At the beginning of IPC-2221A there's a whole section on component density and layout feasibility.

I use the ratio figures mentioned in the standard: 70% for level A, 80% for level B, 90% for level C.  My library is set up by part and I've added an attribute for area, in square mm, and I've created a report format for Pulsonix that will run against both schematic design and PCB to output the total board area and component areas in CSV format for input into a spreadsheet.

It gives a very good indication at the start of a project when I just get a board outline from MCAD to feasibility and in there's been a few cases where the calculation has come in above 90% where I've gone back and said to the MCAD team that they need to reconsider things here.

Most of our boards fit into level A though.

A couple of years ago a company called Adcom presented a paper "Predictability of PCB Layout Density" and created a software program for the task.  You can still find it on their website.

http://www.adcom.co.il/pcb%20layout/pl.html

I found the results didn't fit in with our designs though as it seemed more suited to HDI/BGA layouts.

James


James Head BEng CID+ MIIE MIET
Senior PCB CAD Engineer
Crowcon Detection Instruments Limited
2 Blacklands Way
Abingdon Business Park
ABINGDON
OX14 1DY
Telephone: 01235 557700 extension 289
Fax: 07092024504
E-mail: [log in to unmask]


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