Alexis, 

If you have to have Polarity Markings you might as well add a couple lines that map to the maximum component outline and visible after assembly so that they are at least useful for assembly placement alignment accuracy. I don't like useless silkscreen outlines that are covered up in assembly. The only people who see under component body silkscreens are you, fabrication and assembly covers them up. Some designers think that's artistic but who gets to see the art? What good is that?

Here are some silkscreen guidelines:

1.    No silkscreen outline under the component; these get covered up during assembly and don’t provide any useful purpose (waste of expensive inkjet cartridges) 

2.    All silkscreen outlines visible after assembly process and provide a functional use as alignment marking for assembly registration accuracy 

3.    All silkscreen outlines must be inside placement courtyard

4.    All Silkscreen outlines are mapped to the Maximum Component Body with one exception, the Silkscreen to Pad spacing rule “overrides” the Component Body Mapping.

5.    Silkscreen outlines should map the component body and not go around pads. Excess silkscreen outlines should be avoided to make room for ref des locations. Silkscreen outlines should perform a “hatch” outline along the component package body.

6.    Pin 1 is identified by extending the silkscreen along Pin 1 length to indicate polarity when the package cannot be placed inverted (inverted parts include non-polarized 2-pin parts)

Examples: 
http://www.pcblibraries.com/forum/smt-library-silkscreen-outlines_topic26.html 

Tom

Tom Hausherr CID+, CIT
President
PCB Libraries, Inc.
13730 Sorbonne Court
San Diego, CA 92128
858.592.4828 Office
858.859.5371 Cell
www.pcblibraries.com  

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Alexis Meehan
Sent: Friday, August 08, 2014 8:53 AM
To: [log in to unmask]
Subject: [DC] Silkscreen/AOI

We are considering removing all silkscreen from our boards in order to save $$. However, manufacturing says we need to keep polarity and pin 1 markings in silk because the AOI can only read contrasting colors, and putting those in etch would not work.
If we put any silk at all on the board, we won't be saving anything and might as well just keep all the silk, right?
what are your experiences with this?
Thank you,
Alexis Meehan


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