Electrolytic Capacitor Mounting

[Clbraddock]

This is just something I've wondered for awhile and been unable to ever find an answer googling.

It seems that radial electrolytic capacitors are often mounted a little bit above the board/pcb supported by their leads and sometimes some glue. Why are they mounted this way instead of flush with the bottom of the capacitor touching the pcb. I believe the glue is to prevent mechanical/vibration damage, but why have the leads sticking out to raise the caps higher? I assume there is a reason, but I haven't been able to figure it out.

 

[My3gger]

Easier to get them out when wrong value or expensive lytic is all we have at the moment? Cap vents are at the top, i don't think having them away from the pcb will change anything if magic smoke with insides are released during failure It happens.

 

[ccaudle]

Why are they mounted this way instead of flush with the bottom of the capacitor touching the pcb

PCBs sometimes get washed after reflow to remove flux residue, if the caps are flush with the PCB it can trap the wash fluid underneath. Being lifted just a little make sure all the fluid will drip or be blown out.

 

[JohnRoberts]

I am not aware of any stipulation regarding height above the PCB surface for through hole electrolytic caps. SMD electrolytic caps sit flush to the PCB.

JR

 

[My3gger]

PCBs sometimes get washed after reflow to remove flux residue, if the caps are flush with the PCB it can trap the wash fluid underneath. Being lifted just a little make sure all the fluid will drip or be blown out.

He probably meant distance of several cm as was seen on several pictures of GSSL circulating around. One of those was mine, i did it only to try it out with too high capacitance values.

 

[Tubetec]

Ive seen it happen a few times where electrolytics mounted close to the board and stuck down with glue eventually end up with dry joints . Its wasnt too much current caused it , my guess is temp difference ,expansion and contraction of the internal components of the capacitor caused it .
Allowing a small gap and then using silicone to help support the component means things have room to move when they heat up ,so it wont put strain on the lead outs .
The really strong contact adhesive used in some Japanese boards to secure down the caps doesnt allow any movement and they were the board I typically found this failure mode on .

 

[CJ]

Components move all over the place during wave soldering. Every time the tank gets cleaned out, there was like a Mouser BOM worth of parts at the bottom of the tank. Maybe those lyrics were bouncing around.