How can I connect two parallel boards with an FPC, both boards with components only on the top side?

Question

I need to connect two PCBs together that have components only on the top side. I hoped to connect them with a flex cable mated on the top side of the PCB, like the image below (green are the PCBs, black are the connectors, and brown is a flex board between the PCBs).

I have been looking at this connectors They are nice and small. With a 0.35 mm pitch the 60 pin connector is only 12.5 mm long.

The problem is that I don't have the space for the cable bend radius to be able to use this kind of connectors. So I would like something similar but in a right angle version to connect the PCBs like this. All the right angle connectors I found are quite a bit bigger and I am really tight on space. Plus It also needs to be high speed I need to get PCIe gen 2 over the connector. I have been looking for right angle connector but the smallest I can find are 0.5 mm pitch and that makes them to big.

As that solution won't work, can somebody recommend a different solution, one that will let me connect these two board together, with components only on the top side?

Answer 1

Your approach would need an SMD board-to-board connector family that has a right-angle member, such as:

• C-T board-to-board, Molex Slimstack: 0.4 mm pitch, up to 40 circuits
• C-E board-to-board, Hirose FX20: 0.5 mm pitch, up to 140 circuits

{Molex SlimStack 54552, 503376, source: Digikey}

For the bottom connector use either the same one, or consider a vertical FFC socket. There seems to be enough space between the boards for a slight shift in the flex PCB to let you do that.

Of course, the obvious solution is to flip the top board upside-down or, at least, place the flex connector on the bottom side. Then you can use two vertical FFC sockets.

Or, you could make the top board out of the same FPC as the tail going to the bottom board.

Consider ACF bonding: The top PCB has just pads on the bottom side. The FPC is heat-staked to the bottom of the top PCB with ACF tape.