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May 2008

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Subject:
Re: 0402 anti-tombstoning land pattern
From:
Werner Engelmaier /* <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Thu, 22 May 2008 14:09:56 EDT
Content-Type:
text/plain
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text/plain (43 lines) 
Hi Gramsey,
The SJ strength is not an issue—however, the solder joint height is. If the 
gap between the soldering pad and the component metallization is small, that 
connection fractures relatively shortly in the live of chip components 
[depending on the size of the T-cycles, of course] and the solder connection hangs onto 
dear life by the fillet—I look at this as a Band-Aid approach.
It is much better to increase that SJ gap because that dimension, h in the 
Engelmaier-Wild creep-fatigue model, is a primary parameter in increasing 
reliability. That increase can come from stacking the CC off the PCB, by gluing it 
down [the glue thermal expands during the soldering process creating a sizable 
gap], by swimming it up [only possible if you do not have a fillet] creating a 
solder ball/column.

Werner
Future workshops:
Reliability Issues with Lead-Free Soldering Processes, June 17, London
Interconnect Failures and Design for Reliability for PCB PTHs, June 17, 
London
Pb-Free Soldering Processes—Survival, Quality, Reliability, August 18, 
Orlando
Reliability Issues with Lead-Free Soldering Processes, September 22, 
Schaumburg
Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle Fracture, 
ENIG), September 22, Schaumburg



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