I have all the spacings set to say 0.2mm which is what I want the minimum spacing to be.
Now I have a pad connected say to ground and the router places a via to ground near to the pad. The via is electrically connected to the pad so from a design point of view it really it doesn't matter that the via is close or even touching the pad, they are both on the same net.
The problem I have is that when the design is sent for manufacture their design check doesn't take into account the fact that the via and pad are connected together and are flagged as violating the 0.2mm minimum spacing and ultimately costs more to manufacture.
So the question is why does the router (pro-router) place a via so close to a pad that it violates the spacing rule and doesn't produce a DRC error. Did I miss something here, some setting I haven't found, is that just how it works?
I repeat that there is no question that the design is compromised, all vias & pads on different nets have proper spacing, its only where they are on the same net the spacing rules seem to be ignored.
This seems to be an issue with your manufacturer. You are correct in everything you say. In fact you can have what is know as VIP which is "via in pad" for dense boards.
I have never had a manufacturer come back to me regarding such a design rule query...
The software was designed to try and apply design rules intelligemtly. Essentially, clearances are to avoid shorts in manufacture. If the pads or vias are on the same net, then it's very rare that the risk of a short would cause any problem. If fact, it's probably only in specific RF situatiions where impedance is critical that it would be likely to have any undesired effect. There's also a possibility of problems with solder paste when a via is close enough to a surface mount pad so the resist doesn't bridge between them.
The issue here is not really one of why Prorouter is violating clearances for items on the same net, but rather one of why the manufacturer's checker is flagging it as an error.
Via to pad spacing
Posted - 30 Apr 2009 : 12:34:24
