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July 1997

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Tue, 15 Jul 1997 21:52:34 -0400 (EDT)
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Hi John,
The use of non-functional lands has a mixed impact on reliability. For FR-4
MLBs, non-functional lands have shown a slight reliability advantage (see
IPC-TR-579, 'Round Robin Reliability Evaluation of Small Diameter Plated
Through Holes in Printed Wiring Boards'), PROVIDED that the presence of the
non-functional lands does not reduce the quality of the drilled holes and
with it the resulting quality of the plated copper barrels (see Engelmaier,
W., "Manufacturing and Reliability Issues of Small-Diameter/High
-Aspect-Ratio Plated-Through-Holes and Vias", IPC Workshop Handout, March
1997). Also, for MLBs with highly CTE-constraining reinforcements (e.g.,
Kevlar fibers), the PTH/PTV copper barrels actually see larger stresses with
non-functional lands (see Bhandarkar, S. M., A. Dasgupta, D. Barker, M.
Pecht, and W. Engelmaier, "Influence of Selected Design Variables on
Thermo-Mechanical Stress Distributions in Plated-Through-Hole Structures,"
ASME J. Electronic Packaging, Vol. 114, No. 1, March 1992, pp. 8-13).
To give you a straight answer, the possible small reliability gain is not
worth the possible manufacturing difficulties.

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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