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July 2005

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Subject:	Re: Trace width ratio to pad
From:	Mary Sugden <[log in to unmask]>
Reply To:	(Designers Council Forum)
Date:	Thu, 28 Jul 2005 00:08:52 EDT
Content-Type:	text/plain
Parts/Attachments:	text/plain (35 lines)

Good solder joints are made in design, not in assembly. Since the earliest
days, the folks in assembly have been forced to develop work-arounds for a
multitude of poor design practices.

Among the worst problems, is poor soldering characteristics due to thermal
imbalances in the conductive pattern. Ideally, all solder joints will have
good thermal characteristics. The first concern is the shape of the solder
land since it is critical to good fillet formation. The next concern is routing
traces into the footprints in a manner that does not heat sink or deform the
solder joint. Having worked in failure analysis for PCB assemblies, I could
talk on this subject for hours.

Many years ago, NASA released a comprehensive study of long term failures in
printed circuitry. Their conclusion was, 85% of all long term failures
could be traced back to the solder joint failures as a result of bad design
practice. That is... the boards were designed to fail.

The IPC Design Standards includes information related to this subject. For
lack of understanding, it is often discounted by designers. All too often,
decisions are made in design for the sake of expediency rather than what's
best for a reliable design.

I believe all PCB designers should be trained and certified in soldering.

Mary Sugden, CID+

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