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Rounded Rectangle Pad Shape
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Tom H View Drop Down
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    Posted: 07 Dec 2023 at 11:36am
V23 & the new V24 have IPC-7352 footprint naming convention and an Option file that turns off the Fabrication and Assembly tolerances and updates all negative solder joint goals to 0.00. 

Note: All Option settings are user definable. 
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eyoung View Drop Down
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Points: 3 		Post Options Post Options   Thanks (0) Thanks(0)   Quote eyoung Quote  Post ReplyReply Direct Link To This Post Posted: 07 Dec 2023 at 11:29am
does PCB Footprint Expert - for Allegro include the new additions and recommendations that have been released in IPC-7352?

Ive noticed in the sample files offered on the PCB Footprint Expert - for Allegro that none of the rectangular pads are rounded when opened up in Allegro 2022 17.4-2019 S038

Our company is considering a footprint/librarian program to help streamline our component creation process.
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Tom H View Drop Down
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Points: 5804 		Post Options Post Options   Thanks (1) Thanks(1)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 18 Oct 2023 at 9:17am
All IPC documents regarding PCB design and land patterns have been downgraded from "Standard" to "Guideline". 

All new Texas Instruments datasheets provide a recommended solder pattern and the pad patterns have 0.05 mm corner radius. 

You decide what settings work best for you. The current Footprint Expert default for Maximum Radius is 0.20 mm (not 0.25 mm) but you can change the Maximum value to anything you want. 

You can also change all pad shapes to be Oblong or Rectangle. Or some component families can have oblong and some rectangle. 

You need to make your own choices, but I would discuss this with an assembly shop because the pad shape affects that manufacturing process. 
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eyoung View Drop Down
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Points: 3 		Post Options Post Options   Thanks (0) Thanks(0)   Quote eyoung Quote  Post ReplyReply Direct Link To This Post Posted: 18 Oct 2023 at 8:38am
Our organization recently bought the IPC standard 7352 and it does consider rounded rectangle pads advantageous espically for Pb-free soldering processes(relevant to us) in comparison with rectangular pads

I cant seem to find where it exactly states that rounded pads strengthens the solder joint, or where these values (below) were determined

  1. Corner Radius = 25% of Pad Width (pad width is the narrowest part of the SMD pad)
  2. Maximum Radius = 0.25 mm, so regardless of how wide the pad is the corner radius will never exceed 0.25 mm (10 mils)
  3. Radius Corner Round-off value is 0.01 mm

Im trying to justify our organization to move towards an update to our procedures to use rounded rectangle pads so that we are up to industry standard.
I want to be able to justify this change with a concrete IPC standard , if available. 
If so, could you point me to the exact one? Or maybe a study that demonstrates these claims.

I appreciate your time and attention on this very much
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Tom H View Drop Down
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Points: 5804 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 18 Oct 2023 at 8:25am
CAD vendors created Rounded Rectangle pad shape. 

Most component datasheets recommend rectangular pad shape. 

IPC recommends oblong pad shape. 

Rounded Rectangle was primarily intended for the pad shape to be similar to the paste mask stencil aperture opening which is created by a laser and has rounded corner openings. 
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eyoung View Drop Down
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Points: 3 		Post Options Post Options   Thanks (0) Thanks(0)   Quote eyoung Quote  Post ReplyReply Direct Link To This Post Posted: 18 Oct 2023 at 7:26am
Which IPC standard has these specific recommendations for rounded rectangles?
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AGONZ67 View Drop Down
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Points: 119 		Post Options Post Options   Thanks (0) Thanks(0)   Quote AGONZ67 Quote  Post ReplyReply Direct Link To This Post Posted: 24 Nov 2014 at 3:36pm
I suppose if there was ample solder that argument could be made. However in the example pictures it appears even with oblong pads there would not be enough solder to fully cover the pads. Six of one half a dozen of the other. Smile
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Thanks, Tom

This is all good information.
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Tom H View Drop Down
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Points: 5804 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 20 Nov 2014 at 6:22am

I just got word from IPC that "Rounded Rectangle" pad shape strengthens the solder joint.

This information will be published in the upcoming IPC-7351C standard.
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Points: 40 		Post Options Post Options   Thanks (0) Thanks(0)   Quote 5not4 Quote  Post ReplyReply Direct Link To This Post Posted: 18 Nov 2014 at 10:45am
Found the answer to #1. SM-782 is the precursor to 7351 standard and no longer in print.
 
But I would still like to know where rounded rectangles stated to be preferred in the 7351.
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