Subtracting soldermask from silkscreen in Gerber files

Community PCB Design
1

Hi guys,

I’ve generated gerber outputs for my PCBs and realized that there are lots of areas where the exposed copper is covered by silkscreen, potentially preventing solderability. I know that some fabrication houses (such as BatchPCB) automatically subtract the (inverted) soldermask layer from the silkscreen layer but many don’t and I’d like to have a general solution to this problem.

http://sourceforge.net/tracker/?func=de … p_id=33921 suggests that this feature has already been requested for gerbv and Gerbtool already has this feature but the latter seems to be very complicated and I’m clueless how to do layer subtraction.

(Please don’t suggest me to include less layers upon generating my gerber files because there are some layers that are very useful and I want them all to be included.)

Thanks in advance!

Laci

2

Produce a solder resist layer (pads 0.08" larger than copper) and call it Silkscreen Scratch.

This is used with the silkscreen as a scratch layer and anything in the pad apetures is removed.

Fab house will likely do it anyway.

However, the best thing is to NOT put legend items there in the first place.

You control where the component name goes, move them.

If the outlines cover the pads then change the footprint so they do not.

3

mattylad:

I couldn’t care less with this issue if all fab houses clipped the silk screen. :slight_smile: I’m dealing with a fab house right now who doesn’t correct it (who probably won’t see any money from me).

Regarding manipulating layers, I’m only interested about the HOW which I cannot seem to find anywhere.

Having silk screen on top of copper can be treated as an error but I woudn’t say it is. In Eagle many components already have this problem and it’s pretty hard to get everything right on a large board. I won’t do any unnecessary work by hand, that’s for sure.

4

Subtracting the soldermask from the silkscreen layer is a good final level of stupidity-proofing the manufacturing process anyway. I haven’t used a PCB manufacturer that didn’t do it, and won’t in the future. It’s easier for them to do it as part of the manufacturing process than it is for you to create your own and give them one or two more layers they have to deal with and understand their purpose.

5

mondalaci:
I’m dealing with a fab house right now who doesn’t correct it

Then do not use them, they are crap. :)

Regarding manipulating layers, I’m only interested about the HOW which I cannot seem to find anywhere.

What software have you got?

You need some Gerber editing software to do it to Gerbers.

You already have the CAD software that produces it and can do it without the need for additional software.

Having silk screen on top of copper can be treated as an error but I woudn’t say it is.

I would, as would many more.

There should be NO silkscreen on any copper features that are to be soldered or used for test points - period.

There are even standards that specify this, or do you not work to any?

In Eagle many components already have this problem and it’s pretty hard to get everything right on a large board.

If you have a problem in the libraries then fix it, leaving it there is making a rod for your own back.

I won’t do any unnecessary work by hand, that’s for sure.

It is not "unnecessary ", it is essential.

If you are not going to correct errors in your library then you are going to have to do manual correction on every design that uses these parts.

Producing Gerbers that are messy with silkscreen features over copper is extremely bad practise, only wishing to fix it in the Gerbers is lazy and poor workmanship.

Do you DRC check your boards before producing your manufacturing files?

I would seem not as that should find these errors, or they are being ignored?

6

mattylad,

Although I appreciate you taking the time to answer me, giving me lectures won’t address my original question regarding fixing the Gerber files. I respect your opinion but I don’t agree on everything that you said and I won’t argue about these issues as chances are Eagle won’t even be my choice of CAD application, so I won’t take the time to fix its libraries.

I use DRC, by the way, but not for the silkscreen.

Laci

7

Actually implementing this at the gerber file level seems like a relatively difficult graphics and formatting problem. (especially difficult to get the results back into gerber format…) (gerber outputs “shapes” at locations. To have the silkscreen clipped by the soldermask would result in new, weird shapes on the silkscreen layers, leading to all sorts of problems.)

I would imagine that at the actual board house, the clipping is a relatively simple photographic process, or happens at a bitmap level just before imaging, where things are much easier… I don’t think that a gerber to gerber utility to do this exists (certainly not for free), and I don’t think I’ve ever heard of a board house that can’t do it; do you want to name names?

If it’s some sort of in-house process, there may be some other process point that is easier/more appropriate to make the modification. For example, it would be relatively easy to do at the gerber-to-postscript phase of some photoplotter output (photoplotters are now commonly postscript, right?)