New process printable conductive metal materials often have to make a compromise between the rheology and conductivity of the material. The binder and carrier used to provide fluidity during printing and adhesion to the substrate affect the conductivity of the final composite layer and prevent current from passing through the wire.
But there is a process that provides a way to make addition preparation and substrate adhesion independent of the conductive requirements of the printed part. Conductive Ink Technology (CIT) has developed a process in which catalytic ink is printed on a substrate and ultraviolet light is cured to provide a fast-processing adhesive base layer. The base layer itself does not have conductivity, but it acts as a catalyst for the electroless deposition of metal layers.
The printed cured substrate is immersed in a commercially available electroless plating bath, and a thick metal layer on top of the base bath is deposited. This two-stage process allows the electroplating bath to be optimized for different substrate materials and different printing tools, without affecting the conductivity of the final process. This process can use most standard electroless metals, including nickel, cobalt, and palladium, but the most commonly used and most widely used is copper. The two stages of the process can be performed online, or electroless plating can be performed as a batch process afterwards.
The typical growth rate of copper ranges from 20 nanometers per minute to 90 nanometers per minute (equivalent to a large volume of copper), which will produce a 30-ohm sheet resistance during the electroplating process of about 10 minutes. The resistivity is usually 2.5 times that of bulk metal (copper), but it depends on the plating bath and the conditions used.
The optimal conduction range of the CIT process is greater than 10 ohms (equivalent to 1.5 to 2 microns of bulk copper). It is suitable for a wide range of applications, including UHF RFID, keyboard membranes, low-current PCBs (signals), low-power heater assemblies, a wide range of sensor applications, and many other flexible and rigid applications. If higher conductivity and higher ampacity are required, post-process plating can also be performed.
The inkjet printing resolution CIT process is designed for piezoelectric printable print heads like Xerox, Konica Minolta, and Spectra. The typical original resolution of these printheads is about 180 to 360 nozzles per inch, which is designed for printing at a resolution higher than 360 dots per inch, and the drop volume is below about 40 pl. This type of printing resolution usually provides a size equivalent to a 100 micron line width on a polyester or polyimide substrate. However, the new generation of grayscale printheads supports variable drop volumes as low as about 32 pl, which allows them to obtain digital print sizes of about 50 microns or less.
Digital Manufacturing System Wide system can be used for digital production of flexible circuits. At the lower end of the range are small development systems such as Dimatix's DMP series. This type of printing press will produce A4 paper at different resolutions by using a disposable 16-nozzle print head. Due to the small number of nozzles on the print head, the output of such systems is low, but it can be perfectly used for development and precise research.
Systems such as the X4000 series from Xennia Technology or the XY100 from Konica Minolta will be more suitable for production. These systems are also based on the A4 format, which uses larger industrial printheads such as the Xaar Omnidot series or Konica Minolta KM512 series. The printing bandwidth of these systems is up to 70 mm and the productivity is up to 1 to 2 square meters per minute. Similar systems can also provide widths of 1 meter or longer, depending on the print head and required configuration.
CIT also worked with Preco to develop MetalJet 6000, a narrow-screen digital printing tool for in-line tape-and-reel production of flexible circuits and radio frequency identification (RFID) antennas. The system can be printed and cured on a 140 mm platform, and can execute our patented electroplating module, which greatly reduces the footprint size and complexity required for in-line electroless plating of network materials. Current printhead technology enables the system to produce flexible circuits at a speed of 0.56 per millisecond (equal to 4.7 square meters per minute), and its typical speed for producing products such as UHF RFID antennas is 0.3 per millisecond (equal to 2.5 square meters per minute) . The system is modular and can be configured to increase production speed and / or deposition thickness.
In most cases, these solutions can submit CAD drawings so that the normal turnaround time of 10 square meters of single-layer board is not more than 1 hour.
The new digital technology provides an additive, processing-free method for producing small and medium-sized PCBs using the rapid process with the least NRE. The ability to separate ejection characteristics and ink adhesion from the electrical properties of the material provides independent control of the conductivity of the wire. Using inkjet printing as a production method provides high productivity and short turnaround time without adding front-end processing costs.
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