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I would like to know if there are some standards or rules to describe parts when generating the BOM or assembly files for manufacturing.

For example, I would describe an SMD capacitor with format 0805 as:

Cap 0.1 µF, X7R, 50 V, ± 10%, SMD 0805

but could be also defined as:

Capacitor 100nF, 50V, X7R, MLCC 0805, ± 10%

or just..

100nF, 50V, 0805

The same apply for Resistances and all other stuff.

Which is the best way to define it?

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    \$\begingroup\$ The best way to define it, is by its product code, that encompasses all the details as set by the manufacturer. Obviously. Unless you want your assembly house to buy whatever cheap crap they can find, of course, which undoubtedly makes for awesomely reliable products. \$\endgroup\$ – Asmyldof Jun 29 '16 at 8:01
  • \$\begingroup\$ Similar to the comment made by @Asmyldof, this is what I do: I assign my own part numbers to the parts I use, and that is what is embedded in the schematic (I also have value and PCB footprint embedded). Then, my BOM contains my part numbers, and in my parts database, I list any qualified parts. That list would include parts from Digi-Key, Mouser and any other distributor that I need to get the part from *with their part numbers). When parts go obsolete, I only need to update the parts database, and not every schematic. \$\endgroup\$ – Mark Jun 29 '16 at 8:12
  • \$\begingroup\$ @Mark, it's worth mentioning that what you're describing is often called an approved materials list. A listing of all the specific manufacturer and part numbers that are acceptable for each particular function, usually designated by an internal part number. \$\endgroup\$ – The Photon Jun 29 '16 at 15:50
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There is, unfortunately, neither a best way, nor a standard way. I have lived through several mergers of companies, who then spend inordinate grief combining incompatible parts databases.

Different people, and different companies, feel they need different information.

There is a different between what information is retained by purchasing, which should be everything, what is shown on when you do a part search into the database, and what is shown on the circuit diagram.

As a rule, only the value should be shown on the circuit by default, and then you should have the option to make further fields visible if they are critical to the application.

The fields that get displayed when you are looking for a part that your company already has in its database (you don't want to use a new part if there is an existing one) should include, as well as tolerance, package size, technology ...

  • whether it is available from multiple sources, or needs to be from a specific manufacturer

  • cost

  • whether there are any gotchas lurking in the datasheet that need to be checked, so a note that Y5U dielectric only supplies 30% of the rated capacitance at rated voltage for instance, or that the power pad must be isolated rather than grounded

  • whether it's in active production or going obsolete shortly

  • RoHS status

  • monthly use, or number of different designs used on. A little used component is a good candidate for future elimination.

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