Well Bill,
Yes the Schematic probably should be at least the start of a BOM because at the early stages of putting a
Design together usually a BOM is required to at least (in a preliminary form) get long lead items on order,
because usually at this stage layout is not close to being ready for any kind of BOM output.
At least in an OEM you want a prelim BOM as soon as possible in the process know it may change a little.
Or at least in most places I have been that was the vehicle to do that.
If you want that BOM to have everything then of course you need symbols for parts like nuts bolts heatsinks etc
Placed on a schematic to drive that. Some CAD systems handle this type of stuff better than others.
I've seen it both ways and a combination there of too.
However if adding hardware to a schematic is frowned upon, then at some point somebody has to make
sure the BOM is a complete entity to order all that is needed for that complete assembly level
after the initial Schematic BOM was output. With integrated Systems I am not sure there is a way
from layout to capture hardware type parts. Basically you don't want these parts to show up in layout.
However if ECAD systems were better with MCAD 3D interface both ways (at least Altium is a bit ahead on this)
Maybe the hardware should be in layout and BOM output, but many ECAD systems will have to get quite a bit better for that.
Here they kind of add batteries to schematic if a battery holder is used, but can't seem to get them to add hardware.
However here the Engineer is responsible for the complete BOM, they end up just adding the hardware after the output from Schematic.
Bottom line all places I have been output from schematic, but after output is where there are many variations
Anywhere from a fair amount of manual manipulation to straight import into Enterprise System.
But yes many Engineers without proper training can really muck up the system.
I don't think it's a trend lately heck back in the mid 80s with Cadnetix we made our schematics such that they had all parts elect & mech.
We made a last sheet of the schematic that never got plotted or published with all of this hardware on it.
Anything that was attached to the PWA at this level was in that schematic.
So yes the schematic output a complete BOM (even firmware # if programmed at that level) that in those early
days wasn't directly imported into an Enterprise system but later was directly into SAP.
I guess it would really depend on what type of corporate environment (ie contract, service or OEM) you are in as which might be more or less beneficial?
Bob Wolfe, CID
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Brooks, William
Sent: Wednesday, June 26, 2013 2:10 PM
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 http://cp.mcafee.com/d/2DRPoQ72hJ5AsCCeKC-CrKrojvvovvKrojvvovd7apJxdZZxZZcSzt5AQsFzDPhOCryoGuXUaaOlIjrayvbCOIBr4SOEDOVKS-CgIy_R-phusoWZOWrbyfc6zBZZDBHFShhlLtDBgY-F6lK1FJ4SCrLP3zzzzzzzwUTsSkUyvkxF_i9QVsTkN3UBQfF8z3USGT2QzMl9qT00jpEV7nvdCBIe4ziWq807r-AVlxa14Qgj9-q89N-21EwDkQgdQYQgj9-q8am9-HIVmd424J8NRkQgrgQgqq81ChVVEwGWq85tDYpquq82fM-ePBm1EwFlKdLdTd_Q4Ns4w-
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
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