Re: [SI-LIST] : Recommendations for High Density PCB to PCB Connection

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From: Laurence Michaels (lmichael@techmail.gdc.com)
Date: Thu Nov 04 1999 - 06:57:14 PST


"D. C. Sessions" wrote:
>
> Laurence Michaels wrote:
> >
> > Doug Piper wrote:
> > >
> > > I'm working on a new project that requires me to make 40 connections from
> > > one PCB to another in a space that's only about 0.2" x 0.5". Does anyone
> > > have any experience or recommendations for making a connection of this
> > > density?
> > >
> > > Doug Piper, Woven Electronics, P.O. Box 189, Mauldin, SC 29662
> > > PH 864-967-1751, FAX 864-963-1761, e-mail: doug.piper@wovenelectronics.com
> > > www.wovenelectronics.com
> >
> > Only recommendation I can make, is possibly some of the press-fit
> > unidirectionally conductive foam material, such as is used on some of
> > the more recent Intel Flash chips.
> >
> > Having done a few calculations, this works out to 400 connections per
> > square inch. If you manage to put more connections in an inch, than
> > most cotton sheets, I want to know how you did it! Connections on the
> > trace level are going to be tight as well. This is going to be 1
> > connection per 2.5 square mils. Assuming equal trace and space
> > requirements, this works out to 0.625 mil trace and space. That's not a
> > standard PCB you're talking about. Are you sure about the space
> > requirements?
>
> You might want to check your math on that density calculation.
>
> 5mm x 12.7mm space for 40 connections comes to about 1.5mm2/contact,
> which is less than the density of an old 1.27mm pitch BGA.
>
> --
> D. C. Sessions
> dc.sessions@vlsi.com

Argh... I was asleep when I did that calculation. Time to check
everything else I did yesterday :-)

0.2*0.5=0.1 square inch.
0.1/40=0.0025 square inches per connection

(calculation error was probably here... 0.0025 square inches does
NOT equal 2.5 square mils... that's what I get for using non-metric
units, and only turning on half of my conversion algorithms.
1 sq in = 10000 sq mil 1 sq meter = 1000000 sq mm)

0.0025 square inches gives 1.6 sq mm per connection
25 square mils gives 1.6 sq mm per connection

I'm not usually that stupid. (I hope)

Thanks,

-- 
Laurence Michaels

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