Allegro - Package Symbols versus Mechanical Symbols

Package Symbols versus Mechanical Symbols

Printed From: PCB Libraries Forum
Category: Libraries
Forum Name: Allegro
Forum Description:
URL: https://www.PCBLibraries.com/forum/forum_posts.asp?TID=2518
Printed Date: 21 Nov 2024 at 10:08pm

Topic: Package Symbols versus Mechanical Symbols

Posted By: tjnash75
Subject: Package Symbols versus Mechanical Symbols
Date Posted: 11 Aug 2019 at 7:35am

I've noticed when I create items like mounting holes, they get created as package symbols as opposed to mechanical symbols.

I'm not sure if I'm doing something wrong, or if this is the default behavior of the tool.

If this is the behavior of the tool, why are things like mounting holes getting created as package symbols (.psm) and not mechanical symbols (.bsm)?

Is this a bug or am I misunderstanding the purpose of mechanical symbols?

Thanks in advance!

Tim

Replies:

Posted By: Tom H
Date Posted: 12 Aug 2019 at 9:42am

There are Plated Through Mounting Holes which are normally in the schematic tied to GND.

There are Non-Plated Mounting Holes which are Mechanical.

What's a .bsm file? Is that a Concept Symbol?

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Posted By: tjnash75
Date Posted: 12 Aug 2019 at 10:44am

I believe Allegro and OrCAD PCB Designer both use psm and bsm files to delineate drawing types:

Package Symbol (.psm): Used for footprints such as SOIC20, BGA, QFP, and so on.

Mechanical Symbol (.bsm) : A generic card outline, mounting hole, tooling hole, board stiffener.

Format Symbol (.osm): A through D size page format, company logo, assembly/fab notes, cross section diagram, and so on.

Shape Symbol (.ssm): Creates a filled polygon (shape) used for custom pads.

Flash Symbol (.fsm): A symbol used to represent a thermal relief connection on a negative plane.

I don't believe the dra file is any different, and that the psm/bsm file is a binary file only used during placement.

I experimented and there's definitely a difference, as changing the file extension broke my ability to place the symbol.

You raise any interesting point about electrical connectivity, though.

I wonder if mechanical symbols (from the tool's perspective) can still have electrical connectivity defined.

I would think that a mechanical stiffener (e.g. a wedge lock) would possibly fall into the same category as a plated through hole, in that respect.

Posted By: tjnash75
Date Posted: 12 Aug 2019 at 4:34pm

I've confirmed that Allegro mechanical symbols don't allow electrical connections, so at the very least plated holes can't be mechanical symbols and connect to a net. How confusing...

Posted By: delovetsky
Date Posted: 17 Feb 2020 at 7:07am

Plated through mounting holes which are electrically connected need to be tested for.

This means it needs to reside with the net list for automated testing.

In Allegro a mechanical plated through hole will not allow a connection and would be voided within a shape.