Hi Khaled,

        I'm afraid there are too many factors for a simple rule.  Equiv ic's is
probably not going to give you a very good answer.  At "maximum" density,
very roughly speaking the surface area of your parts cannot easily exceed
90% of available board area.  I use a spreadsheet with all package types
that I normally use to total up a very accurate part surface area.

        A lot of things can affect that rule though;  You need to account for the
area req'd for vias for smt.  Your assembly/manufacturing rules may require
much more space between parts.  Density is also affected by number of
routing layers and  basic design rules such as min via size and etch
minimums.  Parts both sides can greatly increase density.  Partitions
between ckts can eat up space. Thermal considerations,etc...

        You will usually be better off by making one denser board (albeit more
expensive) than by making daughter boards.  Ideally you would reserve the
daughter board(s) for optional elements of your system.  But again speak
with your board vendors and assy people before making your determination.


        Regards,
                Dave


At 11:34 AM 8/11/99 +0300, you wrote:
>Dear fellow designers,
>I was wondering if there is a rule or a formula for calculating the
>required PCB area upfront without having to go through the placement and
>routing procedures. The situation that I have is a mixed signal design,
>single sided and mixed technology (SMT & THT). With about 530 components
>(SMT&THT) which makes acctualy a configuration of 89 (14 pin Equivalent
>ICs). I want to know upfront if I will have to break the board into some
>smaller daughter boards.
>Thank You in advance.
>
>--
>Best Regards
>Khaled H. Fouad
>PCB Designer / R&D Department
>Tel.: +20 (11) 333414  Ext. : 312       Fax.   : +20 (11) 335613
>BAHGAT Group    http://www.bahgat.com
>Email  : [log in to unmask]
>Second Industrial Zone, Plot 240, 6 October City, Egypt
>
>
Dave Graves
Design Manager
UltraCAD Design
http://www.ultracad.com