Hi Bill,
I've been using the schematics to create BOMs for well over 15 years now on small (10 parts) to large (3000+ parts) designs. In general I've had little issue with doing this as it has always been my view that the sch, pwb, cca and bom are tied together. For us it's always been best to get the exact part defined in the schematic, which than drives netlist and symbols for the board (R,L,C values may in flux, but package usually defined).
On most of the systems that I've used since I entered the industry, the schematics have been the driver pushing forward the netlist and the parts to used in the design. It only seems reasonable to also create the BOMs from it as well. I've done this both with Orcad Capture and DxDesigner. With CIS and DxDatabook, it makes it easy to create boms from here and have consistent data.
It does mean that the schematics and the bom must always be synced, but this is a good thing because then it means that the techs using the schematics have a design that matches the bom used to assemble the board. There are few things worse than having out of date schematics (I've been on that end). And with the advent of intelligent PDFs, the information for repair is at the techs fingertips.
There have been instances in the past where only the bom was updated, and not the schematic, but that can be resolved with good reviews on the ECNs and proper training/encouragement.
I do place "non-electrical" items on the schematic, such as mounting holes and fiducals as a reminder for me. I typically only place items that would be on the pwb though.
I don't use the assy drawing to list a bom at any point because it won't drive our MRP system. We need a bom that is released.
Could one use the schematic to drive other parts? I see little reason someone couldn't use symbols to hold other items such as screws, nuts, bolts or whatever. But the issue there would be that they would need to be stripped from the netlist as not to muck with the layout work. We do occasionally do chassis or box wiring with the schematic tool and other hardware would be part of this. So it would be reasonable in these cases.
As for whether it's right or wrong, it all depends on the processes being used. Having been in a place where I've had to oversee projects with different methodologies, meaning some with boms from the schematics and some with boms independent of the schematics, I've generally seen less mistakes with the boms created from the schematics.
In the end, it's probably what works best for the team.
Best Regards,
-Jeffrey
Jeffrey A. Jenkins CID+,CIT
PCB Staff Designer || L-3 Linkabit || Ph: 858-552-9832 || [log in to unmask]
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Brooks, William
Sent: Wednesday, June 26, 2013 11:10 AM
To: [log in to unmask]
Subject: [DC] Questioning the trend to use the schematic diagram as a Bill of material generation source
I want to examine and get input on is the trend to use the schematic diagram as a Bill Of Material or BOM/Parts List generation sole source...
This subject is on my mind more and more and I think it needs an in depth discussion.
What I see happening is engineers who have not had formal drafting training using the schematic as a vehicle to automatically create a complete BOM for a PWA or PCA depending on where and how you term the printed circuit assembly with all the components installed.
The traditional documentation guide book for drafting of electronic systems has its roots in the Department of Defense standards... which were adopted and published by Global Engineering Documents in a Drawing Requirements Manual which is now in its 11th edition authored by JEROME H. LIEBLICH. If you want to review it, you can find it at www.global.ihs.com
On a separate evolution line is the CAD or EDA companies that create the tools that have been used since the computer was starting to become a graphics engine... we can thank them for the creation of drafting tools that do more than just draft a drawing... without them we would not have our boards done in the time constraints we enjoy today...
My experience predates the computer so I remember using a drafting table and light table to create my boards...
According to historical standards, the controlling document for a Printed circuit assembly is the Bill of Material or Parts List and an Assembly drawing...
All revision control stems from this document that lists the electrical and mechanical parts and processes including the bare board that make up the PCA. The Assembly drawing is the controlling document by which the part is assembled and inspected.
Traditionally the Assembly Drawing was considered the first sheet of a parts list... often if the list was small it would be documented right on the Assembly drawing... but since more often there were so many parts to list we usually made a separate Parts List (Bill of Materials) but it kept the same part number as the BOM and ASSEMBLY drawing and the revision letters typically tracked... though provision was made in the DOD specs to handle the revs separately too, as long as it was referenced on the BOM. So the BOM was the master top level controlling document for building a PCA/PWA.
The way I am seeing the CAD tools being used nowadays is to drive the BOM from the schematic diagram... and because of this many designers and engineers are creating symbols for non-electrical or mechanical parts on the schematic to get the BOM to generate a complete bill of materials for the PCA.
Should we be doing this... ???
All of the implications may not be so obvious to everyone... I would like to get other professional's opinions and observations regarding this practice ...
Best regards,
William Brooks, CID+
Senior MTS (Contract)
2747 Loker Ave West
Carlsbad, CA 92010-6603
760-930-7212
Fax: 760.918.8332
Mobile: 760.216.0170
E-mail: [log in to unmask]
_____________________________________________________________________________
Scanned by IBM Email Security Management Services powered by MessageLabs. For more information please visit http://www.ers.ibm.com
This email is intended only for the use of the party to which it is addressed and may contain information that is privileged, confidential, or protected by law. If you are not the intended recipient you are hereby notified that any dissemination, copying or distribution of the email or its contents is strictly prohibited. If you have received this message in error, please notify us immediately, by replying to the message and deleting it from your computer.
WARNING: Internet communications are not assured to be secure or clear of inaccuracies as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. Therefore, we do not accept responsibility for any errors or omissions that are present in this email, or any attachment, that have arisen as a result of e-mail transmission.
_____________________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------------------------------------
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 16.0.
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL)
For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
---------------------------------------------------------------------------------
CONFIDENTIALITY, EXPORT CONTROL AND DISCLAIMER NOTE: This e-mail and any attachments are solely for the use of the addressee and may contain information that is privileged or confidential. Any disclosure, use or distribution of the information contained herein is prohibited. In the event this e-mail contains technical data within the definition of the International Traffic in Arms Regulations or Export Administration Regulations, it is subject to the export control laws of the U.S. Government. The recipient should check this e-mail and any attachments for the presence of viruses as L-3 does not accept any liability associated with the transmission of this e-mail. If you have received this communication in error, please notify the sender by reply e-mail and immediately delete this message and any attachments.
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------------------------------------
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 16.0.
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL)
For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
---------------------------------------------------------------------------------
|
