Creepage distances in PCB internal layers

[Jaka Racman]

Hi,

I need to desigh planar transformer, but I can find no requirements for creepage distances in internal layers of the multilayer PCB. So far I think it is like that:

-if I can prove that multilayer PCB is voidfree, then I can assume solid insulation. Single layer of insulation must be 0.4mm thick for double insulation and 0.4mm FR4 woud break down at 16.5kV (1100V/mil breakdown voltage). I do not know FR4 specification for working (operational) voltage, only for breakdown voltage, so i have no clue what spacing to use between tracks of the same transformer winding.

-if I can not prove that multilayer PCB is voidfree, then I use creepage distance specified for coated PCB.

Can I prove that PCB is voidfree with 100% hipot testing and how high test voltage should be?

I would be grateful for some guidelines.

Best regards,

Jaka racman

 

[peranders]

I have standards at work in this topic but how high voltages do you have in mind?

 

[Jaka Racman]

Hi,

working (operational voltage) for the whole winding would be 450V and 900V, hipot test is 4kV minimum.

I would be also interested in which standard is applicable. I am familiar with IEC(EN)60664, but I have not found anything about multilayer PCB.

Best regards,

Jaka Racman

 

[peranders]

My gut feeling is that you should avoid what your are planning to do. Why don't you consider an ordinary magnetic device with wires instead of etched traces?

 

[Jaka Racman]

Why don't you consider an ordinary magnetic device with wires instead of etched traces?

Hi.


I have been using planar transformers from Payton for almost ten years. Reasons are:

-repeatabillity
-relatively low leakage inductance
-low form factor
-low losses
-efficient cooling

It is much like difference between point to point wiring and PCB.

Problem with Payton is minimum quantity and tooling fee, since their range of standard products is small and they do custom designs.

Best regards,

Jaka Racman

 

[Ouroboros]

Unfortunately EN60950 (which has a good section on these requirements) isn't available on line. If all else fails, I could scan the relevant sheets from our paper copy here at work.

 

[Jaka Racman]

Hi,

thanks, since my field is medical i was not aware that 60950 deals with that. I will look it up.

Best regards,

Jaka Racman