Vias too close to pads of the same net?

Hello,

why is it that putting a via near a pad of the same net makes a board non-manufacturable?

-Also, why is it bad practice?


I have been told to re-do a double-sided layout because i have a few 0.6mm/1.2mm vias just 0.1mm away from SMD resistor pads of the same net.

...the via "restring" is not touching the pad of the resistor....as i said, it is 0.1mm away...and in any case, it's of the same net.

(-the vias are 0.6mm drill, and 1.2mm overall diameter)


So do you know why this is a bad thing?

What is your pad to via design rule for everything else?

see https://www.edaboard.com/threads/126898/ for this discussion before.

PCB Manufacturers or companies design rules may be quite different. I also don't know the involved technology, so I can't comment the particular case. I think that either copper-to-copper or solder mask rules are affected. There's a special point with same-net copper. Basically, same net copper-to-copper spacing is not absolutely required. But some people want to have a minimum same net spacing to get separated copper etched properly, even if it's same net. Otherwise, connect it by a trace.

Other design rules are related to solder mask. There are two cases. For tented vias, you want a minimum solder mask width to keep the via protected from process chemicals. Having the via annular ring completely covered with solder mask should comply with this requirement. For open vias, a minimum solder mask strip between pad and via copper must be kept to prevent solder drain. So if the via annular ring is completely exposed, 0.1 mm copper-to-copper may be too low.

I hhave heard complaints from PCB assembly unit about via very near to pad. They are telling while soldering ( machine process) solder/ paste is flowing out through the via and the coponent get less soldered. (the same case occured for vias on thermal pads of QFN etc)

It is better to provide a decent clearance from the SMD pad even for the same net .