RE PCB boards

[Dirk Broer]

>I hear this all of the time: when refering to a 2 layer board, does
>that mean front and back, or actually 2 layers (boards) such that there
>is a front, back, and "middle" sandwiched between?

Two layer is normal front and back.

Beyond that you go to "multi-layer" in which the circuit boards are made up of 
multiple 2-layer sections bonded together.  If you ca get away with 2 layers it 
is much easier - and cheaper.  Multilayer ads another level of complexity, 
limits what changes you can do to the board afterwards, and introduces many 
more areas for mistakes.  Typically for multilayer boards we add "Coupons" to 
the layout.  These are little circuits that are made at the same time as the 
main circuit board and can later be destructively tested to insure that the 
main circuit board was done correctly.  Typically the two outermost levels 
become ground planes for EMI shielding.  Your $100 circuit board would quickly 
become a $600 one...  Not to mention to be practicle you would probably need 
software with auto-routing capability.

>BTW, that is great that place in Canada makes those PCB boards.  I'm sick
>of home fab IT SUCKS.  I've spent well over $80 on the different techniques
>of home fab, and even when the boards do come out right, it still takes you
>hours, and hours to do it.

At NASA one of the branches has a milling machine (C&C ? ) hooked to a CAD 
system.  The mill cuts away at the copper clad board - the same mill also 
drills the holes.  No chemical etching!!

Dirk