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TM4C1292NCZAD: landig pad size design TIVA Microntroller

Jon Bilbao
Intellectual 1415 points
Part Number: TM4C1292NCZAD

Hi, 

Customer is working on a layout design where a TIVA microcontroller is populated.

Series: TM4C129x Package: 212-Ball BGA  (0,5mm Ball Pitch)

 Looking through the corresponding datasheets our customer noticed some discrepancy for the size of the recommended “landing pad size”.

The landing pad size varies  0,05mm in the diameter. Source#1: 0,25mm   /  Source#2: 0,3mm

According to the more up to date document (year 2015, Source# 2) our customer suppose a landing pad size of 0,3mm diameter is highly recommended to ensure proper soldering.

Is this assumption correct?

 

Source #1:

http://www.ti.com/lit/an/spma056/spma056.pdf

“System Design Guidelines for the TM4C129x Family of Tiva C Series Microcontrollers”

 Section 3.1.1

Designator B

Source#2:

http://www.ti.com/lit/an/spraa99b/spraa99b.pdf

“Application Report SPRAA9B – March 2008 – Revised 2015”

“nFBGA Packaging”

Page #6

Ball Pitch 0.5

Regards,

Jon

 

  • 0
    TI__Guru*** 132875 points
    Hello Jon,

    Thanks for reaching out about this discrepancy to get it clarified.

    The answer in this case is that you should follow the TM4C Design Guidelines document. That is the correct landing pad size, and I verified this with a layout expert who works with these devices.

    I am not sure who wrote the nFBGA Packaging guideline, but while newer, I believe that is the source for the discrepancy at least in regards to TM4C MCU's. Not sure how other 212-BGA devices are specified, but for TM4C it should have been specified per our design guidelines. I will follow up with the documentation team to see if this can be addressed.

    For some more technical background, if you look at the device datasheet for the package dimensions on Page 1841, you will see that the nominal ball diameter is 0.30mm. To use Non-solder-mask-defined (NSMD) pads, you want the pad to actually be a little smaller than the ball diameter. This is because you want the solder to flow around the ball and onto the sides of the pad to create a strong connection between the ball and the pad. By having a slightly larger ball diameter compared to the size of the NSMD landing pad, it is easier to get the solder to properly flow to sides of the pad as well. When having a matching landing pad size, it is more likely to only have solder flow on the top of the pad and not the sides, thus creating a weaker connection. The risk here is that having a weaker connection between the ball and the pad could result in a failure when the PCB is subject to vibrations. Therefore, we recommend using a landing pad size of 0.25mm which is ideal to ensure strong connection, and that is what is described on our design guidelines.