Brad,
Precisely supportive of my case. but let me explain further. My first job
at a defense contractor involved working with engineers in the mid 70s
Watching five rf engineers slide rule thru all the mathematics to simulate a
board before they cut any pcb. For Prototypes they would start with their
own core material etch it on a work bench etch set up, clean and square the
bad etch off with an exacto, drill their own vias , fill the vias with Z
wires, solder copper foil around the edges of the board, then populate a
board with handmade coils, inductors, etc, They would spend a week
tweaking each board to get the desired performance. My long story ends
up, with the conclusion that had their process control been much better...
etching, drilling and filling vias, quality of coils, etc, they would have
had consistent designs and tweaks might take a few minutes rather than a
week. I'm sure you have seen coils bent so bad on board they don't look
like the orig choke. There is no excuse for RF engineers to think they hold
the patent on black magic for RF design. Vias have been characterized,
trace sizes, material, and so have bends, curves, and miters, etc.
Actually the bends, miters etc do not have any effect on the propagation of
the signal anyway. I know I am going to get blasted on that one but I will
wait to respond.
I would not characterize your designers as voodoo engineering if they are
simulating the design, however I run into many "rf" engineers with a
distant past of tweak and add solder blobs till it works. I don't call that
good engineering, I call it lack of understanding the characteristics of
pcb design. I have mentioned before that I have seen Chinese made rf
designs fabricated on cardboard. Envious am I for the designer who
understood the characteristics of that material and sold me a cheap product
as opposed to designing it on NELCO polyimide or Rodgers material or some
other high end material.
I am getting off the topic...My original statement is ...I would never
design a coil without simulation first and understanding the characteristics
before committing to PCB. Otherwise you are just occupying precious
space. I have digital designs to 2.7 MBits under my belt. The old
"farts" that were there before me insisted that all the high speed design
use rounded corners for all conductors. Did they truly understand what it
did on pcb? No. Could they characterize it? NO ! They just did it because
they taped it like that 30 years ago. Even If I were to show them TDR data
from an independent studies conducted by Ultricad www.ultricad.com they
would still want me round corners. I can kick designers like that where
the sun don't shine. Well Im still there and they aren't.
Mike Reagan
EDSI
Frederick
----- Original Message -----
From: Brad Velander <[EMAIL PROTECTED]>
To: 'Protel EDA Forum' <[EMAIL PROTECTED]>
Sent: Wednesday, June 13, 2001 12:43 PM
Subject: Re: [PEDA] AW: Spiral trace construction?
> Mike,
> I will tell all of our Engineers that you are calling them Voodoo
> Witch Doctors, right? 8^>
> They'll shake their little mojo bags and put a curse upon you, better
watch
> it!
>
> Now seriously, your "voodoo" design is an integral part of microwave
> designs. It is not at all black magic but it can seem that way at times. I
> do not do any of the design but strictly implement the design as given to
me
> by the designer. To date, we have not used circular spiral inductors, we
do
> commonly use squared spiral inductors. The reasons why are beyond me,
quite
> possibly it is because someone a longtime ago told them not to do it
because
> it is too difficult to implement in the CAD tools. This would not be true
at
> this juncture because I would just import the Gerber. I don't know why but
> maybe I will ask a couple of the Engineers today.
> Our microwave designs are typically simulated and verified on
> Anasoft's Symphony & ??? tools and then passed to me for implementation on
> the PCB in Protel. The symphony tools will verify the operation of the
> microwave elements but it is not perfect, after fabrication there is quite
> often a little bit of tweaking going on based upon the actual circuit
> performance. For some other design aspects we also use a couple of
different
> HFSS packages for full field simulation (I think this is an intensive
finite
> element type analysis of all fields and their interactions.).
>
> Brad Velander,
> Lead PCB Designer,
> Norsat International Inc.,
> #300 - 4401 Still Creek Dr.,
> Burnaby, B.C., V5C 6G9.
> Tel. (604) 292-9089 direct
> Fax (604) 292-9010
> website www.norsat.com
>
>
> > -----Original Message-----
> > From: Mike Reagan [mailto:[EMAIL PROTECTED]]
> > Sent: Wednesday, June 13, 2001 8:55 AM
> > To: Protel EDA Forum
> > Subject: Re: [PEDA] AW: Spiral trace construction?
> >
> >
> > Hello All.
> > I wanted to throw in my two cents:
> > While a Spiraled trace to simulate an inductor might be a desirable
> > accomplishment, I try to convince engineers to stay away from
> > this type of
> > design. I call it Voodoo design. Unless the trace is
> > designed first by a
> > very powerful tool that takes into account three dimensional
> > design, the
> > probability of obtaining a coil with any good characteristics
> > is slim and
> > inconsistent. For edge to edge coupling to be effective
> > coupling the traces
> > would have to be closer than 7 mils apart. Then there is "Q"
> > factor for
> > this inductor, meaning it will be a very poor Quality inductor. I
> > personally think and would suggest finding a real component
> > to design in.
> > Your design will be more reproducible and consistent from
> > board to board,
> > because of a number of problems inherent to varied
> > inconsistencies of a
> > fibers in any board. There are a whole lot of reasons why I
> > would stay
> > away from voodoo design. Sorry Bill, I don't mean to insult
> > you, are the
> > only TOP GUN registered on this list. But I wouldn't attempt
> > it unless I
> > could fully simulate it at my desired frequency, with prepreg
> > thickness,
> > with known prepreg material, fiber density, dielectric
> > constant, gnd plane
> > underneath, relative humidity, and it goes on.
> >
> > I will wait for Brad V's Comments on this because he had
> > mentioned his
> > company simulates some of this stuff, right?
> >
> >
> > Mike Reagan
> > EDSI
> > Frederick Md
>
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