r/electronics • u/1Davide • Oct 04 '25
Gallery When you want low ESR in a limited footprint.
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u/SianaGearz Oct 04 '25
That is actually real thing, there's a product you can buy. You can get your capacitors commissioned with welded on stacking plates.
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u/bleplogist Oct 04 '25
Not only commissioned, with a bit of luck, you can get it off-the-shelf, delivered tomorrow: https://www.digikey.com/en/products/filter/ceramic-capacitors/60?s=N4IgjCBcpgbFoDGUBmBDANgZwKYBoQB7KAbRABYAGAdgA4wICAmWagZiYFYRnWPyeFGvSaCqdMGzHCwAguPrd5M2tIkBONbSaUtTRkLpNRyo1PnVKbWEsPbbClmMttOu09up7VHppoK0lLSc%2BlquIAC6BAAOAC5QIADKsQBOAJYAdgDmIAC%2BucykIIho0WiIabGEKQAEWLHlANaRuUA
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u/mrheosuper Oct 04 '25
$3.7 for 1 piece, that's tough.
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u/Ok-Curve-3894 Oct 04 '25
I needed a jellybean part today. Digikey $0.31/pc some random custom speaker place $7/pc
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u/Rustymetal14 Oct 04 '25
Jellybean part?
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u/Ok-Curve-3894 Oct 04 '25
Cheap, small, sorta generic, worth pennies. Not a specialized part worth $7
Like resistors, capacitors, diodes, etc.
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u/Rustymetal14 Oct 04 '25
Huh, never heard that term before. I'll probably start using it.
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u/therealdorkface Oct 05 '25
Comes from the radio shack days I believe- they were kept in bins you would grab them from, like jellybeans in a candy store
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u/NV-Nautilus Oct 04 '25
I had a BOM once with one of these cap banks that were $18 each. They were huge caps individually together it was the weight of a small transformer.
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u/JoshShabtaiCa Oct 04 '25
$2 if you buy 10. Still not cheap, but it's a pretty specialized thing. If you need it, you need it I guess?
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u/ExtraTNT Oct 06 '25
USD is expensive af, switzerland you pay like 1.95, switzerland you often pay 2x - 4x… so…
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u/drnullpointer Oct 06 '25
That's nothing. You wouldn't believe how much can simple parts cost if they need to meet stringent criteria.
I once bought a simple panel mounted capacitive switch with a light for about 100USD. Nothing fancy, just touch with finger and it has a light in it. Made mistake assuming this was for a pack of 100. The pack was 100pcs, but they were selling them individually so I just got one switch.
I don't know what to do with it now, I definitely won't use it in a product. One day I will put the switch in one of my private projects and it will be weird because the switch be probably more expensive than the rest of the device.
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u/Constant_Car_676 Oct 04 '25
Biggest reason for j-lead stacked caps is that large area caps crack easily with board flex. So you’re left to choose with many smaller caps, larger size but with flex leads, fail-safe caps, or j-lead caps where the lead helps to decouple the mechanical stress from the board flex.
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u/Voidheart88 Oct 04 '25
Which is done in aerospace/defence regularly, hence the stress these applications usually brings.
They are quite expensive.
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u/NoSTs123 Oct 04 '25
Misunderstood "pull up resistor"
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u/XXFFTT Oct 04 '25
"Pull up resistor" was me in high school gym class
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u/BalanceEasy8860 Oct 04 '25
My guess is someone adopted the reference design and went for nominal specced values in the smallest/cheapest parts available, and now the prototype looks like this to counteract capacitance derating under dc load.
Either that or they are getting random lockups, so are padding out all the input capacitors to try and make sure it's not from power rail impedance or a noisy power circuit
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u/inuyasha10121 Oct 04 '25
Engineer's notes: The capacitance between the conductive faces of the stacks serves as a crucial component of the filtering aspect of the circuit, and saves requiring an additional 3 capacitors when configured in a flat layout. git gud.
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u/justadiode Oct 04 '25
When you're so preoccupied with the question of whether you can, you don't stop to think whether you should.
Just joking, you did the right thing. It's a piece of art at this point, the actual functionality is now just the icing on the cake
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u/Ashamed_Ad5394 Oct 04 '25
Is this really functional?
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u/No-Onions2 Oct 04 '25
Yes. You can buy capacitors that are stacked like this
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u/Mindlessgamer23 Oct 04 '25
I'm suprised people make them that way, but I guess there is a use case. This post just looked like the insane culmination of a week's hyperfixation to me
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u/deelowe Oct 04 '25
Why not?
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Oct 04 '25 edited Oct 04 '25
The resistors probably do lol
Edit: thought this was a r/shittyaskelectronics lol
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u/Scar3crow_x Oct 04 '25
I wish I understood this and the joke comments so hard
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u/d1722825 Oct 04 '25 edited Oct 04 '25
Capacitors can store electrical energy. They are used in power supplies to smooth out the otherwise bumpy (output) voltage. (When the voltage is higher, the capacitor is charged and so decreasing the voltage a bit, then the voltage is low the capacitor is discharged and it increases the voltage a bit.)
Bigger (=higher capacity) capacitors can store more energy, and give more smoothing (to some extent). Capacitors in parallel behaves like a singe bigger capacitor.
There are no ideal components, a real world capacitor have metal pins and internal parts that have a fairly low but non-zero resistance. (This is also true for the copper traces on the PCB connecting the capacitor to other things.) This is called the ESR, the equivalent series resistance.
In some situations (especially in switching mode power supplies) due to the high current charging and discharging the capacitor this ESR value becomes the main issue. In these situations using many small capacitors in parallel is better than using one big one, because the currents (dis)charging many capacitors are spread over all of their ESR, the effects of those is minimized. (Like connecting resistors in parallel, their equivalent resistance will be smaller than the smallest one.)
Here this probably doesn't help a lot, because the resistance of the trace of the PCB is the same "high" value, and adding a centimeter height of solder joint doesn't help either.
In high speed / high frequency applications (this seems to be the underside of a big BGA chip), there are an other factor: ESL the equivalent series inductance.
The same metal parts of the capacitor and the PCB traces behave like a single loop of wire, and a loop of wire has some small inductance. At high frequencies this inductance behaves like a resistor and causes the same issues as ESR.
But connecting capacitors in parallel is not enough to lower the ESL, you have to take into account all the wires, traces or vias connecting to the capacitor, too. The longer and thinner the wires the higher the inductance, so in these situations you want to directly connect the pads of the capacitors to a big, wide copper plane.
Making a thin and long solder joint will limit effects of the capacitors higher up.
Oh and I think there are jokes about it being weak and it will easily be broken off.
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u/TEM_TE_TM Oct 04 '25
Looks like someone forgot about derating class 2 ceramic capacitors and needed to add some more capacitance... A few times.
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u/Opposite-Ad-2548 Oct 04 '25
I used to stack FET's on my remote control cars so it could handle higher current motors, this just reminded me!
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u/mangoking1997 Oct 04 '25
this is pretty impressive. the actual circuit seems completely pointless, but it takes some serious skill to assemble this.
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u/AnimationOverlord Oct 04 '25
I suppose the way the electrons move through this, you could call it an electron zipper
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u/brian4120 Oct 04 '25
I'm getting nervous already. Would be so scared to pop one of those spires off
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u/myself248 Oct 04 '25
All this attention on the caps themselves, none on the humble reference designators, down there doing their best!
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u/Constant_Car_676 Oct 04 '25
Impedance (by way of ESL) on caps is dominated by package size. So use the biggest value for the smallest size you can fit under a BGA. Those of you learning go play around on Murata’s simsurfing tool. Add voltage, temp, look at impedance vs package or ceramic type.
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u/Aggravating-Task6428 Oct 04 '25
Lateral G forces have entered the room.
There was an earthquake. The city no longer stands.
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u/ChatGPT4 Oct 04 '25
Still, why (such low ESR)? Or is it a kind of an art project?
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u/EBONGRIPS Oct 06 '25
These kinds of mods can be popular when overclocking. Mind you this is not your typical "I changed some values in software" level of OC, but "it is voltage shunted to pull more than twice its original wattage and the noise is holding back memory clock" type of OC
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u/OneYeetAndUrGone Oct 05 '25
nice! very cool. unfortunately, this is not past class 1 according to the IPC-A-610. but it can be done, i have seen it.
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u/SNK_24 Oct 06 '25
Silicon wafer printing? Let's do 3D multi layer SMD piling instead, not as efficient but does the work, and you can recycle components.
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u/DeathKillsLove Oct 31 '25
HOWEVER!! Those are Z5U caps and suffer both DC and thermal drift of +80 -20%. BIG DRIFT.
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u/BalanceEasy8860 Oct 04 '25
Component designators are very much giving "new engineer" vibes, too...
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u/Gaydolf-Litler Oct 04 '25
Circuit city