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Process-Reliability Relationships of Low-Temperature Solders and ECAs
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Authored By:Pradeep Lall, Jinesh Narangaparambil Auburn University NSF-CAVE3 Electronics Research Center Department of Mechanical Engineering Auburn, AL 36849, USA Scott Miller NextFlex Manufacturing Institute San Jose, CA 95131 SummaryFabrication of additively printed flexible hybrid circuits requires the development of component attachment methods with low-temperature processing. Some substrate materials, including thermally stabilized PET and PEN require a peak processing temperature of less than 150C. Several new lowtemperature solder materials have emerged capable of being processed at temperatures in the range of 130-150C to access the benefits of lower warpage, lower energy consumption, and lower carbon footprint. This paper studies the process-performance-reliability relationships for Sn-Bi-Ag and Sn-In solders on additively printed copper metallization. Process recipes have been developed for direct write additive printers to fabricate single-layer and flexible multilayer circuits. Copper ink is a good and cost-effective alternative to silver ink, but its use has lagged due to an increased propensity for oxidation during manufacturing. In this paper, photonic curing has been used to sinter copper ink to make the traces conductive. The method flashes highenergy light that sinter metal particles instantaneously, and the temperature of the substrate remains low. The effect of the different photonic sintering profiles on the mechanical and electrical properties of the printed traces has been studied. Electrical and mechanical performance has been studied through the characterization of the frequency performance of low-pass filters, high-pass filters, and amplifiers fabricated using surface mount components on additively printed metallization. Reliability and the performance degradation of the additively printed circuits have been quantified in flex-to-install applications. In addition, SEM/EDAX has been used to study the intermetallics at the interface of LTS and additively printed circuits. ConclusionsThis paper studied various sintering conditions for additively printed copper on the direct-write platform. Factors studied include preheat, stage speed, and flash energy. The effect of preheating has been studied to assess the ability to mitigate the popcorning of printed metallization. The EDX study was performed to demonstrate that preheating is advantageous. These test results from test vehicle-1 were utilized to investigate the impact of additional curing processes in real-world applications. Depending on the application, the test vehicle's two design incorporates component attachments such as resistors, capacitors, inductors, and LEDs. These are some of the most common circuitry components. The direct-write approach for connecting the components has been established. In order to estimate the percentage variation introduced by the additive printing attachment, the components were tested before and after the attachment. The measured values were well within the rated values of the manufacturer. For this study, the lack of understanding about the various binding materials was taken into account, and correct attachment issues were shown. Compared to silver-based ECA and SnIn low-temperature solders, SnBiAg solder provides the greatest performance. The EDX analysis is also used to address the causes of the failure situations. Based on the study of the test vehicle-1, the functionality of the component attachment was further investigated by building an amplified inverting Op-Amp circuitry. The design was initially modeled in software and compared to the system's real performance. Although a 15V DC source supplied the circuit, no degradation in the printed traces was noticed. This also means that the technology may be used for high-power circuits like this one. The performance comparison produces favorable results, indicating that the process development was carried out in order to develop functioning circuitry. All three binding materials give a fundamental knowledge of the material in high-frequency applications. Initially Published in the SMTA Proceedings |
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