Rounded Rectangle Pad Shape - PCB Libraries Forum

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Tom H

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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

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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

Corner Radius = 25% of Pad Width (pad width is the narrowest part of the SMD pad)
Maximum Radius = 0.25 mm, so regardless of how wide the pad is the corner radius will never exceed 0.25 mm (10 mils)
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

Tom H

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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

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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.

Tom H

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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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Author	Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic
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: 5716	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply 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.
	Stay connected - follow us! X - LinkedIn



eyoung Members Profile Send Private Message Find Members Posts Add to Buddy List New User Joined: 18 Oct 2023 Status: Offline Points: 3	Post Options Post Reply Quote eyoung Report Post Thanks(0) Quote Reply 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 Corner Radius = 25% of Pad Width (pad width is the narrowest part of the SMD pad) Maximum Radius = 0.25 mm, so regardless of how wide the pad is the corner radius will never exceed 0.25 mm (10 mils) 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

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: 5716	Post Options Post Reply Quote Tom H Report Post Thanks(1) Quote Reply 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.
	Stay connected - follow us! X - LinkedIn

eyoung Members Profile Send Private Message Find Members Posts Add to Buddy List New User Joined: 18 Oct 2023 Status: Offline Points: 3	Post Options Post Reply Quote eyoung Report Post Thanks(0) Quote Reply 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.

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: 5716	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply 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.
	Stay connected - follow us! X - LinkedIn