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I’m designing a pcb, which is going to be installed inside a metal chassis. To minimize space I will make it a two sided pcb. (See pictures)

Because there will be parts mounted on the top face of the chassis itself, smaller components like resistors will go on top of the pcb and pretty much everything else will go below hanging from it, including electrolytic capacitors. My capacitors are radial but because the chassis is not very tall, I thought the best way to fit them would be to just bend the leads 90° and mount them sideways like axial capacitors and that way everything fits nicely.

My concern is that probably there will be points of solder from the resistors on top that will end up very close to the body of the capacitors below, probably in direct contact. Could this be a problem in terms of some high voltage difference between the solder point and the inside of the capacitors that could break the outer layer of the capacitors? The circuit will be working with voltages in the 200-350 range.

My thinking process is that if the caps are designed to withstand high voltages inside, there shouldn’t be a problem with some high voltage touching the outer layer of insulation, right?

Top of pcb enter image description here

Bottom of pcb enter image description here

pcb inside of chassis enter image description here

probable points of solder (grey dots) close to body of capacitor enter image description here

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  • \$\begingroup\$ There may be more DFM issues than this and design issues such as heat dissipation from R to C. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 27 '18 at 0:06
  • \$\begingroup\$ Most resistors (in this circuit) will not dissipate anything more than 100mW, they are 1w due to working voltage rating and just overall robust design, in any case all resistors are on the top side close to a metal chassis which will more or less work as a heatsink and could have vents anyway, that's not my problem. I'm will be making these pcbs myself in VERY small batches so DFM is not my problem here either. \$\endgroup\$ – Raz Jul 27 '18 at 0:11
  • \$\begingroup\$ That’s cool. Just Dab on PU like ATX PSU’s. Home Depot or better. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 27 '18 at 0:14
  • \$\begingroup\$ The electrolytic caps should not be bent over into pokey things such as through hole lead solder tails. You should move the pokey things slightly so they don't hit the caps, or work out a reliable way to stand the caps up off of the board. Incidentally, the caps require physical support. You can't just let the leads support them. If you do, the leads may break even just from normal shipping vibration. I also recommend you get assembly quotes now to make sure there are no major issues in terms of assembly process flow. \$\endgroup\$ – mkeith Jul 27 '18 at 1:11
  • \$\begingroup\$ Just to be clear, it is fine to bend over the caps. But you need to keep them off of the pokey things, and physically supoort them with plastic brackets, or with a small amount of PCB grade silicon or polyurethane or something. \$\endgroup\$ – mkeith Jul 27 '18 at 1:12
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There may be more DFM issues than this and design issues such as heat dissipation from R to C.

Use polyurethane bond all Cap to board AND insulate high voltage.

I recall 2.5mm air slot for 2kV transients creepage but here you use >1mm of polyurethane over solder joints and extra for bonding caps after initial tests.

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This is not an answer, just a comment on the layout (I am assuming that is an actual representation, not some abstract PCB picture).

There are four electrolytes on top with something that looks like four fuses on the other side of the board. If you swap them around you will have much smaller overall height of the top without increasing the height of the bottom, which will give you more space in the chassis.

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    \$\begingroup\$ Yes, that is true, however the fuses must go on the bottom side because the chassis lid will be at the bottom, thus making the fuses easier to access, otherwise the pcb would need to be completely uninstalled along with all the wiring just to change a fuse :) \$\endgroup\$ – Raz Jul 27 '18 at 2:31
  • \$\begingroup\$ @Rez yes that may be practical but you are totally nullifying the benefit of putting big components on one side with this design. \$\endgroup\$ – joojaa Jul 27 '18 at 6:06
  • \$\begingroup\$ Then just swap your the definitions of "top" and "bottom". \$\endgroup\$ – Maple Jul 27 '18 at 7:11

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