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[SOLVED] which size should I select for footprint?

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baby_2

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Hi,
Here is the TL1963A-33DCQR foorprint. I want to know which size should I select for width and height of each pin?(1 or 2 and why?)
Capture.JPG

Thanks
 

Hi,

TL1963A-33DCQR

I think referring to the expected tolerances on page 37 can be helpful. I may be wrong but it seems what you marked as 1 is referring to the dimensions to make with solder mask, number two is just a bare pad with no solder mask around the edges, so presumably you wouldn't expect mis-landings. I guess the recommended size might be needed to leave a little bit more room to avoid pins landing on the solder mask.
 
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Thanks all for your good comments
It means solder stencil is always is smaller? could you tell me why?
 

It means solder stencil is always is smaller?
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Not necessarily. I usually assign equal aperture size for copper and stencil. Individual stencil apertures may be adjusted by the assembly house after selecting the stencil thickness according to the components used on the board.
 
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The solder stencil opening will vary depending on the thickness of the stencil used, the idea is to get a certain volume of solder paste on the pad... so if Z is solder screen thickness, you have to adjust X & Y to get the correct volume of paste.
Follow IPC-7351 and do all pad openings 1:1, pastes and solder mask.
 
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In addition, please note the "no soldermask defined pad"dimensions.

What I do for volume manufacturing products, is after designing a board I have my board shop engineer perform a DFM (design for manufacturing) review. They are after all, the process experts and who know their equipment capabilities.
More than once they have spotted design flaws that I have overlooked.

Of course, it helps if you have a good working relationship with the board vendor.
 
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Expand you knowledge of how PCB's are made and the importance of DFM, learn and design PCBs that can be manufactured and assembles otherwise your not doing your job properly.
Dig out and learn the basics from IPC-2221 etc.
Or go do an IPC CID course.
Get a font end package and do your own DFM checks and learn from them.
 
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ALL solder paste openings and solder resist openings in your CAD library should be exactly the same size as the PAD 1:1 Do not change the size in the CAD package...
 
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