Note: Outside of electrical safety standards, there are other regulations that may impact your design and/or material selection, such as those requirements specified in the RoHS Directive.
However, the focus of this topic is based on PCBs/PWBs general requirements from electrical safety standards.
The following are key elements that electrical safety standards will cover when evaluating PCBs/PWBs:
- Material Flammability Rating – Typically, FR4 and approved/certified material. The required flammability rating may be reduced/increased based on available power under NC/SFC.
- Creepage Distances – This is the physical trace spacing over the surface of the PCBs/PWBs. The required creepage distance will vary based on voltage, conformal coating, comparative tracking index (CTI), etc. as applicable.
- Air Clearance (360 Degrees) – If PCBS/PWBs are mounted on standoffs, the required air clearance must also be met. If insulation material is used in lieu of standoffs, the material must meet the required dielectric voltage and approved/certified to at least the required dielectric voltage. The insulation material must have a flammability rating that may be required by the standard.
When a certification engineer evaluates your PCBs/PWBs they will need the following information:
- CTI – It is in your best interest to provide this information if known. Otherwise, the worst-case CTI will be used in determining the required creepage distance.
- Conformal Coating – This is a form of insulation coated over the surface of the PCBs/PWBs. The properties of the coating may impact your creepage distance and dielectric properties.
- Material Flammability Rating – Provide proof of certification/approval based on the specified flammability rating.
- Unpopulated PCBs/PWBs – The engineer will need to physically measure the creepage distances in question.
- Voltage Map – Submit a voltage map of the PCBs/PWBs that the engineer can reference based on voltages when making the measurements.