, and accelerate the development, qualification, and adoption of next-generation packaging materials.
Second, NIST is developing advanced metrology techniques including advanced rheology, spectroscopy, and stress measurements specifically to track how polymers cure, shrink, and deform during manufacturing-factors that directly impact device reliability. As the industry moves toward digital twins and predictive design, accurate measurements become indispensable. Co-author William Chen, Chair of the IEEE Heterogeneous Integration Roadmap for semiconductors, stated: "Modeling without metrology is imagination."
Third, NIST is pioneering research-grade test materials (RGTMs): open, nonproprietary polymer systems that serve as benchmarks. Unlike commercial "black box" materials, RGTMs allow researchers across industry, academia, and government to compare results, improve reproducibility, and feed reliable data into computer models.
The paper also identifies key automotive packaging challenges addressed by the new framework. Silica-based filler in epoxy molding compounds reduces moisture absorption and mitigates the large coefficient of thermal expansion (CTE) mismatch between silicon die (2-3 ppm/°C) and epoxy resin (above 80 ppm/°C), helping limit warpage. For ECU and sensor packages operating at elevated temperatures, this CTE mismatch is a primary driver of interconnect fatigue and field failure. According to Hamed Gholami Derami, strategic technologist for advanced semiconductor packaging at Brewer Science, "Panel warpage is fundamentally driven by thermo-mechanical CTE mismatch and stiffness imbalances across the stack." He noted that multiple polymer types with different glass transition temperatures coexist in the same stack, and that exceeding the glass transition temperature (Tg) of any layer causes a sharp drop in modulus and an increase in CTE, intensifying warpage. Cure shrinkage of polymers was also identified as a source of residual stress that amplifies warpage.
Cross-industry implications are significant. The perspective grew out of a NIST-organized workshop where experts from industry, universities, and government labs agreed on key priorities-including rebuilding U.S.-based supply chains for packaging materials, creating shared databases of material properties, and advancing measurement standards. These priorities are equally relevant to medical device packaging, data center compute modules, and consumer electronics, all of which deploy polymer-encapsulated semiconductor components in thermally or humidity-challenged environments. The NIST CHIPS NAPMP finalized $300 million in award funding under its first Notice of Funding Opportunity for advanced substrates and material research, with awards to Absolics Inc., Applied Materials Inc., and Arizona State University, reflecting the scale of federal investment behind the framework.
Outlook
With some new packaging materials taking 10 to 25 years to reach production, the NIST authors stress that early, collaborative work is essential to meet the reliability timelines imposed by automotive OEM qualification cycles. Efforts led by the NIST CHIPS team aim to accelerate the development, qualification, and adoption of next-generation packaging materials. Automotive suppliers and polymer compounders that align materials qualification programs with the NIST RGTM framework early will be better positioned to meet ISO 26262 evidence requirements and emerging procurement specifications from Tier 1 and OEM customers. Formal standardization outputs and publicly accessible shared material property databases are anticipated as the next deliverables from the CHIPS Metrology Program.
