some new fake parts on a schematic

You need to remove all those "parts" from the files you give the assembly house. They won't know what to do with them.

In most companies, this is handled by having another level of assembly. So you'd have a bare board, and an assembled board. The assembled board would have a parts list that included the components that are soldered on, as well as the other parts that are bolted, glued or tied to the assembly. No place I've ever worked put these "other" parts in the electronic parts list. Even elements like fiducial marks, need to be removed from the BoM.

they'd be marked "not mounted" just like any other option part

so there is already a procedure in place for thing the shouldn't be mounted like fiducials, mounting holes, optional parts etc.

Sometimes we have visible parts on the schematic that are not used, like a resistor or a zero-ohm jumper, a placeholder just in case. Or we have parts that are used on engineering units only, like test connectors. We can set their "MAX" (stock number) attribute to "n/a" or "engr", and they are still accounted for and handled properly.

If we hack the rev A BOM to add in parts that are not on the sch, the list of such parts is sort of off to the side somewhere, things that somebody has to remember. And if we spin the board to rev B, we have to remember to include them again, ad hoc.

I think having everything on the schematic controls all those otherwise invisible parts.

I think the confusion here is that you seem to be equating the BOM and the schematic. A schematic can have multiple BOMs. Yes, I put non-electrical parts on the schematic. The schematic is used by technicians and engineers trouble shooting the board. The BOM is used by manufacturering people who may never see the schematic. You can have a BOM with the part numbers of the PCB assembly with an empty socket, the programmable IC, the program, programming instructions and the label. The part number of the programmable IC is on the schematic as well as the socket. The BOM generated from the schematic is just the starting point. From there you generate assembly BOMs, assembly instructions, and assembly drawings.

Subassemblies.

RL

On 04/12/2022 23:35, John Larkin wrote: <snip>

We (well, the bloke who does the tidy official schematics) put all those on including a spiral to represent solder with its type. It seemed a bit over the top at first, but I suppose it's rigorous.

Suppose you sell a box with a board inside, and it ships with a cable and a wall wart. What's the product structure?

Being reasonable is good engineering.

Our manufacturing people have procedures for soldering and cleaning and all that. They know that parts have to be soldered. I wouldn't try to put all that into a little block on the schematic. But I might want to convey the type of heat sink and nuts and screws and lockwashers. It's got to be documented somewhere.

Some people here seem to be saying the equivalent of "we just do it." I was wondering if we could include these things on the schematic and in the auto-generated BOM from the first, and have that be in a known place, initially and over revisions.

One could add notes "Screw head on top, nut and l/w bottom" or whatever. Or call out the MAX number of some glue, quantity a/r, note "GLUE LM45 TO COOLER" , things that I decide during the schematic entry and have a place to save.

In other words, a schematic need not be restricted to only electronically active parts.

That works but needs multiple higher level (or side detail) drawings and nested BOMs. And it requires both to be developed concurrently. It would be easier for me to put the non-electronic bits on the schematic from the start. AThay gets the loose stuff into the BOM from the start.

We name the firmware on a pcb BOM too.

The Romans didn't make PC boards.

As noted, our layout software generates the BOM from the schematic. There can be multiple BOMs for one PCB, as for instance dash-number versions, and they have to be managed manually. But may as well take care of all the common stuff.

One recent case is that there is a fuseholder on the schematic. We created a new part for the fuse itself, and put that on the schamatic, floating right next to the fuseholder. The fuse part has no pins; it's just a graphic with a stock number attribute, so it gets on the BOM automagically.

That's what I do, "DNP" for do not populate.

It isn't very customary though because screws, nuts and washers are typically considered system assembly parts, not board assembly parts. Unless it is a heat sink, shield or something that becomes an integral part of the finished "ready-to-install" board. However, then they are not DNP to begin with.

At one company they had a small bag of gummibears in the BOM because back then they weren't available in the US but there were in Europe where the boards were made. It worked but only until customs had a cow about it one day. Then the designer got read the riot act.

A PCB assembly has a stock number and an assembly drawing here. If a part is inherently on the board, like a heat sink or a fuse, it and its mounting hardware are considered to be part of the PCA so are on the BOM. All that gets assembled and inspected and usually subassembly tested.

If engineering produces a drawing and BOM, we describe the end result and let manufacturing decide how to stage assembly. If that board is mounted into a chassis with spacers and screws, we put those parts on the chassis drawing and BOM, the next higher assembly.

Some guys at one NASA facility, the Michaud plant in New Orleans, designed an audio amp and had some manufactured there with all the usual NASA parts and standards. It was reported to be a very bad amp.

depends on what the purchase order looks like - whether the accessories are options or part of a sales package with single part number.

RL

I had fun with this in companies at their early stages of 'part numbering' a BOM. You could tell from the part number what stage of the mfring process it could be found in, and where it could be found.

Top level included packing material, labels etc.

Compeeyoodah limits determined the number of possible fields in MRP

IBM and xerox just issued numbers at random. That works too, if the slaves can access a computer terminal.

RL

So if you add one screw to a board, you have a drawing and a BOM for the board, and a next-higher-assy drawing and BOM for the board+screw.

Deep.

If the screw only goes into the board, it should be in the board assembly, probably before refolw or wave.

If the screw attaches the board to a box, then the box, screw and board are in a 'testable' (?) or 'final' assembly, which likely includes a few other bits. Some common sense is required here. Imagine that it's your job just to put in that screw.

Depends on your in-house processes and how close you are to actually filling a purchase order.

RL