via in PCB design

[Shadow_warrior]

Is it recommended to put the vias in the middle of the pad? I am making a 4 layer PCB. I want to connect the SMD(package 1210) components from 1st layer(signal layer) to 2nd layer (ground). So Can I place the via in the mid of the component pad or should I place it near to the component and connect it through track?
Thanking in advance.

 

[dknguyen]

No it is not. Make a small trace and put the via there. The reason is the via can suck up the solder and make the pad dry if you are reflowing. Also, the via may be off-center if the pad is small. But if the via is small and the pad is large, and you are hand soldering you could probably get away with it. In either case, make the via as small as you can.

When you really do need a via in the middle of the pad because space is tight (like breaking out a BGA) special measure are taken that have to be specified to the board house.

 

[ronsimpson]

Some CAD software will through an error if there is a via in a pad. (you can turn off that error)

The reason is the via can suck up the solder and make the pad dry if you are reflowing.

Some times I need to pull heat out of a part into the pads then through via(s) to a pad on the other side of the pcb. The vias will fill with solder so I use extra solder on those pads.

 

[kubeek]

For example with thermal pads under an IC it is inevitable to use vias inside a pad, but like dknguyen said you need to make the via holes as small as possible to prevent sucking off the solder.