Bright vs dark field mask

Discussion in 'Off-Topic' started by EngIntoHW, Jul 3, 2011.

  1. EngIntoHW

    Thread Starter Member

    Apr 24, 2010

    I read in various articles about negative and positive photoresists.
    In order to create a hole in a photoresist, you need one of the following combinations:
    Negative resist and Bright Field Mask
    Positive resist and Dark Field Mask

    I didn't manage to understand what're bright and dark field masks?
    I know how negative and positive resists work.

    Thanks for any help :)
  2. MrChips


    Oct 2, 2009
    There are two kinds of photoresists: positive and negative.
    I will just explain the one most commonly used. Everything just gets reversed with the other kind.

    The copper clad board is first coated with photoresist in a darkroom where there is no UV light.

    When you expose NEGATIVE photoresist to UV light it becomes insoluble to the photoresist developer. Thus this part of the copper is protected and not etched away by the etching solution.

    So to make your printed circuit board you create a PCB layout using black traces to represent the copper traces, copper fills and ground planes etc.

    Next you create a photographic negative of the layout using photographic film. What you now have is a Bright Field Mask, i.e. the copper traces, fills and ground planes are transparent. The rest is opaque to light.

    You then lay the mask on top of the resist coated copper board. A vacuum easel is used to pull the mask into close contact with the copper board.

    You then expose the mask & board combo to UV light for a predetermined time. The UV light penetrates the transparent traces on the mask making the resist insoluble.

    You develop the board and then etch it in your etching solution. This etches away the spaces and leaves the copper traces on the board.

    Hope this helps.
    Last edited: Jul 3, 2011
    EngIntoHW likes this.
  3. EngIntoHW

    Thread Starter Member

    Apr 24, 2010
    Thank you very much mate :)
    It helps a lot