Bridget,

There was an excellent paper written by Paul Mescher of Amkor Anam
addressign "...Surface Mount Assembly of Amkor/Anam BGA Packages".  In this
paper Paul describes the importance of PTH isolation (via isolation) and to
paraphrase him: "No matter what shape or definition technique is used for
the mounting pad, the isolation of the PTH from the mounting pad is an
important feature.  If the PTH is contained within the mounting pad, solder
can and will wick down the PTH.  The amount of solder that wicks depends on
many factors, including PTH finish and coating variations.  Because of this,
the results are somewhat unpredictable.  Some solder joints may be
unaffected, while others will be starved to the point of creating opens.
The worst result is a partially starved joint with severely reduced cross
section.  This joint can have significantly lower fatigue life and result in
early system failure.  Because the quality of the solder joint is guaranteed
by control, rather than inspection, designs/processes that result in random
distributions are generally considered unacceptable, and the PTH-in-pad
design is not recommended."

If you require additional information you may want to talk with Paul
himself.  I do not have his number, but he is located in Chandler, AZ.

Chad Thibodeau
EF Data
Component Engineer
602 333-2138 Phone
602 921-9012 Fax
[log in to unmask]

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