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Best way to design a stacked PCBs circuits [message #169766] Mon, 27 February 2017 13:42 Go to next message
Marco Trapanese
Messages: 291
Registered: May 2007
Senior Member
Hello,
I'm going to develop a circuit that will be composed of two stacked PCB.
Several connectors will provide connections between the two layers.

I wonder which is the best approach in EAGLE to do this.
The simplest way is of course to make different projects, one for each PCB.

The mains drawbacks are:

* lot of signals are the same (those that go with the connectors) so any
changes to their names or net classes must be repeated in the second
project as well

* the same applies for the layout: the positions of mounting holes or
any milling layer must be kept in sync with the PCBs

* last but not least, in the lower PCB I have several tall components.
In the higher PCB I need to provide slots for them. Doing that in
different project is a pain because I need to write down the position of
each one and move the related slots every time I change their placement

I hope there is a better way to design stacked PCB circuits!
Thanks
Marco
Re: Best way to design a stacked PCBs circuits [message #169767 is a reply to message #169766] Mon, 27 February 2017 13:59 Go to previous messageGo to next message
Marco Trapanese
Messages: 291
Registered: May 2007
Senior Member
Il 27/02/2017 14:42, Marco Trapanese ha scritto:

> The mains drawbacks are:
>
> * lot of signals are the same (those that go with the connectors) so any
> changes to their names or net classes must be repeated in the second
> project as well
>
> * the same applies for the layout: the positions of mounting holes or
> any milling layer must be kept in sync with the PCBs
>
> * last but not least, in the lower PCB I have several tall components.
> In the higher PCB I need to provide slots for them. Doing that in
> different project is a pain because I need to write down the position of
> each one and move the related slots every time I change their placement


I add that having a single schematic is better because from a functional
point of view no matter where a component is placed.

I'm going to try to add a couple of routing layers to "simulate" the
other PCB, then I will play with the CAM processor to make the two
different set of gerber files.

What do you think about this solution?
Re: Best way to design a stacked PCBs circuits [message #169802 is a reply to message #169766] Tue, 28 February 2017 15:07 Go to previous messageGo to next message
reece
Messages: 69
Registered: March 2009
Member
On 02/27/17 08:42, Marco Trapanese wrote:
> Hello,
> I'm going to develop a circuit that will be composed of two stacked PCB.
> Several connectors will provide connections between the two layers.
>
> I wonder which is the best approach in EAGLE to do this.
> The simplest way is of course to make different projects, one for each PCB.

I've done this twice. Note that I'm a hobbyist and there may be better
ways to do this.

The first time I had one board hosting a microprocessor and a much
smaller one hosting the front-panel switches. The board with the
switches mounted above the uP board using standoffs and a pin header and
socket. I ended up creating one project and milled break-off tabs
between the two boards. Aligning the pins in one of the two dimensions
was easier because the two boards shared a common edge.

The second time I made a set of 5 boards that mount in a stack using
PC/104 style connectors. These were too large and too complicated to
implement in one project.

What I did was to create a separate sheet in the schematic for the
common connector interface. It was fairly easy to copy everything on
that sheet in the first schematic and paste it into the others. It would
be nice if Eagle allowed you to include a partial schematic into
multiple projects, but that wasn't possible when I started the project.
It may be now; I don't know.

To make sure the connectors all aligned properly I created a library
part that defined the basic board outline including the positioning of
the connectors and the mounting holes. Each project then pulls in the
basic board device on the common connector interface schematic sheet. In
the layout, the lower left corner of this device is placed at the lower
left corner of the board dimensions. I suspect you could use one of the
documentation layers of the device to define the location of your tall
components.

This approach developed over time, so there may be ways to optimize
this. For example, I didn't define any of the connector pins in the
device as having particular nets or functions; I did this in the common
schematic sheet. In retrospect it seems defining them in the device may
have been better.

-Reece
Re: Best way to design a stacked PCBs circuits [message #169890 is a reply to message #169802] Fri, 03 March 2017 09:11 Go to previous message
Marco Trapanese
Messages: 291
Registered: May 2007
Senior Member
Il 28/02/2017 16:07, Reece R. Pollack ha scritto:

> The first time I had one board hosting a microprocessor and a much
> smaller one hosting the front-panel switches. The board with the
> switches mounted above the uP board using standoffs and a pin header and
> socket. I ended up creating one project and milled break-off tabs
> between the two boards. Aligning the pins in one of the two dimensions
> was easier because the two boards shared a common edge.


Right now I've used this approach, even if my case was more similar to
your second example.


> The second time I made a set of 5 boards that mount in a stack using
> PC/104 style connectors. These were too large and too complicated to
> implement in one project.
>
> What I did was to create a separate sheet in the schematic for the
> common connector interface. It was fairly easy to copy everything on
> that sheet in the first schematic and paste it into the others. It would
> be nice if Eagle allowed you to include a partial schematic into
> multiple projects, but that wasn't possible when I started the project.
> It may be now; I don't know.

[...]

Interesting, but it could work if each layer is independent - sharing
only the PCB edges and board-to-board connectors.

My current project is composed of only two stacked PCB but I need to
provide holes in the top one to grant access to the lower PCB (i.e. to
reach a trimmer or a screw).

I need to inspect the coordinates (and the sizes that are not so easy to
measure in EAGLE) of the desired components to place slots and the other
components on the second PCB.

I know it is a different working approach but I'm wondering if any of
the other suite for electronic designs out there provide tool for
stacked PCBs.

Freely speaking: of course a complete support requires a lot of work,
but it could be simple enough to allow the background of an EAGLE Layout
window to be transparent and keep synced position and zoom of another
instance.

In this way it would be easier to design with the other(s) PCB in the
view (with of course a different value of transparency, to avoid to be
confused!)
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