Hi ,
I just want to confirm that this scenario is even possible, it seems that it would lead to Vcc / ground shorts, since one board does not know about the other board’s seeds.
Two 2 layer PCBs stacked with Vcc copper fill and ground copper fill on opposite sides for both boards, is this even possible ?
e.g. :
vcc copper fill| ground fill | ground fill | vcc copper fill
Connect the boards vcc copper fills with a wire.
Andrew.
The best bet is to try this on a simple test board (to keep it simple) and if it doesn’t work as desired post the sketch to see if we can suggest a fix. It is hard to visualize what you are trying to do without a sketch.
Peter
If I understood the original, the idea is to create two separate two layer pcbs, then stack them to create a fake 4 layer pcb by running wires between the 2 boards. One board with the ground fill on the top, the other with the ground fill on the bottom, so that both ground fills end up in the ‘middle’ when stacked.
Sure it is doable. Making sure to have some sort of spacer (insulation) between the boards so that traces do not touch. Fritzing even has a ‘wire’ part for PCB view that could be used to do the connections in the sketch (without stacking the pcbs in the sketch. Actual parts would only be on one of the boards, so any ‘through’ connections would need manually placed connection points on each board to hold the wire that joins them.
A typical pcb layout that is complex enough to need more than 2 layers is likely to have a lot more than power and ground crossing the layers. Each instance would need a wire.
Thanks Merlin and Peter , I will try it out.
Andrew.
I expect a better bet would be switch to something like Kicad and do a real 4 layer board. All 4 layers being glued together is likely to be a lot more reliable than two 2 layer boards soldered together with wires (even if using Fritzing is easier.)
Peter
Hi Merlin,
Isn’t the green solder mask going to insulate the traces anyway? and also the plated holes are also not connected to the copper fill unless they connect to Vcc or Gnd , so when the boards are put against each other , it should work without insulation and where there is a connection it is only Vcc to Vcc and Gnd to Gnd, since non-connected holes look like this under the part’s leads (c4 moved aside for example):
So assuming the board vias are identically placed, there should never be a vcc to gnd connection in the vcc gnd | gnd vcc sandwhich.
So using 2 thinner boards I can solder the through hole parts with no worries and the soldered parts will hold the two boards flush to each other.
Thanks, Andrew.
The problem remains are the ic sockets, I can use wire wrapping dip sockets for the logic ics but for the 28 pin zif socket the pins will be too short. Maybe I should just use Kicad like Peter suggested…
Andrew
That will depend on the specifics of the pcb board layout. A board layer containing ground fill can still contain regular traces as well. Those traces are not going to match with the next layer.
Enough THT leads that go through all layers would normally be sufficient to maintain an air gap for insulation. Just a bit fiddly to get it initially mechanically stable when the first few solder connections are being done.
Depending on the specific functionality of the board, even if the mask is enough for electrical insulation, having the copper traces that close together could introduce unwanted signal cross talk. That is effectively creating a capacitance between the traces on the different layers. That happens anyway, but without separation the effect will be increased.
Hi Merlin,
Thanks for all the advice, I didn’t think about crosstalk. My board files are attached:
boardbnew.fzz (101.6 KB)
boardcnew.fzz (88.9 KB)
Andrew.
You have extra vias (which won’t make any practical difference) in the DRC reports
boardcnew:
boardbnew:
Peter
Thanks, Peter, I will remove them anyways.
Andrew
