TY - JOUR A1 - Mohan, Nihesh A1 - Ahuir-Torres, Juan Ignacio A1 - Kotadia, Hiren R. A1 - Elger, Gordon T1 - Laser sintering of Cu particle-free inks for high-performance printed electronics JF - npj Flexible Electronics N2 - This study investigates laser sintering of Cu particle-free ink (Cu formate tetrahydrate—amino-2-propanol complex) as an alternative to conventional sintering in an oven (under inert/reducing atmosphere). Utilizing benefits of high-speed localized heating using laser, substrate damage can be prevented for low-melting substrates such as Polyethylene Terephthalate (PET). Firstly, a suitable sintering process window is achieved based on energy density for two different flexible polymeric susbtrates: Polyimide and PET using different laser parameters (laser power, scan rate and spot diameter). Subsequently, characterization of laser sintered traces are also made using different laser optic profiles (Gaussian and top hat). Different methodologies for fabrication of metallized Cu layer were also demonstrated. A very low bulk resistivity of 3.24 µΩcm (1.87 times of bulk Cu) was achieved on trace thickness of 0.85 ± 0.15 µm exhibiting good adherence to polymeric substrates. A promising fabrication process of low-cost and reliable flexible printed electronic devices is demonstrated. UR - https://doi.org/10.1038/s41528-025-00389-5 Y1 - 2025 UR - https://doi.org/10.1038/s41528-025-00389-5 UR - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:573-58266 SN - 2397-4621 VL - 9 IS - 1 PB - Springer CY - London ER - TY - JOUR A1 - Mohan, Nihesh A1 - Steinberger, Fabian A1 - Wächter, Sonja A1 - Erdogan, Hüseyin A1 - Elger, Gordon T1 - Additive Manufacturing for Automotive Radar Sensors Using Copper Inks and Pastes JF - Applied Sciences N2 - Radar sensors are critical for obstacle detection and navigation, especially for automated driving. Using the use-case “printing of heating coils on the inside of the front housing (primary radome)” needed for de-icing in winter, it is demonstrated that additive manufacturing (AM) can provide economic and functional benefits for manufacturing of the sensors. AM will allow significant cost reduction by eliminating parts and simplifying the manufacturing process. Different AM technologies for the coils were investigated, first, by applying the conductive traces by fused deposition modeling (FDM), and, second, by printing copper particle-free inks and pastes. The metal layers were electrically and mechanically characterized using a profilometer to measure the trace dimension and a four-point probe to measure the resistance. It was revealed that low-cost conductive filaments with low resistivity and current carrying capacity are commercially still not available. The best option sourced was a copper–polyester-based filament with 6000 µΩcm after printing. Therefore, low-cost particle-free copper inks and commercial copper flake paste were selected to print the heating coil. The Cu particle-free inks were amine-based Cu (II) formate complexes, where the Cu exists in an ionic form. Using contactless printing processes such as ink-jet printing or pneumatic dispensing, the traces could be deposited onto the low-melting temperature (225 °C) polymeric radome structure. After printing, the material needed to be sintered to form the conductive copper traces. To avoid damaging the polymer radome during sintering, two different processes were investigated: low-temperature (<150 °C) sintering in an oven for 30 min or fast laser sintering. The sintered Cu layers achieved the following specific electric resistivities when slowly sintered in the oven: paste 4 µΩcm and ink 8.8 µΩcm. Using laser sintering, the ink achieved 3.2 µΩcm because the locally high temperature provides better sintering. Also, the adhesion was significantly increased to (5 B). Therefore, laser sintering is the preferred technology. In addition, it allows fast processing directly after printing. Commercial equipment is available where printing and laser sintering is integrated. The potential of low-cost copper material and the integration in additive manufacturing of electronic systems using radar sensors as an example are demonstrated in this paper. UR - https://doi.org/10.3390/app15052676 Y1 - 2025 UR - https://doi.org/10.3390/app15052676 UR - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:573-58065 SN - 2076-3417 VL - 15 IS - 5 PB - MDPI CY - Basel ER - TY - CHAP A1 - Mohan, Nihesh A1 - Langer, Stefan A1 - Elger, Gordon T1 - Fluxfree solder paste and process for standard SMD components T2 - 2022 IEEE 9th Electronics System-Integration Technology Conference (ESTC) UR - https://doi.org/10.1109/ESTC55720.2022.9939528 KW - Fluxfree KW - Solder process KW - Surface mount devices Y1 - 2022 UR - https://doi.org/10.1109/ESTC55720.2022.9939528 SN - 978-1-6654-8947-8 SP - 163 EP - 168 PB - IEEE CY - Piscataway ER - TY - CHAP A1 - Mohan, Nihesh A1 - Bhogaraju, Sri Krishna A1 - Lysien, Mateusz A1 - Schneider, Ludovic A1 - Granek, Filip A1 - Lux, Kerstin A1 - Elger, Gordon T1 - Drop feature optimization for fine trace inkjet printing T2 - 2021 23rd European Microelectronics and Packaging Conference & Exhibition (EMPC): Technical Papers UR - https://doi.org/10.23919/EMPC53418.2021.9585004 KW - inkjet printing KW - Ag nanoparticles KW - fine trace KW - surface interactions KW - drop feature KW - ink properties KW - sintering Y1 - 2021 UR - https://doi.org/10.23919/EMPC53418.2021.9585004 SN - 978-0-9568086-7-7 PB - IEEE CY - Piscataway ER - TY - JOUR A1 - Mohan, Nihesh A1 - Ahuir-Torres, Juan Ignacio A1 - Bhogaraju, Sri Krishna A1 - Webler, Ralf A1 - Kotadia, Hiren R. A1 - Erdogan, Hüseyin A1 - Elger, Gordon T1 - Decomposition mechanism and morphological evolution of in situ realized Cu nanoparticles in Cu complex inks JF - New Journal of Chemistry UR - https://doi.org/10.1039/D3NJ05185D Y1 - 2024 UR - https://doi.org/10.1039/D3NJ05185D SN - 1369-9261 VL - 48 IS - 15 SP - 6796 EP - 6808 PB - RSC CY - London ER - TY - CHAP A1 - Mohan, Nihesh A1 - Ahuir-Torres, Juan Ignacio A1 - Bhogaraju, Sri Krishna A1 - Kotadia, Hiren R. A1 - Elger, Gordon T1 - Rapid Sintering of Inkjet Printed Cu Complex Inks Using Laser in Air T2 - 2023 24th European Microelectronics and Packaging Conference & Exhibition (EMPC) UR - https://doi.org/10.23919/EMPC55870.2023.10418323 Y1 - 2024 UR - https://doi.org/10.23919/EMPC55870.2023.10418323 SN - 978-0-9568086-9-1 PB - IEEE CY - Piscataway ER - TY - CHAP A1 - Bhogaraju, Sri Krishna A1 - Mohan, Nihesh A1 - Steinberger, Fabian A1 - Erdogan, Hüseyin A1 - Hadrava, Philipp A1 - Elger, Gordon T1 - Novel Low Temperature and Low Pressure Sintering of ADAS Radar Sensor Antenna Stack T2 - 2023 24th European Microelectronics and Packaging Conference & Exhibition (EMPC) UR - https://doi.org/10.23919/EMPC55870.2023.10418277 Y1 - 2024 UR - https://doi.org/10.23919/EMPC55870.2023.10418277 SN - 978-0-9568086-9-1 PB - IEEE CY - Piscataway ER - TY - CHAP A1 - Steinberger, Fabian A1 - Mohan, Nihesh A1 - Rämer, Olaf A1 - Elger, Gordon T1 - Low temperature die-attach bonding using copper particle free inks T2 - 2024 IEEE 10th Electronics System-Integration Technology Conference (ESTC), Proceedings UR - https://doi.org/10.1109/ESTC60143.2024.10712150 Y1 - 2024 UR - https://doi.org/10.1109/ESTC60143.2024.10712150 SN - 979-8-3503-9036-0 PB - IEEE CY - Piscataway ER - TY - JOUR A1 - Schwan, Hannes A1 - Mohan, Nihesh A1 - Schmid, Maximilian A1 - Saha, Rocky Kumar A1 - Klassen, Holger A1 - Müller, Klaus A1 - Elger, Gordon T1 - Sintering for High Power Optoelectronic Devices JF - Micromachines N2 - Residual-free eutectic Au80Sn20 soldering is still the dominant assembly technology for optoelectronic devices such as high-power lasers, LEDs, and photodiodes. Due to the high cost of gold, alternatives are desirable. This paper investigates the thermal performance of copper-based sintering for optoelectronic submodules on first and second level to obtain thermally efficient thin bondlines. Sintered interconnects obtained by a new particle-free copper ink, based on complexed copper salt, are compared with copper flake and silver nanoparticle sintered interconnects and benchmarked against AuSn solder interconnects. The copper ink is dispensed and predried at 130 °C to facilitate in situ generation of Cu nanoparticles by thermal decomposition of the metal salt before sintering. Submounts are then sintered at 275 °C for 15 min under nitrogen with 30 MPa pressure, forming uniform 2–5 µm copper layers achieving shear strengths above 31 MPa. Unpackaged LEDs are bonded on first level using the copper ink but applying only 10 MPa to avoid damaging the semiconductor dies. Thermal performance is evaluated via transient thermal analysis. Results show that copper ink interfaces approach the performance of thin AuSn joints and match silver interconnects at second level. However, at first level, AuSn and sintered interconnects of commercial silver and copper pastes remained superior due to the relative inhomogeneous thickness of the thin Cu copper layer after predrying, requiring higher bonding pressure to equalize surface inhomogeneities. UR - https://doi.org/10.3390/mi16101164 Y1 - 2025 UR - https://doi.org/10.3390/mi16101164 UR - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:573-64984 SN - 2072-666X VL - 16 IS - 10 PB - MDPI CY - Basel ER -