Using DIPS in the old days was fine for EIC's and area calculations.
But with SMD being predominant you must consider fan-out, or fan-in.
Using fan-out as worst case you can typically add 30% to the area of an
soic type part or 100% to a chip cap (if both pins have vias).
Also, for DIP's we typically used only one side of the board. Now both
are common practice. But you still have to add some fudge factor for
fan-out/fan-in.
Let's NOT get into a discussion of blind or micro-vias. It would hurt ;).
Regards,
Jerry Schwartz, CID
IPC Certified Interconnect Designer
"May the Schwartz be with you"
Jerry Schwartz, CID Designer 3
Harris Corporation GCSD Voice (321)-727-5474
P.O. Box 37, MS 1/9843 Fax (321)-729-5990
Melbourne, FL 32902-0037 Pager (321)-690-9797
mailto:[log in to unmask]
http://harris.com
-----Original Message-----
From: Brooks,Bill [mailto:[log in to unmask]]
Sent: Friday, March 02, 2001 1:15 PM
To: [log in to unmask]
Subject: Re: [DC] Board Density Factor
Hi Jeffrey,
This is an interesting topic... I remember using the 'density factor' back
when it actually meant something. When the 14 and 16 pin DIP was the
predominant package size used on most PCBs we did calculate 'equiv. IC's per
square inch' as a measure of design density. The way you would do that is
see how many parts, (i.e. resistors, caps, diodes, etc..) would fit into the
same area as a 14 pin dip. This would give you an equiv. IC value for your
discretes. Then you divided the number of 'virtual' or equiv. IC's you had
and divided them into the square in. of the board surface. This would give
you a value to compare between designs to give you an idea of how difficult
the board would be to lay out. Today... I think you could do the same with
0805, 1206, sot, sioc, etc. and come up with an equiv. value and it would
correlate with the old density factor fairly well.
Of course, we can push the envelope more now because of improvements in
processes in manufacturing... but anyway, that's how we used to use the
density factor calculation when I was doing hand tape and Mylar.. in the
early 70's and 80's.
Bill Brooks
PCB Design Engineer
DATRON WORLD COMMUNICATIONS INC.
3030 Enterprise Court
Vista, CA 92083
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
mailto:[log in to unmask]
IPC Designers Council, San Diego Chapter
http://www.ipc.org/SanDiego/
http://home.fda.net/bbrooks/pca/pca.htm
-----Original Message-----
From: McGlaughlin, Jeffrey A [mailto:[log in to unmask]]
Sent: Friday, March 02, 2001 9:44 AM
To: [log in to unmask]
Subject: [DC] Board Density Factor
I was recently ask to explain the board density factor calculated by our
layout package. It gave a factor of 0.1 sq. in./14-pin DIP. I translated
that to be 140 pins per square inch so that it made more sense in the two
sided surface mount arena, but was left wondering if there was a better way
of figuring board density. What are you using and why?
Jeffrey A. McGlaughlin, C.I.D.
Sr. PCB Designer
Battelle Memorial Institute
Columbus Ohio
[log in to unmask]
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