I've noticed that on older boards some of the electrolytic capacitors don't sit up straight, they're not totally vertical. I wonder why this happens, is it because they were soldered by hand and the person doing it placed them that way? Were they placed vertically and bent over time? Is it bad to the circuit in any way?
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17\$\begingroup\$ Statistics. There are many ways to be bent, but only one way to be straight. \$\endgroup\$– DKNguyenFeb 15, 2021 at 2:23
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1\$\begingroup\$ @DKNguyen: The two caps in the lower left corner of the photo don’t look like coincidence. \$\endgroup\$– MichaelFeb 15, 2021 at 14:32
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5\$\begingroup\$ Sometimes it's deliberate, to reduce PCB height. \$\endgroup\$– user16324Feb 15, 2021 at 16:18
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2\$\begingroup\$ @Michael No, they just wanted to see what is under the circuit board. \$\endgroup\$– KazFeb 15, 2021 at 16:24
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1\$\begingroup\$ Welcome to EE SE goncalogarcia99! I love your question because I've always wondered about this, but I've never had a chance to ask anyone who might know the answer. \$\endgroup\$– End Anti-Semitic HateFeb 16, 2021 at 4:26
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3 Answers
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More stress is placed on the leads if there is no space between the part and the PCB. Electrolytics are more fragile than some parts because of the semi-liquid electrolyte, which can leak if there is tension on the lead, such as that caused by thermal cycling.
On some equipment, soft standoffs are used to lessen the strain, and prevent vibration. However, some manufacturers just leave a gap between part and PCB. Even if the part were vertical to start, vibration will knock it off axis. Also, as you state, hand assembly leads to random variation.
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2\$\begingroup\$ Ah, so (1) (a) More space mean more leeway to bend, less chance to break, (b) More space means easier to bent, therefore we see more bent caps than non bent one.. (2) I always fit the caps tightly to the PCB surface, so it looks tidy and pretty. Now I know why me technician have not enough engineering curiosity to think deeper to upgrade to engineer. \$\endgroup\$– tlfong01Feb 15, 2021 at 4:59
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1\$\begingroup\$ And then there's handling; could both add strain to caps soldered tight to the board and bend those that are up. Bending can also be a way to get them to stay up during soldering, or access the pads on top of the PCB. \$\endgroup\$ Feb 15, 2021 at 17:20
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In my opinion the reason is quite easy to explain if you consider the manufacturing process.
On such a cheap (yellow coated paper type) PCB the capacitors are mounted by factory workers. These workers need to place the capacitors as quickly as possible at the correct place and observing the polarity. They have no time to bend the capacitor into an upright position. Also: it doesn't matter for the functionality of the electronics.
After mounting usually the soldering is done in a wave soldering machine which could also bend the leads (and the capacitor) in any direction.
answered Feb 15, 2021 at 9:35
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\$\begingroup\$ Can also be a way to get the caps to stay up above the board, where being straight would allow the cap leads to slip down through the PCB holes. \$\endgroup\$ Feb 15, 2021 at 17:21
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1\$\begingroup\$ "They have no time to bend the capacitor into an upright position" very smart answer - obvious and true! \$\endgroup\$– FattieFeb 15, 2021 at 17:27
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The capacitors don't fit the board
In modern PCB design, the dimensions of the capacitor legs are known. The board is designed for that spacing, and production always uses that size of capacitor. With automated assembly, if you really and truly need a different size of capacitor then it's better to redesign the board to fit it. And more often than not, these days they'll be surface-mount anyway.
This was not the case, back in the day. Boards were assembled by hand - and because humans were involved, they could make things fit. There was no urgency to order components with exactly the same leg spacing as the holes in the board, and if it became cheaper to order a different size of component then the company absolutely would.
Then we get to how they were assembled. People used something like this.
You'd clamp the board in the frame and stuff all the components of roughly the same height in. Then you'd pull the padded lid down to hold the components in place as you flipped the board over to solder the underside. You'd repeat this in order of height; typically you'd have one go for all the resistors, diodes and ICs, and then a second round for capacitors and anything else taller. Naturally any component which wasn't firmly in place could fall a bit into the padding, or could get squashed and pushed over by the padding.
All this basically stopped when a production line with wave-soldering machines became the norm for soldering through-hole components. At that point you needed your components mounted reasonably securely, and leaving them waving in the wind wasn't going to work. Reliability studies also found that components tended to fail because of the mechanical stresses between the component legs and body, giving a further reason to mount them more securely.
