Clearance and Creepage:
There is a variety of industry and safety standards that prescribe different spacing requirements depending on the voltage, application and other factors.
What is clearance?
Clearance is the shortest distance through air between two conductors. The rules for clearance vary with the PCB material, voltage, and environmental conditions. The environmental effects are pretty significant. Most commonly, humidity changes the breakdown voltage of air and affects the likelihood of arcing. Dust is another factor since particulates that collect on the surface of the PCB can form a track over time, shortening the distance between conductors.
How to Calculate Clearance:There are many standard calculation tools. With the help of that you can calculate the space or clearance.According to IPC2221 the spacing calculation is given below. As we know the spacing between conductors depends upon voltage between conductors.So with help of this tool we can know the spacing between conductors.
The IPC Standards spacing between conductors is given below:
What is creepage on a PCB?
Similar to clearance, creepage measures distance between conductors on a PCB. However, instead of measuring distance in air, it measures the shortest distance along the surface of the insulation material. Board material and environment also affect creepage requirements. Moisture or particulate accumulation on the board can shorten creepage distance the same way they do for clearance.
when you have a high density design, creepage can be a difficult requirement to meet. Since moving tracks is rarely the first choice, there are a couple other tricks for increasing the surface distance in your design. By adding either a slot between tracks, or a vertical barrier of insulation, you can significantly increase the creepage distance without changing the trace layout on the board.
Pollution Degree:
The pollution degree depends on your intended application. Degree 1 means no pollution or only dry non-conductive one Degree 2 applies where there is non-conductive contamination that might temporarily become conductive due to condensation. This is the most common type for general use equipment. Degree 3 applies to conductive pollution, or to dry non-conductive one which could become conductive due to condensation. If you don't know your PCB or insulator material group, assume worse case IIIb . Creepage distance can be increased by adding an insulated barrier or a slot wider than 1 mm .
