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PCB Design Optimization Starts in the CAD Library |
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bnoel 
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Joined: 14 Mar 2014 Location: Western NY Status: Offline Points: 14 |
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 Posted: 25 Apr 2014 at 4:11am |
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Hello - What determines whether a pad is rectangular in shape versus oblong?
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Tom H
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Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5719 |
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Posted: 25 Apr 2014 at 6:40am |
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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
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Joined: 12 Mar 2012 Location: Milano ITALY Status: Offline Points: 43 |
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Posted: 25 Apr 2014 at 7:44am |
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You mean "Rounded Rectangle is the pad shape of the future"
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Tom H
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Posted: 25 Apr 2014 at 7:47am |
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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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Matthew Lamkin
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Joined: 02 Oct 2012 Status: Offline Points: 284 |
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Posted: 29 Apr 2014 at 8:11am |
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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  |
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Nick B
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Joined: 02 Jan 2012 Status: Offline Points: 1909 |
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Posted: 21 Aug 2014 at 8:52am |
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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. |
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tjnash75
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Joined: 01 Feb 2018 Status: Offline Points: 8 |
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Posted: 10 Sep 2021 at 5:49am |
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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
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Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5719 |
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Posted: 10 Sep 2021 at 9:26am |
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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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MCERQUE4
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Joined: 28 Mar 2024 Status: Offline Points: 3 |
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Posted: 28 Mar 2024 at 9:29am |
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Thanks for share this information!
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WilliamsimC
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Joined: 19 Apr 2024 Status: Offline Points: 14 |
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Posted: 19 Apr 2024 at 2:45am |
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Starting to make the PCB design better begins with the CAD library.
This is where we keep all the parts we'll use to build the design. Making sure these parts are right is super important because they're like the building blocks of our project. When we pick and set up the parts in the library, it helps us make the design process smoother, fix any signal problems, and stop mistakes early on. Also, having a neat CAD library helps us keep things consistent in our designs, lets us reuse parts that work well, and makes it easier for us to work together as a team. So, spending time to make sure our CAD library is in good shape is a smart move for making awesome PCB designs.
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