i have some questions about teh considerations when making a package in
eagle. I'm working on the TPS2490.
the datasheet shows the dimension tolerances for this part in a max/min
format, for instance: width of the chip without pins is shown as 3.1/2.9,
and width with pins is 5.05/4.75. Tim, I believe in the tutorial, you
managed this issue for the chip width (w/o pins) by simply making the line
with which you drew the footprint have a width = to the tolerance. Thus,
for this chip I would make the line 0.1 mm wide to compensate for the +/-
0.2mm overall tolerance. My question is how do we handle the situation with
pin length tolerance?
At this point, to calculate pin length I did the following:
((Min. width w/ pins) - (max width w/o pins))/2 = 0.825mm
As i think about it though, I'm not sure this is the right thing to do as I
am unsure as to what would should constitute the worst case scenario as far
as dimensions are concerned.
Also, once the appropriate pin length is calculated, where should it be
placed with respect to chip width? in other words, should the edge of each
pin be placed at the min (2.9mm/2) from center, the median (3mm/2) from
center, or max (3.1mm/2) from center?
the datasheet also includes dimensions for gauge plane and seating plane.
Do these need to be taken into account, and if so, how do I do that in
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