[sdiy] PCB service firms?

[clark at andrews.edu]

   Hi Barry,

> Where I was coming from is that some of these cheap firms seem to want you
> to use their schematic capture, then layout, software.  Say I use Orcad, I
> then would have to import that schematic in DXF or something I imagine.
> Then if board changes are to be made you do them in their schematic
> software and the netlist to layout phase is quicker.

   Yes, ideally you do want to be able to make a schematic as well as the
PCB with a single program or software suite (such as OrCAD), so that
you are able to make changes without much trouble.

>  The cheap firms do not seem to push just taking your Gerber files - don't
> they want to lock you in to them because you have to use their software?

   That's possible, although I imagine that they still run the same Gerber
and Excellon file format for their production as does everyone else. 
Wouldn't hurt to ask.  :)

> What I heard in the past is that there is a standard panel size and it is
> smart to ask what that is so you can fit as many of your boards on it per
> panel cost as possible.  So that gets you a cheap board cost....

   It depends on if you are talking about prototype level boards or
production based boards.  Prototype boards are usually billed at a
dimensional rate, meaning regardless of how big/small your board is or
how many, you pay a per square inch rate.  This is usually because the
prototype houses cram as many different boards as they can to maximize
the space on the standard sized sheet of PCB material.
   A production house doesn't do this.  They will usually just run one
board on a given sheet (however many it takes to fill the order).  Any
leftover material is then thrown away.  This may affect the price to a
certain degree, but by no means is the major factor in costs at a
production level.  The only thing that does come into play is if you
are running a board that is dimensionally longer than the standard
stock panel (12 inches, I think).  The board house then has to use
larger stock, which usually DOES increase the cost.

> but I know nothing about what an pcb assembly house is
> looking for - the same panel size or individual boards?

   It largely depends on the assembly houses equipment.  For my business,
I like to run things in a panelized form.  IE, multiple boards in an
array.  The size is not too critical, but obviously the larger the
board, the fewer I would put on an array.
   Check out this array:

   http://www.greatlakesmodular.com/images/pnc/pnc_top_sm.jpg

   Since the individual boards are really too small to run through the
assembly process, by panelizing them in an array of 10, it makes it
easier to handle, takes less time to assemble, and is cheaper to have
the PCBs made.  I usually try to panelize things in the neighborhood of
10-11 inches in length and no more than 5 to 6 inches in width (due to
sag issues with scored arrays in wavesoldering).  Larger widths can be
done if stiffeners are used.

   Some additional production information, some assembler machines won't
accept boards smaller than 3" in width due to running automatic board
transport systems.  3" seems to be a common minimum width for the
transports, although some go down to 2" or so.  In order to combat
that, rail guides can be added to widen the board out.
   The assembler I use doesn't have a transport system in it, so I can
actually run pretty much any sized board, but I still prefer to run
panelized arrays.

   Cheers,

   Tony

-----------------------------------------------------------------------
                         Great Lakes Modular

        Custom Design, Engineering, and Manufacturing Services
                      www.greatlakesmodular.com
-----------------------------------------------------------------------