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Wed, 13 Nov 1996 13:14:38 -0500
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Expansion on previous E-Mail given the E-Mail from gfranck:
Previously: You certainly will not get the concave solder fillet without
surface pads, but through-hole connections have significant redundancies as
compared to SMT solder joints and that should not adversely impact
reliability. This of course assumes that the design is otherwise properly
designed. Since you still have pads on the side from which repairs are done,
repair operations should also not be impacted. 
Added:  Z-axis expansion of a .093", 14 layer board is always a concern.
Normally the loading of the PTH is in the middle of the PCB (this is where
failures occur with the exception of failures due to land rotation at the
surface). My assumption is that you use high Tg (180oC) resin and E-3 HTE
copper foils, control maximum possible temperatures during all soldering
processes, and plate at least 1 mil (1.2 to 1.4 mils is better) of copper.
Plating good uniform copper into a .035" (?) drilled hole should not be a
problem with an aspect ratio of ~3. CTE of the PWB in the z-axis is 50+ppm/oC
below Tg and 300+ ppm/oC above Tg more than the copper. Having said all that
you certainly will have a shift of the location of maximum loading towards
the padless PWB side, but my initial guess is that the maximum load will not
significantly increase, particularly when all layers have lands, both
functional and non-functional. Nevertheless, only an FEA analysis or testing
can give a definitive answer. 
            
Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 201-543-2747
E-Mail: [log in to unmask]

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