How to use the MOUNTED attribute of Schematic Symbols.

  andyfierman, 2 weeks ago

This post is to help people to understand what the MOUNTED attribute - associated with each Schematic Symbol placed into a Schematic - is for.

The MOUNTED attribute is a Bill of Materials (BoM) attribute.

  • It is not a PCB attribute.

It is used to indicate if a component is to be mounted on the PCB when it is assembled.

To illustrate by example, suppose it is required to design a PCB with a microcontroller that is in-circuit programmed for the prototype PCBs but in production, the micro is to be supplied pre-programmed by the manufacturer.

The prototype PCBs will need a programming header connector and may need another connector for debugging purposes but the production PCBs do not need them fitted.

  • The point here is that the prototype and the production boards are built using exactly the same PCB.

They both have the same PCB footrpints and tracks on them. They just have different parts fitted according to the Bill of Materials (BoM).

So for the prototype PCBs, the BoM is run with the MOUNTED attribute for all the parts including the programming and debug headers set to Yes but for the production PCB, the BoM is re-run with the MOUNTED attribute for these two headers changed to No.

It does not make sense to interpret the MOUNTED attribute as a PCB attribute because that would imply that a PCB with the MOUNTED attribute for all the parts set to Yes would be made with PCB footprints and tracking for all the mounted parts whilst a PCB made with the MOUNTED attribute for some of parts set to No will be made with those PCB footprints and associated tracking, not present.

  • Therefore changing the MOUNTED attribute like this would generate two different PCBs.

That does not make sense because these are in fact, two different PCB projects not one with two stages in its lifecycle simply indicated by the status of the MOUNTED attribute in the BoM.

Comments

FrankCA

Thanks for clarifying this Andy.

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