Trace Distance to Board Edge

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I have a new contract with boards that have straight edges a... - Jul 30, 2007 by SWAG

If you do everything correct depaneling, features should be ... - Jul 30, 2007 by davef

Thanks, davef. We have one that is 0.015" (edge of trace to... - Jul 30, 2007 by SWAG

So, now you know the tolerance that you and the board fab ha... - Jul 30, 2007 by davef

This board was designed in-house so I was able to get the en... - Aug 01, 2007 by SWAG

It really depends on how thick the board is. 0.063" and you... - Aug 02, 2007 by Hussman

You should be more worried about components cracking from th... - Aug 08, 2007 by Flipit

SWAG

#51232

Trace Distance to Board Edge | 30 July, 2007

I have a new contract with boards that have straight edges and are good for v-score breakout panel design. However, many of the traces are very close to the edge of the board so I am concerned that the traces could be damaged when we run them through the pizza cutter. We are considering going to tabs then routing them but would prefer to not have that extra labor. What is considered a safe distance from trace to board edge for v-score depanel?

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davef

#51233

Trace Distance to Board Edge | 30 July, 2007

If you do everything correct depaneling, features should be kept 0.025 thou from the score line.

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SWAG

#51234

Trace Distance to Board Edge | 30 July, 2007

Thanks, davef. We have one that is 0.015" (edge of trace to edge of board) so that might be risky.

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davef

#51236

Trace Distance to Board Edge | 30 July, 2007

So, now you know the tolerance that you and the board fab have in the area of the score line. For more, look at: * Accusystems [accusystemscorp.com] site scoring section for their FAQ. * Merix [Merix.com]: Designing For Manufacturability (DFM) Manual, Scored Board Profiling, Design Guidelines * Fine SMTnet Archives, for instance: http://www.smtnet.com/forums/Index.cfm?CFApp=1&Message_ID=29040

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SWAG

#51276

Trace Distance to Board Edge | 1 August, 2007

This board was designed in-house so I was able to get the engineering to move the trace in to a safe distance from the board edge. I think we're good to go.

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Hussman

#51281

Trace Distance to Board Edge | 2 August, 2007

It really depends on how thick the board is. 0.063" and you guys would be right.

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Flipit

#51347

Trace Distance to Board Edge | 8 August, 2007

You should be more worried about components cracking from the V Score depaneling process. The dual wheel and single wheel pizza cutters from CAB Maestro 2 and 3 can crack components if close to the edge. The Fancort VPD5-330 is a chopper style V score depaneling machine. This machine worked the best for me. No damage using it. However, much more expensive. I did a study with various sized resistors and capacitors at 90 and 0 degrees at various spacing from the score edge. Basically the smaller the component the closer to the edge it can be and not crack. Components parallel to the board edge are more likely to crack. The dielectric of the capacitors makes a difference also. COG,NP0 > X7R >Z5U,Y5V Greater means less likely to crack or in other words NP0 is better than X7R for crack resistance. Don't think that there is a set formula. There isn't! I cracked ceramic resonators at 0.050" from the board edge with CAB M2 and M3 depanelers but not with the chopper depaneler. My entire study was done on 0.031" thick PCB since the thin PCBs are the PCBs where density was most important to us.

The cracking I observed was not from components mechanically hitting against the pizza cutter wheel. It was from stress induced from shearing the PCB material with the pizza cutter. Like an earthquake cracking your foundation.

Chris

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