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 user 2005-06-10 at 10:18:00 am Views: 36
  • #9863
    EPson Prints 20-Layer Board with Inkjet
    Technology Feature_1_Feb_fig1.jpgAt long last inkjet printing technology
    has matured to the point where volume production seems possible. In November
    2004, Seiko Epson Corp of Japan announced the successful application of inkjet
    technology in the manufacture of polyimide substrates, prototyping a board with
    20 circuit layers (see Fig), and ultra-thin modules with surface-mounted
    passives and integrated circuits (IC). These prototypes were disclosed to the

    The firm also announced that it would “Volume produce 2-layer
    chip-on-film substrates using the new technology in 2007, for use in Seiko Epson
    display products.” This marks the first clear date for practical application of
    inkjet circuit printing technology by a major manufacturer.

    Seiko Epson
    positions the prototypes as “the first implementation of multi-layer circuit
    boards, which have only been on the wish list until now.” The 20-layer board
    used inkjet printing not only for the interconnects, but also for the dielectric
    film between them. Interconnects and vias connecting layers were formed with an
    organic material using Ag microparticles. Total board thickness is only 240um,
    including 40um thick polyimide substrate. The polyimide substrate is first
    printed with a dielectric film, making it possible to strip off the circuits and
    recycle the boards separately if needed.

    Keys to Implementation

    The key point to implementing
    the multi-layer boards is the ability to use inkjet technology to print
    dielectric films of any pattern, absorbing height differences on the bottom
    layer caused by vias, interconnects and other features. For sections with vias
    and interconnects, the thickness and pattern of the dielectric film are changed
    to ensure a flat upper surface. This minimizes the effects of lower layers on
    higher layers, and makes it possible to print 20 or more layers, the firm

    The other key point in commercial implementation was using a
    multi-head printer comprising multiple consumer-spec print heads, thereby
    boosting productivity. Just like line printers, which print an entire line at
    once, the new printer is capable of printing all the circuits across the entire
    width of the board, at once. This approach also eliminates the need for
    alignment in the “line” direction. Because the heads are not moved in the line
    direction, there is a problem in that each head nozzle can only draw one thin
    line at a time. Seiko Epson resolved this problem by moving the heads back and
    forth for each layer to overprint as needed.

    There is some expectation
    that boards made with inkjet technology can be used in radio frequency
    identification (RFID) tags and similar applications, but the necessary
    conductivity to high-frequency currents has yet to be verified. Seiko Epson uses
    Ag microparticles coated with an organic material to print interconnect patterns
    on the dielectric film, then bakes the boards at 150 to 200*C to create the
    interconnects. Normally Ag interconnects formed through this method lack
    sufficient line width uniformity, raising the possibility of soaring impedance
    under high-frequency current flow. A spokesperson at Seiko Epson commented:
    “True, resistance is two to three times higher than bulk Ag. It is no better
    than bulk, but all we need is for the results to be within the permissible