Need for board edge to copper clearance

[nikhil2402]

Hi All,

I am aware that we need to keep a copper clearance from board edge. However, I am unable to understand the reason to do this ? Can anyone help me understand the need for this ? What is the drawback if the clearance is not kept ? I am in a scenario where I have the surface more right angled SMA. The pads of the SMA have to go till the edge of the PCB. How can I avoid this ?

I know that few manufacturers can produce PCBs that has the copper poured till the edge of the PCB but they fail to give me clear reason why they recommend to keep some clearance from the edge.

Thanks

[robertferanec]

mostly because when the board is cut out, there will be stress in the areas around the edges and if you route tracks very close, these tracks can be damaged. Also don't forget about tolerances, machine may not cut it exactly where it suppose to.

so I would mostly worry about tracks. You can have pads up to the edge, e.g that is how castellated holes are created.

also, keep in mind possible short circuit at the edge of the pcb (shortenings copper between layers if a metal is touching the edge and copper goes up to the edge)

[qdrives]

Are you talking about outer layer or inner layer?
For inner layers there is another important aspect - oxidation. This will essentially cause the board to break open, allowing more moisture in. That in turn allows for more oxidation. In the end you can delaminate the PCB.

https://www.mclpcb.com/pcb-guide/

https://www.candorind.com/pcb-delamination-causes-cures/

[nikhil2402]

Hi Robert and qdrives,

Thanks a lot for the replies. It clears my question.