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AD8317 footprint doubt

Category: Datasheet/Specs
Product Number: AD8317

Hello,

I am currently integrating an AD8317 (replacement for a HMC611LP4) in one of my products. The footprint (LFCSP 8 pins) is not given in the datasheet. There is an application note to help the design with this package (https://www.analog.com/en/resources/app-notes/an-772.html). 

I've finaly download a footprint from Ultra Librarian but the footprint I get does not quite respect the AN-772. 

The pad width on the footprint is 0.254mm and the max pin width in the datasheet is 0.3mm. The AN-772 state that the foot print should a least fit the pin.

The thermal pad on the footprint is 0.6mm wide. If I consider the worse case coponent side I get a 0.3mm wide thermal pad and 0.2mm isloation betwen thermal and pad. In this configuration the distance between the pin and the thermal pad of the footprint is 0.05mm. It's a bit narrow, but maybe this configuration is impossible to obtain?

The AN-772 say a lot about the thermal pad: vias, paste quantity... The footprint given got no via and the paste layer is just the basic one. For the via I assume that for a little component like this thermal vias are not necessary. More, with a 0.3 to 0.6mm thermal pad it's tricky to put some 0.3mm vias under it. 

Ad8317 datasheet:

Ultra Librarian footprint:

Thank's a lot

Parents
  • Hello Djoe,

    First, a disclaimer: the PCB land pattern design guide in AN-772 is for guideline purpose only. Please be sure to consult with your PCB fabrication and assembly vendors for their recommendations and requirements. 

    Although preferred in most cases, pin pad widths are not required to be bigger than the maximum pin widths, especially if doing so would increase the possibility of solder bridging. To avoid solder bridging, the minimum required metal-to-metal clearance is 0.2mm. Your land pattern should be adjusted to meet this requirement. In addition, AN-772 Table II specifies recommended maximum pad widths for various pin pitches. For 0.5mm pitch, Xmax is 0.28mm which is smaller than maximum package pin width.

    The Ultra Librarian AD8317 footprint appears to be appropriate for most applications. If you have concerns and questions on Ultra Librarian's methodology and guideline for generating this footprint, please leave a Model Feedback for them to review.

    As for the thermal vias under the exposed paddle, they are not absolutely required for this IC. However, they can help lower ground path impedance. 

Reply
  • Hello Djoe,

    First, a disclaimer: the PCB land pattern design guide in AN-772 is for guideline purpose only. Please be sure to consult with your PCB fabrication and assembly vendors for their recommendations and requirements. 

    Although preferred in most cases, pin pad widths are not required to be bigger than the maximum pin widths, especially if doing so would increase the possibility of solder bridging. To avoid solder bridging, the minimum required metal-to-metal clearance is 0.2mm. Your land pattern should be adjusted to meet this requirement. In addition, AN-772 Table II specifies recommended maximum pad widths for various pin pitches. For 0.5mm pitch, Xmax is 0.28mm which is smaller than maximum package pin width.

    The Ultra Librarian AD8317 footprint appears to be appropriate for most applications. If you have concerns and questions on Ultra Librarian's methodology and guideline for generating this footprint, please leave a Model Feedback for them to review.

    As for the thermal vias under the exposed paddle, they are not absolutely required for this IC. However, they can help lower ground path impedance. 

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