Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

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SMT Stencil design

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#84667

SMT Stencil design | 19 March, 2020

Hello, can someone share good practise how to calculate how many percent solder paste can be applied on solder mask for better solderability (by increasing stencil aperture). In eg, aperture is increased 30 percent, could it be more? Where find this kind of information? Thank you.

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#84669

SMT Stencil design | 19 March, 2020

Overprinting until the solder paste start detaching from the joint and start forming solder balls. Based on finish, chemistry and type solder mask this number will be different.I also wouldn't call it "better solderability".

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#84673

SMT Stencil design | 19 March, 2020

I tend to go by extending it by a distance rather than a per centage. For example 10 thou over.

Does anyone else give a distance rather than a per centage? For long pads on connectors where I need more solder, a per cent doesn't make sense to me.

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#84681

SMT Stencil design | 20 March, 2020

If you just want a little more paste and don't care where it ends up I guess percentage is OK, but if you're trying control where it ends up it makes sense to specify how far, and in which direction(s).

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DWL

#84683

SMT Stencil design | 20 March, 2020

I've done over printing for Pin in Past applications and you'd be surprised how much you can over print and still end up with an acceptable solder joint and no solder balls.

As others pointed out, there are a lot of variables involved, so trial and error or a DOE might be in order for your specific application.

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