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I'm building an Eagle component for an LSM115J.

The connectors on this part have fairly large tolerances (1.85-2.21mm width, 0.76-1.52mm length). There is no recommended land pattern.

Should I go for the largest size (so the part will never need to be partially soldered on top of the stop mask), the smallest size (so the part has a well-defined placement) or something in the middle?

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That package is an SMB. Here is Diodes Inc. suggested footprint for their SMB (almost the same):

enter image description here

The IPC footprint expert would give you a somewhat different footprint (more prone to shorting in the center IMO).

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  • \$\begingroup\$ So, larger than the maximum. \$\endgroup\$ – Simon Richter Jul 28 '14 at 8:32
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Ideally, you'll want to make the land as small as possible, but if there is a stated maximum tolerance, then it would be wise to include up to that just in case you actually get a part that is on the high-end. Maybe even go a teensy bit more, but that is only if you don't feel comfortable soldering with little margin for error.

If it turns out the pieces that you get are smaller than the land you made, great, they will be easier to solder and rework if need be.

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