IPC-7351 and SMD Pad Shapes

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   The Default is IPC-7351C (which was never released primarily due to Dieter Bergman's passing). 
The IPC 1-13 Land Pattern Committee worked on 7351C for 6 years and approved the new IPC J-STD-001 solder joint goals and the updated Naming Convention. 

We had to remove references to IPC-7351C and replace it as PCB Libraries. 

However, we do support IPC-7351B and IPC-7352 Options. 

We do not default to 7351B or 7352 because the solder joint goal tables do not compare with the recommendations from IPC J-STD-001 (but IPC-7351C did). 

However, Footprint Expert does default to the mathematical model for pad stack calculations for pad size and placement. This model takes into consideration the min/max tolerances of the component package terminal leads from the mfr. datasheet. 

The downside of using the terminal tolerances is that they are sometimes too robust and not realistic. And if you study the mfr. recommended patterns from millions of datasheets, they don't use the min/max terminal tolerances. They use the Nominal package dimensions. 

So even though IPC went to great lengths to create this mathematical model - uploads/3/IPC-7352_Mathematical_Model.zip

Component manufacturers do not use it for their recommended patterns displayed in their datasheets. 

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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: 5718	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 31 Jul 2024 at 10:44am
	The Default is IPC-7351C (which was never released primarily due to Dieter Bergman's passing). The IPC 1-13 Land Pattern Committee worked on 7351C for 6 years and approved the new IPC J-STD-001 solder joint goals and the updated Naming Convention. We had to remove references to IPC-7351C and replace it as PCB Libraries. However, we do support IPC-7351B and IPC-7352 Options. We do not default to 7351B or 7352 because the solder joint goal tables do not compare with the recommendations from IPC J-STD-001 (but IPC-7351C did). However, Footprint Expert does default to the mathematical model for pad stack calculations for pad size and placement. This model takes into consideration the min/max tolerances of the component package terminal leads from the mfr. datasheet. The downside of using the terminal tolerances is that they are sometimes too robust and not realistic. And if you study the mfr. recommended patterns from millions of datasheets, they don't use the min/max terminal tolerances. They use the Nominal package dimensions. So even though IPC went to great lengths to create this mathematical model - uploads/3/IPC-7352_Mathematical_Model.zip Component manufacturers do not use it for their recommended patterns displayed in their datasheets.
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bab27 Members Profile Send Private Message Find Members Posts Add to Buddy List New User Joined: 01 Sep 2024 Status: Offline Points: 13	Post Options Post Reply Quote bab27 Report Post Thanks(0) Quote Reply Posted: 03 Sep 2024 at 11:30pm
	Hello, What are the main difference between IPC7351B and 7352 for land pattern dimension? Does IPC7351B use the tolerance RMS value like IPC7352 ? It could be interesting to have a standard footprint size 1206 with nominal size (_N) and tolerance and the associated footprint calculation with the IPC7351B, 7352 and PCBlibrairies. Thank you.

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: 5718	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 19 Sep 2024 at 1:53pm
	IPC-7351B adds Fabrication and Assembly Tolerances to calculate the resulting pad stack. IPC-7352 removes the Fabrication and Assembly Tolerances for pad stack calculations. PCB Libraries (IPC-7351C) is only the Footprint Naming Convention. The typical package dimensions for a 1206 footprint are: Length = 3.20 +/- 0.20 Width = 1.60 +/- 0.20 Terminal Lead = 0.50 +/- 0.25 The package dimensions and tolerances calculate the pad stack size and spacing.
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WilliamsimC Members Profile Send Private Message Find Members Posts Add to Buddy List New User Joined: 19 Apr 2024 Status: Offline Points: 14	Post Options Post Reply Quote WilliamsimC Report Post Thanks(1) Quote Reply Posted: 24 Sep 2024 at 12:18am
	Hi Susan, In my opinion, PCB Libraries chose to make the IPC-7352 approach an option instead of the default for a few key reasons. One important factor is library consistency. They want to ensure that users are fully aware of the changes and understand the implications of opting into the IPC-7352 approach. By not imposing this change on everyone, they help prevent any confusion or errors that might arise if users aren’t prepared for the differences. Additionally, allowing users to choose the IPC-7352 option gives them flexibility. Some users may have established workflows or preferences that work well for them, and it’s important to respect that. This way, users can transition to the new approach at their own pace, ensuring they’re comfortable with it before making the switch. Overall, it’s about providing choices while maintaining clarity and consistency in the library. Thanks, WilliamsimC

Nick B Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 02 Jan 2012 Status: Offline Points: 1909	Post Options Post Reply Quote Nick B Report Post Thanks(0) Quote Reply Posted: 24 Sep 2024 at 12:36am
	Well said, quality and consistency is what it's all about. https://www.pcblibraries.com/forum/whats-wrong-with-your-footprint_topic3404.html
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