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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.

  • 0

    the second image shows 4 outlines which u do not need if u r talking about negative masks.

  • 0 in reply to masamasa

    For military and avionics, mask is pulled back 5 mils minimum from the board edge to minimize dust contamination or FOD as boards are routed out from the fabrication panel.   

    Fabricators anticipate negative artwork.  Occasionally, I need mostly exposed ENIG on the back side for thermal dissipation and we've been tripped up by that..  Had to help scrape mask off the backside of half a dozen boards to avoid waiting two weeks to remake them.

  • +1

    Hi Dp09, the soldermask is always provided in this negative image. Soldermask gerber always shows where we don't want mask. Historically this also reduced the file size on old machines. There is no need to provide data describing everywhere soldermask is needed, just where it isn't. This is the standard for sodlermask which producers understand, so there is no need to translate a negative soldermask image to positive for the producers. They understand this format better. So solder-paste gerber layers should be positive but soldermask should always be in negative format. 

    Totally agree with the info above regarding pull back on the board edge! We did this in automotive pcbs also. The soldermask should stop before the board edge so you should see a pcb outline on this layer by way of "negative soldermask". This technique helps the mask to remain healthy after the milling machine cuts out the pcbs. If we cut through the soldermask with the milling tool then we disturb its integrity which may lead to extra moisture intake or contamination at these edges.

  • 0

    sometimes the pullback is not needed on the soldermask. for us, we do not need the pullback.  so u need to contact ur manufacturer.

  • 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.

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