VF3xx LQFP176 exposed pad connection?

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VF3xx LQFP176 exposed pad connection?

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Contributor I

Hi

According to the LQFP package drawing 98ASA00452D, there is an exposed copper pad underneath the package. Described as exposed flag in the package drawing document.

http://cache.freescale.com/files/shared/doc/package_info/98ASA00452D.pdf

I can't find any reference to this pad in the F-series datasheet.

http://cache.freescale.com/files/microcontrollers/doc/data_sheet/VYBRIDFSERIESEC.pdf

Or the f series reference manual.

http://cache.freescale.com/files/32bit/doc/ref_manual/VYBRIDRM.pdf?fasp=1&WT_TYPE=Reference%20Manual...

I have only found references to pins 1-176.

Have I missed something in the manual?

What is the exposed pad connected to? I'm assuming ground.

/Erik

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Senior Contributor V

Hello Erik,

Good catch! I will mention it our documentation.

This exposed ("belly") pad is connected to VSS (ground) internally, so, please, provide a pad of the board tied to the the internal GND plane with numerous vias - for both electrical and thermal purposes.

To prevent solder from being "sucked" into the the via "tubes", consult your board fabricator; usually vias either filled with metal (better thermal conductivity but more expensive) or tented on the top (worse thermal conductivity but much cheaper) are used in this case.

Regards, Naoum Gitnik.

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Senior Contributor V

Hello Erik,

Good catch! I will mention it our documentation.

This exposed ("belly") pad is connected to VSS (ground) internally, so, please, provide a pad of the board tied to the the internal GND plane with numerous vias - for both electrical and thermal purposes.

To prevent solder from being "sucked" into the the via "tubes", consult your board fabricator; usually vias either filled with metal (better thermal conductivity but more expensive) or tented on the top (worse thermal conductivity but much cheaper) are used in this case.

Regards, Naoum Gitnik.

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Contributor I

Hello Naoum

Thank you for the clarification.

Best regards

Erik

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