altiumpcb-designvia
Does anyone have a Altium query/selector that targets vias in SMT pads? I'm routing a very dense HDI board, and would like to make rules that exclusively target vias that are inside a component pad and not normal vias or offset (dog-bone style) vias next to BGA pads.
(I'm aware of the tradeoffs involved in putting vias in pads, and the board house is going to fill and plate over them. I'm using Altium Designer release 27009 (Dec 2012)).
Vias in the pads are useful in high speed designs since they reduce trace length and therefore inductance (i.e. the connection goes straight from pad to plane rather than pad-trace-via-plane)
You have to check whether your PCB house can do this though, and it may cost more (via will need to be plugged and plated over to provide a smooth surface) If you can't put the via in the pad, putting directly adjacent and using more than one can help reduce inductance.
They are also useful for Micro-BGA designs, where space is very limited and traditional fanout techniques cannot be used.
A via-in-pad (or capped/plated via) is not to be confused with a "tented via", which is a standard via with soldermask covering the hole (hence "tented")
To illustrate the advantage, here is an example of a TQFP footprint fanout with standard vias and via-in-pads:
It's easy to see why the via-in-pad version is preferable for high speed designs that need to keep inductance low.
The reason it's more expensive is due to the complex process (compared to standard vias) and potential problems (e.g. plating bulging with expansion of plug, or dimpling)
This document discusses various plugging techniques.
Here is a run through of the process:
When you're setting up a new PCB rule, you can type "query text" to match objects to which the rule should apply.
When I do what you're trying to do, I just use "isVia" as the query text and then set the Connect Style to Direct Connect:
I'm not sure how to exclude your QFN's thermal stitching vias though...
Best Answer
I can think of two ways:
Method 1
This method assumes that the vias are created as part of the component, and not placed on the pcb directly.
Method 2
Give the via some property that will make them easy to filter out. For example, make all diameters of via in pads odd numbers that are very close to your desired drills, like 0.099mm instead of 0.1mm. That way you can filter by drill diameter (or some other attribute).