A point of detail... as Juan's comment prompted me to want to clarify...
Most of us who have been designing for some years have used the silkscreen legend layer as the assembly drawing for expediency sake and have been successful doing that... however a true assembly drawing should do more than just tell you where the parts go on your board.
The very normal silkscreen layer requirement for reference designators to be visible when the part is installed would make the assembly drawing have all the reference designators outside the part if that is what you used to make it... This is not always ideal.
Some of us make a separate layer in our library parts for the assembly layer... this layer can have an accurate depiction of the part in the correct orientation and any polarizing features clearly identified... since the assembly layer does not get printed as the 'silkscreen legend', it can cover pads or whatever else is there in the CAD design since it is specifically for the assembly drawing only and not printed on the board surface. When plotting the assembly drawing we turn off the silkscreen layer and turn on the assembly layer so we get a true depiction of the part shown and can have the reference designators inside the part. :)
William Brooks, CID+
Senior MTS (Contract)
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-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Robert Wolfe
Sent: Tuesday, April 01, 2014 10:23 AM
To: [log in to unmask]
Subject: Re: [DC] Assembly standard + best practices
Juan,
Well you could look at IPC 2221 which has some info about that, or actually IPC spec IPC-D-325 will have more However if part body is big enough to fit large enough text for readability in the size document you are printing, Ref Des should be inside body of part for assembly dwg.
Where parts are too small I usually put them as close as possible to where they are placed in silkscreen. Example SOT-23 This helps in inspection etc.
Any silkscreen must be visible when part is installed though.
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Juan Vega
Sent: Tuesday, April 01, 2014 12:38 PM
To: [log in to unmask]
Subject: [DC] Assembly standard + best practices
Hello,
Can someone help me pointing out which standard should I consult in order to do a Printed circuit board assembly drawing?
I am trying to find, which is the best practice for location of reference designators (inside the part drawing, outside).
Best regards!!
Juan Vega | Product Enngineer | Branson Ultrasonics Emerson Industrial Automation | Lote #4 Carretera Nacional KM 8.5 Modulo Industrial America | Nuevo Laredo| Tamaulipas | 88277 | Mexico T + 011 52 867 711 0821 | F + 011 52 867 711 0811 [log in to unmask]<mailto:[log in to unmask]>
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