Reference Designators for Components in BOM but Not Mounted on PCB - Page 1
Forum section: electronics / general

author: MixedSignalSystems
author_rank: Contributor
timestamp: January 20, 2018, 12:26:16 am
content: In my schematics, I like to add components that are not necessarily mounted on the PCB to ensure that they are captured in the Bill of Materials (BOM) output by my CAD tool.These might include the PCB itself, an enclosure, screws, standoffs, light pipes, cables, etc.It's useful to capture all these in a BOM that is well controlled so that kits are built up correctly and nothing is overlooked.I am wondering if there are standard Reference Designators that people use for these items.Right now, I use:PCB for a PCBENC for an EnclosureMP for a Mechanical Part, e.g. a screw or standoffAre there any standard alternatives that people use for these?Any suggestions on a Reference Designator for a Light Pipe. MP doesn't seem quite right but it does do the trick.Also, any suggestions on a Reference Designator for a cable, e.g. USB cable.Happy to hear any suggestions that people might have.Thanks,Kieran

author: Mattylad
author_rank: Regular Contributor
timestamp: January 28, 2018, 12:30:05 am
content: Whatever you call them, putting them on the main sheets gets confusing to the reader.What I used to do was make a seperate sheet for non schematic BOM only parts.This way I could also output the BOM for the whole assembly by including this sheet when printing or not.

author: Omgitskillah
author_rank: Newbie
timestamp: January 28, 2018, 04:28:00 am
content: Hi Mattylad,I don't think what you are doing is conventional at al. The PCBA BOM is only for components that get mounted on the PCB. After you receive the PCBAs from the manufacturer, you may the PCBA itself as an individual component and list it in an general product assembly BOM.That's how most people I have worked with do it.I hope that helps.Cheers

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 28, 2018, 04:53:07 am
content: I normally do that, with a note (in the Comment or Description field) about where it goes, if applicable. (The PCB item is pretty obvious where it belongs in the assembly, of course.)Tim

author: Mattylad
author_rank: Regular Contributor
timestamp: January 31, 2018, 10:37:52 pm
content: Omgitskillah, I was referring to things like screws, mica washers, heatsinks et all - the stuff used on a PCB that is not shown on the circuit.If you add things like this onto the schematic then it just looks a mess, if you do not add them then when you output a BOM it is short of these things and you need to manually add them to your final BOM.When I first did this (on the main schematic sheet) I had QA coming up saying "ere whats these things on the drawing?" lolHowever, if you use a separate sheet (one that is generally not printed) then you can add the additional items without them obscuring the schematic itself.I know of many companies that have taken this up and used it very well - being able to print the whole PCB assembly BOM by opening the schematic.The PCB itself becomes a part within the libraries and also gets called up in the BOM when this is added to the schematic.This way - the whole BOM is in line with the schematic and any changes made to it, i does not have to be "just" the schematic BOM, it can be the "product" bom especially if you have no other way of managing it (I.e. no MRP system).Yes it's not conventional, this is because convention is to generally use a seperate spreadsheet for the BOM, this is generally not in sync with the actual schematic and errors and mistakes happen often. Using the method I have mentioned keeps the whole assembly in sync.MattyCID+

author: MixedSignalSystems
author_rank: Contributor
timestamp: February 01, 2018, 02:36:13 am
content: Quote from: Mattylad on January 31, 2018, 10:37:52 pmHi Matty,I also use this approach and find that it works quite well for most designs that I work on.I know of a number of semiconductor companies that also use this approach for their evaluation boards, etc.For considerably more complex products like a smartphone (multiple PCBs, etc.), an alternative approach may be more appropriate but including everything on the PCB schematic works very well for most designs that I encounter.Usually, but not exclusively, I place all the additional components on a separate sheet at the end of the schematic.I add a MOUNTING_STYLE attribute to all the parts in my part libraries to allow readers of the BOM to clearly identify whether or not a component is physically mounted on the PCB.Sent from my SM-G920F using Tapatalk