schematics

I had a customer complain that part values shown on our schematic don't match the BOM.

We never reissue a released schematic of a given rev letter. Different versions (dash numbers) of a board can have different stuffing, and that's defined by the BOM for that rev and dash number. One PCB can have multiple BOMs. An ECO can also change part values, and we update the appropriate BOMs, with a comment to note the event.

We treat the schematic as a reference drawing that not control configuration. The BOMs and assembly drawings control configuration.

I know that some people do update the visible part values on a schematic if an ECO changes something. And I assume that if they have multiple versions, each stuffing option would have to have a corresponding, up-to-date schematic. Lots of schematics, maybe.

What do you do?

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John Larkin         Highland Technology, Inc 
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John Larkin
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Put FS (factory select) as the value of every component. lol

More seriously, we have so called "variants" for which the visibility can be turned on. Then again, we don't provide schematics to customers. It is a black box with specifications and performance data.

Reply to
Simon S Aysdie

Minor revisions/changes such as 'design tolerance/error' get covered by ECOs with appropriate BOM change. Option type things get covered by a new part number/bom/schematic update. One circuit/multiple boms lead to build errors.

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Reply to
TTman

That is why large companies who care about revision control do just that, they put schematics under revision control. When a controlled drawing is released they note exactly who has it so they can provide an updated copy when a new revision is released. I've never worked at a company where at very least they didn't provide a revision number on the drawing which could be used to match to the revision number on a board. You do indicate revision numbers on your boards right? It doesn't need to be in the PCB. I add that with a label.

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Rick
Reply to
rickman

Some people just don't show the values.

Does your PCB cad software manage variants? Do you update the schematics with every variant or ECO?

I don't usually provide full schematics to customers, snippets sometimes, but these guys are special and have rules. And they have taken over the FPGA design from us, secret proprietary stuff, so they need to understand the hardware.

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John Larkin         Highland Technology, Inc 
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John Larkin

The PCB part and rev number is on the silk.

A bare board might be 22D123A

22 is product line

D means bare board (literally the drill drawing)

123 is a sequence number, sort of a model number

A is the rev.

The assembled board is 22A123-9A

where 9 is the variant/dash number. The corresponding BOM is file

22A123.9A. We often have multiple product versions, namely dash numbers.

Rev B would have a new set of released documentation. We usually build the latest rev, but we could decide to build a couple of 22A123-17A any time we wanted.

I ask because we are planning a new massive company data base that has to include our current drawing/BOM system. PADS doesn't have provision for multiple versions of a schematic, but I was wondering if some PCB software does. Or, more generally, how people manage variants.

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John Larkin         Highland Technology, Inc 
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Reply to
John Larkin

Edit the drawing and save it as a.pcb

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Rick
Reply to
rickman

I've never done it that way, personally, but Altium does allow you to produce variations in component parameters.

You can't put in an inductor symbol where a resistor was, when you happen to stuff it with a ferrite bead instead of a resistor. But you can change the value and part number.

I suppose some would still be irritated by a ferrite chip being "R72". For them, there's Simon's first suggestion. Or just don't give them schematics at all...

As for my work, personally, yes, the schematic is a reference (mainly a visible netlist), and PCB/BOM variations (if any) take precedence.

Tim

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Reply to
Tim Williams

The schematic contains the symbol and a reference designator (e.g. C 32, R12, J1...)

The BOM shows the reference designator, the part number and description . e.g C31 CDR01BX123FKUR Capacitor, Ceramic Chip, 12000pF... C32 M49470B12345 Capacitor, Tantalum .... ... R12 M55342K02B1E00UR Resistor, Chip, 1KOhms, 1%...

J1 M24308/7.... Connector, 9 pin D-sub. That way, you do not need to revise the schematic, only the BOM, unless you add or remove a part.

Reply to
bob.quintal

Once in a while I really mess up and have to load, say, a cap instead of a resistor. So we stuff a cap in the R56 site, and the BOM calls out a cap for R56. Productions rolls collective eyes and does it. We don't show it on the schematic until the next letter rev, where we'd likely fix the problem a better way anyhow.

We show value * on the schematic for parts that are not stuffed but might be if ever needed.

OK, Thanks.

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John Larkin         Highland Technology, Inc 
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John Larkin

I expect other more modern packages do similarly, but Altium at least supports saved history, backups (you know those things when the software crashes?..), and fairly basic repository/SVN.

You're not going to diff a binary file to any useful degree, and there's not really an obvious way to diff a SCH/PCB, at least not the way they've structured their files. So you just get submitted snapshots. Which is still good for keeping track of revs.

Not that Altium helps you much for your existing database. You can import PADS stuff at, eh, maybe an hour's expense per design (give or take rebuilding libraries, parameters, connectivity and such). But that kind of conversion process is always a pain.

Tim

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Reply to
Tim Williams

n be turned on. Then again, we don't provide schematics to customers. It is a black box with specifications and performance data.

Yes... sort of. Some add-on custom stuff makes it work.

The specific parts that have variable "values" are what holds the variant i nformation. Each variant (assembly) is given a "dash number," and the part "reports to the assembly" via the schematic. The following isn't exactly how my company does it, but you get the idea:

..-.

See that .. has to be identical for each variant case. It is a way of defining options. The . stuff may or may not exi st, and ultimately, there it all one unique part number with a revision.

All ..-. assemblies that are to exist are EC O'd into the system. (Each has its own BOM.) In a certain sense, the BOM is the thing itself because it contains *all* information needed to constru ct the device. (Granted, some references to "standard" documents are more pointer than the information itself.)

- A part defined without any variant info exists in all variants the same w ay. That is, a part has a base definition---usually an internal inventory n umber. A part lacking variant info simply uses the default (base definition ) in all assemblies covered by the schematic.

- A part with specified variant info is special in the listed variant assem bly, and default in all other assemblies were it is not defined.

Say there are three variants, -1, -2, and -3 of assembly 99.88.77-X._, wher e "X" is the variant place holder and "_" is some revision number. Say the default part in the schematic is 11.22.33-123 (the part itself could be "a variant," if it was a subassembly!) Say -1 and -3 for the assembly uses t he default part, but -2 uses 11.22.33-987. Then attached to the *instance* of the part in the schematic is some variant info in addition to the base d efinition. The attachment is usually called either a property or attribute of the instance.

Say the reference designator (the "instance" for this purpose) is SA001. Th ere are different ways to "database" this into a part instance, so what I p resent isn't "the way," it is "a way."

SA001 {Part Number}, {11.22.33-123} ; the default {variant PN}, {2}, {11.22.33-987} ; variant "-2" uses this instead

The way I did it is where there can be as many {variant PN} as you want, wh ere the first property ({2} ought to be unique, or a DRC error results. BO M exports parse this information to the respective BOMs.

The schematic tool will allow you to make any of this information visible o n the schematic, in some fashion.

In theory a part could have a base definition that was not used in any vari ant. (Never seen that happen.)

The whole reason this variant method arose is because of "options" and the desire not to completely replicate and maintain otherwise identical SCH/PCB databases. The intent is to save work and lessen errors of copying/differ entiating.

Ah, you're on the government dole. Don't feel bad---we have all sinned.

Reply to
Simon S Aysdie

Huh?

...there *is only* one unique part number (with a revision) for an assembly.

Reply to
Simon S Aysdie

My schematics generally have to reflect the real life systems. If there are several versions there are several schematics or, in simple cases, it is foot-noted in the schematic. Such as

R251 non-install assy 1234-5678 (for Mars systems) 249ohms assy 2345-6789 (for Jupiter systems)

If there were a BOM-schematic discrepancy I could be in hot doo-doo on some projects. Where the Federales might waltz in.

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Regards, Joerg 

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Reply to
Joerg

yeh, I'll also say the schematic is the master and the BOM is generated from that

how about stuff like like changing a part to something equivalent but better, i.e. 1% in stead of 5%, industrial temp instead of commercial because that was what you could get?

-Lasse

Reply to
Lasse Langwadt Christensen

So a resistor value is not declared on the schematic? Only the BOM? That has intellectual purity.

We show all values, but some of them can be "wrong." Both systems have features.

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John Larkin         Highland Technology, Inc 
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John Larkin

I sometimes do that, but only if I anticipate the versions at design time. New dash numbers can happen later. Sometimes we have *lots* of dash numbers.

They're not allowed in here.

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John Larkin         Highland Technology, Inc 
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Reply to
John Larkin

That's ok but in many cases must first be formally ECO-released, then also released for use in this particular system. If it's not done that way a mess can result and I've seen it happen: Sales guy offers a much better deal for an electrolytic. "Hey, it even has a lower ESR so you get a better cap for less money!". The contract manufacturer made the huge mistake of accepting without a formal blessing from the customer. In consequence none of the units passed final inspection and some were sent to me for investigation. They ended up doing a rush order and scrapping thousands of circuit boards because what mattered was leakage and that was vastly higher with the "better" capacitor.

Even with something as mundane as a resistor this can happen. Like when a guy wanted to switch to a metal film type but did not realize that it needed a high pulse rating. Which the 10% carbon resistor had but the 1% metal film didn't. I caught that one in time.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Technically that requires a schematic update every time a new dash number is to be released. Luckily in this day and age they don't have to clear-cut whole forests for that anymore.

If you put the matching procedure in place you could also point to another document such as a spreadsheet or database from the schematic, for resistor values and such. But if that's done a lot a schematic can gradually become unintelligible.

Agencies such as FAA and FDA usually don't ask for permission.

There's an old joke going around in Germany. A bar in a rough part of town has the usual fights at night. Occasionally some scary dude comes in, throws a knife or something. Once a week the ambulance shows up, occasionally someone even dies. All the while the music keeps playing and everyone remains unfazed.

One night a meek little guy comes in. No tattoos, and he even wears a suit. "Good evening, gentlemen. Miller, tax compliance investigator". The whole joints empties out in milliseconds.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

We sell to aerospace companies, but none of our gear flies, so we're OK there.

We don't sell food and beer, we consume them!

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John Larkin         Highland Technology, Inc 
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John Larkin

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