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Where to find TI diagram PCB footprint for PD(S-PQFP-G128) TQFP128 package TM4C1294NCPDT.

Genatco
Guru 55913 points
Other Parts Discussed in Thread: TM4C1294NCPDT

The TQFP-128 package diagram in datasheet is not the same thing as (S-PQFP-G128) footprint layout of PCB pads.

http://www.ti.com/lit/ml/mpqf013/mpqf013.pdf

The layout of PCB pads mathematically measures 12.420mm given 0.4mm spacing, is that (center) of pin dimension line 12.4mm hard to tell? Measured from what might be the center of the 2 pins is hard to know for sure even at extreme magnification.

Pin width 0.23mm to 0.13mm  +0.05 (M) is the tolerance? Some vendor appear to infer both as max/min other vendors seem to add the min to the max when no (M) tolerance is given. These 2 dimensions seem to have a very wide variance, + 0.05m (M) added we get 0.28mm to 0.18mm almost double the pin width. My footprint pads are now 0.226mm wide, any wider causes DRC rules violations in the space between pads, again we get 12.42mm with .226mm wide pin @0.4mm centers x 32 pins/side. BYW (,) UIA is a Euro standard separator, (.) is same thing SAE standard.  

1. Where to find the TI recommended G128 solder mask area details and or solder paste stencil diagrams? 

2. TI takes measures for smaller packages to relate solder mask details. TQFP package is seeming highly prone to solder shorts given the density of pins. Is that an incorrect assumption?

  • 0
    TI__Guru**** 244400 points
    Hello BP101,

    The CAD symbol and foot print can be downloaded from http://webench.ti.com/cad/

    The file will be in bxl format and the instructions can be used to convert the same to the EDA tool that you have. I have soldered QFP package by hand using 2 solder heads. It is difficult but making sure that the solder paste is cleaned after a few pins will help.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 55913 points
    Hi Amit,
    Wish the datasheet would have mention CAD being available before making all custom footprints for every TI chip especially the TQFP128 was very difficult. The solder paste mention is a smaller area inside each pad applied prior to parts placement via a stencil necessary for solder flow process. Some blogs say it helps keep solder from balling up causing bridges etc.. .

    Thanks :)
  • 0 in reply to Genatco
    TI__Guru**** 244400 points
    Hello BP101,

    The webench link is one that is being populated for the new devices and the process of moving the older devices continuously happen.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 55913 points
    Hi Amit,
    The PCB tool we are using does not support importing footprints. The DXF file export can import to ACAD but that will not likely have the stencil or any included dimensions. That is the nature of DXF - is only the scale outline of the foot print.

    Is there a mechanical drawing PDF that shows the recommended pad dimensions, spacing, solder mask keepout and stencil layout?
  • 0 in reply to Genatco
    TI__Guru**** 244400 points
    Hello BP101,

    That would be in the data sheet for the device.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 55913 points

    Hi Amit,

    That is not the footprint in the datasheet it is the TQFP device package for the most part and not one detail about the recommended pad size is printed. That detail is highly important and our AutoCAD license is expired so we can't import the DXF files.

  • 0 in reply to Genatco
    TI__Guru**** 244400 points
    Hello BP101,

    That is the foot print. The data sheet gives the pad size as max 0.23 and min 0.13 (mm). With the max size of the pad as 0.23 there is still a gap of 0.17 between adjacent pins.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 55913 points

    Hi Amit,

    Ok makes since now the +.05mm (M) tolerance is Median not absolute maximum yet still no solder mask or solder paste stencil dimension are shown in PDF. So the (M) is the expected Median tolerance in case median it reflects the expected size more often is 0.18mm? In SAE we use (NM) nominal in place of (M) and CAD standards for tolerance in the dimensions area are not exactly the same between standards.  

    Below are some custom footprints I made using the metric system was highly educational to say the least.

    The purple is solder paste, orange is surface pad, green boarder is solder mask keep out dimension .05mm-.07mm area surround top surface pad and solid green is top solder mask. All these were created using dimensions included in the vendor datasheet diagram. The yellow box is the naked TQFP footprint, has none of the above attributes. Ignore the inches shown in brown popup, footprint was made in metric but the editor defaults to inches and I didn't switch the grid to mm.

  • 0 in reply to Genatco
    TI__Guru**** 244400 points
    Hello BP101,

    Having the bxl file imported to the Cad tool format (since the license has expired) would have eased your task.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 55913 points
    Hi Amit,

    Now at .194mm spacing between pads .04mm centers and 12.420mm end to end enter of pin. The board house DRC rule has .1778mm minimum annulus was generating 128 errors with a .023mm wide pad, so remade them .0226mm and 128 errors disappeared. Knowing what the recommended medium density solder mask keep out and solder paste are should be if any at all would help.

    This is my first PCB with a SMT chip in XL footprint so the mystery widens is the solder paste and keep out even recommended by TI when automated parts placement is expected?

    These kind of questions are fully disclosed in other TI datasheets for chips having smaller footprint size but omitted in the TM4C1294NCPD datasheet for what ever reason?
  • 0 in reply to Genatco
    TI__Guru**** 244400 points
    Hello BP101,

    I think doing the same with the original set of cad files would answer that question. Our board house does do smaller keep outs.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 55913 points
    Hi Amit,

    Trying to express PCB tool can not import foot print files. That ability a logical reason for using Ultra Librarian in PCB programs that allow importing foot prints. Otherwise the engineer is left to freeze outside the circle of enlightenment?

    Perhaps TI could be more flexible with the TM4C1294NCPDT footprint disclosure, not excluding parts in the PDF. Honestly the PDF should have that information as most TI data sheets do include such detail better than many vendors out there.
  • 0 in reply to Genatco
    TI__Guru**** 244400 points
    Hello BP101,

    I have used Ultra Librarian to generate the symbol and footprint for both Eagle CAD and Altium. The whole intent of doing so was to reduce the chances of error when doing the same via a datasheet.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 55913 points
    Hi Amit,

    Both very expensive licensed programs?

    Can you please post share that foot print diagram with the forum, that is if it has dimension lines etc...
    Perhaps I did something wrong but can not see the actual footprint in Ultra Librarian, is that normal?
  • 0 in reply to Genatco
    TI__Guru**** 244400 points
    Hello BP101

    UL does not show the footprint but generates the CAD tool specific files. These have to be imported in the correct CAD tool and then you can use it. You may want to try the free version of Eagle CAD.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 55913 points

    Hi Amit,

    That is not entirely correct and Ultra Librarian will show the properly configured footprint with all vendor dimensions.

    The user must select display all layers to see the solder mask/paste areas. TI has not entered any dimensions for the mask area as several examples included in Ultra have dimension lines and numbers.

    Again we have to guess the width and length of the very elongated pad,  mask border and solder paste areas?

    BTW: The oversize numbers on the pads are not very impressive and become indistinguishable.

     

     

  • 0 in reply to Genatco
    TI__Guru**** 244400 points
    Hello BP101,

    You can file a support request to Webench Team to get the data also available.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 55913 points

    Hi Amit,

    The point being made was the recommended dimensions for the footprint layout are missing in the TM4C1294NCPDT datasheet.

    Your response was that is because Ultra Librarian is being used in lue of providing footprint dimensions in the datasheet.

    Shouldn't missing dimensions actually be an internal matter.

    Would be nice to confirm the dimensions for our recently updated custom footprint is within recommended tolerance. Good thing we double check all this and discovered that .020mm discrepancy since corrected. There was a slight shift pads laid down in the -x direction, TQFP128 package was the very first custom part entry made in the PCB library. Would advise TI double check (S-PQFP-G128) Ultra Librarian footprint, the inside arc of each pad appears lopsided. Perhaps adding dimensions at the same time might help reveal minor errors. 

     

  • 0 in reply to Genatco
    Guru 47900 points

    Might it be that some industry standard(s) exist for such device - and that your search among multiple, other vendors for that exact TQFP device - may reveal certain "commonalities?"   

    It's doubtful that this vendor would "blaze a new trail" - thus if frustrated here (and vendor's rep is in NO WAY responsible - you must realize) your expanding search for a "near standard" may provide (some) cover & comfort...

    In addition - you may survey (your) board house & several others - seeking their opinion in your regard...