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70 PCB007 MAGAZINE I SEPTEMBER 2022 In addition, the use of photonic soldering/sin- tering makes these conductive pastes practical on lower cost substrates such as paper, plastic films, or other organic materials not suitable for immersion in acid plating baths. PCB007 References 1. Tatsuta, all4-pcb.us. 2. "Nano-Copper Paste for Solid Copper Via Fill," by Sujatha Ramanujan, IPC APEX EXPO 2015. 3. "PTH Core-to-Core Interconnect Using Sin- tered Conductive Pastes," by Michael Matthews, et al, IPC APEX EXPO 2012. 4. "Cu Conductive Paste as Via Filling Materials for Through Silicon Via and Through Glass Via," SMTA International, Nov. 15, 2021. 5. "Photonic Soldering," by Happy Holden, PCB007 Magazine, December 2021. Happy Holden has worked in printed circuit technology since 1970 with Hewlett-Pack- ard, NanYa Westwood, Merix, Foxconn, and Gentex. He is cur- rently a contributing technical editor with I-Connect007, and the author of Automation and Advanced Proce- dures in PCB Fabrication, and 24 Essential Skills for Engineers. To read past columns, click here. Sintering Sintering refers to a process where a mixture of particles is fused together, usually thermally. Sintering mixtures can be used as structures, dielectrics, and conductors. Conductive sin- tering products have been used in electronics for some time with ceramic thick-film technol- ogy (cermet). Cermets require high tempera- tures (>800°C) for sintering while conductive pastes based on polymers sinter at much lower temperatures (<220°C). ese polymer thick films (PTFs) are typically uncured liquid poly- mers, usually epoxy or acrylic based, filler with conductive particles. As the polymer cures and shrinks, the particles encounter each other and the substrates, making the connection. Fortu- nately, we now have technology such as pho- tonic sintering 5 that will sinter the conductors without heating the substrate. Conclusion When considering the process of filling blind-vias or through-hole vias with plat- ing, the new conductive copper-based TLPS pastes are faster, nearly as conductive, and possibly lower in cost than the plating process. Figure 3: A TLPS Cu paste is pressed into various substrates and sintered. Results show both blind vias and through-hole vias passed all reliability tests 4 .