Forgive my lack of knowledge and experience here. I am working on a project (for which I am using KiCad to design the boards). My main board cannot have any through hole components on it and For the sake of cost savings I cannot find a SMD version of one of the components. My thought was to just put that one component on it;s own tiny board, and the design allows for that easily.
I was thinking to put three pads on the edge of the small auxiliary board and put a socket on the main board where the auxiliary board can plug into the main board, leaving the main board horizontal and small auxiliary board vertical at 90deg to the main board. I was thinking of something similar to what was on the insertion portion of old school video game cartridges like Nintendo games. And then some form of SMD socket on the main board to accept that. It only needs three connections and to carry 2A of current.
I was thinking this was called a “board edge connector”, but using that search term on vendor websites lead me to believe I was wrong. I know this has to exist. What am I looking for?
There are many makes of board-board connectors. There are several connectors that are able to mate with 1.6mm PCB, requiring no second connector as such. In general, SMD connectors seem to be more expensive than through hole, if only because the sales volume is lower.
There are not many connectors with 3 conductors, plenty with more. Mechanical aspects may also be a consideration.
A picture is worth a thousand words… even a rough sketch may give us a better idea.
Let me see what I can come up with…
TE have a bunch of connectors in the MicroMatch range, they are relatively cheap, with polarity and retention.
Maybe the combination highlighted is suitable?
I was thinking something like this on the main board, so I could ust put copper pads on the auxiliary board and not use two connectors.
I hope that displays what I’m thinking well. Forgive my crude model, I didn’t have much time to throw it together and it’s not scaled very well.
I spent a while looking for a similar solutions, without much success.
I can’t think of any card edge connectors like that which are SMD, only through hole. You could mount the connector on the daughter board, but that restricts you to connecting to the edges of the main board. Card edge connectors are often not cheap, two connectors can work out cheaper than a single edge connector. PCI-E 36 way connectors are cheapish even though they have more conductors than you need (and not SMD).
An additional problem with card edge connectors is that they work loose with any sort of vibration, or shock, so you would need to design some bespoke method of holding the card in place.
The Micro-Match range was the best I found for cheapness, availability, and mechanical robustness. There are quite possibly similar ones from other manufacturers. An alternative might be the common 0.1" connectors, but I haven’t seen any locking connectors for board-board, only for IDC cable headers.
Hmm… maybe the solution isn’t as simple as I had hoped.
The main board cannot have any through hole components or anything that extends past the back side of the board at all.
I may end up stuck with a ribbon cable between them? But that adds even more mechanical design issues…
(I will confess that it’s early in the day and I’m too lazy to do the legwork to investigate possible solutions.)
Is it required for this to be an actual separable connector? Could it be something like a right-angle pin header that solders to both boards during initial assembly, and stays mated for the life of the product? There are SMT versions of pin headers, both pins and sockets, in various pitches.
(For a moment I will lapse into rumor mongering, not based on extensive personal experience or controlled testing: Surface-mount connectors may or may not be more expensive than their through-hole versions. I don’t recall any examples where the SMT version was truly less expensive than the THD version. More significant is the reputation of SMT connectors for decreased ruggedness and lower reliability. The pins that anchor a THD connector to the board seem to significantly increase it’s ability to withstand the forces of mating and unmating the connector pair.)
No. It certainly does not need to be a separate connector or removable.
If it wasn’t for the need to have the bottom of the main board perfectly flat I would just put the through hole micro relay on the same board and be done with it.
The problem lies in the fact that the back of the (main) board will have capacitive touch keys on it and will be mated directly to the enclosure using the recommended double sided adhesive tape.
I wish SMD high current relays weren’t so high in price, but they are.
I certainly don’t blame you for not wanting to get into a bunch of research for someone else’s project, and I do appreciate any and all advice or input. I am just very new at this and keep leading myself down a rabbit hole every time I have a new idea.
I was thinking of something like this (from Samtec, but I’m sure there are others):
The relay mounting board would sit vertically and solder in place. Two rows of contacts increase the mechanical integrity, even though they aren’t needed for electrical connections.
I will look into that.
Now I know what to look for.
I actually just stumbled across a SMD magnetic relay that is only .92 higher in cost than the through hole relay I was thinking of using. That may end up being a better option.
Then again, I can’t find it in stock anywhere…
Sullins has a lot of board-edge connector sockets. For example:
These are in-stock at DigiKey
Keep in mind, that you may need hard gold plating on your board that is plugging into this to allow multiple inserts/removals. Bare copper will corrode and typical gold plating will rub off.
Also, your high-current requirement can be addressed by assigning multiple thinner pins to a single power line. The Sullins connector I linked handles 1A per pin, so I would assign 2-3 for your application.
Here’s a datasheet from Sullens. The website goes down to 5/10 pins, while the data sheet implies that it is available in fewer pins.
That gives me another very viable option to look into
Regarding card edge connectors, take a look at this thread:
There are examples of surface mount parts from 3M (3M SPD08-020-RB-TR) and the Samtec MEC1 series. They are not cheap though. If size is not a constraint the Samtec part might be the mechanically most sturdy one.
Thank you everyone for your help and suggestions. It turns out that the best solution is going to be to just quit trying to be cheap and use the surface mount relay. The price increase is actually less that the cost of connector(s).