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From [log in to unmask] Fri Sep 13 08: |
45:32 1996 |
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To add my input to the argument:
Keeping the non-functional lands in the board does decrease the Z-axis
expansion at soldering temperatures by about 10-30%, mainly, because above
the Tg the Z-Axis expansion is great for the resin systems, but copper
remains the same. As mentioned, the difference in expansion will make a
difference on whether you have lifted lands or not after HASL or soldering, I
have seen this demonstrated several times . Of course, the boards with the
thinner dielectric benefit the most. The hole-wall pullaway, if this is a
concern, is also decreased and many people subjected to the 40% rule will now
pass this requirement if non funtional lands are retained . The fabricators,
of course, want them removed as they increase the probability of shorts or
other etching defects and removing them will increase yield.
Phil Hinton
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