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What Do Know About Soldermask?

John T

Should PCB designers supply exact soldermask information in the artwork files when ordering boards? And should this be 1:1 with pad-size?


After some time at Cadence, a vast difference is very apparent between various designers. Some PCB designs exhibit strict rules regarding soldermask openings, gaps and sizes.

However, many other designers simply export soldermask artworks with an exact 1:1 replica of each components’ copper pad sizes. What are the pros and cons; and what about paste mask artworks?

Please let us know what you expect or do? Should designers: 
A. Supply 1:1 soldermask. Let the PCB Fabricator decide.
B. Supply exact custom soldermask. The Fabricator must follow the artwork precisely. 
C. Supply exact custom soldermask AND solder-paste information should also be supplied.  

Example of SM gap control affecting copper exposure

  • DG202504226528

    I used to do B, but the last few years, I've been doing the A since my fab prefers it.

  • avant

    B. We don't want any changes between multiple board runs or from different fabricators. 

    If a soldermak change is made, some designs might require requalification and testing from our customers.

    Some of our components such as 0201 capacitors, do not have a soldermask bridge between the pads.

    The soldermask parameters are determined and controlled by our manufacturing team working with our fabricators.

    We don't provide paste stencils to our bare board fabricators. 

    I'll add that we manufacture hundreds of thousands of OEM assemblies per year, so our manufacturing parameters are strict.

  • excellon1

    Hi John,

    We use option B for the soldermask. For things like having a soldermask between IC Pads, the minimum physical width of the soldermask is related to the web-width of the mask. Typically the minimum LPI printable web width is 4Mil. For most things we typically target 10Mil oversize. On option B there is all ways going to be some fabrication margin so saying follow the mask requirements precisely may not offer a + margin which could actually be better or easier for the manufacturer to make the board. As long as the minimum is met, we are good with that.

    We also use option C. Normally the pad size will be the solder paste land size. In addition our preference for the pads is to use "Rounded Rectangle pads" so as to provide some relief to the solder paste screen. On very fine pitch components such as a 0201 part, we use round pads. This will allow a solder mask between the pads.

    Best Regards.

  • John T
    in reply to DG202504226528

    Hi DG, yes this is what I can see on many user designs. This seems quite common for specific design types such as bga laden designs. An example concern I have is that some things the pcb fabricator might prefer to do which the pcb assemblers ( or designer) might not want. Examples: how does this affect via openings, via in pads or adjacent to pad. I also have concerns for DFN type components with diepads and what happens underneath. 

    Do you find any other advantages or disadvantages to ordering boards this way?  

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