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(EHD) jet printing. Examples are shown in Figure 2. • Laser ablation: Popular with Amkor-Korea and Siemens, lasers can ablate circuit trenches and vias, making them easy to fill with silver or MOD inks. • Direct printing: Also conducted with lasers or LED light sources. e laser catalyzes the photosensitive metallization to become conductive. • Aerosol printing: Prints at room temperature with a resolution of 15 mm L/S. e Ag MOD has high conductivity and a short curing time at 120°C. ick, 10 mm printing can be achieved with multiple passes. • Copper highlights: e initial test shows a resolution of <100 mm but needs to be cured under nitrogen. Summary ere are many methods now available to met- allize UHDI substrates. In addition to the long- traditional electroless Cu, graphite, or sputter- ing, we now have MOD inks and pastes, even for prototyping. Figure 3 shows a portable MOD jet printer available today. PCB007 References 1. "HDPUG Keynote-Advanced Packaging Sub- strate/Ultra HDI Update," by Gene Weiner, PCB West, October 2024. 2. SMTA Technical Knowledge, UHDI Symposium, January 2024, and UHDI Pavilion, October 2024. 3. Happy's Tech Talk #1: VeCS," by Happy Holden, PCB007 Magazine, October 2021. Happy Holden has worked in printed cir- cuit technol- ogy since 1970 with Hewlett- Packard, NanYa Westwood, Merix, Foxconn, and Gentex. He is currently a contributing technical edi- tor with I-Connect007, and the author of Automation and Advanced Pro- cedures in PCB Fabrication, and 24 Essential Skills for Engineers. To read past columns, click here. Figure 2: Newer methods of MOD printing: a) laser ablation and then filling; b) direct laser printing; c) aerosol jet printing of silver MOD; and d) aerosol printing of copper MOD 2 . Figure 3: An MOD inkjet prototype method of printing: the circuitJet 2 . 56 PCB007 MAGAZINE I APRIL 2025