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Re: MMC PCB



Original poster: "Mark Broker by way of Terry Fritz <twftesla-at-qwest-dot-net>" <broker-at-uwplatt.edu>

Michael,

I used some of Kepro's 2 oz 1/16" G10 boards to make my MMC.  I believe I
made the traces around .30" wide to connect the caps, with a .75" trace
along the top and bottom to connect the three strings together.  My 
boards work pretty good, and the look even better.  The hardest part was
drilling the holes, which really wasn't hard - just time consuming.  I
enlisted the help of two friends to solder the caps and resistors together
:-)  I 
have only had two problems - a bad solder joint (which forced me to remove
the Conformal Coating I sprayed on the back), and had a very small arcover
problem with the resistors!  Don't know how.  I ended up 
spending about an hour with my friend's Dremel removing any sharp points
from the caps and resistor leads.

Regarding trace width,  2oz clad is .0027(5)" thick.  Make sure that the
area of the trace is greater than the area of the cap leads.  Then, make
the main "busses" that width times the number of parallel strings.  If you 
can, it's probably best to stack the PCB boards vertically using 1/4-20
Brass threaded rod than it is to hook up multiple boards end-to-end.

Making PCBs is easiest and looks the best if you have access to either a
PC-controlled mill or use the photosensitive clad with a mask.  In my
experience, the mill won't look as good, nor will it leave as clean an edge.

As far as keeping the traces short, leave enough room between the caps
souch that 4kV will not arc between them (if you're using Geek Caps, which
I think you are - the name is familiar :-)  You could stick a cap in a 
piece of thin PE tube, or place a thin piece of PE or PP between the caps,
and a thicker one between the strings.  But that's really going overboard.
ABout 1/8" between caps in a string, and about .75" between 
strings (between cap leads) is what I used on my MMCs, and is less than
what we used on the The Geek Group's MMCs.

Good luck

Mark Broker
The Geek Group's Chief Engineer


8/10/01 7:57:09 AM, Tesla list <tesla-at-pupman-dot-com> wrote:

>Original poster: "Michael Rhodes by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <rhodes-at-fnrf.science.cmu.ac.th>
>
>I am laying out a printed circuit board (standard G10-Epoxy) for
>my MMC array.  I realize the traces have to be heavy enough
>for the high pulse currents but short enough to minimize inductance.
>Are there any 'gotchas' going this route such as high voltage
>breakdown of the PCB, etc?  Anyone else build an MMC this
>way?
>
>--Michael
>
>
>
>