Conductive ink technology for digital printing of flexible circuits
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New Technology
Printable conductive metal materials often have to compromise between rheology and conductivity of the material. The binder and carrier used to provide flow during printing and adhesion to the substrate affects the conductivity of the final composite layer and prevents current from passing through the wire.
However, there is a process that provides a means of adhering the additive preparation and substrate adhesion to the printing portion. Conductive Ink Technology (CIT) has developed a process in which a catalytic ink is printed on a substrate and the ultraviolet light is cured to provide a fast-processed adhesive substrate. The base layer itself does not have conductivity, but it acts as a catalyst for electroless deposition of the metal layer.
The printed cured substrate is immersed in a commercially available electroless plating bath and a thick metal layer is deposited on top of the substrate. This two-stage process allows the plating bath to be optimized for different substrate materials and different printing tools, without affecting the conductivity of the final process. Most of the standard electroless metals, including nickel, cobalt and palladium, are used in this process, but the most common and widespread use is copper. The two stages of the process can be performed in-line or after electroless plating can be performed as a batch process.
The usual growth rate of copper ranges from 20 nanometers per minute to 90 nanometers per minute (equivalent to large volume copper), which produces a 30 ohm sheet resistance during the plating process of about 10 minutes. Usually the resistivity is 2.5 times that of bulk metal (copper), but it depends on the plating bath and the conditions used.
The optimum conduction range for 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 PCB (signal), low power heater assemblies, a wide range of sensor applications and many other flexible and rigid applications. Post-process plating can also be performed if higher conductivity and greater current carrying capacity are required.
Inkjet printing resolution
The CIT process is designed for piezoelectric controllable printheads manufactured by Xaar, Konica Minolta and Spectra. These printheads typically have a native resolution of about 180 to 360 nozzles per inch and are designed to print at resolutions above 360 dots per inch with drops below about 40 pl. Such printing resolutions typically provide 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 results in digital print sizes of about 50 microns or less.
Digital manufacturing system
A wide range of systems are available for digital production of flexible circuits. Located at the lower end of the range are small development systems such as Dimatix's DMP series. This type of press will produce A4 paper at different resolutions by using a disposable 16-jet print head. Due to the small number of nozzles on the print head, the throughput of such systems is low, but it is perfect for development and precise research.
Systems such as the X4000 series from Xennia Technologies 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 the Konica Minolta KM512 series. These systems have a print bandwidth of up to 70 mm and a productivity of 1 to 2 square meters per minute. Similar systems can also provide widths of 1 meter or more, depending on the print head and the desired configuration.
CIT has also teamed up with Preco to develop the MetalJet 6000, a narrow-web digital printing tool for in-line tape-and-reel production of flexible circuits and radio frequency identification (RFID) antennas. The system prints and cures on a 140 mm platform and implements our patented plating module, which greatly reduces the footprint and complexity required for in-line electroless plating of network materials. Current printhead technology enables the system to produce flexible circuits at a rate of 0.56 per millisecond (equivalent to 4.7 square meters per minute), which typically produces 0.3 times per millisecond (equivalent to 2.5 square meters per minute) for products such as UHF RFID antennas. . The system is modular and can be configured to increase production speed and/or deposition thickness.
In most cases, these solutions submit CAD drawings that allow a typical turnaround time of a 10 square meter single-layer board to be no more than one hour.
to sum up
The new digital technology provides a process for adding and processing small and medium-sized PCBs using the fastest NRE process. The ability to separate jet characteristics and ink adhesion from the electrical properties of the material provides independent control of wire conductivity. The use of inkjet printing as a production method provides high throughput and short turnaround time without adding front-end processing costs.