Re: dieletric strength question

["Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

15 kV/mil????  I'd go for 1.5 kV, perhaps, with no design margin.  15 kV/mil
= 15 MV/inch = 590 kV/mm, which is somewhat more than the breakdown strength
for  mica(50 kV/mm in 1mm thick, 100-200 for 0.1 mm), polyethylene (40
kV/mm), PTFE(Teflon)(25 kV/mm).

Any composite is going to have a lower breakdown strength than a pure
material, because of the field concentrations caused by the differing
dielectric constants (epsilon) of the component materials.


30 kV in .0625 inch PCB is only 500V/mil, which is probably about the max
that you'd feel safe at, and you'd want to make real sure that there weren't
any voids in the substrate, rough edges or corners on the traces, etc.

Perhaps 15 kV/mm would be a more believable puncture voltage spec for
glass/epoxy?  (1 mm = ca 39.4 mil)

-----Original Message-----
From: Tesla list <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Friday, September 08, 2000 11:44 AM
Subject: Re: dieletric strength question


>Original poster: "Steve" <Steve-at-g8cyerichmond.freeserve.co.uk>
>
>No problems here, epoxy pcb has a puncture voltage of 15kV per mil or
>thereabouts. I have made caps for tank circuits running at 10kV, and have
>tested them to 30kV, using 1/16th board. Details are on my website
>http://www.teslauk-dot-com
>Steve
>----- Original Message -----
>From: Tesla list <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Friday, September 08, 2000 1:17 AM
>Subject: dieletric strength question
>
>
>> Original poster: jmonty-at-flash-dot-net
>>
>> I had a friend pose me the following question that someone on the
>> list probably can answer off the top of his or her head.
>> Here's the question.
>>
>> "I've made a capacitor out of double sided epoxy circuit board for
>> the cold end of the resonator in the two meter cavity amp. It needs
>> to take 3KV and just by looks I'd say it does. Guess as a last
>> resort I could hook it up to HV but my heart won't take many more
>> shotgun explosions going off in the shack.
>> It measures .050, including the copper, which is a few mils."
>>
>>
>> Any help in determining a ball park puncture voltage would be most
>> appreciated.
>>
>> Jeff Montgomery
>> Palestine, Texas
>>
>>
>>
>>
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