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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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SMTA-Samy

#84781

SMT Stencil design | 21 April, 2020

Why are you trying to overprint?

Take some time to review this presentation by Chrys Shea titled SPECIFYING STENCILS TO OPTIMIZE PRINT PERFORMANCE.

https://www.smta.org/chapters/files/Uppermidwest_Chrys_Shea_Presentation_Upper_Midwest_Expo.pdf

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#84788

SMT Stencil design | 23 April, 2020

Stencil editing is something that you have to do to do well. And you have to look at the boards after the screen printer and after the oven. Reading white papers ain't gonna cut it.

And then there will always be part pad combos that will introduce some new problem.

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SMTA-Davandran

#84816

SMT Stencil design | 30 April, 2020

I am seeing a lot of solder ball for PIP process. is it due to the paste height go beyond 0.2mm.? what is the DOE need to focused for PIP process?

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SMTA-Davandran

#84817

SMT Stencil design | 30 April, 2020

Do considering AR and 5 balls rule during designing stencil aperture. it give better paste release. Aperture redesigning need to look into symptom that we are seeing on AOI. It will be given us idea hows to improve aperture design to improve SMT first pass yield.

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#84821

SMT Stencil design | 1 May, 2020

It could be the paste or the profile. (or something else) You should try changing those one at a time.

Also maybe try less paste and using preforms.

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SMTA-Aakash

#84892

SMT Stencil design | 21 May, 2020

Refer to IPC 7525 (Stencil Design Guidelines). You will find a lot more information there.

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