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IPC-7351C Pin 1 Polarity Marking

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=1530
Printed Date: 18 Nov 2024 at 8:18pm


Topic: IPC-7351C Pin 1 Polarity Marking
Posted By: SteveD
Subject: IPC-7351C Pin 1 Polarity Marking
Date Posted: 08 Jan 2015 at 4:38pm
When the new version 6 comes along matching the new way of doing IPC pin 1 designators, does that mean that polarized cap, diode, etc silkscreen will be mirrored?  E.g. pin 1 on the left, silkscreen opening on the left now instead of on the right?


Replies:
Posted By: Tom H
Date Posted: 08 Jan 2015 at 6:35pm

Great question!

There are 3 different silkscreen polarity markers:

  1. Leads extend from the component
  2. Leads under the component
  3. Chip and Molded Body 2-pin component

When the terminal leads extend beyond the body of the component package the silkscreen polarity marker is a Line that runs the full length of the pad and is visible after assembly.

When the terminal leads are under the component package (BGA, LGA, CGA, PQFN, PSON, DFN, etc.) the silkscreen polarity is removal of silkscreen. This is because the placement courtyard on "Bottom Only" terminals hugs the component package and there is no room to place a visible silkscreen polarity marker that is located inside the placement courtyard (not enough room). Note: the full silkscreen outline component boundary is shown and where the silkscreen is missing, that's pin 1. Intended for high density part placement.

The Chip and Molded Body 2-pin component the silkscreen polarity wraps around pin 1 (or Cathode) and is visible after assembly. Where non-polarized Chip and Molded Body only have parallel side component  silkscreen lines that map to the package length.




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Posted By: SteveD
Date Posted: 02 Feb 2015 at 5:51pm
Is there ever any real need for a pin 1 dot any more?   If not, why is it there in UserDefaults?

Posted By: Tom H
Date Posted: 02 Feb 2015 at 7:42pm

The Silkscreen Pin 1 Dot is only there because some people asked for it.

You can turn the Silkscreen Dot off in the "Drafting > Silkscreen" preferences by changing the value to 0 (zero). This is applicable for any outline that you don't want.




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Posted By: SteveD
Date Posted: 02 Feb 2015 at 9:46pm
Can I turn it off just for the component I am currently editing, or will the user defaults override what I do and put it back in while I build?  Generally speaking our preference is for ICs and connectors to have a dot, but passive components likes R's and C's and I's not to.

BUT we do not want to have different user defaults for the special cases.  We want just one user default file for the whole library of all part types and the ability to override the default for any particular footprint instance.  Make sense?

Posted By: jameshead
Date Posted: 03 Feb 2015 at 5:32am
Our CAD tool, Pulsonix, has an automatic feature that clips the silkscreen automatically over solder mask clearances on the CAM output to prevent silkscreen over pads.

I only raise this because on every PCB Libraries footprint that I've generated since they added back in the silkscreen "dot" I've found the majority of dots on any board are automatically "clipped".

Since you then have a PCB with dots on some components but maybe not on other components of the same type in a more dense area it doesn't make sense to use them as an after-assembly aide for checking.

The assembler should never be using the silkscreen to generate assembly data prior to assembly anyway - I make that clear in all my documentation.  That's what the assembly drawing is for.

Just my tuppence half-pennies worth.

Posted By: SteveD
Date Posted: 03 Feb 2015 at 1:18pm
Our assemblers are students and usually jump right in without an assembly drawing soldering by hand.  They know what is what.  But they may have forgot which way is which.  The dot will help, and the new IPC way is harder to see.

Posted By: SteveD
Date Posted: 03 Feb 2015 at 2:33pm

There is an unanswered question above for you Tom - 5th post in this thread.

Also, now when I create a new user preferences file with the preference of a 0.0 pin 1, then close PCBLE, then open PCBLE, and look at the preferences, its back to 0.40.  It will not go away, although it remembers my user suffix choice.  There seems to be no way to create a UserPreferences.dat with no pin 1 on the silkscreen.  Can you hear me screaming?

Posted By: Tom H
Date Posted: 03 Feb 2015 at 2:37pm

You can turn off any outline in User Preferences by changing the value to 0 (zero).

In the V2015.08 pre-release there is also a provision for separation of Silkscreen and Pin 1 Dot.

i.e.: You can now turn of the Silkscreen Outline and keep the the Dot (they are now independent of each other).




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Posted By: SteveD
Date Posted: 03 Feb 2015 at 4:43pm
I talked to Jeff, and it is confirmed that there is a bug saving silkscreen settings in the User Preferences file.

Posted By: Tom H
Date Posted: 03 Feb 2015 at 5:33pm

Great! I'm glad Jeff acknowledged the bug and he will fix it for the V2015.08 release.

Thanks for pointing this issue out. We prefer bug free software.




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Posted By: Nick B
Date Posted: 03 Feb 2015 at 9:49pm

Steve, please download/try the new pre-release from here - http://www.PCBLibraries.com/downloads" rel="nofollow - www.PCBLibraries.com/downloads



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Posted By: SteveD
Date Posted: 03 Feb 2015 at 10:44pm
I have been using .08 since early afternoon.  It has the same problems.  Has it changed since 5 pm?

Posted By: Nick B
Date Posted: 03 Feb 2015 at 10:52pm
Yes, a new build was posted about an hour ago.

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Posted By: SteveD
Date Posted: 04 Feb 2015 at 12:58pm
The 08 version seems now to let me save the silkscreen drafting preferences.  However, it does not display them consistently.  Sometimes they are blanked out even when the preferences file is saved, loaded, and editor is restarted.

FYI: Another bug that Jeff took note of for me is that when you are in the editor, you have the ability to set several drafting items and see them as they would appear when you click OK.  However, when you build the part(s), the user preferences for drafting override anything that had been entered, and you lose that work.  Apparently this is because you are not allowed to edit items under the drafting tab - even though they are not grayed out..... a royal garden path.

What we need is a way to override the defaults part-by-part and build them the way they look while editing them.  There are exceptions to every rule.

Posted By: Tom H
Date Posted: 05 Feb 2015 at 8:41am
All of the issues that were reported should be fixed in a new V2015.08 pre-release uploaded today.

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