Information about High Voltage PCBs

I ask for help PCB designers,who has succesful experience with High Voltage (until 5 kV) PCBs.
1. Minimal distance between conductors with and without coating, depending on
Voltage.
2. What coating is most common and recommended for HV boards.
3. The 2 sided board (FR4) thikness depending on voltage between layers.
4. References to appropriate materials in the net.
5. Anything else.

Great thanks in advance,
Varuzhan

min pcb track high voltage

I ask for help PCB designers,who has succesful experience with High Voltage (until 5 kV) PCBs.
1. Minimal distance between conductors with and without coating, depending on
Voltage.
2. What coating is most common and recommended for HV boards.
3. The 2 sided board (FR4) thikness depending on voltage between layers.
4. References to appropriate materials in the net.
5. Anything else.

Click to expand...

1. I cannot answer this since I dont have any data now but you can search the net.
2. You can use clear laquer spray anless you need something more specific for the purpose. I did this in the pass and it worked great. Laquer I mean the one used to protect metals or wood from moisture etc.
3. only a suggestion here: You can create a double sided board by sticking 2 single sided back to back in order to increase distance.
4. Dont know this
5. Do not use sharp edges, this is a rule. Design you PCB with round corners and not 90 degrees. Soldering of all components must lead to a round, semisphere shape, hence cut the leads of the components, bend them and then solder them in order to end in a round shape, avoiding edges.

I know I am not very helpfull but this is what I could suggest from the minor experience I have on HV.

pcb high voltage clearance

I have a NEMA standard which I cannot post here, but can give you some data. The NEMA standard is 1-111-1 & 2 and specifies minimum clearances and creepage distance in inches.

For example:

Industrial control, 2500~5000V-> 2" clearance, 3.5" creepage

Does this make any sense ? There are 6 categories with different clearance and creepage values, but Industrial control is the only one that goes up to 7200V.

I'm not sure where to find clearance/creepage values for traces between FR4 (layers).

Hope this helps.
Mariano

layout high voltage clearance

Dear Mariano,

Thank you very much. But I am afraid your figures 2500~5000V-> 2" clearance, 3.5" creepage are too fantastic, if I understand well. Does 2" means two inches?
I have never seen such boards.
Then 2500V is twice less than 5000V, so they will need different clearance.
Besides, proper coating should dramatically decrease the necessary clearances.
That was my question about.

Varuzhan

ipc pcb voltage inch

I only have experiences on AC 220V PCB ....

Track to track clearance is minimum 2.5mm
Minimum PCB thickness for double side FR4 is 1.6mm

book on creepage on pcb

Varuzhan,

You are absolutely right. This values are too much, but this is what the standard says. I wonder in what kind of applications somebody would use cleareances this big.

On the other hand, there are groups in this standard where the clearances change considerably:

General industrial control: 0~50V > 0.150"
Industrial control with poler restrictions: 50~300 > 0.063"
General use where transients are known and controlled: 0~50V > 0.030"
....
For use where transients are known and controlled and power supply is limited: 0~36V > 0.012"

I guess this depends on the standard considered and the application that you have.

I also found a standard, ANSI/IPC-D-275 with different values: 0~100V > 0.004" ... 100~300V > 0.008" ... 300~500V > 0.010" ... more than 500V > 0.0001" per volt

Still I do not know what happens netween conductors in different layers. Does somebody have the answer on this?

Mariano

Added after 1 minutes:

Here goes a dumb question:

What is the difference between clearance and creepage ??

Mariano

pcb voltage rating between layers

Ok, seems now there are two of us, who needs to know more about HV PCBs.
I received the answer below in another forum. As you can see, the values of Robert are much more realistic. Besides he answered about the thikness.
I have seen a 2KV power supply in size of about 1.5"x1"x0.5", which cannot be
made even with Robert's figures.
That is why any new information will be highly appreciated.

Varuzhan


Re: High Voltage PCB
Posted By Robert Tarzwell on 1/21/2005 at 2:40 PM
hi the problem with highvoltage pcb is many factors contribute to the engeineering design, the 5 kv you mention is it dc or spicky ac, at 5 kv you will get some corona and must deal with it, rounded solder joints, rounded trace design, FR4 does not like corona, also we need to worry at waht altitude will he board operate at great diffrence between sea level and 14,000 ft or even 50,000 in a plane.

most of the specifications for dialectric are fresh lamiante fr4 agedges to only 300 to 600 volts per mill after 3 months under a car hood.

the best coating is still solder mask, but you can get two coats applied for better protection, for conformal coatings locktight have quite a few good ones.

on a two sided board for typcal 5 k volts i would not go below 20 mils thickness per layer and .059 standard can handle it.
very little on the net I did write a book a few years ago on high voltage pcb but its out of print now .
robert Tarzwell
Sierra proto express bought the rights to my high voltage book and plan on having it as a hand out you may want to contact them.

voltage across surface pcb

Creepage is across a surface - IE- the outside of a board, clearance would be when there is no surface to creep across IE internal to a board. wxw.creepage.com has a calculator for creepage spacing based on EN60950 - the values for layer to layer spacing i believe are also in that document I think it's posted somewhere in this forum.

SiGiNT

high voltage track protection in pcb designing

I again want to ask somebody, who has a real experience with HV PCBs.
Recently I have designed a small HV converter board, with about 10mm clearance for 2000V. We have tested it in 3500m heigh and very high humidity conditions. It worked well, but I hope to decrease the board size, using good coating.
That is why I am asking really experienced people.

Varuzhan

kv pcb distance

my rule is 3mm/kV. it worked up to 2.5kV(on the surface). Dielectric strength of FR4 is about 30-35kV/mm(between two sides). you can see properties of FR4 here: **broken link removed**
But, if you device is subject to regulation (60950, 60601 or whatever else) you have to use creepages and clearances from the standard.

voltage clearance spec for fr4

Really I use successfully the same norm: 10mm for 3kV. But, please, look to:
**broken link removed**
and you will see, that they have power supplies so small, that it is impossible to
make with standards norms and even with 3mm/kV.
That is why I am looking for experience with coatings, which can significantly
reduce the required clearances.

Varuzhan

creepage internal layer

I overlooked their site - for sure, they use some sort of protective gluing, at least for smaller power supplies. Yes, it is allowed. The only concern is to proove, that the gluing has no air bubbles inside. After it you can use not surface voltage rating, but rating of the glue itself - practilally 30-60kV/mm.

hv conformal coating pcb

Can one recommend what type of glue or coating is best for such purpose?

Varuzhan

high voltage creepage distance calculator

I can't recommed a specific type for you - each manufacturer names it in a different way. Try to searh google for "epoxy resin" or "silicon rubber".

clearance

There are a lots and lots. That is why I am asking for standard and proven one.

Varuzhan

voltage rating pcb

vdaniel said:

There are a lots and lots. That is why I am asking for standard and proven one.

Varuzhan

Click to expand...

For example, our matufacturer used a material "Epoxidharz Araldit F" from CIBA GEIGY. But I affraid it will be useless for you. During transition from development to manufacturing I just asked manufacturer for some suitable material.
Alex

High Voltage PCB

This article may help you a little.

**broken link removed**

High Voltage PCB

hi ,
As per ipc standard 2500v conductor clearance is 13.795 mm for permanent coating.

bare boards are 30mm clearance is enough.

Re: High Voltage PCB

@kvmanikandan - which IPC standard is that?
Thanks!

Re: High Voltage PCB

Hello,

I was wondering if any of you knew what creepage distance I should use for 3kV.

I currently have 55.14mm, where the two contacts are separated by a 10mm high wall and 6mm high (3mm diameter) contacts are surrounded by a 6mm high barrier.
The attached file better illustrates this.

I was wondering if this was adequate protection for a high pollution degree(2,3).
Also, if any of you had any recent articles or studies that involved high voltage creepage distances like this example.

Thanks,
John