Hello Amol
Since all electronic components are now designed, registered and fabricated
using the metric system, would not it be easier to ask for a 0.5mm pitch
device with lands of 0.25mm by 0.7mm?
This is one of the windmills I continue to joust and I am constantly
curious why we in the US continue to be so wedded to such an arcane and archaic
measurement system as that which we inherited/adopted from our English
forefathers.
Consider the following from the web:
The metric system originated in France in the 1790's, a few years after
Jefferson's proposals. (note: Jefferson proposed to metric English system for
the US in the 1780 time frame where there were to 10 inches to the foot,
10 feet to a decade, 100 feet to a rood, 1000 feet to the furlong and 10,000
feet to the mile) During the mid-nineteenth century, as expanding trade
demanded a consistent set of measurements, use of the metric system spread
through continental Europe. As they imported goods from Europe or exported
goods to Europe, Americans became increasingly aware of the metric system. In
1866, Congress legalized its use in an act reading:
It shall be lawful throughout the United States of America to employ the
weights and measures of the metric system; and no contract or dealing, or
pleading in any court, shall be deemed invalid or liable to objection because
the weights or measures expressed or referred to therein are weights or
measures of the metric system.
As a result, the U. S. has been "metric" since 1866, but only in the sense
that Americans have been free since that time to use the metric system as
much as they like. Although there has always been popular resistance to
changing the traditional measures, the metric system has actually enjoyed
strong support from American business leaders and scientists since the late
nineteenth century. In 1875, the U.S. was one of the original signers of the
Treaty of the Meter."
and I might add that we continue to move towards complete metrication of
our national measurement systems "inch by inch"... ;-)
Joe
In a message dated 10/16/2009 10:55:25 A.M. Pacific Daylight Time,
[log in to unmask] writes:
I am looking at a 19.7 mil pitch QFN device with a center pad and
peripheral pads at 9.8x27.5 mils, and a 176 pin fine pitch QFP with 11.8x63 mil
pads with HASL finish and without any soldermask in between the peripheral
pads!...has anybody seen this type of a board design before? Any stencil
design suggestions?
I have a couple of pictures I have requested Steve to post for me
regarding the parts ( I am awaiting Steve's reply)
Thanks,
Amol
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