The below recommendation was posted on Technet. I did not keep the email and I can not remember who to give credit for it. Once implemented we dramatically reduced defects. My policy is to go with what I know. The component vendors are not right often enough with respect to manufactuing recommendations for me to trust them everytime.

> For QFNs in general, we make sure the land pattern sticks out enough 
> to be able to touch a fine soldering tip to it and to provide 
> additional paste to the pin pad joints -- I believe this is around 15 
> mils. You have to keep the pin pad joints and ground pad joint 
> separated with a solder mask dam. Make sure the soldermask is never on 
> the ground pad on one side and off on the other (all off or all on so 
> there's no teetering and consider solder mask registration specs).
> Don't do one large ground pad stencil aperture or the part floats on 
> top of the solder bubble. 


-----------------------------------------
Leif Erik Laerum
Quality Assurance Manager
Texas Memory Systems
[log in to unmask]
Tel: (713) 266-3200 x468
www.texmemsys.com

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of William Noel
Sent: Tuesday, December 13, 2011 1:52 PM
To: [log in to unmask]
Subject: [TN] TI Paste Recommendations

Hello all - I am working on creating a 24 pin QFN footprint for my CAD library.  Is there a valid reason for making the solder paste smaller than the actual pad outline?  I notice that TI consistently seems to recommend a smaller paste outline than pad outline.  Additionally, they recommend a series of small square paste squares to appear on the thermal pad rather than a single smaller square of paste.  Essentially, IPC-7351 recommendations are different than the TI recommendations.  Any help?  Thank you.

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