Default PAD shape for SOP and SOIC packages?
Printed From: PCB Libraries Forum
Category: PCB Footprint Expert
Forum Name: Questions & Answers
Forum Description: issues and technical support
URL: https://www.PCBLibraries.com/forum/forum_posts.asp?TID=522
Printed Date: 19 Nov 2024 at 5:26am
Topic: Default PAD shape for SOP and SOIC packages?
Posted By: sgdavies
Subject: Default PAD shape for SOP and SOIC packages?
Date Posted: 29 Aug 2012 at 1:38am
Hi, I noticed that the default PAD shape is rectangle for SOP and SOIC packages, I seem to remember from the old calculator that the default setting for this type of package was oval? so I am wondering What is best, does IPC now say that its best to have oval pads or rectangle pads? Thanks and Regards Stephen Grant-Davies
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Replies:
Posted By: Tom H
Date Posted: 29 Aug 2012 at 8:38am
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In the upcoming IPC-7351C, we're pushing for "Rounded Rectangle" to be the new default standard. IPC-7351B promotes Oblong pad shape, but in our Polls, over 60% of PCB designers use rectangle pad shape. However, PCB Libraries, Inc. does not in any way promote the use of any specific pad shape. This is totally up to the user discretion in "Setup > User Preferences > Components > Surface Mount > Family > Default Pad Shape" You need to talk to your manufacturers and ask them what pad shape they prefer. I worked as a contractor at Lockheed Martin Space Systems earlier this year. I was asked to build IPC compliant SOIC library parts, so I used Oblong pad shape. When the EE engineer got the part placement check prints, he immediately instructed me to change every pad shape to Rectangle. So I don't want to argue with anyone over this subject. The user is in control now. You can create 3 user .dat files. One with Oblong pad shape, one with Rectangular pad shape and one with Rounded Rectangular pad shape and instantly build 3 different CAD libraries using the same FPX file. |
Posted By: sgdavies
Date Posted: 30 Aug 2012 at 5:00am
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I am with you on the "rounded rectangle" as a default, its what they had at Ericsson. at the moment the rounded rectangle doesn't add pads to the footprint (Allegro 16.5), as the pad stack would need to reference a shape. I will add it to the bug list Cheers Tom
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Posted By: jameshead
Date Posted: 30 Aug 2012 at 7:10am
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I'm in the 40% then. I use the oval as default and a rounded rectangle to indicate pin 1. Realistically it's not going to show pin as well as an assembly diagram or silkscreen on the finished pre-populated PCB but it does show orientation and pin clearly on the screen when I'm working on the design so I can turn off the assembly diagram layer and have a less cluttered view on the monitor. There's been a discussion on how the viscosity of lead-free solders means that a rounded-rectangle or oval pad makes no difference then a rectangular pad at the end of the day. I can't point out a specific paper on this - just what's been discussed amongst peers at training courses and the like. A rectangular pad, and to a little greater extent, an oval pad does give you slightly more flexibility in routing tracks around obstacles so perhaps you can squeeze one more track through gap then you might otherwise have been able to do. It's good the tool lets everyone do what they want here. |
Posted By: Tom H
Date Posted: 29 Dec 2012 at 11:14am
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Here are the "Pad Shape" results from our latest poll. What Pad Shape do you use most of the time for PCB library parts?
However, Rounded Rectangle seems to be the upcoming standard in our next poll question. Will you ever consider using Rounded Rectangle pad shape in the future?
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Posted By: sevan
Date Posted: 17 Jul 2013 at 7:29am
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@sgdavies: You remind of the old days when oval pads were used. I haven't seen oval pads lately. Most of the time its rectangular. Nowadays, I do see rounded rectangular pads. I was told that rounded rectangular pads are for the best results. I like the rounded rectangular pads more than the rectangular pads as in my view it adds more coolness of the PCB and a little change from the contemporary designs. ------------- http://www.7pcb.co.uk/PCB-Assembly" rel="nofollow - pcb assembly services |
Posted By: Tom H
Date Posted: 17 Jul 2013 at 7:45am
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Yes, Rounded Rectangle pad shape is the future for most SMT parts (except BGA). It will become very popular after IPC-7351C is released in 2014. ------------- Stay connected - follow us! https://twitter.com/PCBLibraries" rel="nofollow - X - http://www.linkedin.com/company/pcb-libraries-inc-/" rel="nofollow - LinkedIn |
Posted By: sgdavies
Date Posted: 17 Jul 2013 at 7:51am
I agree  and it looks so much better too.
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