PCB Libraries Forum : Dimensional Principles of IPC-7351B

PCB Libraries Forum : Dimensional Principles of IPC-7351B https://www.PCBLibraries.com/forum/ Mon, 06 Apr 2026 10:50:03 +0000 Fri, 14 Feb 2025 11:14:00 +0000 http://blogs.law.harvard.edu/tech/rss Web Wiz Forums 12.07 360 https://www.PCBLibraries.com/forum/RSS_post_feed.asp?TID=1744 <![CDATA[PCB Libraries Forum]]> https://www.PCBLibraries.com/forum/forum_images/PCBLForumLogo.gif https://www.PCBLibraries.com/forum/ <![CDATA[Dimensional Principles of IPC-7351B : Hi Tom.That was what our findings...]]> https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post13791.html#13791 Author: KoryJohnsonTek
Subject: 1744
Posted: 14 Feb 2025 at 11:14am

Hi Tom.

That was what our findings were/are.

When you mentioned the knee, we were not seeing any reference in any of our datasheets for what the represents.

Maybe it was just a matter of us misunderstanding your intent, I guess.

Your Amax is in agreement with our Amax, which is the same as what IPC stated to me in a follow-up email.

Thank you for your follow-through and patience!

]]> Fri, 14 Feb 2025 11:14:00 +0000 https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post13791.html#13791 <![CDATA[Dimensional Principles of IPC-7351B : Here is the original drawing from...]]> https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post13776.html#13776 Author: Tom H
Subject: 1744
Posted: 06 Feb 2025 at 3:59pm

Here is the original drawing from 20 years ago when we were helping IPC define the difference between Gullwing and Outward L-Bend (Mini Gullwing) terminal leads.

]]> Thu, 06 Feb 2025 15:59:39 +0000 https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post13776.html#13776 <![CDATA[Dimensional Principles of IPC-7351B : Respectfully, I would like you...]]> https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post13775.html#13775 Author: KoryJohnsonTek
Subject: 1744
Posted: 06 Feb 2025 at 1:32pm

Respectfully, I would like you to rethink the original poster's question. According to the IPC's note 1, an SOx part will usually always follow Note 1, and not the standard goal if Amax is the max lead expansion. Smin is calculated (in simple terms) as Lmin-(2*Tmax), and that is always going to be less that Amax - by your definition. What is it that we are missing? We understand what you are trying to say, but it seems like there is something missing somewhere, because you seem very sure of it, and we are very sure of the opposite. I really think that the poster's comment about this being the knee-to-knee dimension is correct, and it follows what you showed 05 Aug 2015 at 8:57pm.]]> Thu, 06 Feb 2025 13:32:40 +0000 https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post13775.html#13775 <![CDATA[Dimensional Principles of IPC-7351B : This thread explains the difference...]]> https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post13774.html#13774 Author: Tom H
Subject: 1744
Posted: 06 Feb 2025 at 9:23am

This thread explains the difference between the Gullwing and Outward L-Bend terminal leads of SOT packages.

The image that illustrates the A-Max going to the Gullwing Knee was wrong. A-Max is the dimension from Toe to Toe, (not Knee to Knee).

]]> Thu, 06 Feb 2025 09:23:28 +0000 https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post13774.html#13774 <![CDATA[Dimensional Principles of IPC-7351B : Hi Tom.I realize this thread is...]]> https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post13773.html#13773 Author: KoryJohnsonTek
Subject: 1744
Posted: 06 Feb 2025 at 9:13am

Hi Tom.

I realize this thread is 10 years old, but we are just now looking at this from the IPC standard perspective and were trying to understand Amax and what it means.

After reading this thread, we are still confused. Are you still saying that Amax is the maximum lead expansion that IPC calls out in their calculations?

It seems contrary to what we are see in the IPC formulas. How does your Amax have anything to do with whether the leads are bent inward? drj-bbe made a good point that it would seem to be related to what they showed, which you insisted it is not the case, given your second-to-last image.

If the calculations are only about lead expansion and minimum lead length, it would seem that any calculation would always follow the exception in note 1.

]]> Thu, 06 Feb 2025 09:13:37 +0000 https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post13773.html#13773 <![CDATA[Dimensional Principles of IPC-7351B : This picture illustrates what...]]> https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post7137.html#7137 Author: Tom H
Subject: 1744
Posted: 05 Aug 2015 at 8:57pm

This picture illustrates what the IPC-7351B text condition for Gull Wing lead is referring to.

When the Terminal Leads bend inward.

]]> Wed, 05 Aug 2015 20:57:56 +0000 https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post7137.html#7137 <![CDATA[Dimensional Principles of IPC-7351B : Sorry for the late reply especially...]]> https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post7135.html#7135 Author: Tom H
Subject: 1744
Posted: 05 Aug 2015 at 8:27pm

Sorry for the late reply especially for such a simple question, it's been really busy lately.

Amax = the Lead Span

3D model created by Library Expert.

]]> Wed, 05 Aug 2015 20:27:15 +0000 https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post7135.html#7135 <![CDATA[Dimensional Principles of IPC-7351B : I cann't find dimension "A"...]]> https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post7133.html#7133 Author: drj-bbe
Subject: 1744
Posted: 04 Aug 2015 at 8:11pm

I cann't find dimension "A" mentioned above in SMD reference calculator. It seems only for chip component.

Could you tell me which size is for the dimension "A" ?

Thanks.

]]> Tue, 04 Aug 2015 20:11:03 +0000 https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post7133.html#7133 <![CDATA[Dimensional Principles of IPC-7351B : Please download the SMD Reference...]]> https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post7132.html#7132 Author: Tom H
Subject: 1744
Posted: 04 Aug 2015 at 7:52pm

Please download the SMD Reference Calculator.

All values and dimensional assignments are displayed.

You can change the calculation values and observe the resulting land pattern results.

Download here -

http://www.pcblibraries.com/forum/ipc7351-smd-pth-reference-calculators_topic785.html

]]> Tue, 04 Aug 2015 19:52:56 +0000 https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post7132.html#7132 <![CDATA[Dimensional Principles of IPC-7351B : I have mark Amax and Smin below,...]]> https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post7131.html#7131 Author: drj-bbe
Subject: 1744
Posted: 04 Aug 2015 at 6:38pm

I have mark Amax and Smin below, is it correct?

]]> Tue, 04 Aug 2015 18:38:31 +0000 https://www.PCBLibraries.com/forum/dimensional-principles-of-ipc7351b_topic1744_post7131.html#7131