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IPC-7251

Printed From: PCB Libraries Forum
Category: PCB Footprint Expert
Forum Name: Questions & Answers
Forum Description: issues and technical support
URL: https://www.PCBLibraries.com/forum/forum_posts.asp?TID=1798
Printed Date: 07 Oct 2024 at 3:22pm

Topic: IPC-7251

Posted By: drj-bbe
Subject: IPC-7251
Date Posted: 25 Nov 2015 at 2:33am

Hi all:

I cannot find IPC-7251 in IPC website, it haven't released?

What is the standard for through hole land calculation in Library Expert?

Thanks in advance.

Replies:

Posted By: Tom H
Date Posted: 25 Nov 2015 at 5:48am

The IPC Land Pattern committee decided a year ago to merge IPC-7251 for through-hole into the new IPC-7351C.

You can download several documents here - http://www.pcblibraries.com/downloads" rel="nofollow -

Posted By: drj-bbe
Date Posted: 25 Nov 2015 at 7:45pm

Thank you very much. I have other questions below:

The calculation formula below for pad diameter is different with IPC-2221B 9.1.1, how to set "pad to hole ratio" and "minimum annular ring"?

http://www.pcblibraries.com/forum/ipc7351-smd-pth-reference-calculators_topic785.html" rel="nofollow - http://www.pcblibraries.com/forum/ipc7351-smd-pth-reference-calculators_topic785.html

The calculation of pad diameter in IPC-7351C will not consider "Standard fabrication allowance" which in IPC-2221B Table 9.1, right?

Posted By: Tom H
Date Posted: 25 Nov 2015 at 8:55pm

Set all the Through-hole user preferences -

Preferences > Terminals > Through-hole

The current default settings are from IPC-2221 but will also be in IPC-7351C.

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Posted By: drj-bbe
Date Posted: 26 Nov 2015 at 12:59am

Thanks, but I still confused on below two calculation method for a pad:

IPC-2221B calculation formula is:

Land size, minimum = Hole size + 2*Min. annular ring(Min 0.05mm) + fabrication allowance

IPC-7351C calculation formula will be:

Pad diameter = Hole size + 2*Min. annular ring(Min 0.2mm), or = Hole size * pad-to-hole-ratio, whichever is larger.

But calculated result will be different between above two calculation method, IPC-7351C defined a proportional annular ring, IPC-2221B defined same size annular ring even though hole size go up, right?

This is for minimum pad design, the annular ring seems smaller than normal, is there suggestion for normal pad size?

Posted By: Tom H
Date Posted: 26 Nov 2015 at 10:44am

Library Expert only uses "Hole Over Lead" from IPC. Everything else uses the PTH Reference Calculator located here -

http://www.pcblibraries.com/forum/ipc7351-smd-pth-reference-calculators_topic785.html%20" rel="nofollow - http://www.pcblibraries.com/forum/ipc7351-smd-pth-reference-calculators_topic785.html

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