Document Control questions with Variant Schematics

Hi Ian,

You did not specify which of Cadence tool you are using for schematic.

We are using OrCad, which can handle Variants. Most our designs are used in different assemblies and Engineer Designers here preferred to deal with ONE schematic rather different schematic for each variant. To do this we opted to add User Property to symbols in OrCad to identify which variant build any given component is used.
On Documentation side they have written a customized tool that recognizes UP field out put in BOM. This customized tool can dump a separate BOM for each variant into company inventory database.

We find out handling ECO/ECR are much easier this way.


Regards,

Pantheon

Whoops! I forgot cadence is composed of 10,000 tools that don't work the same way. :)

We're using SPB 15.7 with concept hdl and allegro pcb.

Concept has the ability to repopulate the base schematic on demand and not maintain separate variant schematics. But how will the service department service the variant models without schematics? And when a variant is revised per an ECO, where is that ECO number and date recorded on the variant?

I can think of ways around this by using external (not with the cadence database) control documents, but I really hope that cadence has better document control capabilities than this.

Thank you!

-Ian

Here is an example approach that may answer some of your questions:

Given that PCB assembly part number is likely to change multiple times without requiring artwork iterations. We chose to create new Cadence Projects using the Fab part number. This choice provides an unchanging base part number on Cadence Project, along with the ability to capture multiple assembly numbers (and in your case schematics)in one project. It is also not practical to recreate a Cadence Project for each assembly number change (a variant). Keep in mind our projects contain one .brd file.

If an artwork change occurs or if the design is not interchangeable (forward or backward compatible) it falls under the new number versus a revision category a new fab number is assigned and a new Cadence project is created.

Or to simply, if you don't like variants or tabulation, consider a one to one relationship. One assembly to one part nuimber to one project. New numbers are cheap.

Richard Van Os

GE Healthcare

Hello Richard,

We also build many variants from one board. One project had 78 variants using one board. We typically pull a part number for the board at the beginning of the project. Usually during the course of adding variants, changes have to be made to the circuit board. At those times, we pull a new part number for the circuit board and build new variants from that. Eventually, the older variants will migrate to the newer circuit board. The project with 78 variants used three different board part numbers over its development lifetime. The variant migration is a much more difficult issue with cadence, but I'm first trying to grasp the more basic concepts of cadence document control.

In the case of cadence, I could put the part number of the variant as the variant name. But I do not see how to populate any ECO information (ECO number, date, approval stamp) onto the variant schematics. There are custom text variables, but they only apply to the whole project - not to just a specific variant.

We used PCAD in the past and we had to have a separate schematic for each variant. We had to maintain a separate master schematic which netlisted to the board. It was very difficult to keep the daughter schematics netlistable to the board. Often during migration from one board to another, we would lose some of the original variant information.

My hope is that cadence can manage this information better than PCAD did (which wasn't very well). The variant editor gives me hope, but I need to be able to pass more than component value changes to the variants. I know cadence must have been programmed to deal with ECOs, I just don't understand how it's supposed to work.

Thank you,
Ian Overholt

Ian,


We just started using the variant editor 6 months ago so I am by no means an expert. This is how we use it.

We apply our different values with the variant editor at the BOM level. Which means we manually creating multiple variant.dat files for each part number. This is where you can also handle hardware and do not install instances.

The variant editor has the DNI (do not install) at attribute at the BOM level . Using multiple variant.dat files and this property provides one way for us keep track of each configuration. Unfortunately this data in not tied to or driven by the schematic.

Another approach could be:

If you have multiple schematics you could drive different values using the schematic. To handle parts that are not installed there is a BOM_IGNORE property you can look into.

DNIs parts appear in a separate area of the BOM while BOM_IGNORE will omit the parts from the BOM.

I hope this helps

Richard V
GE Healthcare