The use of underfill materials is necessary with flip-chip interconnect technology to redistribute stresses due to mismatching coefficients of thermal expansion (CTEs) between dissimilar materials in the overall assembly. Underfills are formulated using organic polymers and possibly inorganic filler materials. There are a few ways to apply the underfills with flip-chip technology. Traditional capillary-flow underfill materials now possess high flow speed and reduced time to cure, but they still require additional processing steps beyond the typical surface-mount technology (SMT) assembly process.
Studies were conducted using underfills in a temperature range of -190 to 85°C, which resulted in an increase of reliability by one to two orders of magnitude. Thermal shock of the flip-chip test articles was designed to induce failures at the interconnect sites (-40 to 100 °C). The study on the reliability of flip chips using underfills in the extreme temperature region is of significant value for space applications. This technology is considered as an enabling technology for future space missions.
Flip-chip interconnect technology is an advanced electrical interconnection approach where the silicon die or chip is electrically connected, face down, to the substrate by reflowing solder bumps on area-array metallized terminals on the die to matching footprints of solder-wet-table pads on the chosen substrate. This advanced flip-chip interconnect technology will significantly improve the performance of high-speed systems, productivity enhancement over manual wire bonding, self-alignment during die joining, low lead inductances, and reduced need for attachment of precious metals.
The use of commercially developed no-flow fluxing underfills provides a means of reducing the processing steps employed in the traditional capillary flow methods to enhance SMT compatibility. Reliability of flip chips may be significantly increased by matching/tailoring the CTEs of the substrate material and the silicon die or chip, and also the underfill materials.
Advanced packaging interconnects technology such as flip-chip interconnect test boards have been subjected to various extreme temperature ranges that cover military specifications and extreme Mars and asteroid environments.
The eventual goal of each process step and the entire process is to produce components with 100 percent interconnect and satisfy the reliability requirements. Underfill materials, in general, may possibly meet demanding end use requirements such as low warpage, low stress, fine pitch, high reliability, and high adhesion.
This work was done by Rajeshuni Ramesham of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Electronics/Computers category. NPO-41181
This Brief includes a Technical Support Package (TSP).
Advanced Flip Chips in Extreme Temperature Environments
(reference NPO-41181) is currently available for download from the TSP library.
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Overview
The document titled "Advanced Flip Chips in Extreme Temperature Environments" (NPO-41181) from NASA's Jet Propulsion Laboratory discusses the reliability and performance of advanced flip-chip interconnect technologies under extreme temperature conditions, which are critical for space applications. The research focuses on the use of underfill materials to enhance the reliability of flip-chip assemblies, particularly in environments that experience severe thermal cycling.
The study highlights that traditional reliability assessments of flip chips have been conducted within a temperature range of -50 °C to 150 °C, showing significant improvements in reliability—by one to two orders of magnitude—when using underfills. However, this document presents novel findings on the performance of flip chips subjected to extreme temperatures ranging from -190 °C to 85 °C, a range that had not been previously studied. The results indicate that flip-chip technologies with no-flow fluxing underfills can withstand up to 322 thermal cycles in these extreme conditions without catastrophic failures.
The document details the methodology used in testing, including thermal shock tests designed to induce failures at interconnect sites. It reports that while some failures were observed in specific test boards after extensive thermal cycling, the overall performance remained robust, with no catastrophic failures noted even after 481 Martian thermal cycles. The findings underscore the importance of matching the coefficient of thermal expansion (CTE) between the substrate materials, silicon die, and underfill materials to enhance reliability.
Additionally, the document emphasizes the significance of these advancements for NASA's long-duration deep space missions, where electronic devices must endure harsh environments and maintain high reliability. The use of advanced flip-chip interconnect technology is positioned as an enabling technology for future missions, potentially improving the performance of high-speed systems and reducing the need for precious metal attachments.
In conclusion, the research presented in this document not only fills a critical gap in the understanding of flip-chip reliability under extreme temperatures but also paves the way for future innovations in electronic packaging for space exploration. The findings are expected to have broader technological, scientific, and commercial applications beyond aerospace.
