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I have designed a PCB and there are only through hole components in the top of my board and only some surface mount components in the bottom of the board.

Now, I don't know exactly is TOP SOLDER PASTE file is necessary to I send it to fabricator as same as bottom solder paste or only sending bottom solder paste file is enough because of that I have SMD components only in the bottom ?

Beside of that, please somebody explain for me, generally in the which situations we have to send SOLDER PASTE file to the fabricator ?

Thank you very much for your time

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  • \$\begingroup\$ If the top paste layer is empty, then it is not required for the assembler to have. \$\endgroup\$ – Jeroen3 Nov 18 '18 at 20:10
  • \$\begingroup\$ FAB house shouldn't need paste layers. But if all your gerber layers are in one zip file, that is fine. The FAB house can ignore paste layers. Assembly house will or may use the paste layer and/or soldermask layer to make the stencil. I would say that if you don't send the top paste file to the assembly house, the assembly house may ask for it. Then you will have to explain. But if you send them a file with no paste openings, they may realize that there are no SMT components on the top. \$\endgroup\$ – mkeith Nov 18 '18 at 20:34
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    \$\begingroup\$ The fab house needs the paste layers if they also fabricate stencils, which some of them do. \$\endgroup\$ – Simon Richter Mar 27 at 16:23
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Empty paste stencils are just blank, so generally the fabrication drawing/file would state that there are is no requirement for a (topside) solder paste stencil.

It's generally not a good idea to use a solder mask as a stencil mask, for several reasons:

  1. You may put solder where you don't want any, such as test points, wire entry points, etc.
  2. Paste stencil size are in general not the same as solder mask sizes (they are usually smaller). In cases of thermal pads the stencil area is generally broken up to prevent scooping of the paste during application, and to optimize the amount (most manufacturers provide this information in their mechanical drawing specs).
  3. As the designer, it's your responsibility, not the fabricator's, to provide the fabrication documents and standards. The fabricator can be responsible for manufacturing the final stencil and frame to fit their process flow.
    1. If you're talking about sending the actual solder paste (not the stencil mask) it is unusual for the fabricator to request it, unless it's some kind of specialized mix. Most pastes require refrigeration to prevent degradation and are almost always shipped in cold packs (if from a reputable supplier). If it's a common formulation, a request like that would raise flags for me.
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  • \$\begingroup\$ @a2640 It's Gerber, named after Joseph Gerber. \$\endgroup\$ – Andrew Morton Nov 19 '18 at 9:51
  • \$\begingroup\$ Thank you very much for your answer. Actually, I was going to send my GERBER file to the fabricator, and when I was sending them one of my co worker came and told me even when you don't have SMD components in your board you have to add solder paste file in to your GERBER file. It didn't make sense for me and now with your answers I am sure about that the GERBER file which I've sent to our fabricator doesn't have a problem \$\endgroup\$ – a2640 Nov 19 '18 at 15:24
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Paste layers are used to fabric stencils for screen printing solder paste onto the boards.

Both the fabrication of a stencil and using it are distinct tasks you have to pay for. While some PCB manufacturers may also offer stencil manufacture, it is a distinct service. Further, to fabricate a useful stencil you need to specify the material, dimensions and in theory mechanical interface with the stencil printing machine.

So no, you don't need to include a paste layer when ordering PC boards.

And when having boards assembled, you would not include a paste layer for any side of the board that you did not want to print with solder paste - paying to run a blank piece of stainless steel through a stencil production line and then paying someone to flip the board to a second side in the paste printer only to squeegee around solder paste while depositing none of it wouldn't really make sense ;-)

For through hole components you need a different fabrication process anyway, such as wave soldering or selective soldering. Talk to your assembly house (ie, the vendor who populates the boards, which is not necessarily the one who manufacturers the PCBs) about what services they can provide, what materials those require from you, and what limitations such process imposes on your design.

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