Werner,
What is mechanism of failure for stress concentrations from soldermask-defined
solder openings? - Thanks
James Patten
TRW
> From [log in to unmask] Mon Jul 7 05:34:49 1997
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> Date: Mon, 7 Jul 1997 07:41:20 -0400 (EDT)
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> Subject: Re: Solder joint design rules
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> Gidday Ingemar,
> (Gidday is likely a phonetic spelling of the Australian equivalent of Good
> Day).
> The geometry of a solder joint can be an indicator of improper wetting, which
> certainly can lead to solder joint failures, but in and of itself not very
> important for solder joint reliability with one exception--solder joint
> height. One also should avoid geometries causing stress concentrations, like
> solder-mask-defined soldering openings.
> The reason for all this is that solder joint failures (again with the
> possible exception of improperly wetted solder joints) are not
> stress-driven--they are strain-driven. Solder joints at typical operating
> temperatures (above -23oC) creep readily and therefore do not support
> stresses for long, they give.
> The most important design step for solder joint reliability is the reduction
> in the magnitude of the thermal expansion mismatch. I would recommend using
> the industry document IPC-D-279, 'Design Guidelines for Reliable Surface
> Mount Technology Printed Board Assemblies'.
> While the choice of the solder alloy can make some difference in the
> reliability of solder joints, this difference is small in comparison to other
> more significant factors, i.e. solder joint height, component size, delta-T,
> delta-CTE, lead compliance.
> You may be interested in a workshop on solder joint reliability I will be
> giving at ISHM-Nordic on September 21, 1997 near Oslo. You could get more
> information from Katarina Boustedt, Ericsson Microwave Systems, Core Unite
> Research Center
> Microwave and High Speed Electronics, SE-431 84 Molndal, Sweden, ph: +46 31
> 747 0219, fax: +46 31 747 0317, email: [log in to unmask]
>
> Werner Engelmaier
> Engelmaier Associates, Inc.
> Electronic Packaging, Interconnection and Reliability Consulting
> 23 Gunther Street
> Mendham, NJ 07945 USA
> Phone & Fax: 973-543-2747
> E-mail: [log in to unmask]
>
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