Screaming Circuits: Family Reference


Family Reference

I've written a bit about reference designators here and there. There are a few more factors that we run into now and then. Take the family panel. In case you aren't familiar with the term, it means that you have several different designs laid out into in one panel, as opposed to multiple copies of the same design in one panel.

Using a family panel can be a convenient way to deal with a multi-board design and can sometimes save a bit of money. Just a caution, though. Make sure to check with your fab house first. Some don't like family panels and some won't separate them for you. If you do have them separated prior to assembly, either at the fab house or by you, then you don't have any reference designator worries.

S 065 My-9 600 If you leave them in the panel and wish to have them machine assembled, it can get a bit more complex though. "Why?", you say. I'll tell you why. Generally, most people start at "1" for each new design. i.e. "D1, D2, D3... R1, R2, R3..." If the boards go into the machine independently, that's no problem. However, if you send the panel into a smt assembly robot, it may very well see that as your board having multiple D1's, R1's, etc. That would be rejected as an error in most cases.

If you are using the family panel approach, don't restart your numbering when you move to another one of the designs that will be in the panel. Either continue on from the last number in the prior design, add in a hundred's, with each design getting a different hundred's number or add a unique suffix on each board.

  1. Wrong way: PCB1: "R1, R2, R3, R4, C1, C2". PCB2: "R1, R2, R3, R4, C1, C2".
  2. Right way: PCB1: "R1, R2, R3, R4, C1, C2". PCB2: "R5, R6, R7, R8, C3, C4".
  3. Right way: PCB1: "R101, R102, R103, R104, C101, C102". PCB2: "R201, R202, R203, R204, C201, C202".
  4. Right way: PCB1: "R1A, R2A, R3A, R4A, C1A, C2A". PCB2: "R1B, R2B, R3B, R4B, C1B, C2B".

There are a lot of ways to do this. Just make sure that no reference designators are repeated from one board design to the next. I prefer method #3 myself.

Duane Benson
Is it immediate or extended? Does it matter?

TrackBack

TrackBack URL for this entry:
http://www.typepad.com/services/trackback/6a00d8341c008a53ef01538f878c24970b

Listed below are links to weblogs that reference Family Reference:

Comments

Another trick I like to do is to have all parts on bottom have a prefix of 100 (you can use 1000 too but the text becomes very long and hard to find a suitable space in dense designs). So when you're debugging you immediately know what side of the board a component is on--that is very valuable.

Combining with this idea, I did the same thing on a stackup of PCBs. R1, R2 was on top of PCB#1, R101, R102, ... on bottom of PCB#1, R201, R202 on top of PCB#2, R301, R302 on bottom of PCB#2, ....

If you never have to debug a board than this isn't that useful. But with the right tools it takes virtually no time to do this sort of thing (I have an EAGLE ULP that renumbers like this) and it's invaluable when you are debugging.

James.

Post a comment

If you have a TypeKey or TypePad account, please Sign In.

« Favorites | Main | So Long Old Friend »