Dimensional Principles of IPC-7351B

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   Hello Tom, 
There is a dimension "Amax" indicated in below principles of IPC-7351B, see below picture. 

But it seems there is no drawing to define which size is for "Amax". 

Could you please help on this question?

Thanks

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drj-bbe Members Profile Send Private Message Find Members Posts Add to Buddy List Advanced User Joined: 08 Jul 2015 Status: Offline Points: 71	Post Options Post Reply Quote drj-bbe Report Post Thanks(0) Quote Reply Topic: Dimensional Principles of IPC-7351B Posted: 04 Aug 2015 at 1:25am
	Hello Tom, There is a dimension "Amax" indicated in below principles of IPC-7351B, see below picture. But it seems there is no drawing to define which size is for "Amax". Could you please help on this question? Thanks



Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5744	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 04 Aug 2015 at 6:08am
	This condition creates a Outward L lead - This lead style has a different calculation then the normal Gull Wing lead style:
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drj-bbe Members Profile Send Private Message Find Members Posts Add to Buddy List Advanced User Joined: 08 Jul 2015 Status: Offline Points: 71	Post Options Post Reply Quote drj-bbe Report Post Thanks(0) Quote Reply Posted: 04 Aug 2015 at 6:38pm
	I have mark Amax and Smin below, is it correct?

Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5744	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply 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
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drj-bbe Members Profile Send Private Message Find Members Posts Add to Buddy List Advanced User Joined: 08 Jul 2015 Status: Offline Points: 71	Post Options Post Reply Quote drj-bbe Report Post Thanks(0) Quote Reply 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.

Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5744	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply 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.
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Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5744	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply 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.
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KoryJohnsonTek Members Profile Send Private Message Find Members Posts Add to Buddy List New User Joined: 03 Oct 2024 Status: Offline Points: 13	Post Options Post Reply Quote KoryJohnsonTek Report Post Thanks(1) Quote Reply Posted: 5 hours 31 minutes ago 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.

Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5744	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 5 hours 21 minutes ago 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).
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KoryJohnsonTek Members Profile Send Private Message Find Members Posts Add to Buddy List New User Joined: 03 Oct 2024 Status: Offline Points: 13	Post Options Post Reply Quote KoryJohnsonTek Report Post Thanks(1) Quote Reply Posted: 1 hour 12 minutes ago 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.