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

Question

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.

John T · Accepted Answer

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.

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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?

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