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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