Mary,
I agree with what everyone is saying. What I was pointing out and seems
to be misconstrued is that the IPC standard is a guideline. Of course,
there are exceptions to every rule. Since I do every project from
schematic capture, part selection and layout, I know all the
characteristics to achieve the desired results. Most of the time, the
designer is one on one with an ineperienced engineer who doesn't/won't
understand the process. You make a good point on PCB designers being
trained in soldering. I have had the privledge of being a A level
certified soldering instructor at the Jet Propulsion Laboratories. I
have also done technical assignments on Voyager I & 2,which are leaving
the solar system as we speak. By the way, my assemblers clamor over who
is going to work on my projects. Have great day y'all.
Cheers,
Ron Scott C.I.D.
Texas Instruments
Storage Products Group
Tel: 214.567.4715
Cell: 972.816.7978
Fax: 972.761.5070
[log in to unmask]
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Mary
Sugden
Sent: Wednesday, July 27, 2005 23:09
To: [log in to unmask]
Subject: Re: [DC] Trace width ratio to pad
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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