Whats the use of open "slot(s)" on a PCB? - Page 1
Forum section: electronics / beginners

author: onesixright
author_rank: Frequent Contributor
timestamp: April 24, 2016, 12:21:46 pm
content: Hiya All,Not sure if its a beginners question, but never the less. It also might already been asked, but i have not a clue how to call "this".So the question is: why is there a "open space" (slot?) in the PCB below the relay (see image) and does this have a name (i'm sure it does)? I have seen it on more PCB's, thought it often has to do with some interference (AC?) ?Maybe someone can explain why and when you need to do this.Thanks!

author: Gyro
author_rank: Super Contributor
timestamp: April 24, 2016, 12:33:25 pm
content: It's a way of increasing 'creepage' distance on the surface of the PCB by adding some clearance (gap) too. The idea is to increase the path length that any current must travel between pads on the PCB. It is sometimes done to reduce leakage current in sensitive circuits and sometimes done to improve the insulation between high voltage and low voltage circuits. In the board you show it is for the second reason.

author: onesixright
author_rank: Frequent Contributor
timestamp: April 24, 2016, 01:26:23 pm
content: Hi Gyro,Awesome thanks for the explanation, now with the correct terms, i was able to find a bit more.Thanks!For others:

author: jitter
author_rank: Frequent Contributor
timestamp: April 24, 2016, 01:28:32 pm
content: There can be another reason.In one of Dave's vids (I believe a Keithley DMM teardown), there was a reference IC that was surrounded by these slots on three sides to prevent mechanical stresses in the pcb reaching and affecting it.Edit: I'm not sure it's this one, but the main board inside this multimeter is riddled with isolation slots, worth to watch:

author: BobsURuncle
author_rank: Regular Contributor
timestamp: April 24, 2016, 04:23:10 pm
content: Also to reduce or isolate flexing of the board to decrease audible noise from piezoelectric vibration in capacitors.

author: ade
author_rank: Unknown
timestamp: April 24, 2016, 05:53:08 pm
content: They can also be used to isolate temperature-sensitive ICs / sensors.

author: Gyro
author_rank: Super Contributor
timestamp: April 24, 2016, 06:37:22 pm
content: Of course if you get it wrong, or overdo it, you can seriously increase the mechanical stress on any components that bridge the gap. I'm thinking of the high voltage isolation cases under vibration.

author: Cerebus
author_rank: Super Contributor
timestamp: April 24, 2016, 10:13:11 pm
content: I don't think anybody has mentioned the magic phrase which is "isolation slot".Others have pretty much covered it but I'll summarise. The isolation can be from:Mechanical stress. Typically associated with voltage references but many components can be affected by changes in the stress on leads or packages and slots can be used as stress relief.Thermal barriers. To stop heat flow between sources of heat (e.g. voltage regulators) and components sensitive to heat (e.g. voltage references). Sometimes, though rarely, used to keep heatinto an area of pcb that holds ovened components such as crystal ovens or heated voltage references.Safety isolation. To keep high voltages (e.g. mains) away from low voltage parts of a circuit. By far the commonest usage and seen between relay coils and contacts, underneath opto-isolators, between the primary and secondary windings of transformers etc.Leakage isolation. To reduce the possible leakage of signals into or out of especially sensitive circuit nodes such as very high impedance amplifier inputs or the capacitors in a sample and hold circuit.

author: BMack
author_rank: Regular Contributor
timestamp: April 25, 2016, 03:20:26 am
content: It's a speed hole, it makes the pixies travel faster through the board.

author: thisguy
author_rank: Contributor
timestamp: April 25, 2016, 04:06:03 am
content: Quote from: BMack on April 25, 2016, 03:20:26 amI hear wiping the board with special wipes can augment this effect.

author: ghinckley68
author_rank: Contributor
timestamp: April 29, 2016, 05:11:46 am
content: If it was an audio product monster cable would patent it and call it quantum flux inhibitor