cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 
gszakacs
Professor
Professor
9,720 Views
Registered: ‎08-14-2007

Datasheets are unclear on usage of die-attach pad for QFN packages

Jump to solution
I've gone through all of the Coolrunner II documentation including the QFN pad design appnote, XAPP439, and the package user's guide.  I can't find anything that specifically says to electrically connect the die-attach thermal pad to the board ground plane.  The mention of thermal vias in XAPP439 seems to imply this.  Also in the Advanced packaging brochure (pn0010951.pdf) there is a cut-away view of a QFN package that shows ground wires going from the leadframe to the die attach.  Was the ground attachment supposed to be intuitively obvious?  Or were the thermal vias supposed to go to isolated copper?

I'm designing-in a CPLD in the QFG48 package and don't have the luxury of re-spinning the board if I get this wrong.  Thanks for any insight.

Regards,
Gabor Szakacs
-- Gabor
0 Kudos
Reply
1 Solution

Accepted Solutions
ljura
Newbie
Newbie
7,336 Views
Registered: ‎09-30-2008

There is an answer in "Device Package User Guide v3.0" (ug112.pdf) on page 23:

 

"The QFN is a molded leadless package with land pads on the bottom of the package. Electrical contact to the PCB is made by soldering the land pads to the PCB. The backside of the die is attached to the exposed paddle through the die attach material which is electrically conductive. The exposed pad therefore represents a weak ground and should be left floating or connected to a ground net."

 

Best regards,

Juri Lyashenko

Message Edited by ljura on 09-30-2008 03:15 AM

View solution in original post

0 Kudos
Reply
1 Reply
ljura
Newbie
Newbie
7,337 Views
Registered: ‎09-30-2008

There is an answer in "Device Package User Guide v3.0" (ug112.pdf) on page 23:

 

"The QFN is a molded leadless package with land pads on the bottom of the package. Electrical contact to the PCB is made by soldering the land pads to the PCB. The backside of the die is attached to the exposed paddle through the die attach material which is electrically conductive. The exposed pad therefore represents a weak ground and should be left floating or connected to a ground net."

 

Best regards,

Juri Lyashenko

Message Edited by ljura on 09-30-2008 03:15 AM

View solution in original post

0 Kudos
Reply