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TM4C129XNCZAD: NFBGA (ZAD) | 212 paste mask (stencil) question

Ivaylo Raynov
Prodigy 10 points
Part Number: TM4C129XNCZAD


Tool/software:

Hello,

I want to create (use) a footprint for TM4C129XNCZAD in Altium Designer.

From your site it seems that the official (approved) source of PCB footprint "NFBGA (ZAD) | 212" is Ultra Librarian. I downloaded it and everything seems fine, except the paste mask (stencil openings) for the pads.

They are very small compared to the pad dimension. Is it intentional and is there a special idea behind that?

I checked in your document SPRAA99C – MARCH 2008 – REVISED MAY 2021 for nFBGA Packaging and as I understand the stencil aperture is the same as pad dimension.

Please advice.

Thank you!

BR,

Ivaylo Raynov

  • 0
    TI__Guru**** 191906 points

    Hi Ivaylo,

    Ivaylo Raynov said:

    They are very small compared to the pad dimension. Is it intentional and is there a special idea behind that?

     Reading the SPRAA99C document, it has the below table showing the Stencil Aperture opening relative to the Pad Size for a 0.5mm Ball Pitch. It is 75%. I'm not understanding what you mean they are very small compared to the pad dimension. It seems fine to me. The symbol has been in public for quite a while by customers and I don't think you will any issue with it. 

  • 0 in reply to Charles Tsai
    Prodigy 10 points

    Hi Charles,

    If you look at the attached picture you will see the small grey point in the center of the pad (that is the paste mask). And on the right you will see how the aperture is specified (again paste mask field). Really small... That is what I get when I open the footprint from Ultra Librarian. Expansion -4mil. Why that?

  • 0 in reply to Ivaylo Raynov
    TI__Guru**** 191906 points

    Hi Ivaylo,

     I must say I'm not a Ultra Librarian expert. My understanding is that Top Paste Expansion is used to control the size of the solder paste. The design rule allows a positive or a negative expansion to either increase or decrease the solder paste layer. In the case of -4mil, it decreases area. The paste area may be small but after reflow, the solder paste turns into a molten state, where it then begins to flow and form a joint between component pins and landing pads and the final area will be larger. 

    https://www.ultralibrarian.com/2021/08/05/the-pcb-soldering-techniques-you-should-know-ulc

  • 0 in reply to Charles Tsai
    Prodigy 10 points

    OK... my idea was that according to your document when the pad is 0.4mm than the stencil aperture is 0.3mm. That's fine. According to Ultra Librarian footprint, the way it is declared, the stencil aperture is about 0.05mm. It seems strange. Just wanted to arise the topic because it is "official" somehow footprint and when open in Altium you see this. I believe the correct is 0.3mm paste mask opening...