electrolytic-capacitorsurface-mount
I’m working on a computer monitor’s power board (to replace a capacitor or two, which I assume is the problem), and found these:
Replacements are easy to find, so no issues there, but I’m curious why the SMD aluminum electrolytic capacitors are on little platforms (or spacers). To buffer swelling maybe?
One pretty simple reason is that the tolerance on Y5V tends to be much flakier numerically than X5R or X7R. Typically -20% + 80%
A less obvious and possibly more profound reason is that the change in capacitance versus temperature is very poor on Y5V. Typically at low temperatures and high temperatures the capacitance might halve in value.
DC voltage can change the capacitance of most capacitors a bit but Y5V are really prone to it. Typically at full rated voltage the capacitance might be a fraction of what it is when low voltages are present.
Just open this data sheet and look at the first few graphs. See also this: -
The picture on page 12 of the Johanson datasheet shows the difference between it and a normal multilayer ceramic capacitor (MLCC):
The part on the left is a normal MLCC. The part on the right is the Johanson part.
The Johanson part is a 4-terminal part, actually a capacitor network with two separate capacitors with one shared terminal. By connecting the "A" and "B" terminals together, you obtain twice the specified capacitance. Because of the feedthrough shape of the ground terminal you also probably achieve lower equivalent inductance and a higher self-resonant frequency.
That said, 90% of designs can be done using normal MLCCs for decoupling. If you need higher self-resonant frequency, I'd recommend to first try using a smaller package than 0805, and only if that isn't adequate, consider using one of these specialized high-cost parts.
Best Answer
Those capacitors are really made similarly to the cylindrical radial lead through-hole capacitors. Two connections come out through a rubber bung (in an aluminum case that is crimped at the bottom to form a seal) and those leads are bend to form SMT leads.
From this Nichicon website (a conductive polymer type is shown, and conventional electrolytics are similar):
The plastic base is just there to provide physical support for the capacitor can so it doesn't flop around too much on the leads.