Electronics > Proteus

Routing 4 layer boards

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Simon:
I am trying to do my first 4 layer board in Proteus. This is proving to be a bit of a nightmare. Okay I’ll admit I have tried to make the auto router work and it does not seem to get it even though I have tried to specify routing pairs et cetera. The idea is to have the bottom layer as a ground plane and the top layer has mostly a ground plane carrying only power stuff that I manually route. Obviously the components all sit on the top layer as surface mount parts so they are going to need a via nearby and a short trace in order to get the connection into the middle pair of layers. I have also tried creating 2 types of via. One that goes through all 4 layers and one that goes from the top layer and only through the 2 internal layers. This via is not being used only the complete through-hole via is used. It also routes all over the top layer before trying to use the inner layers. Am I missing something significant or is the auto route the not really capable of doing for layers like this?

I’m also at a loss as to how I would choose to use a specific via while I am manually routing. Or indeed how do I choose which layer I am going to switch to.

Simon:
I am using PCB cart. As far as I am aware they do do blind and buried via types.

I don't have any special requirements of the routing, there is nothing high-speed et cetera I'm simply trying to avoid EMC problems so am trying to keep anything that might be emitting inside the board.

Simon:
Yes their prototyping does not do blind/buried, as it also has limitations on number of layers and copper weights. I suspect that prototype boards are made on standard setups so that they can get lots of peoples boards on one tool, if they offered all options it would become impossible to group anyones design or they would end up with an expensive process to cover a few designs but that also applies to designs that should be cheaper breaking the "prototype" model. On production orders you are payinf for the tool and are keeping ownership of it so I guess they do as you want and charge you for it. Adding one blind via put the price up by about 15%

mc172:
Unless you're working up at around 6 GHz and beyond, fully stacked vias aren't going to radiate anything or be particularly susceptible to RF. Blind vias are incredibly expensive and completely unnecessary for 99% of the time that people use them. I routinely use fully stacked vias up to 3 GHz. I don't work above 3 GHz much but doubt it would start to become a problem until at least double that.
If you are working up there in microwave voodoo land, you've got more to worry about than vias, such as the slot antenna formed by the thickness of the substrate material.

Simon:
Well I'm not too fussed about blind via's its more about trying to understand how to use proteus, it supposedly chooses the shortest via but then is clearly not doing so. Going for faraday cage style routing cannot be done with the autorouter. I guess if I manually put a via next to each component and force all routing to be on the inner 2 layers this would work.

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