AVR-Chat

My T26 data sheet (12/03) does not seem to say anything
about it, or even that it IS solderable. TI usually notes
things about a thermal-pad quite carefully; nothing seen
here. In fact, this data sheet only has the word "solder"
once, and that refers to the tip region of SOIC pins.

Jim


On Wed, 02 Nov 2005 15:47:04 -0800
 Johnathan Corgan <jcorgan@aeinet.com> wrote:
> Dave VanHorn wrote:
> 
> > The data sheet says that the large pad under the device
> "should" be 
> > soldered to ground.. 
> > 
> > Does anyone have direct knowlege of wether is HAS to
> be?
> > Assume all perimiter ground pins are in fact grounded.
> 
> Not direct knowledge, no.
> 
> Speaking generally, these type pads have three
> roles--thermal
> conduction, EMI reduction, and lowered ground inductance.
> 
> The first is hard to get away from, unless you can
> guarantee the device
> will be operated at a reduced ambient temperature or at a
> reduced power
> consumption, or with a beefier heat sink.  Some parts
> specify different
> limits with or without the pad soldered.
> 
> Having a ground shield under the die can improve noise
> immunity,
> especially in sensitive circuits like ADCs or other mixed
> analog-digital
> chips.  You can get something like this with a circuit
> board ground
> plane underneath, but it's not as close to the die as the
> pad is in the
> package.
> 
> Finally, the large pad can serve as a low-inductance
> ground return that
> helps avoid ground differentials in the chip.
> 
> Personally (not with AVRs, though), for home brew stuff,
> I've put in a
> ground plane on both sides and an array of plated vias
> inside that,
> filling the vias with solder and hoping at least some of
> it gets wicked
> up onto the pad surface.
> 
> Your mileage may vary, of course!
> 
> -Johnathan, AE6HO
> 
> 
> 

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