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I ordered a multiple PCBs which all arrived fine. I never included a stencil because of the high cost for it compared to the PCBs. Now I combined a few board designs to fit on a single stencil, so I can just order one stencil for multiple boards.

I ordered it at JLCPCB and now got an email asking if I want to use the SolderMaskLayer or PasteMaskLayer since they are different sizes. Now I'm a little confused by this question as I just use the default component designs from their library, so this should be a thing for everyone sending them designs.

This is the screenshot they sent me:

JLCPCB response

Below is a screenshot of my design only showing the SolderMaskLayer(purple) and PasteMaskLayer(grey)

My design

I'm really confused about what to choose here. I have the boards in my hand and the SolderMaskLayer(purple) seems to be what I need, since the other one contains the little square cutout which I cannot see on the board.

Original email:

Sorry to bother you, but there is one thing that we want to confirm with you about your stencil order before proceeding.

The pad size in paste layer is different with that in solder mask layer, shall we cut out according to paste layer or solder mask layer?

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    \$\begingroup\$ I can only assume the technician looking over your gerbers is new and inexperienced; I doubt they'll ask this of everyone who sends them gerbers. A lot of inexperienced PCB designers will use identical openings for the paste mask and the solder resist (which is sometimes okay but with certain packages very much not), so maybe they haven't encountered one with different ones before. \$\endgroup\$
    – Hearth
    Commented Sep 4, 2023 at 18:26
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    \$\begingroup\$ Incidentally, are all your vias and through-holes just also shown in grey in the second picture, or are your vias and PTHs present on the paste layer? They shouldn't be, unless you're doing some kind of pin-in-paste thing. \$\endgroup\$
    – Hearth
    Commented Sep 4, 2023 at 18:27
  • \$\begingroup\$ No the through holes are not visible on the grey mask, I should have gotten rid of the multilayer layer as this makes it a bit confusing on the picture. It's also a little confusing as to why some pads are green and some red as the purple arrows don't indicate the problem well. But I told them to go for the solder paste layer(grey) as per Spehro's answer. \$\endgroup\$
    – RektByMemes
    Commented Sep 4, 2023 at 18:38

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Solder paste layer is literally the layer intended to produce a stencil. That's its only purpose.

Typically the solder mask layer (which is used to produce the solder mask) is a bit different size from the solder paste mask for the SMT pads. Also, things like non-tented vias, test points, fiducials, contact fingers and pads for THT components have a solder mask hole, but you don't want them slathered with solder paste.

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    \$\begingroup\$ Ah yes, I forgot about the THT holes. It makes a lot of sense that you want to avoid this. Your explanation made it all clear. Thank you. \$\endgroup\$
    – RektByMemes
    Commented Sep 4, 2023 at 18:35

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