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Paste Mask Question

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    Posted: 24 May 2018 at 5:50am
Hi,

I'd like to ask what is the general guideline for paste stencils. 

Should the stencil be same size as the pad, smaller or greater? 

I know that in BGA packages we want very few solder paste on the pad. And on other packages, I was creating a paste mask figure 70% of the pad. 

I am a bit confused now, and I don't know if should continue to do that or leave it 1:1 and let the assembly plant deal with it.

Thanks,
Theocharis
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2018 at 6:08am
For Standard SMD pads the Paste Mask aperture size is 1:1 scale.

For Thermal Tab pads the Paste Mask Reduction is between 40 - 60%.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote vavouris Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2018 at 6:15am
Thank you! That was fast.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2018 at 6:19am
If you use Rectangle Pad Shape, the Paste Mask aperture will be Rounded Rectangle, so you might as well use Rounded Rectangle for the pad shape too.
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