[SOLVED] How to get impedance control from Gerber files?

[bobsun]

Hello,

I would like to ask a question on Gerber files.

I am referencing the PCB design of a publically released board. I know that the board has impedance control requirement so that certain tracks might need to be made of exact width, but where should I locate this information?

What I have is some Gerber files and their technical reference. When I opened the Gerber file, all I see are layers of copper area in different colors, without any information about impedance control, or special tracks that I could identify.

Could anyone advise me how to get this information from Gerber files?




Thanks,
Bob

 

[FvM]

I don't think, that you find this information in the gerber files, unless a special text layer is added. I think, impedance control procedures have to be agreed with the PCB manufacturer explicitely.

 

[bobsun]

I was wondering how can impedance control information be defined and embedded.

When we talk about impedance control do we define it for a "track" or a "net", which contains paths or nets of tracks? And when PCB file is exported to Gerber file, does Gerber file still preserve these basic nets, tracks and other basic design primitives? If not, I wonder how can a "track" (probably more properly should be called a "path") be specified in Gerber.

When you say "unless a special text layer is added", do you mean to overlay the text such as "this track needs to be impedance controlled" at the position on top of the track that has impedance control requirement?


Bob

 

[FvM]

Yes, placing all kinds of handling instructions on a text layer is quite common. You can expect, that a CAM operator will read in all supplied gerber files and check what's on it. A separate printed or E-Mail instruction will be more likely missed.

In fact, gerber apertures are often exposured with technlogy (e.g. according to copper weight) specific size corrections. Primarly, you would expect a good reproduction of all trace widths without impedance control. Impedance control means, that an expected transmission line impedance is specified for one or more trace width/layer combinations. If no test structures or traces with exposed terminals are present in the design, that allows to probe the impedance, you can refer to a specific aperture code or an unique trace width.

 

[bert_kak]

Hello,

I would like to ask a question on Gerber files.

I am referencing the PCB design of a publically released board. I know that the board has impedance control requirement so that certain tracks might need to be made of exact width, but where should I locate this information?

What I have is some Gerber files and their technical reference. When I opened the Gerber file, all I see are layers of copper area in different colors, without any information about impedance control, or special tracks that I could identify.

Could anyone advise me how to get this information from Gerber files?




Thanks,
Bob

Here is a sample that I made for our PCB manufacturer. hope this helps...

You can add on the fab layer the information about the impedance controlled lines so that whenever you forgot to attach this kind of file, the manufacturer will ask for it.

- KAK

 

[bobsun]

Dear FvM,

What do you mean by "Gerber apeture"?

Bob

---------- Post added at 14:15 ---------- Previous post was at 14:13 ----------

Dear KAK,

This file looks neat, but how did you manage to produce it? When I output PCB information into Gerber files, each layer is with a uniform color and there are only color difference between layers. How did you do to color specific paths?

And what is the software you use? I am using Altium Designer summer 09.


Bob

 

[FvM]

What do you mean by "Gerber apeture"?

Aperture codes are used in gerber files to define the size of pads and traces. Check the Altium documentation for details.

The term has been kept from times of vector photo plotters.

 

[bobsun]

Dear FvM and KAK,

I think this question is answered. Thank you both for the helpful answer.


Bob