help.....
Dear colleagues,

I just work at a layout that is one of these layouts which
need much much more time and trouble than initially
estimated. I hope I'm not the only one who knows this problem.

My question is: Are there any good thumb rules for a good estimate in
advance how long it takes to make a layout for a given schematic/
partlist/ mechanical constraints drawing and how many layers are
necessary? I get usually a schematic and mostly a partlist and with
these informations I must make a good estimate for my customer how
much time it will take and (depends on time indirectly) how much cash
I want. The customers want the estimate ASAP, that means, I have not
much time to check out placement/routing density, the necessary number
of layers etc. And later it ends up with two layers more than the
customer wants to pay for and a lot of unplanned, unpaid night
sessions on my layout PC to get it ready in time or only few days
late.

There are in IPC-2221 3.6.2 "Feasability Density Evaluation" (old
IPC-D-275 : 5.1.1) some calculations based on the size of the parts.
 Is this good usable for determining how much routing area
is available? Has anybody any additional thumb
rules which consider e.g. the electrical structure
(many address/data buses across the board or only analog circuits with
mostly short point-to-point connections) or SMD parts pitch (can I
route between the leads or is the top layer really blocked by 0.5mm
pitch rows, as it is now with my actual nightmare layout - customer
wants 4 layers only with two of them Vcc and GND planes and no routing
- thus I have in reality only one and a half layers effectively for
routing :-(   )?

My dream would be an easy formula which says exactly, how routable is
the board, how many layers are necessary , and how much time/cash
needs the layout.

Thanks, regards
Matthias Mansfeld
-----------------------------------------------
Matthias Mansfeld Elektronik
* Leiterplattenlayout, Bestueckung
Am Langhoelzl 11, 85540 Haar; Tel.: 089/4620 093-7, Fax: -8
Internet: http://home.t-online.de/home/matthias.mansfeld

################################################################
DesignerCouncil E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE DesignerCouncil <your full name>
To unsubscribe:   SIGNOFF DesignerCouncil
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################