( How-To ) Ultra Low-Profile PCB Stacking

Question

Recently I found myself needing to stack two small circuit boards on top of each other for a modulation project. The problem is that the areas I want to connect together on the two boards have no components or traces on them, and traditional pin-style stack ups (even machine headers) leave an unwanted gap between boards.

How can I stack the boards flush with on another and have a minimal gap between them?

I have seen This Question which shows an approach to stack boards permanently flush together, but I need a solution that is removable.

No pads or solder mask either? Do you want it removeable? What is the wavelength? — Tony Stewart EE75, Jul 02 '19 at 16:51
@sunny No, nothing but flat PCB space (minus the connector of course). — Hackstaar, Jul 02 '19 at 20:53
WHat about the other questions.? You need to design both mechanical and electrical interface for stickness without damage to contacts. Didn't U answer your own question? — Tony Stewart EE75, Jul 02 '19 at 21:33
@sunny Yes I was trying to share my discovery with the community. I also found that Escutcheon pins are a great replacement for pin headers if you don't want any protrusions. — Hackstaar, Jul 02 '19 at 22:01
So is this microwave? or did you consider press fit flush Swiss pin sockets used in "some" IC sockets. WOW they are gold plated Roofing nails — Tony Stewart EE75, Jul 02 '19 at 22:12
@sunny No, both boards feature only passives and operate at (relatively) low frequency. — Hackstaar, Jul 02 '19 at 22:15
I believe castellated pads solved this problem long time ago — Maple, Dec 02 '19 at 10:55

Hackstaar · Accepted Answer · 2019-07-02T22:11:50.420

What you need is a new Sycamore contact. They allow you to plug boards together with minimal spacing in between. This is especially useful when making add-ons for a basic board which can be replaced and upgraded.

I would advise you to put a via through the edge of the contact pads (if possible) to prevent the connector ripping off the board in high-stress applications. You will be surprised how long they last!

There are several variations for different pin sizes and top/bottom entry:

Here is a video: Sycamore Contact

This will require compatible male pins on your second board. For my application, female pin headers with long male legs will work, but there may come a time when you wish to attach boards without any noticeable protrusions on either board. SMD male pins that I have found so far are not adequate because they leave a gap between boards. Feel free to comment useful part #s below.

Edit: I found that Escutcheon pins are a great alternative to pin headers for a protrusion-free connection to the Sycamore contact:

The pins are gold-plated for a longer contact life. Add a thin strip of spongy adhesive between the boards and you're good to go!

This reads a lot like an advertisement for this product. Are you affiliated with the company? — asdfex, Dec 02 '19 at 09:09
@ asdfex No, I have no affiliation, but I have used their sycamore contacts before and had a great experience. — Hackstaar, Dec 02 '19 at 15:41

( How-To ) Ultra Low-Profile PCB Stacking

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