Changing a PCB from 2 layer to 4 - pointers?

So I have a PC board design that I’m reworking from 2 layers to 4 on the advice of a friend, as it has 21 ICs, ten 7-segment displays, and 6 LEDs.

As KiCAD currently does not have an autorouter, I’ve been using DipTrace for that functionality (importing directly then using Eagle format to bring the design back into KiCAD for final silkscreen adjustments, Gerber generation etc.)

This process worked well with the initial design and corrected version.

I then added the two inner layers, defined the boundaries for the needed pours, then sent it back into DipTrace’s autorouter.

I had expected it to merely route all the Vdd, Vcc, and ground connections to the two inner layers and keep all the signal traces to the front / back copper.

DipTrace had other ideas.

I wound up with these planes mercilessly slashed into several unconnected sections and multiple ratlines remaining.

Obviously a different approach is needed.

My next step is to work with the previous successful 2-layer route and edit that to manually move the Vdd / Vcc / ground traces to the two inner layers. I may alter the original pours to use part of the inner layers to accommodate most of the segment ‘buses’ for the 7-segment displays.

Any tips I should keep in mind while doing so?

I’d simply keep the 2 layer design, add the inner layers, add copper fills on them and then iteratively improve the design, for example replace now unnecessary Vcc/Vdd traces/fills on the outer layers with vias and see if you can improve routing in other places because of the free available space.

I don’t recommend autorouters at all.


I always have one inner layer unbroken groundplane and use the other inner layer as track. Vdd/Vcc are just run as wide tracks early in the the routing process to keep them sensible.

In regards to the 2 / 4 layer approach, your method is what I ended up doing. I made two pours for 5V and ground, then swapped over the connections from the spaghetti trace placed by the autorouter. I also did some cleanup along the way to fix some truly atrocious traces.

All I have left to do is carve out a bit of the 5V plane to make way for the 12V trace to the LED displays (I REALLY wish I didn’t need 12V in the first place; I would prefer to run everything off the 5V).

As it is, all I have left to do is run through all the traces and tweak as needed.

It has been an eye-opener, for sure.

While I wouldn’t rely solely on an autorouter, I can see how it can be useful in some cases.

I’m noticing one hiccup… the PTH pads that connect to the pour are all solid; no thermal relief even when I have that option set…???

Thermal Reliefs can also be set on different levels. You can set them per pad (which overrides global settings) and you can set them for each Zone.

Isn’t it from lowest priority to highest:


I’ll take another look when I get back to that point. I found a couple more bugs that have caused me to decide to start over on the board I was designing…

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