How do through via's work in a multilayer PCB

Community PCB Design
1

Hi All,

This might be a noob question but still its extremely confusing for me. I am designing a 4 layer PCB and unfortunately dont understand how via’s work. In a 2 layer PCB, a via connects the signal traces from the top to bottom layer. I get that part.

Now if I have a 4 layer PCB with 2 signal planes (top & bottom, layer 1 and 16) and 2 power planes (layer 2:GND, layer15:+3.3V). Layers 1&2 form a core and layers 15&16 form another core.

The setup is (12+1516) in eagle.

In this case, if I used only through via’s how does that work? So if I wanted to connect a signal trace from layer 1(top) to layer 2(gnd), the via would go through all four layers.

–Doesnt that short out layers 2 and 15, thereby shorting out GND and VCC?

–Is each via different such that it only connects certain layers together even though it goes through all of them?

–My mental image of a via is a plated through hole that goes through all layers. Do they have rivets that allow them to connect certain layers and skip others?

Might sound really trivial but any clarification is much appreciated. Due to cost limitations I am avoiding blind/buried vias.

Thanks!

2

The via will have clearance round it when it passes through layers to which it isn’t connected. Check the Gerbers with a Gerber viewer and you will see how it is done.

Leon

3

Thanks. Much appreciated.

The eagle “Supply” layer got me confused because of the apparently inverted gerbers that are generated.

I went back to using polygons as a fill for the supply layer instead of using eagle’s supply layer concept. Much simpler for my understanding.