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October 2002

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Subject:
From:
Seth Goodman <[log in to unmask]>
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Date:
Wed, 2 Oct 2002 23:45:47 -0500
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Guy,

I can't disagree that a 3.5 aspect ratio hole is easy to drill, plate, clean
and it is reliable.  However, for an 0.062" board, this means an 18 mil
finished hole size via, which then requires a 33 to 38 mil pad.  It also
requires a 48 mil anti-pad on the inner layers.  We are talking some serious
real estate here.

This becomes a big problem when we use 6 mil line and space rules to route
between 0.8mm pitch BGA's.  With via pads and anti-pads this big, increasing
the layer count won't always make a design routable.  We can make the board
thinner to allow smaller vias, but only when the board itself is physically
small.  What's your opinion (besides use microvias) when we need high
routing density on an 0.062" thick board?

Regards,

Seth Goodman

Goodman Associates, LLC
Verona, WI
USA


> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Guy Ramsey
> Sent: Friday, September 27, 2002 4:54 PM
> To: [log in to unmask]
> Subject: Re: [TN] PCB design with mask over vias.
>

   ----------- snip -------------

> Can they increase the via size? I am a firm believer in aspect
> ratios less than 3.5.
>
>
>
> Guy Ramsey
> Senior Lab Technician/Instructor
> American Competitiveness Institute
> E-Mail: [log in to unmask]
> Ph: (610) 362-1200 x107
> Fax: (610) 362-1290

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