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As a fab company, if a solder mask file is received, it should be converted to "negative" profile before its used for film print?

dp09

Hi Team,

Check the below image of the solder mask layer. The red color pads and holes need not to be masked. 

If this same file is used for screen print it looks some thing like below image (in panel format) -

So in this case, the pads and holes will be masked and rest of the other area will be unmasked..Is this understanding correct.??

If yes, that means its negative should be generated from allegro and that file to be used for screen print.. right..??

Please share the response ASAP.

Thanks.

Parents
  • 0

    From the perspective of the PCB Cad software used to create the gerbers you are far better off sending out your gerbers in positive format than converting the files to negative.

    At the board house they use negative photo resist for both the solder mask and the board. Typically what happens is when your gerbers are received the board house will create composite's which are negative images of your positive gerbers so that the photo-resist may be imaged. The board house typically expects the artwork to be in a positive format !.

    Best Regards.

Reply
  • 0

    From the perspective of the PCB Cad software used to create the gerbers you are far better off sending out your gerbers in positive format than converting the files to negative.

    At the board house they use negative photo resist for both the solder mask and the board. Typically what happens is when your gerbers are received the board house will create composite's which are negative images of your positive gerbers so that the photo-resist may be imaged. The board house typically expects the artwork to be in a positive format !.

    Best Regards.

Children
  • 0 in reply to excellon1

    Can anyone elaborate what is negative & positive artwork. Is there any significant change noticed when film generated as negative artwork

  • 0 in reply to Schulz Jordan

    Hi Jordan there can be a big difference.

    A simple way to look at it is if you decided to print one of your PCB Layers that contained a large ground plane. By default when you look at the screen and then do a printout all the etch will be positive just like looking at your computer monitor. On the paper you will consume alot more ink to represent any area that is positive. For example that large ground plane would be printed in black so that consumes alot of ink.

    With a negative image it is the opposite. What you see on the computer monitor aka your etch will print out clear instead and the areas of non etch that look clear on the monitor will be black instead.

    So the negative image will consume alot less ink to print out.

    At a board house all the photoresist they use is negative based, so to represent your circuit the board house turns your positive gerber files into negatives so they can expose the photo-resist with UV light.

    Main take away is always generate any artwork as a positive that is destined to go to a board-house. The board house expects this by default. 

    Best Regards.

  • 0 in reply to Schulz Jordan

    Hi Schulz, from my experience yes I would say I almost always sent positive copper artwork layers to the PCB manufacturer. But we need to distinguish between copper artworks and others such as soldermask. Typically I would expect to see soldermask in negative format as this describes only the areas without mask and usually is made up of basic shapes like rectangles and circles; these shapes could take up only about 10% of the board area. The negative artwork of soldermask provides a lot less clutter when overlaying the layers and makes it easy to review on a CAM tool. 

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