PCB Layer Numbering Standards?

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Bob Scott
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PCB Layer Numbering Standards?

Post by Bob Scott » Wed Apr 05, 2006 1:45 pm

Hi All,

I was just curious to find out if there are any industry standards regarding layer numbering when your doing a PCB layout in CAD software like Orcad or Eagle.

My understanding is that they might be as follows for a 2 layer board:

1 Top Silkscreen
2 Top Solder Mask
3 Top Copper layer 1
4 Bottom Copper Layer
5 Bottom Solder mask
6 Bottom Silkscreen

Any help appreciated.

Bob :cool:

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haklesup
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Post by haklesup » Thu Apr 06, 2006 12:50 pm

Thats about right.

In addition to your list, you would also need a board outline layer and a drill file but these should all be generated together by the CAD programs export (gerber) tool.

Copper top and copper bottom form the first pair then the copper layers are just numbered from top down (Inner1, inner2 inner3 etc). The names and numbers assigned to the gerber files may vary from CAD to CAD but there will usually be a log file of some sort with a legend inside.

Your project may include other layers that are not used in manufacturing like dimentions, user notes, mechanical etc.

Most fabs want your gerbers to be in the RS-274X format as the line widths are embedded. If you export in the RS-274D format you will also need to include an aperature file.

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Bob Scott
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Post by Bob Scott » Thu Apr 06, 2006 2:00 pm

Thanks Haklesup. ??

Do you have any suggestions for a schematic and layout CAD program like ORCAD but not priced out of reach of the small electronics designer?
I have used Orcad at KLA-Tencor while I was in San Jose. It's intuitive and impressive, but whoever thinks I, working as a small consulting outfit can personally pay mucho thousands of bucks for this program...they are dreaming.

I've played with the free version of Eagle4 for a couple of days but I understand that one of its output Gerber files may not be compatible with all board houses (something about a "dynamic" file, and its drawing files in a proprietary format.

What schematic and layout program would you recommend that would be available in a price range in between Eagle and ORcad, with generation of Gerber data included?

Thanks again,
Bob :cool:

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philba
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Post by philba » Thu Apr 06, 2006 2:46 pm

They all use a proprietary file format so that's no big deal.

I'm not sure when you mean by eagle produces incompatible gerbers. I've not heard that - can you give us a pointer to info on that topic?

I use eagle and once you get past the UI issues, it's incredibly powerfull, especially for a free piece of sw,

Phil

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haklesup
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Post by haklesup » Thu Apr 06, 2006 3:47 pm

If you can get by with 2 layers and just a few hunderd nodes, just about every vendor has a demo or freeware version.

Electronics workbench has a freeware version with 50 components, 750 pins and 2 layers (I have the power pro version and that has become very expensive in the last 3 years)

I also use CADint but I see that has skyrocketed in price too.

Here is a comprehensive but not complete list you can go through
http://www.mitsi.com/Link/books/CAE.htm

Most EDA vendors assume you are making money when you use their products so are not shy to charge a lot.

Sometimes you can negotiate a deal at the end of the month with the right sales guy.

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philba
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Post by philba » Thu Apr 06, 2006 4:41 pm

haklesup wrote:If you can get by with 2 layers and just a few hunderd nodes, just about every vendor has a demo or freeware version.
but do pay attention to the restrictions. Some are completely full function with size, pin count or device number restrictions. But some expire after a trial period or have restrictions (like no gerbers or saving projects) that make them utterly useless.

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Re: PCB Layer Numbering Standards?

Post by Gorgon » Fri Apr 07, 2006 3:47 pm

Bob Scott wrote:Hi All,

1 Top Silkscreen
2 Top Solder Mask
3 Top Copper layer 1
4 Bottom Copper Layer
5 Bottom Solder mask
6 Bottom Silkscreen
I don't know if you are into SMD, but if you are, you need to make room for paste mask(s) and placement files.

I use an old version of Eagle and I have no problems generating Gerber 274-X files for my pcbs. I have used up to 6 layers with no problems.

If you want to renumber the layers, please think of the maximum number of layer you'll ever make. Today 4 layer is a must if you design for European CE compliance. I would suppose that this is the same in the US for the FCC rules, at least in high speed digital electronics.

TOK ;)
Gorgon the Caretaker - Character in a childrens TV-show from 1968. ;)

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Bob Scott
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Post by Bob Scott » Sat Apr 08, 2006 3:56 pm

Gorgon: Yes, I will be using SMD technology. These paste layers, are they like negatives of the solder mask layers?
You mention parts placements files. Are these layers? Does Eagle generate these files?

Philba: I had a only a few days to get somewhat familiar with Eagle's schematic generator program and it seems similar to the small experience that I've had with Orcad. I can't remember much difference in the UI (User Interface) you mention. I have generated a schematics in both, but never have made a layout, or the need to get past playing with the rubber-band mode.

I wish I could afford Orcad because there is a parts library file available free on the internet that contains a library of all available Digikey parts, but unfortunately, it's only for Orcad and if you try to download it, the serial number of your copy of Orcad is validated before it will download. ie: no using illegal copies of CAD.

I once tried playing with AUTOCAD 3D for DOS back in the 80's. Book cost me $35. After hours and hours of frustration, I swore I'd never attempt Autocad ever again. Some software is best left to drooling geeks.

Bob

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philba
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Post by philba » Sat Apr 08, 2006 4:32 pm

paste layer is different from a mask negative though in practice they are pretty close.

have you looked at the eagle library? it's pretty big. though you should verify every library part, orcad or eagle.

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haklesup
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Post by haklesup » Mon Apr 10, 2006 12:09 pm

The SMT related layers are only really necessary if you plan to do high volume or automated assembly. If you plan only to make a small batch with hand assembly they will be unnessary. It's no problem to generate them. They will be used as input to the CAM system, whatever that may be, at the assembler site or ignored by the fab.

As big as a library gets, I always need to create or modify at least 50% of the components to meet actual needs. Digi key dosen't sell many parts I use anyway.

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philba
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Post by philba » Mon Apr 10, 2006 2:05 pm

haklesup wrote:The SMT related layers are only really necessary if you plan to do high volume or automated assembly. If you plan only to make a small batch with hand assembly they will be unnessary. It's no problem to generate them. They will be used as input to the CAM system, whatever that may be, at the assembler site or ignored by the fab.

As big as a library gets, I always need to create or modify at least 50% of the components to meet actual needs. Digi key dosen't sell many parts I use anyway.

yes, that is true - the paste layer is used to produce a stencil though I've always wondered about using it as input to a CNC device with a paste dispenser.

I hear you on the library. I wind up makes my own parts, even for ones that already exist in the library. In particular, I dislike the way a lot of the schematic symbols are done.

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