How can I interconnect and solder stacked single-layer PCBs?

[kitaprak]

I’m designing a planar transformer on an E-core that requires 8 layers in total (4 primary layers and 4 secondary layers). I can only place two layers on my main board; for price considerations I want to design the remaining six layers as individual single-layer PCBs to stack and solder together.

My main questions:
1. What interconnect strategy to use?
2. What construction, sizing and layout best practises can be used here?

Some more details:
1:40 winding ratio, center taped
2 parallel winding layers for each primary winding (1 turn)
4 serial layers for secondary winding
13A_rms on primary winding

(I've also posted this question to Stack Exchange)

[PCB.Wiz]

.. for price considerations I want to design the remaining six layers as individual single-layer PCBs to stack and solder together.

Is that really cheaper ?
2 layer PCBs are pretty much the bottom of the price curve, and they can reduce your solder joint count, with multiple vias, which come essentially for free.
How many are you making ? 

[kitaprak]

Good point, I’ll actually go with 2-layer PCBs, but I can only use the top half to keep proper isolation between windings. But I still need to stack boards and connect them, which brings me back to the original question.
I'm really unexperienced and I'm looking for the general approach for connecting stacked PCBs, I would be really interested design and soldering techniques.

[PCB.Wiz]

Good point, I’ll actually go with 2-layer PCBs, but I can only use the top half to keep proper isolation between windings. But I still need to stack boards and connect them, which brings me back to the original question.
I'm really unexperienced and I'm looking for the general approach for connecting stacked PCBs, I would be really interested design and soldering techniques.

Also get some prices checks on 4 layer boards, smaller areas are not that costly.
Anything that can reduce your solder joints and PCB area helps, and you may be able to separate low voltage windings with glass fibre tape.

[daisizhou]

Look at the pictures, are you interested?

[kitaprak]

Also get some prices checks on 4 layer boards, smaller areas are not that costly.
Anything that can reduce your solder joints and PCB area helps, and you may be able to separate low voltage windings with glass fibre tape.

Thank you, I will try to come up with something, but I need 1 oz inner layer and it increses the price significantly at JLCPCB. If you have any tips on PCB layout or soldering techniques for connecting the stacked layers reliably, I’d really appreciate it. I'm open to any practical tricks you’ve seen or used!

[kitaprak]

Look at the pictures, are you interested?

Thanks for sharing the pictures, would you be willing to share the source files?

[daisizhou]

Look at the pictures, are you interested?

Thanks for sharing the pictures, would you be willing to share the source files?

I don't have the source file.
This is the physical PCB transformer that I disassembled.
Upon closer inspection, one of them has already been damaged,I plan to remake it, but it looks like it's over 20 layers. Do you need to see detailed pictures?

[kitaprak]

Look at the pictures, are you interested?

Thanks for sharing the pictures, would you be willing to share the source files?

I don't have the source file.
This is the physical PCB transformer that I disassembled.
Upon closer inspection, one of them has already been damaged,I plan to remake it, but it looks like it's over 20 layers. Do you need to see detailed pictures?

Yes, that would be really nice.

[daisizhou]

Look at the pictures, are you interested?

Thanks for sharing the pictures, would you be willing to share the source files?

I don't have the source file.
This is the physical PCB transformer that I disassembled.
Upon closer inspection, one of them has already been damaged,I plan to remake it, but it looks like it's over 20 layers. Do you need to see detailed pictures?

Yes, that would be really nice.

[mtwieg]

I have good news, there is indeed a standard and cheap process for stacking multiple one or two layer PCBs and creating interconnects between them.

It's called a multilayer PCB.

[Terry Bites]

PCB "through pins"? Veropins etc.
I used them in the dark days of DIY dual layer pcbs. A bit of tinned copper wire works a treat if your a skinflint.
https://www.mouser.in/new/mill-max/mill-max-press-fit-pcb-pins/

Castellated edges can be used to quickly solder up a stack of pcbs.
Use a cheap pcb fab to make you a multilayer pcb. It'll be cheaper than a DIY version.
A stack will be a moisture magnet unless you glue/ seal the layers together.