How to Design PCB Stencil to Optimize Solder Paste Uses?

[Ifthekhar.ahammad]

For QFN and other SMD IC packages

For other RLC SMD pacakges

Hello all,

I am using Eagle to design my PCBs. For the last few months, I have been designing mostly with SMD components and I have realized that due to the design of the stencil, I am putting way too much solder paste on the PCB board. I have seen many stencil designs where other than spreading the paste on the whole pad of the component (even for resistors and capacitors), it is spread on some sections of the pad by cutting the stencil in different patterns (reference image added above).

To do something like that do I need to prepare the stencil layer (is it "tCream" or "tPlace" layer?) by myself and send it to the PCB fabrication house or do I need to request the PCB fabrication house to do it for me?

If I need to do that by myself then I would appreciate it if someone can share the knowledge of how to make that kind of modification on the "Stencil layer" in Eagle. And if I need to request the PCB fab house then what technical term should I use to let them know that I need that feature on the stencil?

Thank you all.

[silvio3105]

Solder paste is in tCream/bCream.
Every SMD pad has option called "Cream". Eagle/F3E creates solder paste automatically(if option is checked). If you want to create custom shape cream, then you have to do it manually, with polygon tool.
As far as I know, EAGLE/F3E only can create rectangle SMD shapes. You can create round shape with 100% roundness and same height and width.

And you cannot set expand to opening. Most of the time at work I use -1mil for stencil opening. Here is opening same size as SMD pad.

[Ifthekhar.ahammad]

Thanks for the idea. But why is not auto stencil pattern selection a built-in feature of Eagle? Eagle is already mature enough software, so it should have had this kind of feature built-in already 🤔🤔, Right?

[jorge_garcia]

Hi @Ifthekhar.ahammad 

I hope you're doing well. The image you linked showed many of the possible variations for stencil openings but the most commonly used ones are just variations on the rectangular opening. You usually shrinking the stencil opening by a certain amount is enough. You can do that in the DRC under the Masks Tab, you can specify how much smaller you want the stop mask opening to be. 

If you need to do the custom shape for some reason then the best option is to go into the library disable the default cream mask that's generated and draw in whatever special stencil opening shape you want. This isn't something that's done frequently so for now it's a low priority feature.

Let me know if there's anything else I can do for you.

Best Regards,