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Explanation of Naming Convention

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chads108 View Drop Down
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    Posted: 17 Sep 2014 at 1:49pm

I just created a footprint for a SOT23 and the resulting footprint name suggested is SOT95P230X120-3L18N. 

I understand everything in that name except the L18 part. 

I am assuming it is some reference to a dimension, but I sure can't figure it out in looking at the datasheet. 

What is that referring to?

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Tom H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 2014 at 1:57pm

You have the "Extended Footprint Names" turned on in User Preferences.

The L18 = the Lead Tolerance for a Gull Wing lead form.

The lead tolerance impacts the pad length. A lead tolerance of 0.18 mm is good, but some Gull Wing leads have a tolerance of 0.60 mm to 0.90 mm and that makes a big difference in the pad length.

Without the extended names for gull wing, the IPC-7351 calculator would auto-generate a duplicate footprint name even though the pad lengths could vary in length.

I'll bring this to the attention of the IPC-7351 land pattern committee on Wednesday October 1st in Chicago, IL.

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