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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).

Connection diagram

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.

Hirose BM28 Series

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?

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  • \$\begingroup\$ Please edit the question to be more suitable - you really don't want people answering Yes/No to your question if we have seen such connectors. Also, asking for suggestions what to buy and from where are also off-topic. \$\endgroup\$
    – Justme
    Jul 4, 2023 at 11:03
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    \$\begingroup\$ @Velvel: OP is considering a flex PCB. How else do you expect OP to solder that connector to the flex? \$\endgroup\$ Jul 4, 2023 at 15:40
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    \$\begingroup\$ @DavideAndrea Thanks for clarification. But it looks like OP has 2 regular PCBs connected via 1 flex print. What they're trying to do seems like it should be doable with a single flex PCB. \$\endgroup\$
    – Velvet
    Jul 4, 2023 at 16:10

1 Answer 1

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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

{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.

With one vertical FFC socket

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.

Top board upside-down

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

Top FPC

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.

ACF bonding

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    \$\begingroup\$ Davide thak you very much for your help. The side you shared was very helpful. I think I will look into the Molex connector \$\endgroup\$
    – urbu
    Jul 5, 2023 at 12:08

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