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82 PCB007 MAGAZINE I AUGUST 2019 Novel Catalyst Ink and SAP A novel palladium deposition process has been developed using palladium carboxylate. The palladium carboxylate is dissolved in prop- erly selected organic solvents. The solution—a liquid metal ink (LMI)—is prepared for a catalyst source of an electroless copper plating process. A plated electroless copper formed by LMI palladium is prepared for the SAP. The LMI is applied over a substrate using a bar coater method and the coated film is dried in the at- mosphere in a few minutes. This coating pro- cess proceeds in a cleanroom. The LMI-coat- ed substrate is cured in a convection oven for several minutes to reduce the palladium to metal palladium. Once the substrate surface is covered by the palladium metal layer—which can work as an electroless copper plating cata- lyst—an electroless copper plating can then be applied to achieve about 0.3 microns of copper film. This copper-coated substrate can then support the SAP process (Figure 3). When the base conductor for the SAP is made with this process, the base copper can be very thin (0.3 mm) compared to conventional mSAP, and it is thinner than electroless copper by the conventional catalyst process which is usually 1–2 microns. The etching process is also important to achieve fine-line circuitry. The industry pri- marily uses a copper chloride etchant. An al- ternative, alkaline-based etchant is used for the panel pattern plating process with electro- plated tin used as an etching resist. This etch- ing solution is designed for relatively thick copper foil and the etching speed is too fast to control SAP processes. Hence, a sulfuric acid-hydrogen peroxide system is commonly used for the SAP process. However, with this system, it is possible to generate gas bubbles during the etching, which may influence etch - ing control. The etching solution wettability to the copper can also affect the etching uni- formity. Some surfactant is used to improve the etching. A new solvent-mixed etchant system has been developed for SAP. This solvent reduces surface tension and improves wettability. Al- though a surfactant has the same capability, it also makes unwanted forms and molecu- lar level absorption. The new solvent-mixed etchant is adjusted to relatively slow etch- ing speeds, such as 0.5 microns per minute, and it is suitable for the new SAP system that needs to remove less than 0.5 microns of copper. Figure 3: SAP utilizing LMI.