• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 63 subscribers
  • Views 477 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS73701DRB - Question about the land pattern

Greg
Expert 2031 points
Other Parts Discussed in Thread: TPS737, DP83620

Page 33 of the data sheet for the TPS737xx shows an example land pattern for the DRB package.  The center pad's copper and stencil features are shown, but I don't see any details about the solder mask for the center pad.  Should there be a strip of solder mask between the large center part and the four pads on the ends?

I have used this part before and I have never seen any solder on the outer edge of the part for the 4 ground pads like it does for the main 8 pads.  I did not include a solder mask strip to separate the middle from the outer pads.  It appears to me that the large center part is thieving the solder away from the 4 small ground pads.  It seems a narrow strip of solder mask would prevent that from happening.

The narrow strip I am proposing is kind of "solder mask defined", but I don't think it would affect the orientation of the part during reflow.  Every other copper feature would be non solder mask defined.

Thanks and regards,

Greg

  • 0
    TI__Guru 55940 points
    Hi Greg,

    The main benefit from the thermal pad is the large rectangle centered under the device. As such it is fine if the solder is pulled to the center part; however, if you would like to add a strip of solder mask, this will not hurt the performance either.

    Please note that the Example Stencil Design in the top right corner of the page does show a break.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Expert 2031 points

    Hi Ryan,

    Thanks for the reply to my question.  I followed the suggested stencil layout when I made the component.  I'm thinking that the gap in the stencil between the center pad and the fingers is large enough to absorb most of the solder, which is why I don't see much on the ends of the chip.  It seems the finger terminals should have solder on them, but after reading the following application note, maybe it's unimportant:

    http://www.ti.com/lit/an/slua271a/slua271a.pdf

    On page 15 it says "The exterior fillet formation may vary based on manufacturing factors, such as flux activity, solder volumes, and overall standoff height. Due to factors outside of TI’s control, no assurance for consistent solder fillet heights on the package sides during assembly can be made. IPC-A610D does not require a side fillet, since the side terminations are not plated. While it may appear the wetting is reduced on the side of the component, the solder joint underneath is not affected".

    The more I think about this, the more I realize that it isn't very important for the 4 ground terminals to have solder on the outer edge of the chip.  I have confidence that the center portion of the exposed tab is going to be soldered well enough, so there is excellent electrical and mechanical connection.

    Seeing the metal terminals exposed on the edge of the chip makes me feel like they should be covered by solder with a nice fillet.  But evidently that isn't the case.

    Regards,

    Greg

  • 0 in reply to Greg
    Expert 2031 points

    Hi Ryan,

    I'm surprised that the application note I referred to is not listed on the product page for TPS737.  This isn't an isolated case either.  I currently have an open case regarding the packaging for the DP83620 (https://e2e.ti.com/support/interface/ethernet/f/903/p/477251/1717223).  I was pointed to an application note that explained why the suggested footprint had the paste shifted on top of the solder mask a little bit.  That application note is also not listed on the product page for the DP83620.  Maybe these are two isolated cases, but it seems that TI might need to add a lot of links to packaging and PCB layout application notes.

    Regards,

    Greg

  • 0 in reply to Greg
    TI__Guru 55940 points

    Hi Greg,

    Thanks for the suggestion and linking the application note!  I agree it would be helpful to make this application note more visible and am going to pass your suggestion along on the team here.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Expert 2031 points
    Hi Ryan,

    Your welcome and thanks for passing along the information. Have a great holiday season.

    Regards,

    Greg