Assembly Reference Designator IPC Location

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   Is there a specific IPC specification that specifies the location of the assembly reference designator?
Typically I have placed assembly ref des in the center of the component outline, which seems to be industry standard. 
Is there a specific IPC specification that I can refer to which states something to the effect of "Assembly ref des shall be placed in the center of component outline"?

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AGONZ67 Members Profile Send Private Message Find Members Posts Add to Buddy List Advanced User Joined: 30 Mar 2012 Status: Offline Points: 119	Post Options Post Reply Quote AGONZ67 Report Post Thanks(0) Quote Reply Topic: Assembly Reference Designator IPC Location Posted: 31 Jul 2019 at 10:46am
	Is there a specific IPC specification that specifies the location of the assembly reference designator? Typically I have placed assembly ref des in the center of the component outline, which seems to be industry standard. Is there a specific IPC specification that I can refer to which states something to the effect of "Assembly ref des shall be placed in the center of component outline"?



Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5716	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 31 Jul 2019 at 11:05am
	There is no standard for the placement of the Assembly reference designator. The assembly outline should be a closed polygon and the assembly ref des should be placed anywhere inside that polygon. This way, the assembly shop has clean data to work with and the chance of making a mistake is greatly reduced. When the ref des is placed outside the polygon, it can get confused with another part close by.
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AGONZ67 Members Profile Send Private Message Find Members Posts Add to Buddy List Advanced User Joined: 30 Mar 2012 Status: Offline Points: 119	Post Options Post Reply Quote AGONZ67 Report Post Thanks(0) Quote Reply Posted: 31 Jul 2019 at 2:59pm
	Thanks for the confirmation of that. This is how I have been using them, but we are working with someone who wants assembly ref des to match the silkscreen ref des, which defeats the purpose of the assembly ref des.

Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5716	Post Options Post Reply Quote Tom H Report Post Thanks(1) Quote Reply Posted: 31 Jul 2019 at 3:07pm
	If the customer wants to use the Silkscreen Legend Ref Des as the Assembly Ref Des then they are potentially creating a situation where two similar parts could get swapped. We did that at a company I worked for and sure enough, the assembly shop swapped two same size resistors by mistake and the PCB did not function properly and it took the EE engineer a couple of days to track down the problem. Very costly mistake.
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