Humm. The same size as the component metallization. I do not think a design that followed that advice would satisfy the acceptance criteria in J-STD-001 or IPC-A-610 at Class 3. Many of the SMT device types have some criteria that requires solder to form a fillet extending up the termination. If the land pattern is not slightly larger than the lead, or metallization this is cannot attribute would be difficult or impossible to judge. 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Werner Engelmaier
Sent: Monday, October 03, 2005 11:30 PM
To: [log in to unmask]
Subject: Re: [TN] IPC7351 Questions


Hi Clayton,
First, the biggest difference inpads should be—but rarely is, whether the 
soldering process is wave or reflow soldering. You need a large pad so the wave 
can touch it. for reflow soldering, the pad needs only to be the sam size as 
the component metallization—but rarely is because of old habits.
Second,   because of the drawbridging/tombstoning problem, the pads should be 
as small as possible—quite a contradiction. Trying to avoid this problem 
accounts, at least to some extent, for the various shapes.
I certainly would not use a large, one-size-fits-all pad option.



Werner

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