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PCB Design Optimization Starts in the CAD Library

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bnoel View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bnoel Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 2014 at 4:11am
Hello - What determines whether a pad is rectangular in shape versus oblong?
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Tom H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 2014 at 6:40am

IPC-7351 says that the preferred SMT pad shape should be oblong or rounded rectangle if your CAD tool supports that feature.

Every component manufacturer recommends rectangular pad shape. i.e.: I've never seen a mfr. recommended footprint with oblong pad shape.

PCB Libraries, Inc. recommends D-shape pads for QFN & PQFN and Rounded Rectangle for every other surface mount pad (including Chip components). Rounded Rectangle in the pad shape of the future, where IPC and the component manufacturer can both agree on that.


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Artwork Master ITALY View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Artwork Master ITALY Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 2014 at 7:44am
You mean "Rounded Rectangle is the pad shape of the future"
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Tom H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 2014 at 7:47am

Yes, in the year 2017 most PCB designers will use "Rounded Rectangle" pad shape for surface mount footprints. It meets IPC and the component manufacturers 1/2 way.

IPC = Oblong pad shape

Component Mfr. = Rectangle pad shape

Future = Rounded Rectangle pad shape


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Matthew Lamkin Quote  Post ReplyReply Direct Link To This Post Posted: 29 Apr 2014 at 8:11am
The reason for using the Rounded rectangle pads is because now that most are using lead free solder, they are finding that it does not flow into the corners so rectangular pads are no longer needed.

Although I wouldn't say "most" are actually using them, a great many I see are still using rectangular ones and mixing them up with rounded rectangles upsets them LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nick B Quote  Post ReplyReply Direct Link To This Post Posted: 21 Aug 2014 at 8:52am

This document represents every Surface Mount component family in the PCB Library Expert with graphic illustrations of every 3D STEP model, example Footprint with Silkscreen and updated Solder Joint Goal Tables.

The Library Expert's Surface Mount Component Families

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tjnash75 Quote  Post ReplyReply Direct Link To This Post Posted: 10 Sep 2021 at 5:49am
In the presentation associated with this thread, Tom makes the statement "I would not recommend building Footprints using Metric Units for Inch based PCB design layout. The pad size, drafting items, feature spacing & round-off values are not compatible.  Inch design = Inch libraries & Metric design = Metric libraries".
If I recall, on another occasion Tom mentioned PCB fab houses having to translate everything to imperial units. So, what is the current guidance?  It sounds like if we go completely metric (library and PCB design, it complicates fab.  And if we go completely imperial for library and PCB design, it sounds like we're running counter to the advice of the IPC.  We have traditionally done our PCB designs in imperial units.  That would imply, based on the guidance above, we should be doing the footprints in imperial units as well.  Where the heck do we go from here???
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Tom H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom H Quote  Post ReplyReply Direct Link To This Post Posted: 10 Sep 2021 at 9:26am
The entire electronics industry needs to convert to metric units for both PCB libraries and PCB design. 

People who are still using Imperial units are holding the industry back in the stone age. 

My personal challenge for everyone using Imperial Units is to do everything in millimeters for 5 PCB layouts. Once you find out the superiority of the metric system, you will never go back to Imperial Units. 

It's a short learning curve but it's worth it. 

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