PCB Silkscreen tips?

OakGraphics

Seems like we have a fair amount of people making PCBoards - I have seen no less then 5 pcb's for propellers as of late.·I thought it would be fun to ask for suggestions on how to make good PCBoards and the like.· I am working in Cadsoft Eagle, and my first boards came out pretty good, but my silkscreen looked not very good. (broken text, and the like)·· I have read to use all vector text for eagle, but was wondering if anybody had any suggestions on minimum line thickness and the like.

I also seem to make very busy silkscreens.·· The library parts seem to have too much information for the silkscreen.· What I have done in the past is build a library of parts I am using and 'strip' the silkscreens of erronious stuff.· I like the 'box' approach to outlining parts instead of showing the 'picture' of the part.· Are there any tricks to doing this faster?

What about soldermasks?· I tried a black soldermask board and it was pretty fun.· But it wasent 'glossy' - must not have been a great soldermask.· I know green is common· - what do you guys prefer?· (I know - green is cheeper too. :-) )
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Phil Pilgrim (PhiPi)

The minimum line width for silkxcreens varies from fab to fab and is usually included in the fab's "capabilities" list. Also, silkscreens will drop out if printed on top of vias, so give them a wide berth if you can. Another thing to watch out for is "line gain", the tendency for the ink to spread a little when a line is printed. This means that details that are too close together will blend into a single blob.

Another thing to watch out for is whether your PCB CAD program makes a distinction between "lines" and "wide lines". A "line" is just a vector width no width information. A "wide line" includes width info in its definition. If your design includes any "lines", you may be able to specify their width at postprocessing time, when the Gerbers are created.

One handy tool to have is GCPrevue, a free Gerber viewing program. I always review my Gerbers with GCPreview before I send them off to fab, just to make sure everything got through postprocessing the way I expected it to.

Finally, some fabs will warn you if your silkscreen detail exceeds their capabilities to print; others will not. But most will be willing to help if you ask them.

-Phil

OakGraphics

Thanks Phil for the pointers. I am using Cadsoft Eagle at the moment, and found the problem I had with the first set of boards was not selecting vector text for all text on the board. I have been going through my custom library parts and flipping them back to 'vector'. I also have been trying to set the minimum thickness of silkscreen to 10mil - which I think looks pretty fat.

Timothy D. Swieter

I have always had an opinion about silk screens on PCBs.· Admittedly I have myself have never sat at the computer and designed one and then had it produced so I can't offer any program particulars.· I have done sketches and reviewed artwork and asked a technician to create/modify as needed and those designs were built.·(I am doing a board design for my next hobby project though)
Anyway, my opinion is that the silk screen should be simple.· They·should contain·enough·information for the user of the board to know what to do and not guess.· Just like when you·write a·book, consider your audience.· Part placement is good, but don't go overboard.· The·component names/numbers are a must when it is a design sold to a customer that is suppose to be then be populated as part of a kit.· Key components should also be labeled like MCU, connectors, buttons,·LEDs.· Make the labels functional.· If a buttons is a reset·button then label it reset, not Btn1 or some·other variation.·
I also like to clearly label connectors, headers, and pins.· Be sure that is it clear what signals are on what pins.· If there are jumper settings, then·I try and place a table on the front or back of the PCB silk screen to tell which jumper does what.· Make sure conventions used in the schematic are carried over into the PCB layout/silkscreen and the instruction manual/documentation (if produced) so that it is all consistent.
The best way to learn what is good and what is bad is to be an observer of other designs.· After a while you will gain an opinion of what works and what doesn't.·



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Timothy D. Swieter
tdswieter.com

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One little spark of imagination is all it takes for an idea to explode

Phil Pilgrim (PhiPi)

I definitely agree with Timothy about the part designators/outlines. Unless the board is designed to be assembled as a kit, leave them out. Professional assemblers don't need them, and they just clutter up the design.

-Phil