Here’s a clever hack. Simple, elegant, and eminently cost-effective: using an SMD capacitor to hold your flash media in place!
This is a hack that can pretty much be summed up with just the image at the top of the page — a carefully placed SMD capacitor soldered to a routed tab makes for an extremely cost effective locking mechanism for the nearby SD card slot. There’s just enough flexibility to easily move the capacitor when its time to insert or eject your media.
It’s worth noting that the capacitor in this example doesn’t even appear to be electrically connected to anything. But there’s also no reason you couldn’t position one of the capacitors in your existing bill of materials (BOM). This form of mechanical support will be much cheaper than special purpose clips or mounts. Not a big deal for low-volume projects, but if you’re going high-volume this is definitely something to keep in mind.
If you’re just getting started with SMD capacitors then one of the first things to learn is how to solder them. Also, if you’re hoping to salvage them then try to look for newer equipment which is more likely to have SMD components than through-hole. If you’re planning to use your capacitors for… “capacitance” (how quaint), you can start by learning the basics. And if you want to know everything you can learn about the history of capacitors, too.
Thanks to [JohnU] for writing in to let us know about this one. Have your own natty hacks? Let us know on the tipsline!
FR4 isn’t made for flexing up, it breaks very rapidly. Unless this card is only changed sporadically, this isn’t a good idea overall.
No problem at all flexing FR4 a small amount as long as you get the geometry right.
I do not recommend using an electrically connected capacitor for this.
Ceramic is brittle. It breaks easily. A cracked capacitor can turn into a short circuit.
Neat hack, but don’t actually use the capacitor in the circuit. It will cause you nothing but grief.
If designed right, the cap can be placed on a part of the PCB that doesn’t bend – you control the PCB width to place the bend in a specific place, away from the cap
But isn’t the whole point here that it’s on a PCB part which must bend to insert the SD card?
I like the hack, cheap cost, and better than most solutions I’ve seen.
Mike is trying to say that under the capacitor itself doesn’t need to be very flexible, its the long arm between it and the rest of the PCB that must be – so you can selectively thin the PCB, make that lever really really long, add an extra lamination under the latch capacitor etc to really bias that bend where you want it to be so the whole assembly won’t bend where you don’t.
That said it seems like a stupid thing to put into the circuit intentionally, a component that by its nature must undergo mechanical stresses and is on a small spit of PCB — so what on earth could you be doing on that little strip electrically that actually makes placing a cap their at all logical.
Well yeah, I can see a thinner bit of material and the cap mounted on a wider bit but I’d definitely not want it as part of the circuit function, more because it’s likely to get broken off by a user forgetting or just being clumsy when they’re manipulating the SD card.
Even if it was my design and the user was me 😁
It isn’t part of the circuit. The idea is to use a cheap SMT component as a passive mechanical part
Agreed. And most caps on a modern circuit are decoupling caps. So putting it away from where it is needed is not a good idea.
A resistor would be even cheaper, but you need the height. A capacitor costs only about $0.01 when you buy large enough quantities.
This cap that everyone is worried about? It’s not electrically connected, it could be a ferrite or chunk of tin plated steel. I think this is brilliant and likely to really help reliability in case of shock or vibe and a fine choice if a locking slot isn’t an option.
You could probably also cut and glue something from a food/drink container for this as well, although I’d have to think what.
I usually just 3D print a little widget to do it and superglue it.
Don’t do that. You already have a perfectly serviceable part (the capacitor) on hand, so use that.
Great for planned obsolescence, maybe route main power though a trace on this tab. /s
Nice hack for retaining sd card. the tab reminds me of volume know repair I watched where the pot was supported by routed frp and guaranteed to break the traces if pushed too hard.
Definitely add an extra smd for this purpose – cheapest on the bom you can find.
MLCCs are susceptible to vibrations and mechanical stress. Especially the kind of stress FR4 bending results in.
What’s worse is the failure mode is a dead short (or high leakage)
It looks like the cap in the picture is purely there for mechanical support (and not connected electrically), in which case its a valid approach. Its okay
Yeah, definitely don’t do this with a capacitor that’s actually part of the circuit.
I never had the problem that a (micro) SD card worked itself out of its slot. It looks to me like a solution to a non-existing problem which itself might cause trouble (see above comments).
TBF I have personally experienced MicroSD cards vibrating loose.
We explored soldering the cards down permanently but ended up keeping the socket and putting a dab of RTV on top.
A “nifty hack” when we do it, but I’d bet if we found this on a commercial product we’d decry it as cost-cutting and planned obsolescence…
Still, cool for something embedded where the card won’t get changed much.
Because we saved money instead of using a latching card holder…
How about a bump of solder? Can easily be about the size of a SMD cap.
or a piece of through hole wire soldered.
Or just a snipped of solid copper wired – soldered through hole or smd style.
I do not understand this. It’s probably (at least) the second iteration of this PCB. If I noticed I had a crappy SD card holder that can’t hold an SD card by itself, then my second iteration would be another higher quality SD card holder for the second generation PCB.
A similar hack I do like is to use DO-214 (SMA, SMB or SMC) sized diodes used as “feet” on the underside of the PCB. These are likely the highest SMT parts used on the PCB, so nothing else will touch the table.
But I would not use these diodes as active parts of the circuits. I don’t like mechanical stress on parts of the circuit (Especially with the brittle SMT capacitor that this hack is about). And when they are just mechanical, it’s much easier to place them in a mechanically convenient location. Besides, the cost of such parts is so extremely low that it’s really not worth bothering about.
+1
Vibration has a tendency to work cards loose. Probably some holders will work better, but this seems like an easy to implement solution and requires positive action for removal.
Almost all SD card holders with latching mechanism are of the “push to eject” type, and it’s easy to accidentally push on the card when e.g. connecting cables.
this sounds like a “as seen on tv” problem, realistically how many times have you been bumbling around with a cable so bad the god dammed SD card pops out
One of the bigger problems here is the decision of many of the SBC vendors to place the uSD card in a place that it can be easily removed, even when the thing is in an enclosure. I.e. the edge of the card sticks out of the side of the PCB. And that while the uSD card usually holds the whole OS, and thus should very rarely be ejected. I very much like the eMMC modules on a connector in the way Hardkernel/Odroid uses them. Faster and more reliable then uSD cards, and still removable. But if uSD is used, putting the edge flush with the side of the PCB, or even a few mm inwards would remove all worries about unintentional ejection of the uSD card. Unfortunately “convenience” seems to be a bigger driving force then “quality”.
You are correct hanging the card out so its really easy to access isn’t ideal for everyone, but that doesn’t impact the quality of the design – it just makes it massively inconvenient or convenient whichever one you have depending on your use case.
Really going to depend on the design and usecase isn’t it – some of those push latches don’t take much travel to trigger the release so if the device its in doesn’t hide it really deep to mean you need a tool/fingernail to get close to touching it…
Also if the latch is really low force the SD card’s intertia might be enough to trip it in some situations, and that is assuming there is an retention mechanism at all – so many SD card mounts rely entirely on the friction/gravity or lack of disturbance to keep them in place.
So if I was designing for an amateur rocket camera system or something similarly likely to meet wild forces I’d probably go with a system like this – if the rocket survives its reusable at least a few times before the cap lever fatigues, and probably much lighter than the glueing it down option while providing good retention no matter which way the jerk is applied. But for a dev board that will never leave my desk there would be no point beyond verifying the design.
I recall a lot of failure/corruption in storage of sd being from cases with contact. Foams rubber plastic etc and static charges. While I doubt it would contact the cards contacts on insert removal.. it immediately brought it to mind given a capacitor was the choice here as probably not a great pick.
Dunno, 2cent point.
solving a non-problem. non-locking sd card holders use friction instead. if you have a high-vibration environment and can’t accept the risk of it eventually loosening up, tape and glue are right there for you.
Or even a soldered chip, ISTR some printer manufacturers (Lexmark?) had a TSSOP memory chip that was actually the guts of a 1GB MMC/SD card, kinda wondering if there’s a newer, high capacity version out there for purchase
Yeah, they’re available from JLCPCB. Pretty much not anywhere else, though, I think? Kinda weird but they work.
Interesting, got a stock code or part number to save me the search?
Rube Goldberg nitwits.
Geez ! use a piece of anti-static foam in place of the smd part and super glue it to the pcb.
Problem solved (or rather band-aid’ed).
You’re welcome.
Q’aPla !
Cool, but I would use a little test point hook or something else metal with a wide base. SMD passives snap off like no other…
Might be more useful if it doubled as chassis intrusion or something non important
Or… maybe they should invent a SD carder reader with a latch built-in, imagine if they did? LoL
The latching type can eject from vibration or impact at the right angle, so that doesn’t solve the problem.